DUAL-LINE ACOUSTIC ENCLOSURE AND ASSOCIATED ACOUSTIC ENCLOSURE SYSTEM

Abstract

DUAL-LINE ACOUSTIC ENCLOSURE AND ASSOCIATED ACOUSTIC ENCLOSURE ASSEMBLY The invention relates to an acoustic enclosure (1) comprising a box (2) in which a housing (3) is provided, in which a loudspeaker (4) is mounted, said box (2) comprising an opening (2a) closed by the front part of the loudspeaker (4) and first and second vents (5a, 5b) opening to the outside, the acoustic enclosure (1) further comprising, inside the box (2), a first acoustic transmission line (7) extending between the housing (3) and the first vent (5a), and a second acoustic transmission line (8) extending between the housing (3) and the second vent (5b), the length of the second transmission line (8) being equal to half the length of the first transmission line (7), and the cross-sections of the two transmission lines (7, 8) being constant and identical. Figure to be published with the abbreviation: Figure 1

Description

Title of the invention: ACOUSTIC ENCLOSURE WITH DUAL ACOUSTIC TRANSMISSION LINE, AND ASSOCIATED ACOUSTIC ENCLOSURE ASSEMBLY

[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 forwards, but also sound waves backwards. Indeed, when the loudspeaker diaphragm moves forward, the air in front of the diaphragm is compressed, while the air behind it is rarefied; conversely, when the loudspeaker diaphragm moves backward, the air in front of the diaphragm is rarefied, while the air behind it is compressed. Thus, when the loudspeaker reproduces audio, its diaphragm moves back and forth, creating unwanted pressure or vacuum with each forward or backward movement. A sound wave is therefore created out of phase with the original signal, leading to an acoustic problem.

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

[0004] The main types of existing acoustic enclosures 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 forwards via a vent,

[0007] - the passive radiator enclosure, in which the vent is replaced by a loudspeaker bass guitars 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 loudspeakers 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 constant level at all required frequencies within the human ear frequency range (commonly accepted between 20 Hz and 20 kHz). However, these solutions often require several types of loudspeakers to cover the full frequency band, most often using loudspeakers simultaneously. bass, mid and treble speakers, but also sometimes an additional separate subwoofer for the extreme bass.

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

[0012] - difficulty in having each speaker at the same level,

[0013] - frequency overlap between loudspeakers is virtually impossible calibrate (requires graphical or parametric equalization for approximate correction),

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

[0015] - control of the phase shift according to complex and often frequencies impossible (introduction of unwanted high-order filtering),

[0016] - global equalization is very difficult, and

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

[0018] Some control (or "monitoring") speakers, commonly used in recording studios, may also be based on acoustic transmission line speaker technology, in which the speaker enclosure includes a long duct inside that acts as a guide for the sound waves emitted from the rear of the loudspeaker to a port. However, these existing acoustic transmission line speakers do not cover the entire 20Hz–20kHz frequency range and generally use several loudspeakers to try to achieve a wider spectral range. Some are capable of reaching a minimum frequency of around 40Hz, but the speaker then reaches a very high price (namely, 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] Thus, no loudspeaker currently on the market allows for a substantially flat spectral response over the entire 20Hz - 20kHz frequency range, while also being inexpensive.

[0021] The present invention aims to overcome the drawbacks of the prior art by proposing an acoustic enclosure comprising two acoustic transmission lines that allow the propagation of sound waves emitted from the rear of the loudspeaker to two respective vents, the dimensioning of the two acoustic transmission lines enabling a virtually flat spectral response to be obtained with a single loudspeaker over a very wide frequency band, for example over the entire 20Hz - 20kHz frequency range.

[0022] 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 with traditional loudspeakers currently on the market.

[0023] 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 length and a first constant cross-section, and said second acoustic transmission line having a second length and a second constant cross-section; said second length being equal to half of said first length, and said first and second constant cross-sections being identical.

[0024] Thus, compared to a loudspeaker with a single acoustic transmission line, the loudspeaker with a double acoustic transmission line according to the present invention makes it possible to compensate 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 half the length of the first acoustic transmission line effectively compensates for the acoustic power loss at the different resonance modes of the first acoustic transmission line, resulting in a virtually flat frequency response of the loudspeaker over a very wide frequency band, for example, across the entire 20Hz - 20kHz frequency range, due to the constant cross-sections of the first and second acoustic transmission lines.

[0025] The use of small loudspeakers will make it possible to ensure a maximum bandwidth of up to 20 kHz. Larger loudspeakers will not be able to reach 20 kHz. The use of small loudspeakers will not affect the natural frequency of the first and second acoustic transmission lines. Only the power will be reduced; therefore, it will suffice to add several loudspeakers to achieve the desired power.

[0026] With the present invention, unlike traditional speakers, all edge effects are corrected.

[0027] The present invention is based on acoustic transmission line technology which allows, in the acoustic domain, strict control of the frequency spectrum of the loudspeaker enclosure. 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.

[0028] 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 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.

[0029] 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.

[0030] 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.

[0031] Virtually no equalization is required with the acoustic enclosure according to the invention, which allows for a frequency response made almost flat by the double acoustic transmission line technology, self-compensation for loudspeaker defects, and less sensitivity to room reverberations.

[0032] Since the acoustic resistance of the assembly consisting of the first and second acoustic transmission lines is much higher than the acoustic resistance of a room (having a large volume compared to that of the first and second acoustic transmission lines and therefore no constraints on air pressure variations), this makes the frequency response of the loudspeaker of the present invention 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 non-constant acoustic resistance across frequencies, making them highly dependent on the room configuration.

[0033] 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 120Hz), no need for a separate subwoofer.

[0034] The overall cost of the solution is reduced: a low-end loudspeaker 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 impact on the frequency response or on phase shifts.

[0035] 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.

[0036] Thus, defining a low cutoff frequency for the acoustic enclosure 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:

[0037] Lj = c / (4 * Fc), and L2 = c / (8 * Fc) = Lj / 2,

[0038] where Li 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 Fc is the defined low cutoff frequency (in Hz).

[0039] 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.

[0040] It should be noted that any other form 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 are identical.

[0041] The shape of the cross-section can, for example, be circular, so that each of the first and second acoustic transmission lines constitutes a tubular conduit. The shape of the cross-section can also be rectangular or square to optimize the size of the acoustic enclosure.

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[0051] According to a particular feature of the invention, the constant cross-sections of each of the first and second cross-sections are as follows: [Math.l] where n air is the viscosity of air in Ns / m2, L is the first length in m, F s is the natural resonant frequency of the loudspeaker 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 „ and K is a constant. Thus, dimensioning the first and second constant cross sections of the two acoustic transmission lines according to the 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). According to a particular embodiment of the invention, the first and second constant cross sections are circular, and the diameter Dlt of each of the first and second circular cross sections is as follows: [Math.2] Thus, in the case of circular cross-sections, the above equation 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. According to another particular embodiment of the invention, the first and second constant cross-sections are square, and the length Hr of each side of the first and second square cross-sections is as follows: [Math.3] HR = Thus, in the case of square cross-sections, the above equation for the side length 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.

[0052] 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.

[0053] Thus, each of the first and second acoustic transmission lines can include one or more bends so as to reduce the volume of the acoustic enclosure box, each bend consisting of a 180° revolution of the constant cross-section.

[0054] 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.

[0055] Thus, the staggered arrangement of the parallel internal partition walls in the box makes it possible to create paths serving as acoustic transmission lines between the housing (in which the loudspeaker is mounted) and the two vents.

[0056] Furthermore, the anti-resonance axes significantly reduce the internal resonances of the acoustic enclosure. However, they do not completely eliminate them when used at high power.

[0057] 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 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 makes it possible to guarantee the absence of internal resonances that can seriously impair the quality of the sound reproduction. Unlike anti-resonance axes, the solution by multiplying the cross-sections ensures the total cancellation of internal resonances.

[0058] 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 resonance of the structure will remain weak and therefore negligible.

[0059] 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.

[0060] Thus, this configuration allows for an optimal design of the acoustic enclosure, the front and rear elbow ends allowing a series connection of certain 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.

[0061] The front end also has the housing in which the speaker is mounted.

[0062] The first and second vents are provided either in the front end or in the rear end, preferably in the front end.

[0063] 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.

[0064] Thus, the combination of several acoustic enclosures according to the invention makes it possible to increase the acoustic power, while maintaining a maximum bandwidth.

[0065] The plurality of acoustic enclosures will not affect the total frequency response, nor the phase of the acoustic signal, but will multiply the total permissible power accordingly.

[0066] 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 an even 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.

[0067] The most commonly used electrical impedance in audio amplifiers is 8 Ohms. Thus, if the 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.

[0068] 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.

[0069] 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.

[0070] Thus, the magnetic fastening system may include one or more magnets and allows the acoustic speaker to be removably immobilized inside the housing of the acoustic speaker assembly.

[0071] 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.

[0072] On these drawings:

[0073] [Fig.1] is a schematic cross-sectional view of an acoustic enclosure according to a first embodiment of the present invention;

[0074] [Fig.2] represents curves corresponding to the frequency responses of a conventional acoustic enclosure with a single acoustic transmission line, and the first and second acoustic transmission lines of the acoustic enclosure according to the present invention;

[0075] [Fig.3] represents curves corresponding to the frequency responses of a conventional acoustic enclosure with a single acoustic transmission line and the acoustic enclosure according to the present invention;

[0076] [Fig.4] represents the evolution curve of the acoustic impedance of a line of acoustic transmission as a function of frequency;

[0077] [Fig.5] is a schematic diagram in the field of enclosure acoustics acoustics with acoustic transmission line;

[0078] [Fig.6] represents the evolution curve of the acoustic power of a line of acoustic transmission as a function of its acoustic resistance;

[0079] [Fig.7] is a horizontal cross-sectional view of an acoustic enclosure as an example according to the first embodiment of the invention;

[0080] [Fig.8] is a perspective view of an acoustic enclosure assembly according to a mode realization of the invention;

[0081] [Fig.9] is a perspective view of an acoustic enclosure assembly according to another method of implementing the invention;

[0082] [Fig. 10] is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

[0083] [Fig. 11] is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

[0084] [Fig. 12] is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

[0085] [Fig. 13] is a perspective view of an acoustic enclosure assembly according to yet another embodiment of the invention;

[0086] [Fig. 14] is a schematic diagram of an acoustic enclosure assembly according to a mode of a particular implementation of the invention;

[0087] [Fig. 15] is a schematic diagram of an acoustic enclosure assembly according to another a particular embodiment of the invention;

[0088] [Fig. 16] is a schematic diagram of an acoustic enclosure assembly according to yet another particular embodiment of the invention;

[0089] [Fig. 17] is a vertical cross-sectional view of an acoustic enclosure according to a first variant of the first embodiment of the invention;

[0090] [Fig. 18] is a vertical cross-sectional view of an acoustic enclosure according to a second variant of the first embodiment of the invention;

[0091] [Fig. 19] is a vertical cross-sectional view of an acoustic enclosure according to a mode of specific implementation of the invention;

[0092] [Fig.20] is a partial horizontal cross-sectional view of the acoustic enclosure of the [Fig.19];

[0093] [Fig.21a] 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 [Fig.19];

[0094] [Fig.21b] is a front view of the front end of the acoustic enclosure of the [Fig.21a];

[0095] [Fig.21c] is a front view of the rear end of the acoustic enclosure of the [Fig.21a];

[0096] [Fig.22a] 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 [Fig.19];

[0097] [Fig.22b] is a front view of the front end of the acoustic enclosure of the [Fig. 22a]; and

[0098] [Fig.22c] is a front view of the rear end of the acoustic enclosure of the [Fig.22a]

[0099] If we refer to [Fig. 1], we can see that it represents an acoustic enclosure 1 according to a first embodiment of the present invention.

[0100] The acoustic enclosure 1 comprises a box 2 in which is provided a housing 3 in which is mounted a loudspeaker 4.

[0101] The box 2 includes an opening 2a corresponding to the housing 3, said opening 2a being sealed tightly by the front part of the loudspeaker 4.

[0102] The 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 the 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 the box 2 of the acoustic enclosure 1, without departing from the scope of the present invention.

[0103] The acoustic enclosure 1 further comprises, 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.

[0104] The acoustic enclosure 1 further comprises, inside the box 2, 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.

[0105] 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.

[0106] The first acoustic transmission line 7 has a first length Li and a first constant cross-section Si, and the second acoustic transmission line 8 has a second length L2 and a second constant cross-section S2, where Li = 2 * L2 and Si = S2.

[0107] 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 bent.

[0108] 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.

[0109] Defining a low cutoff frequency for the acoustic enclosure 1 thus allows us to define the first length Li 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:

[0110] Lj = c / (4 * Fc), and L2 = c / (8 * Fc) = Lj / 2,

[0111] where Li 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 Fc is the defined low cutoff frequency (in Hz).

[0112] Compared to a loudspeaker enclosure comprising a single acoustic transmission line, the double acoustic transmission line loudspeaker 1 according to the present invention makes it possible to compensate 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 having a length half that of the first acoustic transmission line 7 makes it possible to compensate for the acoustic power loss at the different resonance modes of the first acoustic transmission line 7, which makes it possible to obtain a virtually flat frequency response of the loudspeaker enclosure 1 over a very wide frequency band, for example over the entire 20Hz - 20kHz frequency range, due to the constancy of the first and second cross-sections Si and S2 of the first and second acoustic transmission lines 7 and 8.

[0113] 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:

[0114] [Math.4] f -344 It 4Lj(

[0115] where fi, is the natural frequency of the transmission line (in Hz), L / , 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.

[0116] An acoustic transmission line allows the transmission of the 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 r hp at the front of the loudspeaker is as follows:

[0117] [Math.5] r^(x) -sin(2^ / x)

[0118] where x is the time (in s), and / is the frequency of the signal emitted by the loudspeaker (in Hz).

[0119] Furthermore, the wave equation r / , exiting the vent of the transmission line is as follows:

[0120] [Math.6] ■ S / Read ) M*) = -rhp\x-MÂ)

[0121] where x is time (in s), L lt is the length of the transmission line, and 344 is the speed of sound in air (in m / s).

[0122] The sign (-) in front of r hp represents the fact that the wave at the rear of the loudspeaker is in opposite phase with respect to the front of the loudspeaker.

[0123] L / , / 344 represents the delay in seconds of a quarter of a period at the natural frequency of the transmission line.

[0124] The equation r res of the resulting sum of the waves from the front of the loudspeaker and the output of the vent of the transmission line is thus as follows:

[0125] [Math.7] rres(x) = rhp(x) +rlt(x)

[0126] By way of 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 loudspeaker frequency is 20 Hz, r„ is then a quarter-period ahead of r hp (it should be a quarter-period behind, but since it is in opposite phase with r, this actually corresponds to a quarter-period lead). When the amplitudes of r„ and r hp are unity, the amplitude of r res is then in this case 1.414 (i.e., the square root of 2).

[0127] Furthermore, when the loudspeaker frequency is 40 Hz, r„ is in phase with r hp, and the amplitude of r res is then 2. When the loudspeaker frequency is 60 Hz, the amplitude of r res is in this case 1.414 (square root of 2). When the loudspeaker frequency is 80 Hz, r„ and r hp are out of phase, and the amplitude of r res is then complementary to zero.

[0128] The constant delay caused by the quarter-wave transmission line therefore has a cancellation effect on both the leading and trailing waves at 4 times the natural frequency of the transmission line. This cancellation is repeated at all multiples of the natural frequency of the quarter-wave transmission line multiplied by 4, that is to say, for example, for a natural frequency of 20 Hz, cancellation occurring at 80 Hz, 160 Hz, 240 Hz, 320 Hz, etc.

[0129] The equation for the amplitude of the resulting wave r res is as follows:

[0130] [Math. 8] "C-4) =2 | sin ( 271 x)l

[0131] where a is the amplitude of r res, f is the frequency emitted by the loudspeaker (in Hz), and / „ is the natural frequency of the transmission line (in Hz).

[0132] In reality, a non-linearity can be identified for the equation of the amplitude of the resulting wave rres as a function of the loudspeaker frequency, since the further the frequency emitted by the loudspeaker deviates from the resonant frequency, the more rapidly the attenuation becomes negligible. Indeed, the slightest phase deviation of the signal will cause phase decoherence and thus eliminate the attenuation.

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[0144] Measurements showed that the phase decoherence was at least of order 8 with respect to the frequency: [Math.9] where c is the phase decoherence factor (unitless), / is the frequency emitted by the loudspeaker (in Hz), and / / , is the natural frequency of the transmission line (in Hz). The evolution 5 of the amplitude can then be represented by the following equation: [Math. 10] s^'f^=^7T which leads to a loss of power for a speaker frequency / at 4 times the natural frequency / ,, of the quarter wave transmission line. 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). To compare the acoustic enclosure with and without correction, an uncorrected acoustic enclosure with a single transmission line of section 2* A and length Li will be compared to the acoustic enclosure 1 according to the present invention with a first transmission line 7 of section A and length Li and with a second transmission line 8 of section A and length L / 2. For the uncorrected acoustic enclosure, the equation for the frequency response 5, of the single transmission line with a natural frequency of 20 Hz is: [Math. 11] =4 / , 20) For the acoustic enclosure 1 corrected according to the present invention, the frequency response 5 2i of the first transmission line 7 with a natural frequency of 20 Hz is represented by the following equation: [Math. 12] S2I( / ) = $& 20) where r / 2 corresponds to the fact that the cross-section of the first transmission line 7 is half that of the uncorrected acoustic enclosure.

[0145] The frequency response s 22^ of the second transmission line 8 is taken at a natural frequency of 40 Hz and represented by the following equation:

[0146] [Math. 13]

[0147] The frequency responses of the three preceding equations are represented on a logarithmic scale on [Fig.2] in which hi corresponds to the response of the uncorrected acoustic enclosure with a transmission line of section 2* A and a natural frequency of 20 Hz, h2i corresponds to the response of the first transmission line 7 of section A and a natural frequency of 20 Hz, and h22 corresponds to the response of the second transmission line 8 of section A and a natural frequency of 40 Hz.

[0148] 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 [Fig.3] in which hi corresponds to the response of the uncorrected acoustic enclosure 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.

[0149] 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 this is truly necessary, but that, in most cases, this equalizer is unnecessary.

[0150] Each of the first and second constant cross sections Si and S2 of the first and second acoustic transmission lines 7 and 8 can be one of circular, oval, rectangular, square and polygonal.

[0151] It should be noted that any other form is possible for each of the first and second cross sections Si and S2, the essential thing being that the cross section is constant over the whole length of the line and that the first and second cross sections Si and S2 are identical.

[0152] 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, the area of ​​each of the first and second constant cross sections Si and S2 must be as follows:

[0153] [Math. 14] Area —

[0154] where / 1 air is the viscosity of air in Ns / m2, L j is the first length in m, F s is the natural resonant frequency of the loudspeaker 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 „ and K is a constant which depends on the shape of the cross sections Si and S2.

[0155] As will be described in more detail below, the denominator 3 in the above equation is related to the paralleling of the acoustic resistances of the first and second acoustic transmission lines 7 and 8.

[0156] The dimensioning of the first and second constant cross sections Si and S2 of the two acoustic transmission lines 7 and 8 in accordance with the above equation thus makes it possible to obtain a maximum acoustic power and a 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).

[0157] 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 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.

[0158] 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.

[0159] The overall cost of the solution is thus reduced, since a low-end 4-inch loudspeaker is sufficient to obtain a high-level acoustic result.

[0160] 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 Li or L2=Li / 2 and its cross-section Si=S2 (or its diameter in the case of a tubular conduit type transmission line).

[0161] 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.

[0162] The larger the cross-section of the acoustic transmission line, the greater the air displacement. On the other hand, the larger the cross-section of the The higher the acoustic transmission line, the less compressed the air will be, and the less it will correct the speaker's imperfections. 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 transformed into compression by the acoustic transmission line to transmit the acoustic power, acting as acoustic resistance.

[0163] The length Li 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.

[0164] The lower cutoff frequency of the first quarter-wave acoustic transmission line 7 is defined according to the equation:

[0165] [Math. 15] p--— rc - 4¾

[0166] where F c is the lower cutoff frequency of the first quarter-wave acoustic transmission line 7 (in Hz), c is the speed of sound in air (approximately equal to 300 m / s), L j is the length of the first quarter-wave acoustic transmission line 7 (in meters), and the coefficient 4 is due to the fact that a quarter of the period of the signal needs to be taken into account.

[0167] For example, for a 4.3-meter quarter-wave acoustic transmission line, the minimum permissible frequency (also called the low cutoff frequency) will be :

[0168] [Math. 16] Fc = 20Hz

[0169] Fig. 4 represents the evolution curve of the acoustic impedance of the first acoustic transmission line 7 as a function of frequency (logarithmic scale).

[0170] It is observed that below Fc, the frequencies are acoustically short-circuited (the acoustic impedance tends towards zero) and that the efficiency decreases significantly.

[0171] On the contrary, above Fc, the acoustic impedance is constant and equal to the acoustic resistance Rdt of the first acoustic transmission line 7.

[0172] The acoustic power Pac is defined by the air pressure multiplied by the air flow rate:

[0173] [Math. 17] Pac = Air pressure * Air flow rate

[0174] The air compression capacity of the acoustic transmission line depends inversely on the cross-section of the acoustic transmission line. The air displacement capacity of the acoustic transmission line depends on the acoustic transmission line cross-section. Thus, the optimal cross-section of the acoustic transmission line must be defined to obtain maximum transmission of acoustic power.

[0175] 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:

[0176] [Math. 18] Delay duration (in seconds) = or 2 (in meters) * 344?« / s

[0177] In this way, the acoustic power at the vents 5a and 5b makes it possible to double the acoustic power at the front of the loudspeaker 4, which makes it possible to ensure very high power efficiency.

[0178] Based on this definition, the acoustic resistance of the acoustic transmission line in the permissible frequency range can be introduced.

[0179] Using the analogy of electrical equations:

[0180] [Math. 19] Power: P = U*l

[0181] [Math.20] Resistance: R-U11

[0182] and by the definition of acoustic power and by replacing the voltage U with the air pressure Pralt and the current I with the air flow rate Da, the acoustic resistance Ratl of an acoustic transmission line in the permissible frequency range can be defined by:

[0183] [Math.21] D _ P,alt Kalt~ Da

[0184] where / ? an is the acoustic resistance of the acoustic transmission line, P rai is the air pressure in the acoustic transmission line, and D a is the air flow rate in the acoustic transmission line and loudspeaker.

[0185] The acoustic resistance of the acoustic transmission line is thus defined by the airflow caused by a pressure applied at the inlet of the acoustic transmission line, according to the following relationship: Acoustic resistance of the acoustic 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 linear mode of the transmission line (i.e., the low cutoff frequency). This is why reference is made here to a resistance and not an impedance.

[0186] It should be noted that, for a significant section of the acoustic transmission line, the air pressure will tend towards zero, and Rall will then be close to zero. On the contrary, for a zero cross-section of the acoustic transmission line (closed enclosure), the air displacement will be zero and R all will tend towards infinity.

[0187] 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. Figure 5 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.

[0188] The use of the equivalent of the voltage divider bridge in the acoustic domain makes it possible to obtain:

[0189] [Math.22] *ralt ~ R^RM l ral!p

[0190] WHERE Pmll is the air pressure of the acoustic transmission line, PmHp is the air pressure of the loudspeaker, Ras is the acoustic resistance of the loudspeaker, and Ratl is the acoustic resistance of the acoustic transmission line.

[0191] And the equivalent of Ohm's law in the acoustic domain gives:

[0192] [Math.23] ~ Rai+Rait ^PruHp

[0193] where D a is the air flow rate.

[0194] Using the definition of acoustic power for an acoustic transmission line:

[0195] [Math.24] Rail ~ ^a^rult

[0196] and, by combining the last three equations, we obtain:

[0197] [Math.25] p 2 “(p 3 rralip

[0198] Taking the derivative of this equation using R alt as a variable, we find that the maximum power is at:

[0199] [Math.26] Rail = Ras

[0200] The maximum power is thus obtained when the acoustic resistance of the acoustic transmission line and the acoustic resistance of the loudspeaker are identical.

[0201] Figure 6 represents the acoustic power curve of the transmission line acoustics P atl as a function of R atl.

[0202] Since R atl varies inversely with respect to the cross-section of the acoustic transmission line, there is thus a direct link between the maximum power of the loudspeaker and the size of the acoustic transmission line, and therefore the size of the acoustic enclosure. Consequently, at a given speaker power, the maximum power output of an acoustic transmission line enclosure depends only on its volume.

[0203] In accordance with the Thiele / Small parameters, the acoustic resistance of a loudspeaker can be written as follows:

[0204] [Math.27] n ________!_______ aS " 2^CmsSlpQna

[0205] where R as is the acoustic resistance of the loudspeaker (not to be confused with the mechanical resistance of the loudspeaker often called Rms, the relationship between the two parameters being: Rms = Ras. Shp2), F s is the natural resonance frequency of the loudspeaker (expressed by the manufacturer in Hertz), C ms is the flexibility of the suspension of the loudspeaker (usually expressed by the manufacturer in mm / N but which will have to 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 will have to be converted to m2 for calculations), and Q ms is the mechanical quality factor (given by the manufacturer without unit).

[0206] 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.

[0207] The use of a circular cross-section for the two acoustic transmission lines 7 and 8 causes a greater loss of useful volume because it increases the volume of the acoustic enclosure structure 1 compared to a rectangular or square cross-section.

[0208] Consequently, the most optimal shape for the cross-section, allowing minimizing the total volume of the acoustic enclosure 1, will be the rectangular or square cross-section.

[0209] It may be noted that using a rectangular or square cross-section will, for the same area, have virtually 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.

[0210] However, for the same surface area, the sound resistance of a rectangular cross-section will always be greater than the sound resistance of a square cross-section. Consequently, to minimize the volume of the acoustic enclosure 1, it will therefore be preferable to use a square cross-section.

[0211] To determine the acoustic resistance of a transmission line with a square cross-section, the formula for hydraulic resistance, provided by RJ Comish in the article "Flow in a pipe of rectangular cross-section" published on October 1, 1928, is used, according to which:

[0212] [Math.28] 1.78 / / . L,

[0213] where R an is the acoustic resistance of the first acoustic transmission line 7 of square section, L j is the length of the first acoustic transmission line 7, H r is the length of one side of the square section of the first acoustic transmission line 7, and p air is the viscosity of air.

[0214] Considering the parallel comparison of the acoustic resistances of the first and second acoustic transmission lines 7 and 8, we obtain:

[0215] [Math.29] J___L ■ 1 Rat Ralt ^aU2

[0216] where R at is the total acoustic resistance of the set of the two acoustic transmission lines 7 and 8, R au is the acoustic resistance of the first acoustic transmission line 7, and R aii2 is the acoustic resistance of the second acoustic transmission line 8.

[0217] By 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:

[0218] [Math.30] R(it ~ Ras

[0219] where R al is the total acoustic resistance of the set of the two acoustic transmission lines 7 and 8, and R as is the acoustic resistance of the loudspeaker 4.

[0220] Given that the acoustic resistance of a transmission line is proportional to its length, we obtain:

[0221] [Math.31] » _ nalt2~ 2

[0222] and therefore:

[0223] [Math.32] 1 _ 1 _ 1 + 2 _ 3 Rat Ris Rilt Rail Rail

[0224] Given the equation for the acoustic resistance of loudspeaker 4:

[0225] [Math.33] "1 aS

[0226]

[0227] Therefore, we obtain: [Math.34] 2jrF s C„Jï hp Q ms =

[0228] Given the equation for the acoustic resistance of the first acoustic transmission line 7 with a square cross-section:

[0229] [Math.35]

[0230] Therefore, when the first and second cross-sections are constant If Si and S2 are squares, the length Hr of each side of the first and second square cross-sections Si and S2 must be as follows to obtain equality of acoustic resistances:

[0231] [Math.36] HR =

[0232] By way of example, the calculation of the length of side H r with the following parameters:

[0233] pair = 1.8 x 10⁵ Ns / m² (air viscosity at 20°C),

[0234] L, = 4.3 m (length of the first transmission line 7 for a minimum frequency response of 20Hz),

[0235] F ,= 151 Hz (manufacturer's data for the natural resonance frequency of loudspeaker 4),

[0236] C ms = 0.00065 m / N (manufacturer's data for the flexibility of the loudspeaker suspension 4),

[0237] S hp = 0.001735 m2 (manufacturer's data or deduced from the diameter of the moving part)

[0238] Dhp = 0.047 m by the following relationship: [Math.37] ^hp~^\ 2 7

[0239] Q ms = 5.5 (manufacturer's data),

[0240] gives:

[0241] H r = 9.3 mm.

[0242] The total volume V / , of the two transmission lines 7 and 8 is then:

[0243] [Math.38]

[0244] [Math.39] Vh =

[0245] Vz, = 0.55 litre.

[0246] 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 taken into account to ensure rigidity as well as the space required for the loudspeaker 4, the volume V / , is multiplied by 2, i.e. a total volume of the acoustic enclosure 1 of 1.1 litres (0.55 * 2).

[0247] On the contrary, 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:

[0248] [Math.40]

[0249] where R ailc is the acoustic resistance of the first acoustic transmission line 7 with circular cross-section, L j is the length of the first acoustic transmission line 7, D lt is the diameter of the first acoustic transmission line 7, and p air is the viscosity of air.

[0250] 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:

[0251] [Math.41] InFSCm.^hpQms = "X

[0252] [Math.42] 2 27rF s C ms S; tp Q ms —

[0253] Therefore, when the first and second constant cross-sections Si and S2 are circular, the diameter Dlt of each of the first and second circular cross-sections Si and S2 must be as follows to obtain equal acoustic resistances:

[0254] [Math.43]

[0255] By way of example, the calculation of the diameter D / , with the following parameters:

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

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

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

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

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

[0261] [Math.44]

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

[0263] gives:

[0264] D lt = 10.2 mm.

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

[0266] [Math.45]

[0267] [Math.46]

[0268] V lt = 0.00053 m3 = 0.53 liter.

[0269] 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 structure of the acoustic enclosure 1 must be taken into account to ensure rigidity as well as the space required for the loudspeaker 4, the volume V / , is multiplied by 2.5, i.e. a total volume of the acoustic enclosure 1 of 1.325 litres (0.53 * 2.5).

[0270] 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.

[0271] Referring to [Fig.7], one can see that an example implementation of the acoustic enclosure 1 according to the first embodiment is shown there.

[0272] It should be noted that, on this [Fig.7], 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.

[0273] The acoustic enclosure 1 shown in [Fig.7] has dimensions of 60 x 220 x 150mm with a first acoustic transmission line 7 of four meters allowing a bandwidth of 20Hz-20kHz to be obtained.

[0274] It should be noted that the use of a first acoustic transmission line 7 with a length greater than four meters makes it possible to reach frequencies below 20Hz. For example, a length of eight meters makes it possible to reach 10Hz, which can be useful for certain acoustic installations.

[0275] 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.

[0276] 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.

[0277] 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.

[0278] 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.

[0279] 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 totally in the case of use at high power.

[0280] 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.

[0281] Since there must be no air leakage except for vents 5a and 5b, it is preferable to use silicone at the end (speaker 4 side) of the conduit 19 intended for the passage of the speaker 4's electrical wire. For the same reason, it is preferable to use a sealing gasket between the opening 2a of the box 2 and the front face of the speaker 4.

[0282] The volume of the 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 partition walls 17) for construct the first and second acoustic transmission lines 7 and 8 in a rigid and stable manner.

[0283] 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.

[0284] Referring to Figures 8 to 13, we can see that different acoustic enclosure assemblies 21, 22, 23, 24, 25 and 26 are shown there according to particular embodiments of the present invention.

[0285] 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.

[0286] 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.

[0287] Thus, the combination of several acoustic enclosures 1 makes it possible to increase the acoustic power of the acoustic enclosure assembly 21, 22, 23, 24, 25 and 26, while maintaining a maximum bandwidth.

[0288] The plurality of acoustic enclosures 1 will not affect the total frequency response, nor the phase of the acoustic signal but will multiply the total permissible power accordingly.

[0289] 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, for a loudspeaker 4 of 10 Watts RMS, is approximately 10 Watts RMS / dm³ or 10 Watts RMS / liter. This value can be reduced by increasing the acoustic resistance of the acoustic transmission lines 7 and 8, and thus by increasing the acoustic resistance of the loudspeaker 4.

[0290] 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.

[0291] Fig. 8 represents an acoustic speaker assembly 21 in a soundbar configuration using two 20W acoustic speakers 1 (60 x 300 x 110mm) to obtain a total power of 40W.

[0292] Figures 9 to 11 represent acoustic speaker assemblies 22, 23 and 24 of shelves using 20W acoustic speakers 1 (60 x 150 x 220mm).

[0293] The acoustic speaker assembly 22 of [Fig.9] comprises two acoustic speakers 1 spaced apart from each other (namely, one 20W acoustic speaker 1 per channel), to obtain two small ambient (or “surround”) speakers.

[0294] The acoustic speaker assembly 23 of [Fig. 10] comprises two 20W acoustic speakers 1 placed side by side, to obtain a 40W center speaker (with an overall size of 60 x 300 x 220 mm).

[0295] The acoustic speaker assembly 24 of [Fig.1 1] comprises two groups of four superimposed 20W acoustic speakers 1 (namely one group per channel), to obtain main speakers of 80W per channel (with an overall size of 240 x 150 x 220mm or 120 x 300 x 220mm).

[0296] Figures 12 and 13 represent high-power acoustic speaker assemblies 25 and 26 using 20W (60 x 75 x 440mm) acoustic speakers 1.

[0297] In [Fig. 12], 4*8 = 32 1-inch acoustic speakers of 20W are used to obtain an overall acoustic power of 640W (with a total size of 480 x 300 x 440mm or 240 x 600 x 440mm).

[0298] In [Fig.13], 16*8 = 128 1-inch 20W acoustic speakers are used to obtain an overall acoustic power of 2560W (with a total size of 960 x 600 x 440mm).

[0299] It should be noted that all acoustic speaker assemblies 21, 22, 23, 24, 25 and 26 will have the same bandwidth (for example, 20Hz to 20kHz).

[0300] Combining several identical loudspeakers 1 also allows, if each of them is individually and very precisely controlled by digital processing, for very precise 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 precision.

[0301] 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.

[0302] The plurality of acoustic enclosures 1 are distributed into a plurality of acoustic enclosure groups 30, each acoustic enclosure group 30 comprising an even 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).

[0303] The most commonly used electrical impedance in audio amplifiers is 8 Ohms. Thus, in the case where the acoustic speaker assembly 27, 28 or 29 is connected to an audio amplifier having an electrical impedance of 8 Ohms, the acoustic speakers 1 will be connected together in such a way that the acoustic speaker assembly 27, 28 or 29 also has an electrical impedance of 8 Ohms.

[0304] The interconnection of several acoustic speakers 1 has no impact on the overall spectrum and phase shift as long as all the acoustic speakers 1 remain identical and powered by the same electrical signal.

[0305] By way of example, ten 10 Watt RMS loudspeakers with a volume of 10 litres will deliver 100 Watts RMS of acoustic power across all frequency ranges.

[0306] The [Fig. 14] represents the connections of an example acoustic enclosure assembly 27 comprising two groups 30 of two acoustic enclosures 1 (each with a loudspeaker 3 of 8 Ohms).

[0307] Fig. 15 represents the connections of an example acoustic enclosure assembly 28 comprising four groups 30 of four acoustic enclosures 1 (each with a loudspeaker 3 of 8 Ohms).

[0308] Fig. 16 represents the connections of an example speaker enclosure 29 comprising eight groups 30 of four speaker enclosures 1 (each with a 4 Ohm loudspeaker 3).

[0309] Thus, each of the acoustic enclosure assemblies 26, 27 and 28 in Figures 14 to 16 has an electrical impedance of 8 Ohms.

[0310] Referring to [Fig. 17], it can be seen that it represents a partial vertical cross-sectional view of the acoustic enclosure 1 shown in [Fig. 7], representing only the first acoustic transmission line 7.

[0311] 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.

[0312] 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.

[0313] A first acoustic transmission line 7 for a full frequency range can consist of 10 to 20 internal partition walls 17 which are almost all the same size and therefore all have the same internal resonant frequency. This can cause the acoustic enclosure 1 to vibrate and thus strongly affect the frequency response.

[0314] 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 enclosure acoustics 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.

[0315] The same structure with anti-resonance axes 18 can also be applied to the second acoustic transmission line 8.

[0316] Referring to [Fig.18], it can be seen that it shows 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.

[0317] 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 four cross-sections of the four ducts will give the same total cross-section and therefore the same acoustic resistance. The thickness of the horizontal partitions must remain small so as not to have too much of an impact on the sum of the cross-sections.

[0318] 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 total cancellation of internal resonances. It is therefore a preferred solution, especially when the loudspeaker 1 is subjected to high acoustic power.

[0319] This variant thus has two advantages:

[0320] - it reduces the possibilities of resonance even more than the antiresonance axes 18 internal, and

[0321] - it allows the construction of the acoustic enclosure 1 layer by layer (construction by molding then assembly).

[0322] In [Fig. 18], to form the first acoustic transmission line 7, the acoustic enclosure 1 has four identical and stacked stages 31, and a closing top cover 32, which makes it possible to create four superimposed ducts 33 having the same length and the same cross-section, the total cross-section 34 of the four cross-sections of the four ducts 33 being equal to the cross-section of the duct in [Fig. 17], such that the cross-section of each duct 33 is equal to one-quarter of the cross-section of the duct in [Fig. 17].

[0323] In practice, the four stages 31 and the upper closing cover 32 are injection molded or manufactured by 3D printing, then the four stages 31 are stacked and fixed together (for example, by gluing or screwing), then the upper closing cover 32 is fixed onto the last stage 31 (for example, by gluing or screwing), the various elements being assembled to present an airtight seal, particularly via joints and / or directly via adhesive. Advantageously, a polyurethane-based adhesive should be used.

[0324] The same structure with multiple sections can also be applied to the second acoustic transmission line 8.

[0325] 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 resonance of the structure will remain weak and therefore negligible.

[0326] 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.

[0327] In order 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.

[0328] A hole may 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.

[0329] To ensure the absence of vibration of each acoustic enclosure 1 within the acoustic enclosure assembly 21, 23, 24, 25, and 26, felt pads may also be placed on the four inner faces of the slots in the enclosure of the acoustic enclosure assembly 21, 23, 24, 25, and 26. The clearance between the slot and the enclosure 2 of the acoustic enclosure 1 must be adjusted to allow for relatively easy insertion of the acoustic 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, since this may vary depending on the composition of the felt, if the felt is 1 mm thick, once the acoustic enclosure 1 is in place, the felt pads on each of the four faces must be compressed by 0.5 mm).

[0330] For ease of use, several loudspeaker units 1 (for example, 2, 4, or 8) may be joined together. It will therefore be necessary to adapt the size of the slots in the enclosure of the loudspeaker assembly 21, 23, 24, 25, and 26 accordingly. This will be particularly useful for large loudspeaker assemblies containing 16, 32, or 64 or more loudspeaker units 1. Since a group of 8 loudspeaker units 1 can weigh around 5 kg, it would not be practical to group 16 or more together. The actual weight of a group of loudspeakers acoustics 1 depending on the characteristics of the loudspeakers 4 used, this limit may therefore change accordingly.

[0331] Referring to Figures 19 and 20, one 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.

[0332] 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.

[0333] 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 conduits 36 while maintaining the constant cross-section of the acoustic transmission lines 7, 8.

[0334] 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.

[0335] In order to optimize the volume of the acoustic enclosure 1, it is preferable to use ducts 36 with a square cross-section.

[0336] The number of horizontal conduits 36 required to constitute the two acoustic transmission lines 7 and 8 is defined according to the lengths Li 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.

[0337] The front and rear end fittings 37 and 39 can, for example, be molded or 3D printed. The 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.

[0338] The three parts of the 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.

[0339] 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.

[0340] The central part 35 has twenty-four horizontal conduits 36 with a square cross-section distributed in six columns and four rows.

[0341] Sixteen horizontal ducts 36a (namely, two-thirds of the ducts 36, shown in dark on [Fig.21a]) 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 [Fig.21a]) are used to form the second acoustic transmission line 8.

[0342] 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 the 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.

[0343] The front end 37 has seven front elbows 38a (in dark on [Fig.21b]) used to connect the conduits 36a in pairs for the first acoustic transmission line 7, and three other front elbows 38b (in light on [Fig.21b]) used to connect the conduits 36b in pairs for the second acoustic transmission line 8.

[0344] The front end 37 further has a first inlet duct 38c of square cross-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 cross-section to connect the second acoustic transmission line 8 to said housing 3.

[0345] The front end 37 further has a first outlet conduit 38e of square section to connect the first acoustic transmission line 7 to the first vent 5a, and a second outlet conduit 38f of square section to connect the second acoustic transmission line 8 to the second vent 5b.

[0346] The rear end 39 has eight rear elbows 40a (shown in dark on [Fig.21c]) used to connect the conduits 36a in pairs for the first transmission line acoustic 7, and four other rear bends 40b (clearly shown in [Fig.21c]) used to connect the ducts 36b in pairs for the second acoustic transmission line 8.

[0347] 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.

[0348] The central part 35 has sixty horizontal conduits 36 with a square cross-section distributed in ten columns and six rows.

[0349] Forty horizontal ducts 36a (namely, two-thirds of the ducts 36, shown in dark on [Fig.22a]) 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 [Fig.22a]) are used to form the second acoustic transmission line 8.

[0350] The front end 37 has nineteen front elbows 38a (in dark on [Fig.22b]) used to connect the conduits 36a in pairs for the first acoustic transmission line 7, and nine other front elbows 38b (in light on [Fig.22b]) used to connect the conduits 36b in pairs for the second acoustic transmission line 8.

[0351] The front end 37 further has a first inlet duct 38c of square cross-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 cross-section to connect the second acoustic transmission line 8 to said housing 3.

[0352] The front end 37 further has a first outlet conduit 38e of square section to connect the first acoustic transmission line 7 to the first vent 5a, and a second outlet conduit 38f of square section to connect the second acoustic transmission line 8 to the second vent 5b.

[0353] The rear end 39 has twenty rear elbows 40a (in dark on [Fig.22c]) used to connect the conduits 36a in pairs for the first acoustic transmission line 7, and ten other rear elbows 40b (in light on [Fig.22c]) used to connect the conduits 36b in pairs for the second acoustic transmission line 8.

[0354] 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.

[0355] 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

Demands

1. 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 said first and second constant cross-sections being identical.

2. 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.

3. 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.

4. Acoustic enclosure (1) according to claim 3, characterized in that the area of ​​each of the first and second constant cross sections is as follows: [Math.47] Area = where / 1 air is the viscosity of air in Ns / m2, L / , 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 suspension of the loudspeaker (4) in m / N, S hp is the area of ​​the moving part of the loudspeaker (4) in m2, Q ms is the mechanical quality factor of the loudspeaker (4) at F „ and K is a constant.

5. Acoustic enclosure (1) according to claim 4, characterized in that the first and second constant cross-sections are circular, and the diameter Dlt of each of the first and second circular cross-sections is as follows: [Math.48] Dlt =

6. Acoustic enclosure (1) according to claim 4, characterized in that the first and second constant cross-sections are square, and the length Hr of each side of the first and second square cross-sections is as follows: [Math.49] H, =

7. Acoustic enclosure (1) according to any one of claims 1 to 6, 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).

8. Acoustic enclosure (1) according to claim 7, characterized in that the acoustic enclosure (1) further comprises internal partition walls (17) arranged parallel to each other 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 antiresonance axis (18) passing through all the parallel internal separating walls (17).

9. Acoustic enclosure (1) according to any one of claims 1 to 8, 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).

10. 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 9, 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.

11. Acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) according to claim 10, 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 an even 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.

12. Acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) according to any one of claims 10 and 11, characterized in that it further comprises a housing having a plurality of locations configured to respectively receive the plurality of acoustic enclosures (1).

13. Acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29) according to claim 12, characterized in that, at the bottom of each location in the housing of the acoustic enclosure assembly (21; 22; 23; 24; 25; 26; 27; 28; 29), a fastening system magnetic is installed and configured to cooperate with the box (2) of the associated acoustic enclosure (1).

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