speaker

Abstract

The present invention relates to a speaker configured to be installed in a seat assembly. The speaker includes: a diaphragm having a first radiation surface and a second radiation surface, wherein the first radiation surface and the second radiation surface are located on opposite surfaces of the diaphragm; a drive unit configured to move the diaphragm based on an electrical signal; and a speaker support structure, wherein the diaphragm is suspended from the speaker support structure via one or more speaker suspension elements. The speaker support structure encloses a volume configured to receive sound generated by the second radiation surface, wherein the speaker support structure includes one or more porous material areas, the one or more porous material areas having a specific airflow resistance in the range of 300 Pa.s / m to 5000 Pa.s / m, wherein the one or more porous material areas are configured to allow the sound generated by the second radiation surface to leave the volume enclosed by the speaker support structure via the one or more porous material areas. The inventors have found that a speaker having these characteristics is capable of emitting sound in a high-mid-high frequency range (e.g., 300 Hz to 3 KHz) with high directivity while suppressing blowing noise that may otherwise distract a user whose one or both ears are located at a listening position close to the speaker.

Description

Technical Field

[0001] The present invention relates to loudspeakers. Background Art

[0002] A growing trend in the automotive industry is to integrate loudspeakers into car seats in order to create local sound zones for each passenger. This provides personalized messages and individual music selections for each passenger. To improve speech intelligibility and music reproduction quality, a high acoustic contrast between seats is desirable. This way, the sound produced at one seat does not interfere with the listening experience of the listener in other seats. One way to increase the acoustic contrast is to place the loudspeakers as close as possible to the listener's ears.

[0003] However, there are natural limits to how close the loudspeakers can be mounted to the listener's ears. For example, the loudspeakers 1a, 1b are integrated into the front wing of the car headrest (i.e., so that Figure 1a The proximity of the speakers to the user's head (as shown in FIG) can lead to reduced freedom of movement, reduced field of view, and auditory fatigue. These negative effects caused by the proximity of a closed structure that partially surrounds the head are known as the "jail effect". For the comfort of the passenger, it is best to avoid these negative effects.

[0004] If Figure 1b Mounting the loudspeakers 1a, 1b in a headrest farther away from the user's ears as shown in FIG. 1 will reduce the acoustic contrast.

[0005] Figure 1a and Figure 1b The loudspeakers 1a, 1b have a conventional loudspeaker design, in which the magnet unit (loudspeaker driver) is mounted in a closed box that prevents the sound generated by the first (forward) radiating surface from interfering with the sound generated by the second (rear) radiating surface. When the diameter of the diaphragm is small compared to the wavelength of the sound generated, this gives the loudspeaker a monopole characteristic, resulting in the sound being radiated omnidirectionally (i.e., with similar amplitude in all directions), which is generally true for this application (where the diameter of the diaphragm is typically in the range of 20 mm to 80 mm; and the wavelength is the typical telephone voice band of 300 Hz to 3 kHz).

[0006] Since the loudspeaker is mounted in a closed box, the cavity acts as an additional spring, which increases the loudspeaker resonant frequency of the loudspeaker, since the diaphragm cannot move as easily. At significantly below the resonant frequency, for a constant voltage input, mounting the loudspeaker in a closed box results in a decrease in the radiated SPL (sound pressure level). At the resonant frequency, mounting the loudspeaker in a closed box results in an increase in the SPL. In other words, the transfer function (=SPL as a function of frequency at a constant voltage) decreases significantly below the resonant frequency, and increases at the resonant frequency.

[0007] In order to increase the ratio of the radiated on-axis power to the total radiated power, a well-known technique is to use Figure 2a The loudspeaker 1 shown in FIG. 1 has no enclosure. This creates two different lobes, front and rear, resulting in a figure-of-eight radiation pattern with reduced ("narrowed") radiation at the sides. Since the acoustic path length between the first (forward) radiating surface and the second (rear) radiating surface is very short, the overall efficiency is low due to acoustic short-circuiting (the flow from positive pressure to negative pressure at each point in time causes cancellation and reduced electroacoustic conversion efficiency; or, more generally, the anti-sound from the rear reaches and cancels the sound in the front). One remedy for the low output efficiency is, for example, by extending the radiator in a rearward direction (not shown). Figure 2a The cabinet shown in Figure 2 was used to increase the path length between the front and rear of the diaphragm. However, this requires a larger mechanical structure and does not solve the problem that the stronger rear lobe is actually as loud as the front lobe.

[0008] Loudspeakers whose diaphragms are large compared to the wavelength of the sound they produce are directional. For studio and professional audio applications where the goal is to produce sound in the far field (>1 meter), this is easy to achieve in the typical telephone voice band of 300Hz to 3KHz, but difficult to achieve at low frequencies.

[0009] For professional audio and recording studio applications, and for listening in the far field of a loudspeaker, it is well known that at low frequencies, the defined leakage of an otherwise closed but large enclosure can reduce the rear radiation lobe and result in a cardioid radiation characteristic that focuses the radiated sound power toward the listener. Figure 2b An example of such an arrangement is shown in . Here, the loudspeaker 1 driver is mounted to back-radiate into a cavity which is in turn vented via a flow resistance element 35. The combination of volume and flow resistance causes an additional phase shift to be produced on top of the physical path length between the front and rear of the diaphragm. The choice of flow resistance opening location and cabinet dimensions for such an arrangement is typically optimized by about one octave at bass frequencies (e.g. between 60Hz and 120Hz). At higher frequencies, the path length between the sound produced by the first (forward) radiating surface and the second (rear) radiating surface becomes large compared to the wavelength, and Figure 2b The radiation characteristics of the loudspeaker setup shown in are close to those of a monopole.

[0010] for Figure 2bIn arrangements of the type shown in FIG. 1 , the size of the enclosure aperture area provided with the flow resistor element 35 is typically similar to the radiating surface area of ​​the loudspeaker driver. The material typically employed is a thick sheet of foam or felt or the like. The inventors have observed that large volume displacements through the flow resistor element can result in undesirable blowing noises generated by eddies at the micropores or fibers of the flow resistor. This is not a major concern for professional recording and studio applications, as the loudspeakers are typically listened to in the far field and the flow resistor is typically back mounted.

[0011] Loudspeakers for far-field listening applications are usually equipped with powerful motor systems to achieve high mid-band sensitivity. This goes hand in hand with high electrical damping at the resonant frequency that reduces the output. The Qes (electrical Q factor, electrical quality factor) values ​​of such speakers are usually in the range of 0.3 to 0.6.

[0012] The inventors have observed that Figure 2b Another generally undesirable characteristic of the arrangement shown in is that the Qms (mechanical Q factor, mechanical quality factor) of the built-in speaker is reduced compared to a separate speaker drive unit. Friction at the flow resistor affects the reverse radiation impedance of the speaker, increasing mechanical losses and thus reducing the output near the speaker's resonant frequency. Although the Qms of an unboxed speaker may be >10, when enclosed in a box with a flow resistor, the Qms may drop to values ​​below 1.

[0013] The present invention has been designed in view of the above considerations. Summary of the invention

[0014] In a first aspect, the present invention provides:

[0015] A speaker, comprising:

[0016] A diaphragm having a first radiation surface and a second radiation surface, wherein the first radiation surface and the second radiation surface are located on opposite surfaces of the diaphragm;

[0017] a drive unit configured to move the diaphragm based on an electrical signal; and

[0018] a loudspeaker support structure, wherein the diaphragm is suspended from the loudspeaker support structure via one or more loudspeaker suspension elements;

[0019] Wherein, the speaker support structure encloses a volume configured to receive sound generated by a second radiation surface, wherein the speaker support structure includes one or more porous material areas, and the one or more porous material areas have a specific airflow resistance in the range of 300Pa.s / m to 5000Pa.s / m, wherein the one or more porous material areas are configured to allow sound generated by the second radiation surface to leave the volume enclosed by the speaker support structure via the one or more porous material areas.

[0020] The inventors have discovered that a speaker having these characteristics is capable of emitting sound in a highly directional mid-to-high frequency range (e.g., 300 Hz to 3 KHz) while suppressing blowing noise that might otherwise be distracting to a user whose one or both ears are located at a listening position close to the speaker, such as might be the case when the speaker is mounted in a headrest.

[0021] The speaker may be configured to be used with the ear of a user located at a listening position close to the speaker. For example, the speaker may be configured to be used with the ear of a user located at a listening position less than 50 cm (more preferably less than 40 cm, more preferably less than 30 cm, more preferably less than 25 cm, more preferably less than 20 cm or more preferably less than 15 cm) from the first radiation surface of the diaphragm.

[0022] The speaker can be configured to be mounted in a seat assembly, for example by being mounted in a headrest included in the seat assembly (e.g., as discussed below in conjunction with the second aspect of the invention). The seat assembly can be configured for use in a vehicle. One approach is to mount the speaker in a seat assembly, wherein the speaker can be configured for use with an ear of a user located in a listening position proximate to the speaker, for example, as described above.

[0023] The specific airflow resistance reflects the air resistance per unit surface area of ​​the material and is independent of thickness (two materials of different thicknesses can have the same specific airflow resistance). The specific airflow resistance of a porous material area can be measured in accordance with ISO 9053.

[0024] ISO 9053 specifies standard methods (Method A or Method B) for making airflow measurements to measure the airflow resistance - R [Pa.s / m3], specific airflow resistance - Rs [Pa.s / m] and resistivity - r [Pa.s / m2] of a material sample with a given surface area (S) and thickness (t). These measurements are discussed in more detail in GB1908551.3 (titled "Measurement of Airflow Resistance").

[0025] In some cases, the specific airflow resistance of one or more regions of porous material is in the range of 300 Pa.s / m to 4000 Pa.s / m.

[0026] Preferably, the specific airflow resistance of one or more porous material areas is in the range of 500Pa.s / m to 3000Pa.s / m. As can be seen from the experimental data below, it has been found that this range is particularly preferred to provide highly directional sound in the mid-to-high frequency range (e.g., 300Hz to 3KHz) while suppressing blowing noise.

[0027] It will be appreciated by those skilled in the art that useful embodiments may be found throughout the range of specific airflow resistance values ​​described above, although other elements of the loudspeaker will need to be adjusted accordingly. For example, at the lower end of the range of specific airflow resistance values ​​(e.g., 300 Pa.s / m or 500 Pa.s / m), the enclosed volume of the support structure and the surface area of ​​the porous material need to be small enough to avoid the loudspeaker acting as a dipole (see below). Figure 8a At the upper end of the range of specific airflow resistance values ​​(e.g., 3000 Pa.s / m or 5000 Pa.s / m), the enclosed volume of the support structure and the surface area of ​​the porous material need to be large enough to avoid the loudspeaker acting as a closed box (see below). Figure 8d ).

[0028] The loudspeaker support structure preferably comprises a rigid frame from which the diaphragm is suspended via one or more loudspeaker suspension elements.

[0029] One or more porous material regions may be formed of a material having a specific airflow resistance within the above ranges (eg 300 Pa.s / m to 5000 Pa.s / m or 500 Pa.s / m to 3000 Pa.s / m) which covers one or more openings in the rigid structure.

[0030] Preferably, the magnet unit is directly attached to or forms at least a part of a rigid frame from which the diaphragm is suspended via one or more loudspeaker suspension elements.

[0031] Particularly preferred is an example in which the magnet unit forms at least part of a rigid frame on which the diaphragm is suspended, as this helps to ensure compactness of the loudspeaker, which is advantageous if the loudspeaker is to be mounted in a headrest.

[0032] In examples where the magnet unit forms at least part of a rigid frame on which the diaphragm is suspended, one or more porous material regions (of the one or more porous material regions) may be formed from a material having a specific airflow resistance within the above range (e.g. 300Pa.s / m to 5000Pa.s / m or 500Pa.s / m to 3000Pa.s / m), which covers one or more openings in the magnet unit.

[0033] The volume enclosed by the loudspeaker support structure is preferably at least 5 cm 3 , more preferably at least 8 cm 3 , more preferably at least 10 cm 3 , and in some examples may be 20 cm 3 This is significantly larger than the volume typically enclosed by an earphone speaker, for example.

[0034] The volume enclosed by the loudspeaker support structure is preferably less than 5 litres, more preferably less than 1 litre, more preferably less than 100 cm 3 This is significantly smaller than the volume enclosed by loudspeakers typically used in professional recording applications, e.g. Figure 2b As shown in .

[0035] The effective radiation area of ​​the diaphragm is S D Can be in 5cm 2 Up to 50cm 2 within the range.

[0036] As is known in the prior art, for a o and inner diameter d i The roll suspension is suspended from the loudspeaker support structure and has a circular diaphragm. The effective radiation area of ​​the diaphragm can be estimated as Where d is half the diameter of the coil suspension (d o +d i ) / 2.

[0037] Alternatively, or for more complex diaphragm geometries, the effective radiating area S of the diaphragm D It can be measured using known techniques, for example, see "Dynamical Measurement of the Effective Radiating area SD" by Klippel GmbH (https: / / www.klippel.de / fileadmin / klippel / Files / Know_How / Application_Notes / AN_32_Effective_Radiation_Area.pdf).

[0038] Preferably, the surface area of ​​one or more porous material regions (or the combined surface area if there are multiple regions) is the effective radiation area S of the diaphragm. D At least 80% of the effective radiation area S of the diaphragm D At least 100% of the effective radiation area S of the diaphragm D In some cases, the surface area of ​​one or more porous material regions may be the effective radiation area S of the diaphragm. D The larger surface area of ​​the porous material area or areas helps reduce blowing noise.

[0039] From the above considerations it can be seen that for a loudspeaker suitable for installation in a headrest, the surface area of ​​one or more areas of porous material (or the combined surface area if there are multiple areas) can be within 10 cm 2 Up to 250cm2 range, and in some cases can be within 10cm 2 Up to 100cm 2 within the range.

[0040] The speaker is preferably a mid-high frequency speaker configured to produce sound in the entire specified frequency band. The specified frequency band may include at least 500 Hz to 2 KHz, more preferably 300 Hz to 3 KHz, and in some cases, the specified frequency band may include 300 Hz to 20 KHz or even 150 Hz to 20 KHz.

[0041] The drive unit may be an electromagnetic drive unit comprising a magnet unit configured to generate a magnetic field in an air gap and a voice coil attached to a diaphragm (usually via an intermediate coupling element, such as a voice coil bobbin, etc.). In use, the voice coil may be energized (current is caused to flow through the voice coil based on an electrical signal) to generate a magnetic field that interacts with the magnetic field generated by the magnet unit and causes the voice coil (and thus the diaphragm) to move relative to the magnet unit along the main axis of the loudspeaker. The magnet unit may include a permanent magnet. The voice coil may be configured to be located in the air gap when the diaphragm is stationary. Such drive units are well known.

[0042] The resonant frequency of the loudspeaker may be in the range of 150 Hz to 500 Hz. These resonant frequencies are desirable for a mid-high frequency loudspeaker as defined above.

[0043] The magnetic flux density of the magnet unit in the air gap may be in the range of 0.1 T to 0.5 T. This is weaker than the magnetic flux density required for far field applications, but as will be seen from the following discussion, a loudspeaker with a smooth frequency response at smaller listening distances may be provided.

[0044] Preferably, the Qes (electrical Q factor) of the loudspeaker is above 5, more preferably above 10. This defines a "weak" motor, which, as can be seen from the experimental data below, is beneficial for loudspeakers that are used close to the user's ear.

[0045] Preferably, the loudspeaker has a Qms (mechanical Q factor) of less than 2. This defines the damping provided by the one or more regions of porous material (plus contributions from other damping elements) which, as can be seen from the experimental data below, is beneficial for loudspeakers used close to a user's ear.

[0046] Qes and Qms are well-defined parameters for characterizing loudspeakers that are well known in the art and are defined, for example, in the famous papers by Thiele (Loudspeakers in Vented Boxes, Parts I and II) and Small, RH (Direct-Radiator Loudspeaker System Analysis).

[0047] Another known parameter is Qts (total Q factor, total quality factor), which is calculated as follows:

[0048] Qts=(Qms×Qes) / (Qms+Qes)

[0049] The directivity of a loudspeaker can be defined via the following parameters, as defined in Acoustics, Beranek, LL, McGraw-Hill, 1954:

[0050] Directivity factor Q(f): This is the ratio of the intensity on a specified axis of the acoustic radiator at a given distance r to the intensity that the point source would produce at the same location if the point source radiated the same total acoustic power as the radiator.

[0051] Directivity Index DI(f): This is expressed in dB as the value of the expression DI = 10log(Q).

[0052] Preferably, the loudspeaker according to the first aspect of the present invention has a directivity index of 3 dB or more in a specified frequency band (e.g., as described above, e.g., 300 Hz to 3 kHz), more preferably 3.5 dB or more, more preferably 4 dB or more. In some cases, the directivity index in a specified frequency band (e.g., as defined above, e.g., 300 Hz to 3 kHz) may be 4.8 dB or more. The directivity index may be measured at a listening distance (distance from the sound source) of 1 meter.

[0053] The theoretical ideal cardioid has a directivity index of 4.8 dB, so a speaker with a directivity index of 3 dB or more or 4 dB or more is clearly directional. Here, for completeness, we note that a speaker can be more directional than the theoretical ideal cardioid, so that its directivity index is substantially greater than 4.8 dB, for example, as discussed below. Fig.16 and Fig.17 As shown in the experimental data of , this type of loudspeaker can be said to have "supercardioid" directivity. When the diaphragm becomes large compared to the wavelength, the loudspeaker will typically have a directivity index higher than 4.8dB.

[0054] In some cases, a loudspeaker having a directivity index of approximately 4.8 dB (corresponding to a theoretical ideal cardioid) within a specified frequency band (eg, as defined above, e.g., 300 Hz to 3 KHz) may be preferred.

[0055] For the avoidance of any doubt, the loudspeaker may have a spur which causes the directivity index to drop below 4 dB at a single frequency within the specified frequency band (e.g. where the circumference of the loudspeaker support structure is within the wavelength range), while the directivity index remains above 4 dB for substantially the entire specified frequency band. To avoid such spurs, the directivity index of the loudspeaker may preferably be measured in accordance with ISO 266 at a "standard" centre frequency within the specified frequency band for 1 / 3 octave bands, as follows Fig.17 (For a specified frequency band of 300 Hz to 3 KHz, this would mean measuring the directivity index at 315 Hz, 400 Hz, 500 Hz, 630 Hz, 800 Hz, 1 KHz, 1.25 KHz, 1.6 KHz, 2 KHz, and 2.5 KHz.) Alternatively, the directivity index of the loudspeaker may be measured over the entire specified frequency band using 1 / 3 octave smoothing, as shown below: Fig.16 as shown in .

[0056] Nevertheless, it is preferred that the loudspeaker has a directivity index (without spurs) above 4 dB for the entire specified frequency band (eg, as defined above, e.g., 300 Hz to 3 KHz).

[0057] Preferably, within a specified frequency band (e.g. as defined above, e.g. 300 Hz to 3 kHz), the SPL (sound pressure level) measured on the main radiation axis of the loudspeaker according to the first aspect of the invention is at least 6 dB higher for substantially the entire specified frequency band than the SPL measured at the same listening distance (distance from the sound source) at 180° to the main radiation axis. In other words, within the specified frequency band, the rear lobe (SPL at 180°) should be at least -6 dB relative to the forward lobe. For these measurements, the SPL may be measured at a listening distance of 1 meter.

[0058] For the avoidance of any doubt, the loudspeaker may have a spur which causes the SPL difference (on the main axis, 180° from the main radiating axis) to drop below 6 dB at a single frequency within the specified frequency band, while the SPL difference is still at least 6 dB for substantially the entire specified frequency band. To avoid such spurs, the SPL values ​​of the loudspeaker may preferably be measured in accordance with ISO 266 at a "standard" center frequency within the specified frequency band for 1 / 3 octave bands (for a specified frequency band of 300 Hz to 3 kHz, this would mean measuring SPL values ​​at 315 Hz, 400 Hz, 500 Hz, 630 Hz, 800 Hz, 1 kHz, 1.25 kHz, 1.6 kHz, 2 kHz and 2.5 kHz). Alternatively, the SPL values ​​may be measured over the entire specified frequency band using 1 / 3 octave smoothing.

[0059] Nevertheless, preferably, within a specified frequency band (e.g. as defined above, e.g. 300 Hz to 3 kHz), the SPL of the loudspeaker measured on the main radiation axis is at least 6 dB higher (without spurs) for the entire specified frequency band than the SPL measured at the same listening distance 180° to the main radiation axis.

[0060] Preferably, within a specified frequency band (e.g., as defined above, e.g., 300 Hz to 3 KHz), the directivity index of the loudspeaker is above 4 dB for substantially the entire specified frequency band, and within the specified frequency band, the SPL of the loudspeaker measured on the main radiation axis is at least 6 dB higher for substantially the entire specified frequency band than the SPL measured at the same listening distance 180° from the main radiation axis.

[0061] A second aspect of the present invention may provide a seat assembly comprising one or more speakers according to the first aspect of the present invention.

[0062] The seat assembly may include a headrest, with one or more speakers mounted in the headrest of the seat assembly. In some examples, the headrest may be removable from the rest of the seat assembly. In other examples, the headrest may be integral with the rest of the seat assembly. In some seats (e.g., shell seats for automobiles), the headrest may be integral with the rest of the seat, making it unclear where the backrest ends and the headrest begins.

[0063] The present invention does not require that the one or more speakers be mounted in a headrest of a seat assembly, because, for example, the one or more speakers may be mounted in a seat assembly without a headrest, or may be mounted in a portion of a seat assembly that is not a headrest, such as a seat backrest (e.g., an upper portion of such a backrest).

[0064] The seat assembly is preferably configured to allow sound generated by the first radiating surface of the or each speaker according to the first aspect of the invention to propagate away from the seat assembly, for example via the opening or the acoustically transparent portion.

[0065] Similarly, the seat assembly is preferably configured to allow sound generated by the second radiating surface of the or each speaker according to the first aspect of the invention to propagate away from the headrest, for example via the opening or acoustically transparent portion.

[0066] The seat assembly may include:

[0067] The first speaker according to the first aspect of the present invention, wherein the first speaker is located in a headrest for use by a first ear of a user located at a listening position close to a first radiation surface of a diaphragm of the first speaker (e.g., less than 50 cm, more preferably less than 40 cm, more preferably less than 30 cm, more preferably less than 25 cm, more preferably less than 20 cm, more preferably less than 15 cm from the first radiation surface of the diaphragm of the first speaker); and

[0068] The second speaker according to the first aspect of the present invention is located in a headrest for use by the second ear of the user at a listening position close to the first radiation surface of the diaphragm of the second speaker (for example, less than 50 cm, more preferably less than 40 cm, more preferably less than 30 cm, more preferably less than 25 cm, more preferably less than 20 cm, more preferably less than 15 cm from the first radiation surface of the diaphragm of the second speaker).

[0069] The seat assembly may include one or more additional speakers.

[0070] For example, the seat assembly may include one or more woofers for producing sounds at bass frequencies. Bass frequencies may include frequencies in the range of 60 Hz to 80 Hz, more preferably frequencies in the range of 50 Hz to 100 Hz, and more preferably frequencies in the range of 40 Hz to 100 Hz. In some cases, the woofer may additionally be used to produce sounds at higher frequencies than described herein, for example up to (or even exceeding) 250 Hz or 300 Hz. This may be useful if the speakers described in accordance with the first aspect of the invention are not suitable for producing sounds below these frequencies.

[0071] For example, exemplary speakers that can be used as woofers in the seat assembly are described in WO2019 / 121266, WO2019 / 192808, WO2019 / 192816, GB1907267.7 (including any subsequent publications based on this application), and GB1907267.7 (including any subsequent publications based on this application). Other disclosures related to providing suitable woofers are also disclosed in PCT / EP2019 / 084950 and GB1907610.8.

[0072] If the seat assembly comprises one or more woofers, the loudspeaker according to the first aspect of the invention may be used as a mid-high frequency unit, for example, operating in a frequency band comprising 300 Hz to 3 kHz, more preferably 300 Hz to 20 kHz.

[0073] If the seat assembly does not include one or more woofers, the speaker according to the first aspect of the invention may be used as a full-range frequency unit (albeit within potentially limited low-frequency capabilities), for example, operating in a frequency band comprising 60 Hz to 3 kHz (more preferably 60 Hz to 20 kHz).

[0074] The headrest of the seat assembly (if present, see above) may have a rigid headrest frame, e.g. including one or more mounting pins for mounting and rigidly attaching the headrest frame to a rigid seat frame as described below (these mounting pins are conventional in automotive headrests, where two mounting pins are typically used). The speaker support structure for the or each speaker according to the first aspect of the invention may be part of or fixedly attached to the rigid headrest frame.

[0075] Preferably, the seating assembly is configured to position a user seated in a seating portion of the seating assembly such that the user's ears are located in the listening position as described above.

[0076] Preferably, the seating assembly is configured to position a user seated in a seating portion of the seating assembly such that a first ear of the user is located at a first listening position as described above and a second ear of the same user is located at a second listening position as described above.

[0077] The seat assembly may have a rigid seat frame.The speaker support structure of the or each speaker according to the first aspect of the invention may be part of or fixedly attached to the rigid seat frame.

[0078] The seat assembly may be configured for use in a vehicle, such as an automobile (in which case the seat assembly may be referred to as a "car seat") or an aircraft (in which case the seat assembly may be referred to as an "aircraft seat").

[0079] The seat assembly can be a seat for use outside a vehicle. For example, the seat assembly can be configured for use at home, such as a seat for computer gaming, a seat for studio monitoring, or a seat for home entertainment.

[0080] In a third aspect, the present invention may provide a headrest as described above in conjunction with a seat assembly according to the second aspect of the present invention (without requiring any other aspects of the seat assembly). The headrest may be configured to be installed in a seat assembly (e.g., a seat assembly according to the second aspect of the present invention).

[0081] In a fourth aspect, the present invention may provide a vehicle (eg, a car or an airplane) having a plurality of seat assemblies according to the second aspect of the present invention.

[0082] The present invention includes any combination of the aspects and preferred features described, unless such a combination is expressly impermissible or should be explicitly avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Embodiments and experiments illustrating the principles of the present invention will now be discussed with reference to the accompanying drawings, in which:

[0084] Figure 1a Shown are loudspeakers 1a, 1b integrated into the front tabs of a car headrest.

[0085] Figure 1b Shown are loudspeakers 1a, 1b integrated in a car headrest without a front protrusion.

[0086] Figure 2a The loudspeaker is shown without cabinet mounting.

[0087] Figure 2b A loudspeaker mounted in a cabinet with a defined leakage is shown.

[0088] Figure 3a to Figure 3c A first loudspeaker according to the present disclosure is shown.

[0089] Figure 4a and Figure 4b Shown include Figure 3a to Figure 3c An exemplary headrest for two of the first speakers shown in FIG.

[0090] Figure 5 A second speaker according to the present disclosure is shown.

[0091] Figure 6A third loudspeaker according to the present disclosure is shown.

[0092] Figures 7a to 7c A fourth speaker according to the present disclosure is shown.

[0093] Figure 8 to Fig.17 The experimental results are shown. DETAILED DESCRIPTION

[0094] Various aspects and embodiments of the present invention will now be discussed in conjunction with the accompanying drawings. Other aspects and embodiments will be apparent to those skilled in the art. All documents mentioned herein are incorporated herein by reference.

[0095] The inventors have recognized a need for a loudspeaker having as high a ratio of on-axis radiated energy to total radiated energy as possible. When used close to the listener's ear (e.g., when incorporated into a car headrest), such a loudspeaker can allow the listening level of each user (passenger) to be improved as the distance between the user's ear and the loudspeaker associated with their car seat increases, without disturbing other passengers in the vehicle cabin. Furthermore, it is desirable that the above-mentioned ratio of on-axis energy radiation to off-axis energy radiation be as high as possible over a wide frequency range, particularly in the speech band between 300 Hz and 3 kHz, to which the human ear is very sensitive.

[0096] The speaker may be able to reproduce frequencies above and below the typical speech band, for example operating as a mid-high frequency unit up to 20KHz, and ideally, with some mid-low frequency capability down to 100Hz. To extend the frequency range below the operating range, the speaker may be combined with a bass (low frequency reproduction) speaker.

[0097] Furthermore, it is desirable that the loudspeaker be compact and operate without the need for an additional back cavity and the adverse effects associated with an additional back cavity (and an additional back cavity is an additional enclosed volume external to the loudspeaker support structure which causes the resonant frequency to be raised and the transfer function to overshoot, as discussed above in conjunction with typical closed box designs).

[0098] It is also desirable that the speaker be capable of being used for loud music playback (where all occupants of the car are listening to the same music and mutual interference is not an issue) while still remaining low cost for mass market applications.

[0099] As can be seen from the above background discussion, while there are existing speaker technologies configured to improve the directivity index of a speaker, all of these speaker technologies suffer from significant disadvantages when used in a headrest.

[0100] The loudspeakers described herein are intended for near-field listening use, for example, at the ears of a user located at a listening position less than 50 cm (more preferably less than 40 cm, more preferably less than 30 cm, more preferably less than 25 cm, more preferably less than 20 cm or more preferably less than 15 cm) from the first radiating surface of the diaphragm included in the loudspeaker. These loudspeakers may be used, for example, in a headrest.

[0101] Figure 3a to Figure 3c A first speaker 101 according to the present disclosure is shown, wherein Figure 3a shows a cross section (side view) of the first loudspeaker 101, Figure 3b The exterior of the first speaker 101 is shown (side view), and Figure 3c The underside (bottom view) of the first speaker 101 is shown.

[0102] The loudspeaker 101 includes a diaphragm 110 having a first (forward) radiating surface 112 a and a second (rear) radiating surface 112 b , wherein the first radiating surface 112 a and the second radiating surface 112 b are located on opposite sides of the diaphragm 110 .

[0103] The speaker 101 further includes a driving unit 120 configured to move the diaphragm 110 based on an electrical signal.

[0104] The drive unit 120 is an electromagnetic drive unit that includes a magnet unit 122 configured to generate a magnetic field in an air gap and a voice coil 124 attached to the diaphragm 110 via an intermediate coupling element (in this case, a voice coil bobbin 126). In use, the voice coil 124 can be energized (current flows through the voice coil 124 based on an electrical signal) to generate a magnetic field that interacts with the magnetic field generated by the magnet unit 122 and causes the voice coil 124 (and therefore the diaphragm 110) to move relative to the magnet unit along the main axis 103 of the speaker 101.

[0105] The loudspeaker 101 also includes a loudspeaker support structure 130, wherein the diaphragm 110 is suspended from the loudspeaker support structure 130 via one or more loudspeaker suspension elements 140, 142. The loudspeaker suspension elements 140, 142 are configured to position the voice coil in the air gap when the diaphragm is stationary. In this example, the loudspeaker suspension elements are a support ring 140 and a roll suspension 142.

[0106] The diaphragm 110 , voice coil 124 , and voice coil bobbin 126 together form a “moving” assembly.

[0107] The magnet unit 122 and the loudspeaker support structure 130 together form a "non-moving" component.

[0108] The loudspeaker support structure 130 encloses a volume Vf configured to receive sound generated by the second radiation surface 112 b of the diaphragm 110 .

[0109] The first radiation surface 112 a of the diaphragm 110 is configured to generate sound emitted from the speaker 101 .

[0110] In this example, the speaker support structure 130 includes multiple porous material areas 135 with a specific airflow resistance in the range of 300 Pa.s / m to 5000 Pa.s / m, wherein the porous material areas 135 are constructed to allow sound generated by the second radiation surface 112b to leave the volume Vf enclosed by the speaker support structure 130 via one or more porous material areas 135.

[0111] The specific air flow resistance of the porous material area 135 is in the range of 300 Pa.s / m to 5000 Pa.s / m, more preferably in the range of 500 Pa.s / m to 3000 Pa.s / m.

[0112] In this example, the speaker support structure 130 includes a rigid frame 134 to which the diaphragm 110 is suspended via speaker suspension elements 140, 142. In this example, the magnet unit 122 is directly attached to the rigid frame 134 (rather than, for example, to a cabinet to which the rigid frame 134 is attached). The rigid frame 134 has a mechanical structure that is generally thin and acoustically transparent, and connects the moving components and the non-moving components.

[0113] In this example, the porous material region 135 is formed of a material having a specific airflow resistance within the above range (eg, 300 Pa.s / m to 5000 Pa.s / m or 500 Pa.s / m to 3000 Pa.s / m), which covers one or more openings in the rigid frame 134 .

[0114] In this case, the material covering the one or more openings in the rigid frame 134 is a tightly woven cloth having a specific airflow resistance within the above range. As will be appreciated by those skilled in the art, the cloth can cover the openings in a variety of ways. For example, the cloth can be ultrasonically welded to the rigid frame 134 (which can be made of plastic, for example), and the rigid frame 134 can be made by overmolding plastic on the cloth. Heat staking and gluing (where the cloth is inside or outside the rigid frame 134) are both options.

[0115] Figure 3a to Figure 3c The key difference between the first loudspeaker 101 shown in FIG. 1 and a conventional loudspeaker is that the loudspeaker support structure 130 encloses a very large volume (approximately 26 cm in this example) for the effective radiation area of ​​the diaphragm 110 (and the selected magnet unit size). 3) and has a very large external surface area and is covered by a material having a specific airflow resistance within the above range.

[0116] The magnet unit 122 can be seen through the notch 123. Figure 3a to Figure 3c 1. In view of the larger volume Vf enclosed by the support structure 130 of the first loudspeaker 101 shown in FIG. 1 , the recess 123 is included for fixing the magnet unit 122 to a conventional (smaller) frame.

[0117] As can be seen from the following discussion, this combination of a large surface area of ​​the speaker support structure relative to the effective radiating area of ​​the diaphragm 110 and the high flow resistance region achieves a low flow velocity through the high flow resistance region while avoiding blowing noise that is uncomfortable to a user whose ear is close to the first radiating surface of the diaphragm 110. In addition, the surface area of ​​the high flow resistance region is selected to obtain a desired tuning frequency, thereby providing a desired cardioid radiation pattern without generating blowing noise that is uncomfortable to a user whose ear is close to the first radiating surface of the diaphragm 110.

[0118] Note that a similar desired tuning frequency (and cardioid pattern) can be achieved with a small hole and low flow resistance, but this will result in an unpleasant blowing noise, see e.g. Figure 2b , where a small hole with relatively low flow resistance produces a blowing noise that can be uncomfortable for the user if the user sits close to the speaker (but the user will not sit close to the speaker). Figure 2b The speaker is shown sitting as this speaker is typically designed for far-field use).

[0119] The first speaker 101 is preferably a mid-high frequency speaker configured to generate sound within at least one designated frequency band.

[0120] Figure 4a A first exemplary headrest is shown, which includes two first speakers 101a, 101b therein. In this example, the first speakers 101a, 101b are used as full range speakers (specified frequency band = 100 Hz - 20 KHz).

[0121] Figure 4b A second exemplary headrest is shown, which includes two first speakers 101a, 101b therein. In this example, the first speakers 101a, 101b are used as mid-high frequency speakers (designated frequency band = 300Hz-20KHz).

[0122] exist Figure 4bIn the example shown in , the headrest includes one or more woofers 102 (one woofer 102 is shown here) for producing sounds at bass frequencies (e.g., in the range of 50 Hz to 100 Hz). For example, exemplary speakers that can be used as woofers 102 in headrests (or seats including headrests) are described in WO2019 / 121266, WO2019 / 192808, WO2019 / 192816, GB1907267.7 (including any subsequent publications based on this application), and GB1907267.7 (including any subsequent publications based on this application), in which it has been shown that it is advantageous to incorporate a woofer into a headrest to operate as a dipole. Other disclosures related to providing a suitable woofer are also disclosed in PCT / EP2019 / 084950 and GB1907610.8.

[0123] exist Figure 4a and Figure 4b In the exemplary headrest shown in , the first speakers 101a, 101b are included in the front protruding wing portion of the car headrest. In these examples, the frames of the speakers 101a, 101b, 102 can be rigidly attached to the headrest frame, which itself can be configured to be rigidly attached to the frame of the seat (not shown).

[0124] Figure 4a and Figure 4b The exemplary headrest shown in may be included in a seat assembly that is configured to position a user seated in a seat portion of the seat assembly such that a first ear of the user is located at a first listening position as described above and a second ear of the same user is located at a second listening position as described above.

[0125] Figure 5 A second loudspeaker 201 according to the present disclosure is shown in cross-section (side view). Like features corresponding to previous embodiments have the same reference numerals.

[0126] exist Figure 5 In the second speaker 201 shown in FIG. 1 , the magnet unit 222 extends from the rigid frame 234 ( Figure 5 ) extends out from the back to allow for an increased volume Vf.

[0127] Figure 6 A third loudspeaker 301 according to the present disclosure is shown in cross-section (side view). Like features corresponding to previous embodiments have the same reference numerals.

[0128] exist Figure 6In the second speaker 201 shown in FIG. 1 , the magnet unit 322 is completely surrounded by a rigid frame 334 to allow the surface area of ​​the porous material at the base of the speaker to be increased. Here, the rigid frame 334 includes a portion 334a that rigidly holds the magnet unit in position above the base of the speaker to allow the base of the speaker unit to be aligned with the base of the speaker. Figure 3c includes an increased porous material surface area compared to the example shown in .

[0129] Figures 7a to 7c A fourth speaker 401 according to the present disclosure is shown, wherein Figure 7a shows a cross section (side view) of a fourth loudspeaker 401, Figure 7b The exterior (side view) of the fourth speaker 401 is shown, and Figure 7c The underside (bottom view) of the fourth loudspeaker 401 is shown. Like features corresponding to previous embodiments have the same reference numerals.

[0130] In this example, the magnet unit 422 forms part of a rigid frame 434 from which the diaphragm is suspended via a loudspeaker suspension element 442 (in this example, the support ring is omitted for compactness, but the coil suspension 442 is retained). In other words, the frame 434 and the magnet unit 422 are combined.

[0131] In this example, the porous material area 435 is formed of a material having an airflow resistance within the above range (300Pa.s / m to 5000Pa.s / m or 500Pa.s / m to 3000Pa.s / m), which covers one or more openings in the magnet unit 422 (note that in this example, the tone of the porous material area is darker than the rigid frame, which is opposite to the tone shown in the previous figures).

[0132] In this example, the diaphragm 410 is selected to have a low profile, and the volume Vf enclosed by the support structure 430 (rigid frame 434, which in this example includes the magnet unit 422, covered by a material with a specific airflow resistance within the above range) is approximately 10 cm 3 , so the speaker is better than Figure 3a to Figure 3c The loudspeaker shown in is more compact and the openings of the porous material are Figure 3a to Figure 3c The example shown in has a reduced surface area compared to that shown in. Nevertheless, in view of the following experimental data, the inventors believe that sufficient performance can still be obtained using such a loudspeaker.

[0133] In this example, the flux guiding components of the magnet unit 422 are made of a high permeability material such as soft iron, and their cross-section is large enough to keep the magnetic resistance low despite the opening of the magnet unit as described above. In this example, the opening in the magnet unit 422 is covered by material from the inside rather than the outside.

[0134] In the examples shown in Figures 3 to 7, the porous material area is formed by a cloth with a specific airflow resistance within the above range (e.g., 300Pa.s / m to 5000Pa.s / m or 500Pa.s / m to 3000Pa.s / m), which covers one or more openings in the rigid frame.

[0135] The fabric serves three functions: (i) providing a defined mechanical resistance to allow for a magnet unit with a higher electrical Q; (ii) providing the desired directivity (cardioid radiation pattern); and (iii) preventing dust from entering the inner cavity of the speaker, thereby reducing the risk of debris entering the air gap. Figure 6 In the example case shown in the illustration, the fabric also helps protect the back of the speaker.

[0136] In the field of acoustics, fabrics with specific airflow resistance ranging from about 5 Pa.s / m to 4000 Pa.s / m are commercially available, for example:

[0137] Fabric solutions for acoustic devices and components (Sefar) [full reference given below], discloses that fabrics with specific airflow resistance ranging from 5 Pa.s / m to 3300 Pa.s / m are available (note that the unit of specific airflow resistance is provided in this disclosure as "Rayl (MKS)", which is the same as Pa.s / m in SI unit).

[0138] Product News - Acousstex HD (Saati) [full reference given below], discloses that fabrics with specific airflow resistance ranging from 360 Pa.s / m to 4000 Pa.s / m are available (note that the units of specific airflow resistance are provided in this disclosure as "MKS Rayls", which is the same as Pa.s / m in SI units).

[0139] Typically, such fabrics are filter fabrics formed from a very fine mesh.

[0140] Fabrics with a specific airflow resistance in the range of 4000 Pa.s / m to 5000 Pa.s / m are not common in the acoustics field, but this is only because there is currently little commercial demand for acoustic fabrics in this range (the flow rates generated are very low). However, the inventors believe that such fabrics are available for non-acoustic technical purposes, and in any case, the inventors believe that manufacturers of existing fabrics can easily adopt existing technology to produce fabrics with a specific airflow resistance in the range of 4000 Pa.s / m to 5000 Pa.s / m.

[0141] For the sake of completeness, we note that in existing car speakers, in order to reduce the risk of dust / debris entering the air gap and to protect the back of the speaker, it is known to use a cloth commonly known as "dust scrim". In order to provide acoustic transparency, the specific airflow resistance of the dust scrim is usually very low, usually below 100 Pa.s / m. For the examples shown in Figures 3 to 7, a cloth with a generally higher specific airflow resistance (or a larger surface area) is selected in order to provide the desired directivity (cardioid radiation pattern) without generating an unpleasant blowing noise.

[0142] Experimental data

[0143] Unless otherwise stated, the following experimental results were obtained for loudspeakers with the following characteristics:

[0144] · Figure 3a to Figure 3c The structure of the first speaker 101 shown in FIG. 1 has an effective radiation area S of the diaphragm. D =

[0145] 8.8cm 2 (Radiation diameter is 3.4cm), volume Vf is 26cm 3 ;

[0146] · depth (in the direction of the main axis 103) 20 mm;

[0147] The outer diameter of the fabric is 48mm;

[0148] A region of porous material with defined specific airflow resistance (formed by the fabric covering the openings in the rigid frame 134) with a combined surface area of ​​32 cm 2 The combined surface area is considered here to be Figure 3b The area of ​​the cylindrical outer surface of the cloth covering the rigid frame 134 shown in FIG. Figure 3c The sum of the areas of the fabric covering the rearward annular opening around the magnet unit (flush with the back of the speaker) shown in . Note that this calculation ignores the Figure 3b and Figure 3cThe thin legs of the rigid frame 134 can be seen in FIG. As described below, the defined specific airflow resistance of the fabrics used in the experimental results discussed below is different.

[0149] The magnetic flux density in the air gap is 0.55 T (referred to herein as a "strong" magnet unit).

[0150] Figures 8a to 8d are simulation results showing the effect of cloth-specific airflow resistance on radiation patterns, where the left side of these graphs only shows the radiation patterns of 100 Hz, 200 Hz and 400 Hz, and the right side of these graphs only shows the radiation patterns of 800 Hz, 1600 Hz and 3150 Hz. In reality, the left graphs would be mirrored to the right (because the radiation patterns are rotationally symmetric around the 0° axis), and the right graphs would be mirrored to the left, but for clarity, this is not shown here.

[0151] exist Figures 8a to 8d In the example, the specific air flow resistance of the fabric is selected as follows:

[0152] · Figure 8a ("Dipole" example): 0Pa.s / m

[0153] · Figure 8b (“Supercardioid” example): 1000Pa.s / m

[0154] · Figure 8c (“Heart-shaped” example): 1600Pa.s / m

[0155] · Figure 8d (“Closed box” example): 5000 Pa.s / m

[0156] for Figure 8a The material's specific airflow resistance (acoustic impedance) is below the ideal range for that particular loudspeaker configuration, meaning that the directivity pattern follows the figure-8 characteristic of a dipole across the frequency range. Here, the loudspeaker effectively acts as a pure dipole with no monopole component, because the acoustic impedance is so small that it is almost negligible.

[0157] for Figure 8b , the specific airflow resistance increases to the range of 0.5 kPa.s / m to 1 kPa.s / m, which is towards the lower end of the ideal range of specific airflow resistance for this particular loudspeaker construction. This leads to Figure 8b The hypercardioid pattern shown in . As the acoustic impedance of the cloth increases, the monopole component increases, while the dipole component decreases. This pattern may be desirable for applications where it is desirable to maximize the attenuation at 120° or -120°.

[0158] for Figure 8c, the specific airflow resistance increases to a range of 1 kPa.s / m to 2 kPa.s / m, which is toward the upper end of the ideal range of specific airflow resistance for this particular speaker construction. Figure 8c This results in a cardioid pattern with some supercardioid directivity approaching higher frequencies, as shown in . At 400 Hz, the cardioid pattern is ideal for some applications because at this frequency the monopole and dipole components are perfectly balanced, note that the back lobe of the dipole is just as strong as the back radiation of the monopole, but is out of phase with each other, resulting in complete back cancellation.

[0159] Figure 8b and Figure 8c It is shown that within a specified frequency band (here 100 Hz to 3150 Hz), the SPL on the main radiation axis for the supercardioid and cardioid examples is at least 6 dB higher for substantially the entire specified frequency band than the SPL at the same listening distance 180° from the main radiation axis.

[0160] Figure 8b and Figure 8c Both the hypercardioid and cardioid patterns are potentially useful, albeit for different purposes. Figure 8c The cardioid pattern shown in is usually more preferred because it radiates least toward 180° (backwards). However, for some uses, such as if another person (who does not want to hear the sound produced by the speaker) is located at 120° or -120° relative to the speaker, Figure 8b The hypercardioid pattern shown in may be more preferred.

[0161] for Figure 8d , the specific airflow resistance increases to over 2 kPa.s / m, which is above the ideal range for this particular loudspeaker construction. Here, the directivity pattern approaches Figure 8d The directivity pattern of the monopole shown in . This is because the acoustic impedance of the cloth is so large that airflow through the cloth becomes negligible and the supporting structure including the cloth effectively provides a closed box and the associated omnidirectional radiation.

[0162] Fig. 9 shows the corresponding combination Figures 8a to 8d Relationship between simulated electrical input impedance and frequency for the specific airflow resistance values ​​in question.

[0163] As shown here, in the case of a dipole (corresponding to Figure 8a ), the impedance peak corresponds to the free air resonance frequency fs of the loudspeaker. In the case of a closed box (corresponding to Figure 8d), the resonant frequency fc is determined according to the well-known formula for a closed box (i.e., fc = fs*sqrt(Vas / Vb+1)), and the overall quality factor of the resonance (Q factor, Qts, as defined above) is also shifted by the same factor sqrt(Vas / Vb+1), where Vas is the equivalent air compliance and Vb is the box volume (which, for our purposes, corresponds to the internal volume enclosed by the support structure, referred to above as Vf). Determining Vb is not easy, because the textbook formula assumes an adiabatic volume, while the volume inside the support structure is small, and the magnet unit has a large number of isothermal surfaces. The effective acoustic volume is larger than the geometric volume mentioned above.

[0164] For the case of a closed box, a higher resonant frequency and a larger resonant amplitude are not preferred.

[0165] In the case of a supercardioid (corresponding to Figure 8b ) and the cardioid case (corresponding to Figure 8c ), the resonant frequency is not significantly shifted upward compared to the dipole case, but the overall Q factor (Qts) of the resonance is significantly reduced. This is due to the mechanical damping provided by the airflow through the acoustic impedance covering the frame.

[0166] The cardioid and supercardioid cases have similar resonant frequencies as a dipole (a good thing) and lower resonant amplitudes than a dipole (also a good thing).

[0167] Fig.10 shows the corresponding combination Figures 8a to 8d Simulated peak displacement vs. frequency for a 2V rms input voltage for the specific airflow resistance values ​​discussed.

[0168] As from Fig.10 As can be seen in Figure 2, only the closed box case is prominent, where the displacement is significantly smaller and the frequency peak is higher at the box resonance frequency fc.

[0169] Because the peak displacement of the cardioid and supercardioid cases is greater than that of the closed enclosure case, the speakers in these cases will need to allow for greater excursions, much like the free air case (dipole case).

[0170] In near-field applications, where the user's ear is located at a listening position as close as 10 cm (versus >1 m for far-field applications) from the first radiating surface of the loudspeaker, the required loudspeaker sensitivity may be much smaller, e.g. 90 dB / 1 W / 1 m (far field) versus 90 dB / 1 W / 10 cm (near field).

[0171] The inventors have observed that this opens the possibility to equip the loudspeaker with much weaker magnet units than loudspeakers designed for far-field listening.

[0172] Fig.11a shows the simulated frequency response (SPL) for a listening distance of 10 cm, while Fig.11b The simulated electrical input impedance for a case where the frame is covered with a cloth having a specific airflow resistance of 1.8 kPa.s / m, with two different magnetic flux densities in the air gap: the solid line corresponds to 0.55 T (referred to herein as a "strong" magnet unit), while the dashed line corresponds to a reduced magnetic flux density of only 0.16 T (referred to herein as a "weak" magnet unit). As expected, reducing the magnetic flux density reduces the SPL, especially at higher frequencies ( Fig.11a ). However, reducing the magnetic flux density will also suppress the impedance peak at resonance ( Fig.11b ).

[0173] In more detail, for weak magnet drivers, the sensitivity to mid- and high frequencies is reduced by about 20dB, but due to the reduction in electrical Q factor, the loss is only 10dB at about 200Hz to 300Hz. This results in a more balanced frequency response and a very smooth electrical input impedance curve.

[0174] Figures 12 to 17 Shown are (not simulated) measurement results from experimental work.

[0175] Fig.12 Measurements at a distance of 1 m are shown for a loudspeaker comprising a weak magnetic unit as defined in conjunction with FIG. 11 , mounted in an infinite baffle with an input voltage of 2 V and the frame of the loudspeaker not covered with cloth. It can be seen that the weak magnetic unit provides almost no back electromotive force (EMF), resulting in a very high electrical Q factor and uncontrollable behavior at the resonant frequency. As a result, a huge peak can be seen at resonance (which is unfavorable); and lower SPL can be seen at higher frequencies (which is also unfavorable). Such a loudspeaker would be considered unusable as the sound would be severely boomy.

[0176] Fig.13 The same loudspeaker (as described above in conjunction with Fig.12 s / m (cardioid case). Here, the resulting frequency response is very smooth and the Total Harmonic Distortion (THD) is very low (at -50dB) throughout the mid-high frequency band and only moderately increases towards the low frequencies. The flow resistance is tuned to reduce the mechanical Q factor and allow it to effectively dominate the back EMF, resulting in a predominantly mechanically damped loudspeaker and a smooth frequency response.

[0177] Thus, the combination of a weak magnet system and the use of a cloth with a specific airflow resistance of 1600 Pa.s / m (in the case of a cardioid) results in a loudspeaker that is very useful at close range (although such a loudspeaker will not be particularly useful in the far field).

[0178] A stronger magnet unit (not shown) would result in Fig.13 The results shown in are worse because the frequency response will be uneven. Near the resonant frequency, stronger back EMF causes additional electrical damping and reduces output, while at high frequencies, stronger motors increase sensitivity. So you end up with something that is too low at 300Hz and too high at 3kHz (and above).

[0179] Fig.14 shows the corresponding combination Fig.12 The loudspeaker in question ("open back") and the combination Fig.13 Measured electrical impedance of the loudspeaker in question ("with cardioid frame") Relationship between the electrical input impedance and frequency.

[0180] Fig.14 As shown, by using a heart-shaped support structure ("cardioid support structure"), the electrical impedance curve of the loudspeaker is virtually flat even at the resonant frequency due to the mechanical damping, making it much easier to drive with any amplifier, even with passive filtering components, than with an open ("open back") cardioid support structure. By using a ferrofluid, it is not uncommon for small loudspeakers to have essentially only mechanical damping, but the viscosity of the ferrofluid (and thus the damping provided by the ferrofluid) has a strong temperature dependence, whereas the flow resistance provided by the cardioid support structure is independent of temperature and does not decay.

[0181] By now it can be easily appreciated that the mechanical Q factor is an indicator of whether the chosen fabric is suitable for a given loudspeaker and open frame area size: if the flow through the fabric (= porous material area) is chosen appropriately, the mechanical Q factor will be low, resulting in a strong suppression of the loudspeaker resonances and the desired directivity pattern, while at the same time a moderate upward shift of the resonant frequency due to the additional monopole component.

[0182] Figures 15a to 15c shows the combined Fig.13 Measured far-field directivity (listening distance = 1 m) of a loudspeaker described by ("cardioid support structure").

[0183] As Fig.15a and Fig.15b As shown, in the frequency range of 300Hz to 1250Hz ( Figure 15a to Figure 15b ), the radiation pattern follows a cardioid characteristic. It tends to the upper limit of the relevant band at 3150Hz ( Fig.15c ), the directivity takes on a more hypercardioid pattern, as expected from the simulation. For higher frequencies, the directivity of a dome is replaced, as it becomes larger compared to the wavelength, and the power spectral density in music and speech is reduced anyway. Therefore, the acoustic contrast originating from off-axis radiation becomes less important.

[0184] Fig.16 The results are shown for a "strong" magnet system with 0.55 T at a listening distance of 1 meter (distance from the sound source) using 1 / 3 octave band smoothing. Figure 3a to Figure 3c The relationship between the far-field directivity index of the first speaker 101 and the frequency is shown in FIG.

[0185] As shown here, the directivity index within the specified frequency band of interest (here 300 Hz to 3 KHz) is easily above 4 dB for substantially the entire specified frequency band.

[0186] Generally speaking, it is preferred to have Figure 15a to Figure 15b The maximum reverse damping shown in (cardioid characteristic), rather than the supercardioid characteristic (tending to the upper limit of the frequency band, such as Fig.15c ) or dipole characteristics (as shown in Figure 8a As shown in Figure 15 and Fig.16 It has been shown that a directivity index of about 4.8 dB is considered to be almost the best that can be achieved if no back lobe is desired and the diaphragm size is small compared to the wavelength.

[0187] Fig.17 The far-field directivity index of the first loudspeaker 101 (i.e., the fourth loudspeaker 401 in which the frame 434 and the magnet unit 422 are combined) shown in Figure 7 at a listening distance of 1 meter (distance from the sound source) is shown. This time, the directivity index is shown at "standard" center frequencies within a specified frequency band of interest (here 300 Hz to 3 KHz) for 1 / 3 octave bands (i.e., at 315 Hz, 400 Hz, 500 Hz, 630 Hz, 800 Hz, 1 KHz, 1.25 KHz, 1.6 KHz, 2 KHz, and 2.5 KHz).

[0188] Used for Fig.17 The magnetic flux density of the fourth speaker 401 in the experimental results shown in FIG. 4 is 0.12 T, which is higher than that used to obtain Fig.16 The magnetic flux density of the first loudspeaker 101 in the experimental results shown in is much lower, but this is mentioned only for the sake of completeness, as the magnetic flux density is not believed to have a significant effect on directivity.

[0189] Fig.16 and Fig.17The comparison between shows some of the trade-offs that come with using a more compact speaker (such as the fourth speaker 401 of FIG. 7 ). In particular, Fig.17 and Fig.16 The comparison between Figure 3a to Figure 3c The larger first speaker 101 (26 cm 3 ) compared to the more compact fourth speaker 401 (10cm 3 ) is more directional for higher frequencies. Further experimental work done by the inventors (the results of which are not shown here) also showed that Figure 3a to Figure 3c Compared to the larger first speaker 101 shown, the more compact fourth speaker 401 of FIG. 7 has a significantly smaller output at low frequencies, which means that the more compact fourth speaker 401 of FIG. 7 is more suitable for use in combination with a mid-bass speaker, while Figure 3a to Figure 3c The larger first speaker 101 shown in FIG. 1 is more suitable for use in combination with a bass box.

[0190] The features disclosed in the above description, the following claims or the accompanying drawings (expressed in their specific form or as means for performing the disclosed functions or as methods or processes for obtaining the disclosed results) may, where appropriate, be used alone or in any combination of these features to implement the invention in its different forms.

[0191] Although the present invention has been described in conjunction with the above exemplary embodiments, many equivalent modifications and variations will be apparent to those skilled in the art when this disclosure is given. Therefore, the above exemplary embodiments of the present invention are considered to be illustrative rather than restrictive. Various changes may be made to the described embodiments without departing from the spirit and scope of the present invention.

[0192] To avoid any doubt, any theoretical explanations provided herein are provided to enhance the reader's understanding. The inventors do not wish to be bound by any of these theoretical explanations.

[0193] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0194] Throughout the specification (including the following claims), unless the context requires otherwise, the words "comprise", "comprising" and variations such as "include", "it includes" and "it includes", will be understood to implicitly include the stated integers or steps or combinations of integers or steps but not to exclude any other integers or steps or combinations of integers or steps.

[0195] It must be noted that the singular forms "a", "an", and "the" used in this specification and the appended claims include plural referents unless the context clearly indicates otherwise. Ranges may be expressed herein as from "about" one particular value and / or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when a value is expressed as an approximation by using the antecedent "about", it should be understood that the particular value forms another embodiment. The term "about" in relation to a numerical value is optional and means, for example, + / - 10%.

[0196] References

[0197] Many publications are cited above to more fully describe and disclose the present invention and the current state of the art to which the present invention belongs. The complete citations of these references are provided below. The entire contents of each of these references are incorporated herein.

[0198] ·ISO 9053-1:2018 published October 2018

[0199] ·ISO 266:1997 published March 1997

[0200] ·"Dynamical Measurement of the Effective Radiating area SD",KlippelGmbH

[0201] ·Acoustics,Beranek,LL,McGraw-Hill,1954

[0202] ·Thiele,AN,"Loudspeakers in Vented Boxes,Parts I and II",J.AudioEng.Soc.,vol.19,pp.382–392(May 1971);pp.471–483(June 1971).

[0203] ·Small, RH, "Direct-Radiator Loudspeaker System Analysis", J.AudioEng.Soc., vol.20, pp.383–395 (June 1972).

[0204] ·"Fabric solutions for Acoustic devices and components" (Sefar)https: / / www.sefar.com / en / 609 / Product-Finder / Filter-Components / Acoustic / Fabric-solutions-for-Acoustic-devices-and-components.pdf? Folder=6916771

[0205] ·"Product News-Acousstex HD"(Saati)http: / / www.saati.com / sites / default / files / elemento-download / ACOUSTEX%20HD_4.pdf

[0206] WO2019 / 121266

[0207] WO2019 / 192808

[0208] WO2019 / 192816

[0209] PCT / EP2019 / 084950

[0210] GB1907610.8 (including any subsequent publications based on this application)

[0211] GB1907267.7 (including any subsequent publications based on this application)

[0212] GB1908551.3 (including any subsequent publications based on this application)

Claims

1. A speaker configured to be installed in a seat assembly, the speaker comprising: a diaphragm having a first radiation surface and a second radiation surface, wherein the first radiation surface and the second radiation surface are located on opposite surfaces of the diaphragm; a drive unit configured to move the diaphragm based on an electrical signal; and a loudspeaker support structure, wherein the diaphragm is suspended from the loudspeaker support structure via one or more loudspeaker suspension elements; wherein the speaker support structure encloses a volume configured to receive sound generated by the second radiating surface, wherein the speaker support structure comprises one or more areas of porous material, the one or more areas of porous material having a specific airflow resistance in the range of 300 Pa.s / m to 5000 Pa.s / m, wherein the one or more areas of porous material are configured to allow sound generated by the second radiating surface to leave the volume enclosed by the speaker support structure via the one or more areas of porous material; The surface area of ​​the one or more porous material regions is the effective radiation area S of the diaphragm. D at least 80%.

2. The loudspeaker according to claim 1, wherein The specific airflow resistance of the one or more porous material regions is in the range of 500 Pa.s / m to 3000 Pa.s / m.

3. The loudspeaker according to claim 1, wherein: The loudspeaker support structure includes a rigid frame to which the diaphragm is suspended via one or more loudspeaker suspension elements.

4. The loudspeaker according to claim 3, wherein: The one or more porous material regions are formed from a material having a specific airflow resistance in the range of 300 Pa.s / m to 5000 Pa.s / m, the material covering the one or more openings in the rigid frame.

5. The loudspeaker according to claim 3, wherein: The driving unit is an electromagnetic driving unit including: a magnet unit configured to generate a magnetic field in an air gap; and a voice coil attached to the diaphragm.

6. The loudspeaker according to claim 5, wherein: The magnet unit is directly attached to or forms at least a part of the rigid frame, and the diaphragm is suspended from the rigid frame via one or more loudspeaker suspension elements.

7. The loudspeaker according to claim 5, wherein: The magnet unit forms at least a part of the rigid frame, the diaphragm is suspended from the at least a part via one or more speaker suspension elements, and the one or more porous material areas are formed by a material having a specific airflow resistance in the range of 300Pa.s / m to 5000Pa.s / m, which covers one or more openings in the magnet unit.

8. The loudspeaker according to claim 5, wherein: The magnetic flux density of the magnet unit in the air gap is in the range of 0.1T to 0.5T.

9. The loudspeaker according to any one of claims 1 to 8, wherein: The volume enclosed by the loudspeaker support structure is less than 100 cm 3 .

10. The loudspeaker according to any one of claims 1 to 8, wherein: The speaker is a mid-high frequency speaker configured to generate sound within a whole designated frequency band, the designated frequency band including at least 300 Hz to 3 KHz.

11. The loudspeaker according to any one of claims 1 to 8, wherein: The resonant frequency of the speaker is in the range of 150 Hz to 500 Hz.

12. The loudspeaker according to any one of claims 1 to 8, wherein: The speaker has a Qes greater than 5 and a Qms less than 2.

13. The loudspeaker according to any one of claims 1 to 8, wherein: The speaker has a directivity index of 4 dB or more over the entire designated frequency band within a designated frequency band of 300 Hz to 3 kHz.

14. The loudspeaker according to any one of claims 1 to 8, wherein: Within a specified frequency band of 300 Hz to 3 kHz, the SPL of the loudspeaker measured on the main radiation axis is at least 6 dB higher for the entire specified frequency band than the SPL measured at the same listening distance 180° from the main radiation axis.

15. A seat assembly, comprising: Headrest; Seat part; as well as A first speaker, the first speaker being a speaker according to any one of claims 1 to 14, wherein the first speaker is located in the seat assembly for use by a first ear of a user at a listening position located below 50 cm from a first radiation surface of a diaphragm of the first speaker when the user is seated in the seat portion of the seat assembly.

16. The seat assembly of claim 15, wherein: The first speaker is mounted in the headrest of the seat assembly such that sound generated by the first and second radiation surfaces of the first speaker is allowed to propagate out of the seat assembly via an opening or a sound-transparent portion of the seat assembly.

17. The seat assembly according to claim 15 or 16 further includes a second speaker, the second speaker being a speaker according to any one of claims 1 to 14, wherein the second speaker is located in the seat assembly for use by the second ear of the user at a listening position located below 50 cm from the first radiation surface of the diaphragm of the second speaker when the user is sitting in the seat portion of the seat assembly.

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