Speaker enclosure with two acoustic transmission lines, and associated speaker enclosure assembly

Abstract

The invention relates to a speaker enclosure (1) comprising a box (2) in which a cavity (3) is formed, in which a loudspeaker (4) is mounted, wherein the box (2) comprises an opening (2a) closed off by the front part of the loudspeaker (4) and first and second vents (5a, 5b) opening to the outside, the speaker enclosure (1) further comprising, inside the box (2), a first acoustic transmission line (7) extending between the cavity (3) and the first vent (5a), and a second acoustic transmission line (8) extending between the cavity (3) and the second vent (5b), wherein the length of the second transmission line (8) is equal to half the length of the first transmission line (7), and wherein the ratio of the area of the second constant cross section to the area of the first constant cross section is within the range [1 / √2; 1].

Description

DUAL-LINE ACOUSTIC ENCLOSURE AND ASSOCIATED ACOUSTIC ENCLOSURE SYSTEM

[0001] The present invention relates to the field of acoustic enclosures, and in particular to an acoustic enclosure with a double acoustic transmission line and to an associated acoustic enclosure assembly.

[0002] A conventional loudspeaker emits sound waves both forward and backward. This is because, when the speaker cone moves forward, the air in front of it is compressed, while the air behind it is rarefied. Conversely, when the cone moves backward, the air in front of it is rarefied, while the air behind it is compressed. Therefore, when the loudspeaker reproduces audio, its cone moves back and forth, creating unwanted pressure or vacuum with each movement. This generates a sound wave that is out of phase with the original signal, leading to an acoustic problem.

[0003] To overcome this acoustic problem, it is known to place the loudspeaker in an acoustic enclosure to allow the loudspeaker to reproduce the original audio signal more faithfully.

[0004] The main types of existing loudspeakers are:

[0005] - the closed enclosure, in which the waves emitted towards the rear of the loudspeaker are isolated within the enclosure,

[0006] - the vented enclosure, in which the waves emitted towards the rear of the loudspeaker join the waves emitted towards the front via a vent,

[0007] - the passive radiator enclosure, in which the vent is replaced by a bass speaker without a motor (coil and magnet), and

[0008] - the dual speaker enclosure.

[0009] All these types of existing loudspeakers attempt to correct the defects of the speakers with varying degrees of effectiveness and introduce an undesirable high-order frequency response.

[0010] Complex solutions also exist to try to achieve an optimal and consistent level across all required frequencies within the range of human hearing (generally accepted as between 20Hz and 20kHz). However, these solutions often require several types of speakers to cover the full frequency range, most often using bass, midrange, and treble speakers simultaneously, but sometimes also a separate subwoofer for the lowest bass frequencies.

[0011] The weaknesses of these solutions, which use multiple speakers, are numerous:

[0012] - difficulty in getting each speaker to the same level,

[0013] - Frequency overlap between speakers is virtually impossible to calibrate (requires graphic or parametric equalization for approximate correction),

[0014] - very sensitive to the physical characteristics of the speaker,

[0015] - Controlling phase shift according to frequencies is complex and often impossible (introducing unwanted high-order filtering),

[0016] - overall equalization is very difficult, and

[0017] - sensitive to reverberations in the room where the speaker is placed.

[0018] Some monitor speakers, commonly used in recording studios, may also be based on acoustic transmission line (ATL) speaker technology. In this design, the speaker incorporates a long duct that guides sound waves from the rear of the driver to a port. However, these existing ATL speakers cannot cover the entire 20Hz–20kHz frequency range and typically use multiple drivers to attempt a wider spectral range. Some are capable of reaching a minimum frequency of around 40Hz, but these speakers then come at a very high price (several thousand euros).

[0019] US patent application US5821471A discloses a loudspeaker enclosure comprising a loudspeaker and a single acoustic transmission line. However, in this document, the dimensions (i.e., the length and cross-sectional area) of the single transmission line are not optimal, such that this existing loudspeaker enclosure does not achieve maximum acoustic power and maximum efficiency while maintaining a substantially flat spectral response over a very wide frequency range. Indeed, for this type of loudspeaker enclosure, a loss of acoustic power occurs due to the various resonance modes of the single acoustic transmission line.

[0020] Japanese utility model applications JPS6068789U and JPS54124533U, as well as Japanese patent application JPH04235500A, also disclose acoustic enclosures according to the prior art. However, none of these existing acoustic enclosures achieves a substantially flat spectral response over a very wide frequency range.

[0021] Thus, no loudspeaker currently on the market can achieve a virtually flat spectral response across the entire 20Hz – 20kHz frequency range, while also being inexpensive.

[0022] The present invention aims to resolve the drawbacks of the prior art, by proposing an acoustic enclosure comprising two acoustic transmission lines which allow the propagation of sound waves emitted from the rear of the loudspeaker towards two respective vents, the particular dimensioning described below of the two acoustic transmission lines (aiming to obtain equality of acoustic resistances between the loudspeaker and the assembly consisting of the first and second acoustic transmission lines) making it possible to obtain, with a single loudspeaker, an optimization of power and a substantially flat spectral response over a very wide frequency band, for example over the entire frequency range of 20Hz – 20kHz.

[0023] The present invention thus makes it possible to improve the audio reproduction of the loudspeaker which can provide the most faithful sound possible with maximum efficiency compared to traditional loudspeakers currently on the market.

[0024] The present invention therefore relates to an acoustic enclosure comprising a box in which a housing is provided in which a loudspeaker is mounted, said box comprising an opening closed by the front part of the loudspeaker and first and second vents arranged on the same face of the acoustic enclosure and opening to the outside, the acoustic enclosure further comprising, inside the box, a first acoustic transmission line extending between a first inlet end opening into the housing and configured to receive sound waves emitted from the rear of the loudspeaker and a first outlet end opening into the first vent, and a second acoustic transmission line extending between a second inlet end opening into the housing and configured to receive sound waves emitted from the rear of the loudspeaker and a second outlet end opening into the second vent,in order to propagate the sound waves emitted from the rear of the loudspeaker towards the first and second vents; said first acoustic transmission line having a first constant length and cross-section, and said second acoustic transmission line having a second constant length and cross-section; said second length being equal to half of said first length, and the ratio between the area of ​​the second constant cross-section and the area of ​​the first constant cross-section being within the interval, .

[0025] Thus, compared to a loudspeaker with a single acoustic transmission line, the double-transmission loudspeaker according to the present invention compensates for the acoustic power loss associated with the different resonance modes of a single transmission line. The use of a second transmission line half the length of the first compensates for the acoustic power loss at the various resonance modes of the first transmission line, resulting in a virtually flat frequency response over a very wide frequency range, for example, across the entire 20Hz–20kHz range, due to the constant cross-sections of the first and second transmission lines.

[0026] Using small speakers will allow for a maximum bandwidth of up to 20 kHz (or even higher if the speaker allows it). Larger speakers will not be able to reach 20 kHz. Using small speakers will not affect the natural frequency of the first and second acoustic transmission lines. Only the power will be reduced; therefore, simply adding more speakers will be enough to achieve the desired power.

[0027] With the present invention, unlike traditional speakers, all edge effects are corrected.

[0028] The present invention is based on acoustic transmission line technology, which allows for strict control of the frequency spectrum of the loudspeaker enclosure in the acoustic domain. It can provide a virtually flat spectral response from the highest to the lowest frequencies, where the latter are defined by the length of the acoustic transmission lines according to a simple linear relationship.

[0029] The acoustic enclosure according to the invention is independent of the loudspeaker's resonant frequency. Even if the loudspeaker has a resonant frequency of 80 Hz or even higher than 120 Hz, this will not prevent the acoustic enclosure from reaching lower frequencies such as 20 Hz or even less, depending solely on the lengths of the first and second acoustic transmission lines.

[0030] Since the acoustic transmission line architecture has no limit in the high frequencies, the highest frequency of the acoustic enclosure will be limited by the maximum frequency that the loudspeaker can provide.

[0031] The present invention makes it possible, with a single loudspeaker, to cover at least the entire frequency range of 20Hz – 20kHz. Furthermore, with the present invention, there is no frequency overlap management or uncontrolled phase shift, which reduces unwanted resonance / rejection behavior.

[0032] Virtually no equalization is required with the loudspeaker according to the invention, which allows for a frequency response made almost flat by the dual acoustic transmission line technology, self-compensation for loudspeaker defects, and less sensitivity to room reverberations.

[0033] Since the acoustic resistance of the combined first and second transmission lines is significantly higher than the acoustic resistance of a room (which has a large volume compared to the first and second transmission lines and therefore no constraints on air pressure variations), the frequency response of the loudspeaker of the present invention is virtually independent of its location, as well as the size and furnishings of the room in which it is installed. In contrast, conventional loudspeakers generally have low and variable acoustic resistance across frequencies, making them highly dependent on room configuration. Nevertheless, it may still be useful to correct for any linearity defects in the loudspeaker in the center frequency range (between 200 Hz and 10 kHz) to achieve a perfectly flat frequency response.

[0034] The acoustic enclosure according to the present invention has a high power efficiency (acoustic power / electrical power) for almost all frequencies: use of both the front and rear acoustic power of the loudspeaker (the rear acoustic power being reproduced through the first and second vents with the same frequency response as the front acoustic power by simply adding fixed delays), high dynamic range, ability to obtain a full range in a small volume, the minimum frequency response does not depend on the resonant frequency of the loudspeaker (for example, 20Hz can be achieved with a loudspeaker having a resonant frequency of 80Hz or even greater than 120Hz), no need for a separate subwoofer.

[0035] The overall cost of the solution is reduced: a low-end speaker is sufficient to obtain a high-level acoustic result (the solution can be used for professional acoustic solutions), compatibility with class D amplifiers even at low frequencies (low reactive power feedback), fully scalable in power by combining several loudspeakers without impacting the frequency response or phase shifts.

[0036] According to a particular feature of the invention, the first acoustic transmission line is a quarter-wave transmission line, and the second acoustic transmission line is an eighth-wave transmission line.

[0037] Thus, defining a low cutoff frequency for the loudspeaker allows us to define the first length of the first quarter-wave transmission line and the second length of the second eighth-wave transmission line according to the equations:

[0038] L1 = c / (4 * F c ), and L2 = c / (8 * F c ) = L1 / 2,

[0039] where L1 is the first length (in m), L2 is the second length (in m), c is the speed of sound in air (in m / s), and F c is the defined lower cutoff frequency (in Hz).

[0040] According to a particular feature of the invention, each of the first and second constant cross sections is one of circular, oval, rectangular, square and polygonal.

[0041] It should be noted that any other shape is possible for each of the first and second cross sections, the essential thing being that the cross section is constant over the entire length of the line and that the first and second cross sections have the same shape.

[0042] The cross-section can, for example, be circular, so that each of the first and second acoustic transmission lines forms a tubular conduit. The cross-section can also be rectangular or square to optimize the size of the acoustic enclosure.

[0043] According to a particular feature of the invention:

[0044] - the first and second constant cross-sections are identical, and the area of ​​each of the first and second constant cross-sections is as follows:

[0045] ; Or

[0046] - the ratio between the area of ​​the second constant cross-section and the area of ​​the first constant cross-section is equal to , And

[0047] And ;

[0048] where air is the viscosity of air in Ns / m², L1 is the first length in m, F s is the natural resonant frequency of the speaker in Hz,C ms is the flexibility (or compliance) of the loudspeaker suspension in m / N,S hp is the surface area of ​​the moving part (or diaphragm) of the loudspeaker in m²,Q ms is the mechanical quality factor (or mechanical overstress coefficient) of the loudspeaker at F s , and K is a constant.

[0049] Thus, dimensioning the first and second constant and identical cross sections of the two acoustic transmission lines according to the first equation above allows the acoustic resistance of the assembly consisting of the first and second acoustic transmission lines to be equal to the acoustic resistance of the loudspeaker, which makes it possible to obtain maximum acoustic power and maximum efficiency of the loudspeaker, in addition to an almost flat spectral response of the loudspeaker over a very wide frequency band (for example, over the entire frequency range 20Hz – 20kHz).

[0050] Furthermore, the dimensioning of the first and second constant cross-sections of the two acoustic transmission lines with an area ratio of allows both the acoustic resistance of the assembly consisting of the first and second acoustic transmission lines to be equal to the acoustic resistance of the loudspeaker, but also the acoustic resistances of each of the two acoustic transmission lines to be equal to each other, which makes it possible to optimally reduce vent noise caused by the movement of air in the acoustic transmission lines.

[0051] According to a particular embodiment of the invention:

[0052] - the first and second constant cross-sections are identical and circular, and the diameter D lt The value of each of the first and second circular cross-sections is as follows:

[0053] ; Or

[0054] - the first and second constant cross-sections are circular, the ratio between the area of ​​the second constant cross-section and the area of ​​the first constant cross-section is equal to and the diameter D lt1 of the first circular cross-section is and the diameter D lt2 of the second circular cross-section is .

[0055] Thus, in the case of identical circular cross-sections, the first equation above for the diameter allows the acoustic resistance of the assembly consisting of the first and second acoustic transmission lines to be equal to the acoustic resistance of the loudspeaker. Furthermore, the dimensioning of the first and second circular cross-sections with an area ratio of Furthermore, it allows the acoustic resistances of each of the two acoustic transmission lines to be equal to each other, which helps to reduce vent noise.

[0056] According to another particular embodiment of the invention:

[0057] - the first and second constant cross-sections are identical and square, and the length H r The following is true for each side of the first and second square cross-sections:

[0058] ; Or

[0059] - the first and second constant cross-sections are squares, the ratio between the area of ​​the second constant cross-section and the area of ​​the first constant cross-section is equal to and the lengthH r1 of the first square cross-section is and the lengthH r2 of the second square cross-section is .

[0060] Thus, in the case of identical square cross-sections, the first equation above for the side length allows the acoustic resistance of the entire system consisting of the first and second acoustic transmission lines to be equal to the acoustic resistance of the loudspeaker. Furthermore, the dimensions of the first and second square cross-sections with an area ratio of Furthermore, it allows the acoustic resistances of each of the two acoustic transmission lines to be equal to each other, which helps to reduce vent noise.

[0061] According to a particular embodiment of the invention, the first and second constant cross-sections are rectangular, and the ratio between the area Area2 of the second constant cross-section and the area Area1 of the first constant cross-section is equal to and the widthL r1The first rectangular cross-section is identical to the width L r2 of the second rectangular cross-section, the height H r1 of the first rectangular cross-section is and the height H r2 of the second rectangular cross-section is .

[0062] Thus, this particular embodiment allows for optimization of the total volume of the acoustic enclosure, by limiting the structural volume losses of the acoustic enclosure.

[0063] According to a particular feature of the invention, each of the first and second acoustic transmission lines has at least one bend between its input end and its output end, so as to have a serpentine shape between its input end and its output end.

[0064] Thus, each of the first and second acoustic transmission lines may include one or more bends in order to reduce the volume of the acoustic enclosure box, each bend consisting of a 180° revolution of the constant cross-section.

[0065] It should be noted that the elbows could also take other angles, for example 90° elbows, without departing from the scope of the present invention.

[0066] According to a particular feature of the invention, the acoustic enclosure further comprises internal partition walls arranged parallel inside the box to form the first and second acoustic transmission lines, the acoustic enclosure further comprising an anti-resonance device configured to attenuate the resonances of the structural elements of the acoustic enclosure, said anti-resonance device consisting of a plurality of anti-resonance axes arranged inside the box, each anti-resonance axis passing through all the parallel internal partition walls.

[0067] Thus, the staggered arrangement of the parallel internal partition walls in the box allows for the creation of paths serving as acoustic transmission lines between the housing (in which the loudspeaker is mounted) and the two vents.

[0068] Furthermore, the anti-resonance axes significantly reduce internal resonances within the speaker enclosure. However, they do not completely eliminate them when used at high power levels.

[0069] Alternatively, and without departing from the scope of the present invention, each of the first and second acoustic transmission lines could also consist of a plurality of parallel superimposed acoustic transmission sub-lines, each acoustic transmission sub-line being made up of a sealed duct having the length of the corresponding acoustic transmission line, the sum of the areas of the constant cross-sections of the plurality of ducts corresponding to the area of ​​the constant cross-section of the corresponding acoustic transmission line. This configuration ensures the absence of internal resonances that can seriously impair the quality of sound reproduction. Unlike anti-resonance axes, the solution involving multiple cross-sections ensures the complete cancellation of internal resonances.

[0070] It should be noted that these two anti-resonance methods are only necessary if the cross-section of the acoustic transmission lines is large. If the cross-section remains small, the vibrations due to structural resonance will remain weak and therefore negligible.

[0071] According to a particular feature of the invention, the acoustic enclosure box comprises a central part in which several horizontal ducts are formed, a front end in which several front bends are formed corresponding to the horizontal ducts, and a rear end in which several rear bends are formed corresponding to the horizontal ducts, each of the front and rear bends being configured to connect two adjacent horizontal ducts, such that the horizontal ducts, the front bends and the rear bends form the first and second acoustic transmission lines inside the box.

[0072] Thus, this configuration allows for an optimal design of the acoustic enclosure, the front and rear elbow ends allowing a series connection of some horizontal ducts (namely, two-thirds of the ducts) to form the first line of acoustic transmission and also allowing a series connection of the remaining horizontal ducts (namely, one-third of the ducts) to form the second line of acoustic transmission.

[0073] The front end also has the housing in which the speaker is mounted.

[0074] The first and second vents are arranged either in the front end or in the rear end, preferably in the front end in order to recover all of the acoustic energy that comes out of the vents.

[0075] The present invention also relates to an acoustic enclosure assembly comprising a plurality of acoustic enclosures as described above, the loudspeakers of the plurality of acoustic enclosures being electrically connected to each other in at least one way among series and parallel.

[0076] Thus, the combination of several acoustic speakers according to the invention makes it possible to increase the acoustic power, while maintaining maximum bandwidth and electrical compatibility with the amplifier associated with it (the electrical resistance must remain within the permissible range of the amplifier, often between 4 Ohms and 8 Ohms).

[0077] The plurality of acoustic speakers will not affect the total frequency response, nor the phase of the acoustic signal, but will multiply the total permissible power accordingly.

[0078] According to a particular feature of the invention, the plurality of acoustic enclosures are distributed into a plurality of acoustic enclosure groups, each acoustic enclosure group comprising a number of acoustic enclosures electrically connected in parallel, the acoustic enclosure groups being electrically connected in series, so that the electrical impedance of the acoustic enclosure assembly is compatible with an audio amplifier.

[0079] The most common electrical impedance used in audio amplifiers is 8 Ohms. Therefore, if a speaker system is connected to an audio amplifier with an electrical impedance of 8 Ohms, the speakers will be connected to each other in such a way as to also present an electrical impedance of 8 Ohms.

[0080] According to a particular feature of the invention, for each group of loudspeakers, the loudspeaker assembly comprises a digital sound field processing (DSP) unit, each loudspeaker in said group of loudspeakers being electrically connected to the DSP via a respective Class D audio amplifier.

[0081] Thus, the amplification stage is integrated into each group of loudspeakers, which simplifies wiring and reduces costs.

[0082] According to a particular feature of the invention, the acoustic enclosure assembly further comprises a housing having a plurality of locations configured to respectively receive the plurality of acoustic enclosures.

[0083] According to a particular feature of the invention, at the bottom of each location of the housing of the acoustic enclosure assembly, a magnetic fastening system is installed and configured to cooperate with the associated acoustic enclosure box.

[0084] Thus, the magnetic fastening system can include one or more magnets and allows the speaker to be removably immobilized inside the housing of the speaker assembly.

[0085] To better illustrate the object of the present invention, we will describe below, by way of illustration and not limitation, preferred embodiments, with reference to the attached drawings.

[0086] In these drawings:

[0087] is a schematic cross-sectional view of an acoustic enclosure according to a first embodiment of the present invention;

[0088] represents curves corresponding to the frequency responses of a conventional single-line acoustic enclosure, and of the first and second acoustic transmission lines of the acoustic enclosure according to the present invention;

[0089] represents curves corresponding to the frequency responses of a conventional acoustic enclosure with a single acoustic transmission line and of the acoustic enclosure according to the present invention;

[0090] represents the curve of evolution of the acoustic impedance of an acoustic transmission line as a function of frequency;

[0091] is a basic diagram in the field of acoustics of an acoustic enclosure with an acoustic transmission line;

[0092] represents the curve of evolution of the acoustic power of an acoustic transmission line as a function of its acoustic resistance;

[0093] is a horizontal cross-sectional view of an acoustic enclosure as an example according to the first embodiment of the invention;

[0094] is a perspective view of an acoustic enclosure assembly according to an embodiment of the invention;

[0095] is a perspective view of an acoustic enclosure assembly according to another embodiment of the invention;

[0096] is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

[0097] is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

[0098] is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

[0099] is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

[0100] is a schematic diagram of an acoustic enclosure assembly according to a particular embodiment of the invention;

[0101] is a schematic diagram of an acoustic enclosure assembly according to another particular embodiment of the invention;

[0102] is a schematic diagram of an acoustic enclosure assembly according to yet another particular embodiment of the invention;

[0103] is a vertical cross-sectional view of an acoustic enclosure according to a first variant of the first embodiment of the invention;

[0104] is a vertical cross-sectional view of an acoustic enclosure according to a second variant of the first embodiment of the invention;

[0105] is seen in vertical cross-section of an acoustic enclosure according to a particular embodiment of the invention;

[0106] is a partial horizontal cross-sectional view of the acoustic enclosure of the;

[0107] is a perspective view of the central part of a sound enclosure according to a first variant with 24 conduits of the particular embodiment of the;

[0108] is a front view of the front end of the acoustic enclosure;

[0109] is a front view of the rear end of the acoustic enclosure;

[0110] is a perspective view of the central part of a sound enclosure according to a second variant with 60 conduits of the particular embodiment of the;

[0111] is a front view of the front end of the acoustic enclosure;

[0112] is a front view of the rear end of the acoustic enclosure;

[0113] represents the cross sections of the two transmission lines of the acoustic enclosure according to a particular embodiment of the invention for an optimal configuration of its volume;

[0114] is a functional diagram of a chainable amplified speaker block according to the present invention;

[0115] is a functional diagram of a standard chaining of amplified speaker blocks;

[0116] is a functional diagram of a chaining as an example of amplified speaker blocks with a digital signal splitter (for example, according to the Spdif standard);

[0117] is a functional diagram of a standard chaining of two blocks of amplified stereo speakers;

[0118] is a functional diagram of a chaining system as an example of stereo amplified speaker blocks;

[0119] is a functional diagram of an example chaining of stereo amplified speaker blocks with a digital signal splitter (for example, according to the Spdif standard);

[0120] is a functional diagram of a standard daisy chain as an example of multi-channel amplified speaker blocks; and

[0121] is a functional diagram of an example chaining of multi-channel amplified speaker blocks with a digital signal splitter (for example, according to the Spdif standard).

[0122] If we refer to the figure, we can see that it represents an acoustic enclosure 1 according to a first embodiment of the present invention.

[0123] The acoustic enclosure 1 includes a box 2 in which is provided a housing 3 in which is mounted a loudspeaker 4.

[0124] Box 2 includes an opening 2a corresponding to housing 3, said opening 2a being sealed airtight by the front part of the loudspeaker 4.

[0125] Box 2 further comprises first and second vents 5a and 5b opening to the outside, said first and second vents 5a and 5b being arranged on the same face of box 2 of the acoustic enclosure 1, namely the front face having the opening 2a. It should be noted that the first and second vents 5a and 5b could also be arranged on another face of box 2 of the acoustic enclosure 1, without departing from the scope of the present invention.

[0126] The acoustic enclosure 1 further includes, inside the box 2, a first acoustic transmission line 7 extending between a first inlet end 7a opening into the housing 3 and configured to receive sound waves emitted from the rear of the loudspeaker 4, and a first outlet end 7b opening into the first vent 5a.

[0127] The acoustic enclosure 1 further includes, inside the box 2, a second acoustic transmission line 8 extending between a second input end 8a opening into the housing 3 and configured to receive sound waves emitted from the rear of the loudspeaker 4, and a second output end 8b opening into the second vent 5b.

[0128] The first and second acoustic transmission lines 7 and 8 thus allow the propagation of sound waves emitted from the rear of the loudspeaker 4 towards the first and second vents 5a and 5b.

[0129] The first acoustic transmission line 7 has a first length L1 and a first constant cross-section S1, and the second acoustic transmission line 8 has a second length L2 and a second constant cross-section S2, where L1= 2 * L2 and S1= S2.

[0130] Since the opening 2a and the vents 5a and 5b are formed on the same side of the box 2, the acoustic transmission lines 7 and 8 are angled.

[0131] The first acoustic transmission line 7 is a quarter wave transmission line, while the second acoustic transmission line 8 is an eighth wave transmission line.

[0132] Defining a low cutoff frequency for the acoustic enclosure 1 thus allows us to define the first length L1 of the first quarter-wave transmission line 7 and the second length L2 of the second eighth-wave transmission line 8 according to the equations:

[0133] L1 = c / (4 * F c ), and L2 = c / (8 * F c ) = L1 / 2,

[0134] where L1 is the first length (in m), L2 is the second length (in m), c is the speed of sound in air (in m / s), and F c is the defined lower cutoff frequency (in Hz).

[0135] Compared to a loudspeaker with a single acoustic transmission line, the double acoustic transmission line loudspeaker 1 according to the present invention compensates for the acoustic power loss associated with the different resonance modes of a single acoustic transmission line. The use of a second acoustic transmission line 8, half the length of the first acoustic transmission line 7, effectively compensates for the acoustic power loss at the different resonance modes of the first acoustic transmission line 7. This results in a virtually flat frequency response for the loudspeaker 1 over a very wide frequency range, for example, across the entire 20Hz – 20kHz range, due to the constant cross-sections S1 and S2 of the first and second acoustic transmission lines 7 and 8.

[0136] Indeed, a quarter-wave acoustic transmission line of a given length in the frequency range located at 4 times the natural frequency of the acoustic transmission line is defined by the following equation:

[0137]

[0138] phew lt is the natural frequency of the transmission line (in Hz),L lt is the length of the transmission line (in m), 344 is the speed of sound in air (in m / s), and 4 corresponds to the division into quarter waves.

[0139] An acoustic transmission line allows the transmission of acoustic power generated by the rear of the loudspeaker. Depending on its length, this transmission line causes a delay relative to the wave originating from the rear of the loudspeaker. When the signal emitted by the loudspeaker is a pure sine wave with a predefined frequency, the wave equation... hp The following is located on the front of the speaker:

[0140]

[0141] where x is the time (in s), and fest is the frequency of the signal emitted by the speaker (in Hz).

[0142] Furthermore, the equation of onder lt The output from the transmission line vent is as follows:

[0143]

[0144] where is the time (in s),L lt is the length of the transmission line, and 344 is the speed of sound in air (in m / s).

[0145] The minus sign (-) in front hp represents the fact that the wave at the rear of the speaker is in opposite phase to the front of the speaker.

[0146] L lt / 344 represents the delay in seconds of a quarter of a period at the natural frequency of the transmission line.

[0147] The equation res The sum of the waves from the front of the loudspeaker and the output of the transmission line vent is as follows:

[0148]

[0149] For example, when the length of the quarter-wave transmission line is 4.3 meters (i.e., a natural frequency of the transmission line of 20 Hz) and the frequency sent to the loudspeaker is 20 Hz, r lt is then a quarter of a period ahead of r hp (she should be a quarter of a period behind, but knowing that she is out of phase with r hp (This actually corresponds to a lead of one quarter of a period). When the amplitudes of lt etr hp are unitary, the amplitude of res is then in this case 1.414 (that is, square root of 2).

[0150] Furthermore, when the frequency sent to the speaker is 40 Hz, r lt is then in phase with hp , and the amplitude of res is then 2. When the frequency sent to the speaker is 60 Hz, the amplitude of resis in this case 1.414 (square root of 2). When the frequency sent to the speaker is 80 Hz, r lt etr hp are then in opposite phase, and the amplitude of res is then the zero complement.

[0151] The constant delay caused by the quarter-wave transmission line therefore cancels out both the leading and trailing waves at four times the natural frequency of the transmission line. This cancellation occurs at all multiples of the natural frequency of the quarter-wave transmission line multiplied by four; that is, for example, for a natural frequency of 20 Hz, cancellation occurs at 80 Hz, 160 Hz, 240 Hz, 320 Hz, and so on.

[0152] The equation for the amplitude of the resulting wave res is as follows:

[0153]

[0154] where is the amplitude of res ,fest the frequency emitted by the speaker (in Hz), etf ltis the natural frequency of the transmission line (in Hz).

[0155] In reality, a non-linearity can be identified in the equation for the amplitude of the resulting wave. res depending on the frequency emitted by the speaker, since the further the frequency emitted by the speaker deviates from its natural frequency... lt The more rapidly the attenuation becomes negligible, the more significant the phase shift in the signal will cause phase decoherence and thus eliminate the attenuation. Measurements have shown that the phase decoherence is at least of the 8th order with respect to the frequency.

[0156]

[0157] where is the phase decoherence factor (unitless), fest the frequency emitted by the loudspeaker (in Hz), and f lt is the natural frequency of the transmission line (in Hz).

[0158] The evolution of the amplitude can then be represented by the following equation:

[0159]

[0160] which does indeed lead to a loss of power for a frequency emitted by the loudspeaker at 4 times its natural frequency lt of the quarter-wave transmission line.

[0161] The acoustic enclosure 1 according to the present invention makes it possible to correct this defect, by using two parallel acoustic transmission lines 7 and 8, with a one-to-two ratio between their lengths. For example, for a first quarter-wave transmission line 7 with a length of 4.3 meters (therefore a natural frequency of 20 Hz), the second eighth-wave transmission line 8 must have a length of 2.15 meters (therefore a natural frequency of 40 Hz).

[0162] To compare the acoustic enclosure with and without correction, an uncorrected acoustic enclosure with a single transmission line of section 2*A and length L1 will be compared to the acoustic enclosure 1 according to the present invention with a first transmission line 7 of section A and length L1 and with a second transmission line 8 of section A and length L1 / 2.

[0163] For the uncorrected acoustic enclosure, the equation for the frequency response1 of the single transmission line with a natural frequency of 20 Hz is:

[0164]

[0165] For the acoustic enclosure 1 corrected according to the present invention, the frequency response 21 The first transmission line 7 with a natural frequency of 20 Hz is represented by the following equation:

[0166]

[0167] where ½ corresponds to the fact that the cross-section of the first transmission line 7 is half that of the uncorrected acoustic enclosure.

[0168] Frequency response 22 The second transmission line 8 is taken at a natural frequency of 40 Hz and represented by the following equation:

[0169]

[0170] The frequency responses of the three preceding equations are represented on a logarithmic scale, where h1 corresponds to the uncorrected response of the loudspeaker with a transmission line of 2*A cross-section and a natural frequency of 20 Hz. 21 corresponds to the response of the first transmission line 7 of section A and with a natural frequency of 20 Hz, and h 22 corresponds to the response of the second transmission line 8 of section A and of natural frequency of 40 Hz.

[0171] The resultant of the first and second transmission lines 7 and 8 of the acoustic enclosure 1 according to the present invention corresponds to the sum of the responses of the two transmission lines 7 and 8 and is represented on a logarithmic scale on the in which h1 corresponds to the response of the acoustic enclosure uncorrected to a single transmission line and h2 corresponds to the frequency response of the acoustic enclosure 1 with double acoustic transmission line according to the present invention.

[0172] It can thus be seen that the level variation at 80 Hz (i.e., 4 * 20 Hz) decreases from 9 dB to less than 2 dB with the two acoustic transmission lines 7 and 8. By using the two acoustic transmission lines 7 and 8, the frequency response h2 of the loudspeaker 1 according to the present invention is therefore almost flat. It should be noted that the small variations in the frequency response h2 of the loudspeaker 1 according to the present invention can easily be corrected by an equalizer if absolutely necessary, but that, in most cases, this equalizer is unnecessary.

[0173] Each of the first and second constant cross sections S1 and S2 of the first and second acoustic transmission lines 7 and 8 can be one of circular, oval, rectangular, square and polygonal.

[0174] It should be noted that any other shape is possible for each of the first and second cross sections S1 and S2, the essential thing being that the cross section is constant over the entire length of the line and that the first and second cross sections S1 and S2 have the same shape.

[0175] In order that the acoustic resistance of the assembly consisting of the first and second acoustic transmission lines 7 and 8 is equal to the acoustic resistance of the loudspeaker 4, when the first and second constant cross-sections are identical, the area of ​​each of the first and second constant cross-sections S1 and S2 must be as follows:

[0176]

[0177] where air is the viscosity of air in Ns / m², L1 is the first length in m, F s is the natural resonant frequency of the speaker in Hz,C msis the flexibility (or compliance) of the loudspeaker suspension in m / N,S hp is the surface area of ​​the moving part (or diaphragm) of the loudspeaker in m²,Q ms is the mechanical quality factor (or mechanical overstress coefficient) of the loudspeaker at F s , etKest is a constant which depends on the shape of the cross sections S1 and S2.

[0178] As will be described in more detail below, the denominator 3 in the equation above is related to the paralleling of the acoustic resistances of the first and second acoustic transmission lines 7 and 8.

[0179] The dimensioning of the first and second constant cross sections S1 and S2 of the two acoustic transmission lines 7 and 8 in accordance with the equation above thus makes it possible to obtain maximum acoustic power and maximum efficiency of the acoustic enclosure 1, in addition to an almost flat spectral response of the acoustic enclosure 1 over a very wide frequency band (for example, over the entire frequency range 20Hz – 20kHz).

[0180] The acoustic enclosure 1 according to the invention is independent of the resonance frequency of the loudspeaker 4. Even if the loudspeaker 4 has a resonance frequency of 80 Hz or even greater than 120 Hz, this will not prevent the acoustic enclosure 1 from reaching lower frequencies such as 20 Hz or even less depending solely on the lengths of the first and second acoustic transmission lines 7 and 8.

[0181] Since the acoustic transmission line architecture has no limit in the high frequencies, the highest frequency of the acoustic enclosure 1 will be limited by the maximum frequency that the loudspeaker 4 can provide.

[0182] The overall cost of the solution is thus reduced, since a low-end 4-inch speaker is sufficient to achieve a high-level acoustic result.

[0183] As indicated above, for each of the first and second acoustic transmission lines 7 and 8 of the acoustic enclosure 1, the parameters to be taken into account to obtain a substantially flat spectral response are its length L1 or L2=L1 / 2 and its cross-section S1=S2 (or its diameter in the case of a tubular conduit type transmission line).

[0184] Since the cross-section of the acoustic transmission line has an impact on the spectral response, it must be constant over the entire length of the acoustic transmission line to obtain a substantially flat response.

[0185] The larger the cross-section of the acoustic transmission line, the greater the air displacement. Conversely, the larger the cross-section of the acoustic transmission line, the less the air will be compressed, and the less it will correct the imperfections of the loudspeaker 4. This is why the cross-section of both acoustic transmission lines 7 and 8 must be optimally chosen to maximize acoustic power. This is due to the volume of air displacement that must be converted into compression by the acoustic transmission line to transmit the acoustic power, which acts as acoustic resistance.

[0186] The length L1 of the first quarter-wave acoustic transmission line 7 defines the minimum permissible frequency, i.e. the low cutoff frequency of the acoustic enclosure 1.

[0187] The lower cutoff frequency of the first quarter-wave acoustic transmission line 7 is defined according to the equation:

[0188]

[0189] where c is the low cutoff frequency of the first quarter-wave 7 acoustic transmission line (in Hz), is the speed of sound in air (approximately 300 m / s), L1 is the length of the first quarter-wave 7 acoustic transmission line (in meters), and the coefficient 4 is due to the fact that a quarter of the signal period needs to be taken into account.

[0190] For example, for a 4.3-meter quarter-wave acoustic transmission line, the minimum permissible frequency (also called the low cutoff frequency) will be:

[0191]

[0192] La represents the evolution curve of the acoustic impedance of the first acoustic transmission line 7 as a function of frequency (logarithmic scale).

[0193] We observe that below F c , the frequencies are acoustically short-circuited (acoustic impedance tends towards zero) and the efficiency decreases significantly.

[0194] On the contrary, above F c The acoustic impedance is constant and equal to the acoustic resistance R alt of the first acoustic transmission line 7.

[0195] The acoustic power of a PAC (Peak Airflow) is defined by the air pressure multiplied by the air flow rate:

[0196]

[0197] The air compression capacity of the acoustic transmission line depends inversely on its cross-sectional area. The air displacement capacity of the acoustic transmission line depends on its cross-sectional area. Therefore, the optimal cross-sectional area of ​​the acoustic transmission line must be determined to achieve maximum acoustic power transmission.

[0198] Each of the two acoustic transmission lines 7 and 8 allows the acoustic power to be transmitted from the rear of the loudspeaker 4 to the respective vent 5a or 5b without changing the spectrum but only with a fixed delay:

[0199]

[0200] In this way, the acoustic power at vents 5a and 5b doubles the acoustic power at the front of speaker 4, ensuring very high power efficiency.

[0201] Based on this definition, the acoustic resistance of the acoustic transmission line in the permissible frequency range can be introduced.

[0202] Using the analogy of electrical equations:

[0203]

[0204]

[0205] and by defining acoustic power and replacing the voltage U with air pressure P ralt and the current I by the air flow D a , acoustic resistance R alt The acoustic transmission line within the permissible frequency range can be defined by:

[0206]

[0207] whereR alt is the acoustic resistance of the acoustic transmission line, P ralt is the air pressure in the acoustic transmission line, and D a is the airflow in the acoustic transmission line and the loudspeaker.

[0208] The acoustic resistance of the transmission line is defined by the airflow caused by a pressure applied at the inlet of the transmission line, using the following relationship: Acoustic resistance of the transmission line = Air pressure applied / Airflow caused. This relationship remains true at constant or transient pressure, provided that the pressure remains above the minimum frequency of the transmission line's linear mode (i.e., the low cutoff frequency). This is why we refer to it here as a resistance and not an impedance.

[0209] It should be noted that, for a significant section of the acoustic transmission line, the air pressure will tend towards zero, R alt will then be close to zero. Conversely, for a zero cross-section of the acoustic transmission line (closed enclosure), the air displacement will be zero and R alt will tend towards infinity.

[0210] An acoustic enclosure with an acoustic transmission line can thus be modeled in the field of acoustics by its equivalent in the field of electricity. The diagram represents a voltage divider in the field of acoustics, which includes an acoustic model of a loudspeaker 15 and an acoustic model of an acoustic transmission line 16.

[0211] Using the equivalent of a voltage divider in the acoustic domain allows us to obtain:

[0212]

[0213] whereP ralt is the air pressure of the acoustic transmission line, P raHp is the speaker's air pressure, R as is the acoustic resistance of the speaker, andR alt is the acoustic resistance of the acoustic transmission line.

[0214] And the equivalent of Ohm's law in the acoustic domain is:

[0215]

[0216] whereD a is the airflow rate.

[0217] Using the definition of acoustic power for an acoustic transmission line:

[0218]

[0219] And, by combining the last three equations, we obtain:

[0220]

[0221] Taking the derivative of this equation using R alt As a variable, we observe that the maximum power is found at:

[0222]

[0223] Maximum power is thus obtained when the acoustic resistance of the acoustic transmission line and the acoustic resistance of the loudspeaker are identical.

[0224] La represents the acoustic power curve of the acoustic transmission line P alt depending on R alt .

[0225] Given that R altSince the cross-section of the acoustic transmission line is inversely related to the cross-sectional area, there is a direct link between the maximum power output of the loudspeaker and the size of the acoustic transmission line, and therefore the size of the loudspeaker enclosure. Consequently, for a given loudspeaker power output, the maximum power output of an acoustic transmission line loudspeaker enclosure depends only on its volume.

[0226] According to the Thiele / Small parameters, the acoustic resistance of a loudspeaker can be written as follows:

[0227]

[0228] whereR as is the acoustic resistance of the loudspeaker (not to be confused with the mechanical resistance of the loudspeaker, often called R ms The relationship between the two parameters is as follows: R ms = R as S hp ²),F sis the natural resonant frequency of the loudspeaker (expressed by the manufacturer in Hertz),C ms is the flexibility of the speaker suspension (usually expressed by the manufacturer in mm / N but which must be converted to m / N for calculations),S hp is the surface area of ​​the moving part of the loudspeaker (usually expressed by the manufacturer in mm² but which must be converted to m² for calculations), and Q ms is the mechanical quality factor (given by the manufacturer without units).

[0229] To allow the calculation of the cross-sectional area of ​​the acoustic transmission line so that the acoustic resistances of the loudspeaker and the acoustic transmission line are equal, it is sufficient to express the equation of the resistance of the acoustic transmission line.

[0230] Using a circular cross-section for both acoustic transmission lines 7 and 8 causes a greater loss of usable volume because it increases the volume of the acoustic enclosure structure 1 compared to a rectangular or square cross-section.

[0231] Consequently, the most optimal shape for the cross-section, allowing to minimize the total volume of the acoustic enclosure 1, will be the rectangular or square cross-section.

[0232] It can be noted that using a rectangular or square cross-section will, for the same surface area, have almost no impact on the acoustic resistance value as long as the ratio of the dimensions does not exceed approximately 5; beyond this value, effects come into play which tend to increase the acoustic resistance.

[0233] However, for the same surface area, the acoustic resistance of a rectangular cross-section will always be greater than the acoustic resistance of a square cross-section. Consequently, to minimize the volume of the acoustic enclosure 1, it is therefore preferable to use a square cross-section.

[0234] To determine the acoustic resistance of a transmission line with a square cross-section, the formula for hydraulic resistance, provided by RJ Cornish in the article "Flow in a pipe of rectangular cross-section" published on 1 er October 1928, is used, according to which:

[0235]

[0236] whereR alt is the acoustic resistance of the first acoustic transmission line 7 of square cross-section, L1 is the length of the first acoustic transmission line 7, H ris the length of one side of the square section of the first acoustic transmission line 7, and µ air is the viscosity of air.

[0237] By comparing the acoustic resistances of the first and second acoustic transmission lines 7 and 8, we obtain:

[0238]

[0239] whereR at is the total acoustic resistance of the entire set of the two acoustic transmission lines 7 and 8,R alt is the acoustic resistance of the first line of acoustic transmission 7, andR alt2 is the acoustic resistance of the second acoustic transmission line 8.

[0240] Applying the equality of acoustic resistances between the loudspeaker and the assembly consisting of the first and second acoustic transmission lines 7 and 8, we obtain:

[0241]

[0242] whereR atis the total acoustic resistance of the entire set of the two acoustic transmission lines 7 and 8, andR as is the acoustic resistance of the speaker 4.

[0243] Given that the acoustic resistance of a transmission line is proportional to its length, we obtain:

[0244]

[0245] and therefore:

[0246]

[0247] Given the equation for the acoustic resistance of loudspeaker 4:

[0248]

[0249] Therefore, we obtain:

[0250]

[0251] Given the equation for the acoustic resistance of the first acoustic transmission line 7 with a square cross-section:

[0252]

[0253] Therefore, when the first and second constant cross-sections S1 and S2 are identical and square, the length H rThe following should be true for each side of the first and second square cross-sections S1 and S2 to obtain equal acoustic resistances:

[0254]

[0255] As an example, calculating the length of side H r with the following parameters:

[0256] µ air = 1.8 x 10 -5 Ns / m² (air viscosity at 20°C),

[0257] L1 = 4.3 m (length of the first transmission line 7 for a minimum frequency response of 20Hz),

[0258] F s = 151 Hz (manufacturer's data for the natural resonance frequency of speaker 4),

[0259] C ms = 0.00065 m / N (manufacturer's data for the flexibility of the speaker suspension 4),

[0260] S hp = 0.001735 m² (manufacturer's data or deduced from the diameter of the moving part D) hp = 0.047 m by the following relationship:

[0261]

[0262] Q ms = 5.5 (manufacturer's data),

[0263] given :

[0264] H r = 9.3 mm.

[0265] The total volume V lt of the two transmission lines 7 and 8 is then:

[0266]

[0267]

[0268] V lt = 0.55 liters.

[0269] To obtain the total volume of the complete acoustic enclosure 1, knowing that for a square section, some space is lost and that the volume of the structure of the acoustic enclosure 1 must be considered to ensure rigidity as well as the space needed for the speaker 4, the volume V lt is multiplied by 2, resulting in a total volume of acoustic enclosure 1 of 1.1 litres (0.55 * 2).

[0270] Conversely, to determine the acoustic resistance of a transmission line with a circular cross-section, the hydraulic resistance formula for Poiseuille flow is used, according to which:

[0271]

[0272] whereR altc is the acoustic resistance of the first acoustic transmission line 7 with a circular cross-section, L1 is the length of the first acoustic transmission line 7, D lt is the diameter of the first acoustic transmission line 7, and µ air is the viscosity of air.

[0273] Given that the acoustic resistance of the assembly consisting of the first and second acoustic transmission lines 7 and 8 must be equal to the acoustic resistance of the loudspeaker 4, we obtain:

[0274]

[0275]

[0276] Therefore, when the first and second constant cross-sections S1 and S2 are identical and circular, the diameter D lt The following must be true for each of the first and second circular cross-sections S1 and S2 to obtain equal acoustic resistances:

[0277]

[0278] As an example, the calculation of diameter D lt with the following parameters:

[0279] µ air = 1.8 x 10⁻⁵ Ns / m² (air viscosity at 20°C),

[0280] L1 = 4.3 m (length of the first transmission line 7 for a minimum frequency response of 20Hz),

[0281] F s = 151 Hz (manufacturer's data for the natural resonance frequency of speaker 4),

[0282] C ms = 0.00065 m / N (manufacturer's data for the flexibility of the speaker suspension 4),

[0283] S hp= 0.001735 m² (manufacturer's data or deduced from the diameter of the moving part D) hp = 0.047 m by the following relationship:

[0284]

[0285] Q ms = 5.5 (manufacturer's data),

[0286] given :

[0287] D lt = 10.2 mm.

[0288] The total volume V lt of the two transmission lines 7 and 8 is then:

[0289]

[0290]

[0291] V lt = 0.00053 m 3 = 0.53 liters.

[0292] To obtain the total volume of the complete acoustic enclosure 1, knowing that for a circular section, some space is lost and that the volume of the acoustic enclosure 1's structure must be considered to ensure rigidity as well as the space needed for the loudspeaker 4, the volume V ltis multiplied by 2.5, resulting in a total volume of acoustic enclosure 1 of 1.325 litres (0.53 * 2.5).

[0293] The combined volume of the two transmission lines 7 and 8 with a square cross-section is therefore slightly greater than the combined volume of the two transmission lines 7 and 8 with a circular cross-section, but ultimately results in a smaller volume for the acoustic enclosure 1 due to the reduction in structural volume. Consequently, even though the circular cross-section allows for a slightly smaller surface area, the increased volume of the structure will make the enclosure larger overall. For this reason, a square cross-section should be preferred.

[0294] It should be noted that using two acoustic transmission lines 7 and 8 with the same cross-sectional area can, in some cases, cause an imbalance. Indeed, when the length of the first transmission line 7 is twice that of the second transmission line 8 and their cross-sections are identical, their acoustic resistance being proportional to their length, the acoustic resistance of the first transmission line 7 is twice that of the second transmission line 8. Consequently, air moves more easily in the shorter second transmission line 8, producing more vent noise through it. To avoid this, the cross-sectional areas of the first and second transmission lines 7 and 8 can be modified so that the ratio between the area of ​​the second cross-section 8 and the area of ​​the first cross-section 7 is , which will not only ensure that the acoustic resistance of the loudspeaker 4 is always equal to the acoustic resistance of the two transmission lines 7 and 8 connected in parallel, but also that the acoustic resistances of each of the two transmission lines 7 and 8 are equal to each other.

[0295] Starting from the equation for paralleling the acoustic resistances of the first and second acoustic transmission lines 7 and 8, we have: .

[0296] The new condition is that the two transmission lines 7 and 8 have the same acoustic resistance:R alt = R alt2 , and so .

[0297] Thus, the area Area1 of the cross-section of the first transmission line 7 can be written It should be noted that the number 2 under K could be integrated into this constant, but we keep it to remind you that it corresponds to the case where the two transmission lines 7 and 8 have the same acoustic resistance (as a reminder, in the case where the two transmission lines 7 and 8 have the same cross-section, the number 2 is replaced by the number 3 in the area equation).

[0298] Given that acoustic resistance is a constant, just like µ air The previous equation can be simplified as follows: where K1 is a constant.

[0299] Similarly, for the area ² of the cross-section of the second transmission line 8, we obtain: , either .

[0300] Consequently, to achieve equal acoustic resistance between the two transmission lines 7 and 8, the ratio between their areas must be approximately 0.707. However, the cross-sections of the two transmission lines 7 and 8 will preferably have a similar shape. For example, if a polygonal shape is used for the first transmission line 7, this same shape will also be used for the other transmission line 8 at a scale of 0.707.

[0301] In the specific case of square cross-sections, we have: , and therefore, from when the two transmission lines 7 and 8 have the same acoustic resistance, we therefore obtain .

[0302] Thus, the length H r1 of the first square cross-section of the first transmission line 7 can be written .

[0303] To calculate the length H r2From the second square cross-section of the second transmission line 8, the equation for the equality of the two acoustic resistances can be used: .

[0304] Given that L2 = L1 / 2, we obtain after simplification: , either .

[0305] It should be noted that the case of a rectangular cross-section can be approximated by calculating the area of ​​the square cross-section and keeping this area constant for a rectangular cross-section, knowing that the ratio of the height and width of the rectangle must be between 1.25 and 0.8. Beyond this, an increase in acoustic resistance can no longer be neglected, and it will be necessary to use Poiseuille's equation for a rectangular section to obtain a precise value of the resulting acoustic resistance.

[0306] In the specific case of circular cross-sections, we have: , and therefore, from when the two transmission lines 7 and 8 have the same acoustic resistance, we therefore obtain .

[0307] Thus, the diameter D lt1 of the first circular cross-section of the first transmission line 7 can be written .

[0308] To calculate the diameter D lt2 From the second circular cross-section of the second transmission line 8, the equation for the equality of the two acoustic resistances can be used: .

[0309] Given that L2 = L1 / 2, we obtain after simplification: , either .

[0310] In the particular case where the first and second constant cross-sections are rectangular, and where the ratio between the area of ​​the second constant cross-section and the area of ​​the first constant cross-section is equal to (that is, the first and second transmission lines 7 and 8 have the same acoustic resistance), the total volume of the acoustic enclosure can be optimized using the following conditions: the width L r1 The width of the first rectangular cross-section of the first transmission line 7 is identical to the width L r2 of the second rectangular cross-section of the second transmission line 8, the height H r1 of the first rectangular cross-section of the first transmission line 7 is and the height H r2 of the second rectangular cross-section of the second transmission line 8 is . Thus, this particular dimensioning of the cross sections of the two transmission lines 7 and 8, which is represented in, makes it possible to reduce the structural volume of the acoustic enclosure to a minimum, while improving the aesthetic appearance of the shape of the two vents 5a and 5b.

[0311] If we refer to the diagram, we can see that it represents an example implementation of the acoustic enclosure 1 according to the first embodiment.

[0312] It should be noted that, on this, only the first acoustic transmission line 7 is visible, the second acoustic transmission line 8 being located below or above the latter and therefore not visible.

[0313] The acoustic enclosure 1 shown on the diagram has dimensions of 60 x 220 x 150mm with a first acoustic transmission line 7 of four meters allowing a bandwidth of 20Hz-20kHz.

[0314] It should be noted that using a first acoustic transmission line 7 with a length greater than four meters allows frequencies below 20Hz to be reached. For example, a length of eight meters allows frequencies down to 10Hz, which can be useful for certain acoustic installations.

[0315] The first acoustic transmission line 7 (just like the second acoustic transmission line 8) is bent several times between its inlet end 7a and its outlet end 7b so as to reduce the size of the box 2 and therefore of the acoustic enclosure 1.

[0316] In particular, the acoustic enclosure 1 includes vertical internal partition walls 17 arranged parallel and staggered inside the box 2 to form a path between the rear of the loudspeaker 4 and the first vent 5a, constituting the first serpentine acoustic transmission line 7 between its inlet end 7a and its outlet end 7b.

[0317] These internal vertical separation walls 17 also allow a path to be formed (above or below the first acoustic transmission line 7) between the rear of the loudspeaker 4 and the second vent 5b, constituting the second acoustic transmission line 8 in the form of a serpentine between its inlet end 8a and its outlet end 8b but with a length half that of the first acoustic transmission line 7.

[0318] The acoustic enclosure 1 further comprises, as an anti-resonance device, a plurality of anti-resonance axes 18 arranged horizontally inside the box 2, each anti-resonance axis 18 passing through all of the vertical internal separating walls 17.

[0319] The anti-resonance axes 18 thus make it possible to greatly reduce the resonances of the structural elements of the acoustic enclosure 1. However, they do not make it possible to cancel them completely when used at high power.

[0320] The acoustic enclosure 1 also has a lateral conduit 19 allowing the passage of a connecting wire through it, so as to electrically connect the loudspeaker 4 to a connector 20 located at the rear of the acoustic enclosure 1.

[0321] Since there must be no air leaks except for vents 5a and 5b, it is best to use silicone at the end (speaker 4 side) of conduit 19 intended for the passage of the speaker 4's electrical wire. For the same reason, it is best to use a sealing gasket between opening 2a of box 2 and the front face of speaker 4.

[0322] The volume of box 2 of the acoustic enclosure 1 is thus composed of the volume of the first and second acoustic transmission lines 7 and 8 and the volume of the structural material required (namely, the internal separation walls 17) to construct the first and second acoustic transmission lines 7 and 8 in a rigid and stable manner.

[0323] Advantageously, the structural volume can range from 1 to 1.5 times the volume of the acoustic transmission lines 7 and 8, depending on the material used for the acoustic enclosure 1.

[0324] Referring to Figures 8 to 13, we can see that different acoustic enclosure assemblies 21, 22, 23, 24, 25 and 26 are represented therein according to particular embodiments of the present invention.

[0325] It should be noted that, in these Figures 8 to 13, the first and second vents 5a and 5b have been represented as a single vent 5.

[0326] Each acoustic enclosure assembly 21, 22, 23, 24, 25 and 26 comprises a plurality of acoustic enclosures 1 as described above, the loudspeakers 4 of the plurality of acoustic enclosures 1 being electrically connected to each other in at least one way among series and parallel.

[0327] Thus, the combination of several acoustic speakers 1 makes it possible to increase the acoustic power of the acoustic speaker assembly 21, 22, 23, 24, 25 and 26, while maintaining a maximum bandwidth.

[0328] The plurality of acoustic speakers 1 will not affect the total frequency response, nor the phase of the acoustic signal but will multiply the total permissible power accordingly.

[0329] Since the size of a loudspeaker 4 defines its maximum power, the relationship between the power and the size of a loudspeaker 1 according to the invention is constant and is estimated for a loudspeaker 4 of 10 Watts RMS at approximately 10 Watts RMS / dm² 3 or 10 Watts RMS / litre. This value can be decreased by increasing the acoustic resistance of the acoustic transmission lines 7 and 8 and therefore by increasing the acoustic resistance of the loudspeaker 4.

[0330] For a given loudspeaker 4, since the power of a loudspeaker 1 according to the invention depends linearly only on its size, stacking several loudspeakers 1 will linearly multiply the overall power of the system.

[0331] Lareprésente un ensemble enceinte acoustique 21 en sonbar utilis qui deuxparleurs acoustiques 1 de 20W (60 x 300 x 110mm) permis d’obtenir un pouvoir total 40W.

[0332] Figures 9 to 11 represent acoustic enclosure assemblies 22, 23 and 24 of shelves using 20W acoustic enclosures 1 (60 x 150 x 220mm).

[0333] The acoustic speaker assembly 22 includes two acoustic speakers 1 spaced apart (namely, one 20W acoustic speaker 1 per channel), to obtain two small ambient (or “surround”) speakers.

[0334] The acoustic speaker system 23 includes two 20W acoustic speakers placed side by side, to obtain a 40W center speaker (with a total size of 60 x 300 x 220mm).

[0335] The 24 acoustic speaker system comprises two groups of four 1-inch 20W acoustic speakers stacked on top of each other (i.e., one group per channel), to obtain main speakers of 80W per channel (with a total size of 240 x 150 x 220mm or 120 x 300 x 220mm).

[0336] Figures 12 and 13 represent high-power acoustic speaker assemblies 25 and 26 using 20W acoustic speakers 1 (60 x 75 x 440mm).

[0337] In the, 4*8 = 32 acoustic speakers 1 of 20W are used to obtain a total acoustic power of 640W (with a total size of 480 x 300 x 440mm or 240 x 600 x 440mm).

[0338] In the, 16*8 = 128 acoustic speakers of 20W are used to obtain a total acoustic power of 2560W (with a total size of 960 x 600 x 440mm).

[0339] It should be noted that all acoustic speaker sets 21, 22, 23, 24, 25 and 26 will have the same bandwidth (for example, 20Hz to 20kHz).

[0340] The combination of several identical loudspeakers 1 also allows, if each of them is individually and very precisely controlled by digital processing, for highly accurate sound spatialization. This method is very commonly used to simulate rear speakers from a single soundbar at the front, including a large number of loudspeakers 4 (from ten to several dozen), each individually controlled using the laser effect of light wave propagation, but applied here to sound waves. In the specific case of the present invention, this method is particularly advantageous because the greater the number of loudspeakers 4, the greater the spatialization accuracy.

[0341] Referring to Figures 14 to 16, we can see that they represent different examples of connections of acoustic enclosures 1 in acoustic enclosure assemblies 27, 28 and 29.

[0342] The plurality of acoustic enclosures 1 are distributed into a plurality of acoustic enclosure groups 30, each acoustic enclosure group 30 comprising an (even, in the illustrated examples) number of acoustic enclosures 1 electrically connected in parallel, the acoustic enclosure groups 30 being electrically connected in series, so that the electrical impedance of the acoustic enclosure assembly 27, 28 or 29 is compatible with an audio amplifier (not shown in the Figures).

[0343] The most common electrical impedance used in audio amplifiers is 8 Ohms. Thus, if the speaker assembly 27, 28 or 29 is connected to an audio amplifier with an electrical impedance of 8 Ohms, the speakers 1 will be connected to each other in such a way that the speaker assembly 27, 28 or 29 also has an electrical impedance of 8 Ohms.

[0344] The interconnection of several loudspeakers 1 has no impact on the overall spectrum and phase shift as long as all loudspeakers 1 remain identical and powered by the same electrical signal.

[0345] As an example, ten 10 Watt RMS loudspeakers with a volume of 10 litres will deliver 100 Watts RMS of acoustic power across all frequency ranges.

[0346] Lare represents the connections of an example acoustic speaker assembly 27 comprising two groups 30 of two acoustic speakers 1 (each with a loudspeaker 3 of 8 Ohms).

[0347] Lare represents the connections of an example acoustic speaker assembly 28 comprising four groups 30 of four acoustic speakers 1 (each with a speaker 3 of 8 Ohms).

[0348] Lare represents the connections of an example acoustic speaker assembly 29 comprising eight groups 30 of four acoustic speakers 1 (each with a 4 Ohm speaker 3).

[0349] Thus, each of the acoustic enclosure assemblies 26, 27 and 28 in Figures 14 to 16 has an electrical impedance of 8 Ohms.

[0350] If we refer to the, we can see that it represents a partial vertical cross-sectional view of the acoustic enclosure 1 shown in the, representing only the first line of acoustic transmission 7.

[0351] It is observed that the cross-section of the first acoustic transmission line 7 formed by the vertical internal separation walls 17 has a rectangular shape.

[0352] Since the structure of the first acoustic transmission line 7 is created from rectangular surfaces (internal separation walls 17 constituting the duct of the first acoustic transmission line 7), certain reinforcements must be integrated into the design to avoid unexpected internal resonances.

[0353] A first acoustic transmission line 7 for a full frequency range can consist of 10 to 20 internal partition walls 17, all of which are almost the same size and therefore all have the same internal resonant frequency. This can cause the acoustic enclosure 1 to vibrate and thus significantly affect the frequency response.

[0354] To avoid this, a first solution is to add anti-resonance axes 18 passing through each internal partition wall 17, over the entire width of the acoustic enclosure 1. The diameter of the anti-resonance axes 18 must remain small so as not to have an impact on the cross-section of the duct of the first line of acoustic transmission 7.

[0355] The same anti-resonance axis structure 18 can also be applied to the second acoustic transmission line 8.

[0356] If we refer to the figure, we can see that it represents a partial vertical cross-sectional view of the acoustic enclosure 1 according to a variant of the invention, representing only the first acoustic transmission line 7.

[0357] In this embodiment of the invention, the anti-resonance axes are eliminated and replaced by a multiplication of parallel ducts. For example, instead of a single four-meter duct, three horizontal partitions can be created, forming four superimposed four-meter ducts with a cross-section four times smaller than the initial duct. Since the acoustic resistance of a duct is related to its cross-section, the sum of the cross-sections of the four ducts will result in the same total cross-section and therefore the same acoustic resistance. The thickness of the horizontal partitions must remain small so as not to significantly impact the sum of the cross-sections.

[0358] This variant thus guarantees the absence of internal resonances that can seriously impair the quality of sound reproduction. Unlike anti-resonance axes 18, the solution based on multiple sections ensures the complete cancellation of internal resonances. It is therefore a preferred solution, especially when the loudspeaker 1 is subjected to high acoustic power.

[0359] This variant therefore has two advantages:

[0360] - it reduces the possibilities of internal resonance even more than the anti-resonance axes 18, and

[0361] - it allows the construction of the acoustic enclosure 1 layer by layer (construction by molding then assembly).

[0362] In the, to form the first acoustic transmission line 7, the acoustic enclosure 1 has four identical and stacked stages 31, and a closing upper hood 32, which makes it possible to create four superimposed ducts 33 having the same length and the same cross-section, the total section 34 of the four cross-sections of the four ducts 33 being equal to the cross-section of the duct of the, such that the cross-section of each duct 33 is equal to one-quarter of the cross-section of the duct of the.

[0363] In practice, the four stages 31 and the upper closing cover 32 are injection molded or 3D printed. The four stages 31 are then stacked and fastened together (for example, by gluing or screwing). The upper closing cover 32 is then attached to the last stage 31 (for example, by gluing or screwing). The various elements are assembled to provide an airtight seal, notably by means of gaskets and / or directly by means of adhesive. Advantageously, a polyurethane-based adhesive is used.

[0364] The same structure with multiple sections can also be applied to the second acoustic transmission line 8.

[0365] It should be noted that these two anti-resonance methods are only necessary if the cross-section of the acoustic transmission lines 7 and 8 is large. If the cross-section remains small, the vibrations due to structural resonance will remain weak and therefore negligible.

[0366] Although not shown in Figures 8 and 10 to 13, each acoustic enclosure assembly 21, 23, 24, 25 and 26 could also include a housing having a plurality of locations configured to respectively receive the plurality of acoustic enclosures 1.

[0367] To ensure the immobility of the acoustic speakers 1 in the housing of the acoustic speaker assembly 21, 23, 24, 25 and 26, a magnet placed at the rear of the box 2 of each acoustic speaker 1 and an opposing magnet placed at the bottom of each location in the housing of the acoustic speaker assembly 21, 23, 24, 25 and 26 may be used.

[0368] A hole can also be added next to the magnet placed at the bottom of each location in the housing of the acoustic speaker assembly 21, 23, 24, 25 and 26, to facilitate the extraction of an acoustic speaker 1 by inserting a finger for example.

[0369] To ensure the absence of vibration of each speaker enclosure 1 within the speaker assembly 21, 23, 24, 25, and 26, felt pads may also be used on the four inner faces of the slots in the enclosure of the speaker assembly 21, 23, 24, 25, and 26. The clearance between the slot and the enclosure 2 of the speaker enclosure 1 must be adjusted to allow for relatively easy insertion of the speaker enclosure 1 into the slot while also ensuring that it remains securely in place. To achieve this, the felt must be slightly compressed (for example, as this may vary depending on the felt composition, if the felt is 1 mm thick, once the speaker enclosure 1 is in place, the felt pads on each of the four faces must be compressed by 0.5 mm).

[0370] For ease of use, several loudspeaker units (for example, 2, 4, or 8) can be placed together. It will therefore be necessary to adjust the size of the slots in the loudspeaker enclosure (21, 23, 24, 25, and 26) accordingly. This will be particularly useful for large loudspeaker assemblies containing 16, 32, or 64 or more loudspeakers. Since a group of 8 loudspeakers can weigh around 5 kg, it would not be practical to group 16 or more together. As the actual weight of a group of loudspeakers depends on the characteristics of the drivers used, this limit may vary accordingly.

[0371] Referring to Figures 19 and 20, we can see that they represent the acoustic enclosure 1 designed according to a particular embodiment of the present invention in which the box 2 of the acoustic enclosure 1 comprises a central part 35 in which several horizontal ducts 36 are formed, a front end 37 in which several front bends 38 are formed in correspondence with the horizontal ducts 36, and a rear end 39 in which several rear bends 40 are formed in correspondence with the horizontal ducts 36, each of the front and rear bends 38 and 40 being configured to connect two adjacent horizontal ducts 36, such that the horizontal ducts 36, the front bends 38 and the rear bends 40 form the first and second acoustic transmission lines 7 and 8 inside the box 2.

[0372] The front end 37 also has the housing 3 in which the speaker 4 is mounted, and the first and second vents 5a and 5b.

[0373] Each of the front and rear bends 38 and 40 consists of a 180° revolution of the cross-section of the acoustic transmission lines 7 and 8, which makes it possible to connect and put in series two adjacent horizontal ducts 36 while keeping the cross-section of the acoustic transmission lines 7, 8 constant.

[0374] This particular configuration thus makes it possible to obtain an optimal design of the acoustic enclosure 1, the front and rear ends 37, 39 with bends 38, 40 allowing a series connection of some horizontal conduits 36 (namely, two thirds of the conduits 36) to form the first acoustic transmission line 7, and also allowing a series connection of the remaining horizontal conduits 36 (namely, one third of the conduits 36) to form the second acoustic transmission line 8.

[0375] In order to optimize the volume of the acoustic enclosure 1, it is preferable to use ducts 36 with a square cross-section.

[0376] The number of horizontal conduits 36 required to constitute the two acoustic transmission lines 7 and 8 is defined according to the lengths L1 and L2 of the two acoustic transmission lines 7 and 8, the number of conduits 36 used to form the first acoustic transmission line 7 being twice the number of conduits 36 used to form the second acoustic transmission line 8.

[0377] The front and rear end fittings 37 and 39 can, for example, be molded or 3D printed. The entire duct assembly 36 can, for example, be rigidly assembled and bonded to prevent any internal vibration. The connections between the end fittings 37, 39 and the duct assembly 36 are sealed to prevent any pressure loss to the outside or between the different ducts 36 and elbows 38, 40.

[0378] The three parts of box 2 (namely, the central part 35, the front end 37 and the rear end 39) could also be 3D printed as a single piece, so as to ensure sealing at all points.

[0379] Referring to Figures 21a, 21b and 21c, we can see that they respectively represent the central part 35, the front end 37 and the rear end 39 of an acoustic enclosure 1 as an example, the central part 35 of which has twenty-four horizontal conduits 36.

[0380] The central part 35 has twenty-four horizontal conduits 36 with a square cross-section distributed in six columns and four rows.

[0381] Sixteen horizontal ducts 36a (namely, two-thirds of the ducts 36, shown in dark on the figure) are used to form the first acoustic transmission line 7, and eight other horizontal ducts 36b (namely, one-third of the ducts 36, shown in light on the figure) are used to form the second acoustic transmission line 8.

[0382] It should be noted that different arrangements could also be used, without departing from the scope of the present invention, to change the overall shape of the acoustic enclosure 1 (for example, longer and narrower by using longer ducts 36 and a smaller number of ducts 36, or shorter and wider by using shorter ducts 36 and a larger number of ducts 36). Any other arrangement is possible, the main constraint being that the number of ducts 36 be a multiple of 3. However, some configurations may result in vents 5a and 5b exiting at the rear of the acoustic enclosure 1, which is not preferable to avoid acoustic power losses, particularly at higher frequencies, which are more directional.

[0383] The front end 37 has seven front elbows 38a (in dark on the) used to connect the ducts 36a in pairs for the first acoustic transmission line 7, and three other front elbows 38b (in light on the) used to connect the ducts 36b in pairs for the second acoustic transmission line 8.

[0384] The front end 37 also has a first inlet duct 38c of square section to connect the first acoustic transmission line 7 to the housing 3 in which the loudspeaker 4 is mounted, and a second inlet duct 38d of square section to connect the second acoustic transmission line 8 to said housing 3.

[0385] The front end 37 also has a first outlet duct 38e of square section to connect the first acoustic transmission line 7 to the first vent 5a, and a second outlet duct 38f of square section to connect the second acoustic transmission line 8 to the second vent 5b.

[0386] The rear end 39 has eight rear elbows 40a (in dark on the) used to connect the ducts 36a in pairs for the first acoustic transmission line 7, and four other rear elbows 40b (in light on the) used to connect the ducts 36b in pairs for the second acoustic transmission line 8.

[0387] Referring to Figures 22a, 22b and 22c, we can see that they respectively represent the central part 35, the front end 37 and the rear end 39 of an acoustic enclosure 1 as an example, the central part 35 of which has sixty horizontal conduits 36.

[0388] The central part 35 has sixty horizontal conduits 36 with a square cross-section distributed in ten columns and six rows.

[0389] Forty horizontal ducts 36a (namely, two-thirds of the ducts 36, shown in dark on the figure) are used to form the first acoustic transmission line 7, and twenty other horizontal ducts 36b (namely, one-third of the ducts 36, shown in light on the figure) are used to form the second acoustic transmission line 8.

[0390] The front end 37 has nineteen front elbows 38a (in dark on the) used to connect the ducts 36a in pairs for the first acoustic transmission line 7, and nine other front elbows 38b (in light on the) used to connect the ducts 36b in pairs for the second acoustic transmission line 8.

[0391] The front end 37 also has a first inlet duct 38c of square section to connect the first acoustic transmission line 7 to the housing 3 in which the loudspeaker 4 is mounted, and a second inlet duct 38d of square section to connect the second acoustic transmission line 8 to said housing 3.

[0392] The front end 37 also has a first outlet duct 38e of square section to connect the first acoustic transmission line 7 to the first vent 5a, and a second outlet duct 38f of square section to connect the second acoustic transmission line 8 to the second vent 5b.

[0393] The rear end 39 has twenty rear elbows 40a (in dark on the) used to connect the ducts 36a in pairs for the first acoustic transmission line 7, and ten other rear elbows 40b (in light on the) used to connect the ducts 36b in pairs for the second acoustic transmission line 8.

[0394] It should be noted that different arrangements could also be used with regard to the number of conduits 36 and the location of the front and rear bends 38 and 40 to form the two acoustic transmission lines 7 and 8, without departing from the scope of the present invention.

[0395] In a particular embodiment of the present invention, an amplification stage is integrated into the acoustic enclosure, which allows greater flexibility for the management of cables linking the amplifiers to the acoustic enclosures, but also a reduction in costs.

[0396] When a single central amplifier powers a large number of speakers (for example, more than a thousand), the cost of the amplifier is not linear with respect to its power, and the cost of the amplifier can reach very high sums from a certain power level (for example, for 1000 speakers of 20W each, therefore 20000W in total, a 20000W amplifier can cost almost €100,000).

[0397] Given that the loudspeaker system is highly modular, the loudspeakers 1 according to the invention can be grouped into several blocks 50 that can be chained together indefinitely. Thus, by integrating the amplification stage into the loudspeaker, the cost will remain linear regardless of the number of loudspeakers 1.

[0398] Class D amplifiers are now available, allowing for miniaturization and reduced costs in the amplification stage. For example, Texas Instruments® created the TPA3118 integrated circuit, which provides 60W RMS mono amplification. This integrated circuit measures just 1cm x 1cm x 1mm and requires a small number of external components. Consequently, the entire circuit fits on a 4cm x 5cm circuit board and requires no heat dissipation (no heatsink is necessary). This board is available on the market at a very low cost (less than €1.50).

[0399] It is important to note that since the loudspeaker is capable of operating at very low frequencies, the amplifier's damping factor is crucial. If it is too low, the amplifier's efficiency will likely drop significantly at low frequencies and it will easily saturate, resulting in distortion.

[0400] It is also important to note that, despite the use of transmission lines that allow for a flat frequency response, speaker imperfections may still require correction. To correct these imperfections, it may be necessary to add a digital sound field (DSP) processor capable of equalization over a frequency range from 200Hz to 10kHz. For example, Analog Devices® has created the ADAU1701 integrated circuit. It fits on a 5cm x 7cm circuit board and costs less than €15. This circuit can easily perform frequency response corrections using its parametric equalizer function. Practical experience has shown that six parametric bands are sufficient for very good correction. Since all speakers have virtually the same frequency response, a single DSP board can be shared by several speakers.

[0401] To allow the sharing of a DSP for several loudspeakers, several loudspeakers 1 can be grouped into a single block 50. A block 50 can consist of two to thirty loudspeakers 1 or more depending on the logistics required, knowing that with too many loudspeakers 1 per block, it will make the block 50 more difficult to handle and will reduce the flexibility of the installation in an acoustic room.

[0402] If it is necessary to connect several 50mm blocks together to achieve the desired sound levels, an efficient method must be used to distribute the low-power acoustic signal and prevent degradation as it passes from one 50mm block to another. This is especially important with a large number of 50mm blocks. For example, a concert hall, where the sound levels can be very high, will require a large number of 1-inch loudspeakers and therefore a significant number of 50mm blocks. If the 50mm blocks are daisy-chained, the sound emitted by the first 50mm block must be identical to that at the end of the chain. The appearance of background noise or a delay exceeding 20 ms must be avoided.

[0403] To avoid the appearance of background noise, the use of an end-to-end digital signal could be considered.

[0404] To avoid any time lag in the digital signal, it should not be processed by a DSP from one block to the next. This will allow for a time lag of less than 1 ms for a chain of more than 1000 blocks.

[0405] The signal that will be used to enable this digital transmission may use the Spdif standard (also called S / PDIF, or IEC 958), or any other standard.

[0406] A 50-channel chainable loudspeaker block 1 is shown as an example in the.

[0407] The block 50 comprises a plurality of loudspeakers 1 and a DSP 51, each loudspeaker 1 being connected to the analog output of the DSP 51 via a respective Class D amplifier 52.

[0408] The DSP 51 includes successively, between its stereo analog input and its mono analog output, an analog-to-digital converter (ADC) 53 (whose input is connected to the stereo analog input of block 50), a parametric equalizer 54, a left / right (or multi-channel) channel selector 55 and a digital-to-analog converter (DAC) 56 (whose output is connected to the mono analog output of the DSP 51 itself connected to the various class D amplifiers 52).

[0409] The DSP 51 further includes an asynchronous sample rate converter (ASRC) 57 (whose input is connected to an I2S digital input of the DSP 51) and a mixer 58 (whose output is connected to an I2S digital output of the DSP 51), each of the parametric equalizer 54 and mixer 58 receiving as inputs the output of the ADC 53 and the output of the ASRC 57.

[0410] The block 50 also includes a Spdif / I2S converter 59 (whose input is connected to a digital Spdif Optical / Coaxial input of the block 50), a Bluetooth® I2S receiver 60 and a Wifi I2S receiver 61, as well as a digital input selector 62 located between their outputs and the I2S digital input of the DSP 51.

[0411] Wireless communication modules 60 and 61 have been added to allow for easier use where the situation allows.

[0412] Block 50 also includes a digital reshaping amplifier 63 (with a delay < 1µs and whose input is connected to the digital Spdif input of block 50) and an I2S / Spdif converter 64 (whose input is connected to the digital I2S output of the DSP 51), as well as a master / slave mode selector 65 connecting their outputs to the Optical / Coaxial digital Spdif output of block 50.

[0413] The I2S signal is a digital transmission standard similar to SPDIF but compatible with most DSPs. It comprises three digital signals (four in some cases), whereas SPDIF contains only one. Various integrated circuits exist that enable SPDIF to I2S or I2S to SPDIF conversion. For example, the WM8805 integrated circuit from Wolfson Microelectronics® allows, depending on its configuration, operation in SPDIF to I2S or I2S to SPDIF mode.

[0414] The ASRC (Asynchronous Sample Rate Converter) function is necessary to enable the use of multiple independent I2S sources. This ASRC function is often integrated into DSPs. However, the ADAU1701 does not offer this function internally. Therefore, it will be necessary to add, for example, the CS8421 integrated circuit from Cirrus Logic® to integrate this function.

[0415] It will also be possible to use a more advanced version of the ADAU1701 which integrates the ASRC function, such as the ADAU1452 which integrates 8 independent ASRCs as well as an input and an output Spdif.

[0416] An evolution could be considered to allow compatibility with a multi-channel system.

[0417] Indeed, thanks to Time Division Multiplexing (TDM) technology, it's possible to use up to 8 channels instead of stereo. This solution allows, by selecting the desired channel in blocks of 50, operation in 8 channels, thus enabling compatibility with a 7.1 system often used in home theaters (2 left and right channels, 1 center channel, 2 surround channels, 2 rear surround channels, and 1 subwoofer channel). The ADAU1452 or ADAU1466 is compatible with TDM mode, allowing the management of up to 8 channels. Using these types of circuits doesn't add significant cost and eliminates the need for additional circuits such as I2S / SPDIF converters and external ASRCs. However, to transmit all 8 channels over a single digital cable, the ADAT standard must be used.

[0418] As shown in the diagram, several 50 series blocks can be chained together. The chaining principle is based on the fact that the first 50 series block in the chain must receive the audio source (analog or digital SPDIF input) and be configured in master mode. The output of this first 50 series block is connected to the input of another 50 series block, which is configured in slave mode, via an SPDIF connection using fiber optic cable or coaxial cable. As many 50 series blocks as needed can then be added to the chain, all configured in slave mode.

[0419] As shown in the diagram, the daisy-chaining of the 50 speaker units can also be done using a 66 digital signal splitter (for example, one compliant with the SPDIF standard). Indeed, low-cost SPDIF splitters are available on the market, allowing one SPDIF input to connect to multiple SPDIF outputs. This configuration enables parallel transmission of the digital signal, simplifying cabling and preventing a break in one chain from significantly impacting the overall acoustic reproduction. In the diagram, the daisy-chaining consists of a first 50 unit in master mode, followed by a 50 unit in slave mode, and then the 66 SPDIF splitter with one input and three outputs. Each of the three outputs of the 66 SPDIF splitter is connected to a corresponding sub-chain of 50 units in slave mode.

[0420] As shown in the diagram, when the acoustic installation only requires one 50mm amplifier per channel in stereo, an SPDIF cable can be used to connect the two 50mm amplifiers. The first 50mm amplifier is configured as the master on the left or right channel as needed, and the second 50mm amplifier is configured as the slave on the other channel. Currently, the SPDIF signal only carries two channels for stereo. However, the SPDIF signal can support multichannel audio to support four or more channels. Therefore, it could be considered to use an SPDIF channel extractor to convert a multichannel SPDIF signal to stereo SPDIF to be compatible with the diagram.

[0421] As shown in the diagram, when an acoustic installation requires the use of multiple 50mm blocks per channel (left or right), a single chain can be used for this purpose. Simply configure each 50mm block to the desired channel according to its location in the acoustic room. The left and right channels can be used arbitrarily and are independent of the 50mm block's position in the chain. For example, the first three 50mm blocks (i.e., the first in master mode and then the next two in slave mode) can be on the right channel, then the next three (in slave mode) on the left channel, then the following three (in slave mode) on the right channel, and so on.

[0422] As shown in the diagram, a 66-bit digital signal splitter (for example, following the SPDIF standard) can also be used to facilitate the implementation of the stereo chain. For example, the chain might include a first 50-bit master block for the right channel, followed by a 50-bit slave block for the left channel, followed by the SPDIF splitter, one output of which is connected to a subchain of 50-bit slave blocks for the right channel and the other output of which is connected to a subchain of 50-bit slave blocks for the left channel.

[0423] As illustrated in Figures 30 and 31, multichannel operation requires selecting the desired channel for each block 50. Channels can be selected independently, regardless of a block 50's position in the chain. Since the digital signal transmitted from one block 50 to another systematically contains all channels in the entire chain, there is no particular order to follow.

[0424] The 7.1 Surround multichannel chaining (without Spdif splitter) illustrated as an example includes two initial 50 blocks for the right channel (the first 50 block in master mode and the next in slave mode), then two 50 blocks in slave mode for the left channel, then one 50 block in slave mode for the center channel, then one 50 block in slave mode for the left surround channel, then one 50 block in slave mode for the right surround channel, then one 50 block in slave mode for the right rear surround channel, then one 50 block in slave mode for the left rear surround channel, and finally one 50 block in slave mode for the subwoofer channel.

[0425] Furthermore, the 7.1 surround multichannel daisy chain with digital signal splitter illustrated as an example comprises a first 50-bit master block for the right channel, followed by a 50-bit slave block for the left channel, followed by a 66-bit digital signal splitter (for example, according to the SPDIF standard). The first output of the 66-bit SPDIF splitter is connected to a first sub-chain consisting of a 50-bit slave block for the center channel followed by a 50-bit slave block for the subwoofer channel. The second output of the SPDIF splitter is connected to a second sub-chain consisting of a 50-bit slave block for the right surround channel followed by a 50-bit slave block for the left surround channel. The third output of the 66-bit SPDIF splitter is connected to a third sub-chain consisting of a 50-bit slave block for the right rear surround channel followed by a 50-bit slave block for the left rear surround channel. rear left surround channel.

[0426] It is understood that the particular embodiments which have just been described have been given by way of indication and not limitation, and that modifications may be made without departing from the present invention.

Claims

Acoustic enclosure (1), characterized in that it comprises a box (2) in which is provided a housing (3) in which is mounted a loudspeaker (4), said box (2) comprising an opening (2a) closed by the front part of the loudspeaker (4) and first and second vents (5a, 5b) arranged on the same face of the acoustic enclosure (1) and opening to the outside, the acoustic enclosure (1) further comprising, inside the box (2), a first acoustic transmission line (7) extending between a first inlet end (7a) opening into the housing (3) and configured to receive sound waves emitted from the rear of the loudspeaker (4) and a first outlet end (7b) opening into the first vent (5a),and a second acoustic transmission line (8) extending between a second inlet end (8a) opening into the housing (3) and configured to receive sound waves emitted from the rear of the loudspeaker (4) and a second outlet end (8b) opening into the second vent (5b), so as to propagate the sound waves emitted from the rear of the loudspeaker (4) towards the first and second vents (5a, 5b); said first acoustic transmission line (7) having a first constant length and cross-section, and said second acoustic transmission line (8) having a second constant length and cross-section; said second length being equal to half of said first length, and the ratio between the area of ​​the second constant cross-section and the area of ​​the first constant cross-section being within the interval, . Acoustic enclosure (1) according to claim 1, characterized in that the first acoustic transmission line (7) is a quarter wave transmission line, and the second acoustic transmission line (8) is an eighth wave transmission line. Acoustic enclosure (1) according to claim 1 or 2, characterized in that each of the first and second constant cross sections is one of circular, oval, rectangular, square and polygonal. Acoustic enclosure (1) according to claim 3, characterized in that: - the first and second constant cross-sections are identical, and the area of ​​each of the first and second constant cross-sections is as follows: ; or - the ratio between the area of ​​the second constant cross-section and the area of ​​the first constant cross-section is equal to , And And ;whereµ air is the viscosity of air in Ns / m², L1 is the first length in m, F s is the natural resonant frequency of the loudspeaker (4) in Hz,C ms is the flexibility of the loudspeaker suspension (4) in m / N,S hp is the surface area of ​​the moving part of the loudspeaker (4) in m²,Q ms is the mechanical quality factor of the loudspeaker (4) to F s , and K is a constant. Acoustic enclosure (1) according to claim 4, characterized in that: - the first and second constant cross-sections are identical and circular, and the diameter D lt The value of each of the first and second circular cross-sections is as follows: ; or - the first and second constant cross-sections are circular, the ratio between the area of ​​the second constant cross-section and the area of ​​the first constant cross-section is equal to and the diameter D lt1 of the first circular cross-section is and the diameter D lt2 of the second circular cross-section is . Acoustic enclosure (1) according to claim 4, characterized in that: - the first and second constant cross-sections are identical and square, and the length H r The following is true for each side of the first and second square cross-sections: ; or - the first and second constant cross-sections are squares, the ratio between the area of ​​the second constant cross-section and the area of ​​the first constant cross-section is equal to and the lengthH r1 of the first square cross-section is and the lengthH r2 of the second square cross-section is . Acoustic enclosure (1) according to claim 4, characterized in that the first and second constant cross-sections are rectangular, the ratio between the area Area2 of the second constant cross-section and the area Area1 of the first constant cross-section is equal to and the widthL r1 The first rectangular cross-section is identical to the width L r2 of the second rectangular cross-section, the height H r1 of the first rectangular cross-section is and the height H r2 of the second rectangular cross-section is . Acoustic enclosure (1) according to any one of claims 1 to 7, characterized in that each of the first and second acoustic transmission lines (7, 8) has at least one bend between its inlet end (7a, 8a) and its outlet end (7b, 8b), so as to have a serpentine shape between its inlet end (7a, 8a) and its outlet end (7b, 8b). Acoustic enclosure (1) according to claim 8, characterized in that the acoustic enclosure (1) further comprises internal partition walls (17) arranged parallel inside the box (2) to form the first and second acoustic transmission lines (7, 8), the acoustic enclosure (1) further comprising an anti-resonance device configured to attenuate the resonances of the structural elements of the acoustic enclosure (1), said anti-resonance device consisting of a plurality of anti-resonance axes (18) arranged inside the box (2), each anti-resonance axis (18) passing through all the parallel internal partition walls (17). Acoustic enclosure (1) according to any one of claims 1 to 9, characterized in that the box (2) of the acoustic enclosure (1) comprises a central part (35) in which several horizontal ducts (36) are formed, a front end (37) in which several front bends (38) are formed in correspondence with the horizontal ducts (36), and a rear end (39) in which several rear bends (40) are formed in correspondence with the horizontal ducts (36), each of the front and rear bends (38, 40) being configured to connect two adjacent horizontal ducts (36), such that the horizontal ducts (36), the front bends (38) and the rear bends (40) form the first and second acoustic transmission lines (7, 8) inside the box (2). Acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) comprising a plurality of acoustic enclosures (1) according to any one of claims 1 to 10, the loudspeakers (4) of the plurality of acoustic enclosures (1) being electrically connected to each other in at least one way among in series and in parallel. Acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) according to claim 11, characterized in that the plurality of acoustic enclosures (1) are distributed into a plurality of acoustic enclosure groups (30), each acoustic enclosure group (30) comprising a number of acoustic enclosures (1) electrically connected in parallel, the acoustic enclosure groups (30) being electrically connected in series, so that the electrical impedance of the acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) is compatible with an audio amplifier. Acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) according to claim 12, characterized in that, for each group of acoustic enclosures (30), the acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) comprises a digital sound field processing processor, DSP, each acoustic enclosure (1) of said group of acoustic enclosures (30) being electrically connected to the DSP via a respective class D audio amplifier. Acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) according to any one of claims 11 to 13, characterized in that it further comprises a housing having a plurality of locations configured to respectively receive the plurality of acoustic enclosures (1). Acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) according to claim 14, characterized in that, at the bottom of each location of the housing of the acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29), a magnetic fastening system is installed and configured to cooperate with the box (2) of the associated acoustic enclosure (1).

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