GB2509711A

GB2509711A - Selective or frequency-dependent acoustic damping

Info

Publication number: GB2509711A
Application number: GB1300333.0A
Authority: GB
Inventors: David Corynen
Original assignee: PSS Belgium NV
Current assignee: PSS Belgium NV
Priority date: 2013-01-09
Filing date: 2013-01-09
Publication date: 2014-07-16
Also published as: GB201300333D0; WO2014108373A1

Abstract

A loudspeaker comprises a speaker diaphragm 15.1, 22.1, a speaker housing 15.3, 22.2 and a pass-through or port 15.4, 22.6. Improved audio output characteristics are obtained by employing acoustic members 15.7, 15.8, 22.3, 22.4 that include a substantially flattened body portion and a valve within the body within the pass-through or port. The valve is configured to open to allow at least some sound waves to move through the pass-through or port when in use.The valve may comprise cuts or incisions in the acoustic member (13.2, 23.2, figs 13 and 23).

Description

AUDIO OUTPUT DEVICES

STATEMENT OF INVENTION

The present invention relates to audio frequency damping in audio output devices and is directed to new and improved audio output devices, acoustic members, vehicles including the devices and members, the use of acoustic members in such audio output devices and methods for the manufacture of audio output devices and acoustic members.

BACKGROUND

It is known in this field that audio frequency damping is useful to suppress unwanted acoustic resonances or standing waves in speaker systems in order to optimize a speaker's fidelity across a wide frequency bandwidth. The term "damping" refers to the dissipation of energy in a vibrating system. The greater the damping effect, the more energy is dissipated and the shorter the duration of a vibration. Such damping of acoustic resonances can result from friction between the sound wave and the various media with which the sound wave interacts.

Optimal damping can be achieved in audio output devices by locating a damping material at the point where the velocity of the standing wave created by the speaker diaphragm is maximal. In this way, the interaction of the velocity component of the sound wave with the surface of the absorbing material causes the most effective frictional losses.

It is desirable in audio output devices such as loudspeaker systems to shield the front-side radiation of sound energy from the speaker diaphragm (i.e. the sound waves intended for the listener) from the rear-side radiation (i.e. the sound energy radiated back away from the intended listener) in order to prevent unwanted interference and "acoustic short-circuit". The simplest way to do this is to build a closed housing around the rear-side of the diaphragm thus forming a sealed enclosure behind the speaker diaphragm. An exemplary closed speaker arrangement is depicted in Figure 1, which shows a tweeter having a dome shaped diaphragm 1.1 mounted on a speaker housing 1.2 forming a "closed" speaker enclosure containing a magnet 1.4 and tweeter top-plate 1.5.

The use of a porous material to dampen unwanted acoustic resonances created by the rear-side of the diaphragm in such closed housing systems is known. For instance, Figure 2 depicts a closed speaker system having speaker diaphragm 2.1, speaker housing 2.3 and a porous damping material 2.2 filling the speaker enclosure and Figure 3 depicts the tweeter of Figure 1 having a sheet of felt 3.1 placed on the tweeter top-plate.

However, a drawback of such closed housing systems is that mechanical stiffness of the diaphragm is increased by the enclosed air volume in the speaker housing, which in turn increases the resonance frequency of the speaker, thus reducing the effective bandwidth in the lower frequency spectrum. For example, a 25 mm closed dome tweeter having the typical closed construction depicted in Figure 1 has a typical resonance frequency of 1500 Hz. The tweeter operates at this relatively high resonance frequency because of the relatively small acoustic volume 1.3 enclosed behind the diaphragm. Thus, a limited frequency response at lower frequencies for such a tweeter is observed, limiting the functionality of the tweeter.

It is desirable therefore to extend the effective resonance frequency of audio output devices such as tweeters to lower frequencies.

One way to lower the resonance frequency in such a system would be to increase the closed volume behind the diaphragm in the speaker housing, providing a bulkier speaker unit. However, this solution is not practical for all applications, particularly where it is desirable to provide a speaker having a low profile (for instance in motor vehicles where it is necessary for the speaker to be compact in order to integrate into shallow spaces such as a car door).

It is possible to lower the resonance frequency of a speaker without increasing the enclosed volume within the speaker housing by using the comparatively large volume usually available in the apparatus into which the speaker system is installed as an extended speaker enclosure (e.g. the volume behind the headliner of a car). The most straightforward way to do this is to create a pass-through in the speaker housing, thus allowing the sound waves (and thus air flow) generated by the rear side of the diaphragm to exit the speaker housing through the pass-through into the larger air volume outside the speaker housing. Such an "open" tweeter construction is depicted in Figure 4, which shows a longitudinal cross-section of a tweeter having a speaker diaphragm 4.1 mounted on the speaker housing 4.2, a magnet 4.3, top-plate 4.4 and a pass-through 4.5. In such devices, the large open volume of air relative to the small diaphragm can be approximated to a device having an infinite air volume behind the diaphragm, i.e. an infinite baffle construction.

The advantage of this arrangement is that the resonance frequency of the tweeter is no longer dominated by the stiffness of the enclosed air volume but depends completely on the stiffness of the diaphragm suspension and the moving mass of the mobile diaphragm system (e.g. voice-coil, diaphragm and a part of its suspension).

The result is a driver with an extended low frequency response (see Reference Example 1 and Figures 5 and 6).

However, a drawback of this open construction is that the cavity created by making a pass-through in the speaker housing will have a dominant resonance situated in the operating frequency range of the tweeter. This "Helmholtz resonator" is created by the interaction of the air volume behind the diaphragm 4.6 with the air mass 4.5 inside the pass-through (see Figure 4) and causes severe frequency response irregularities (see Reference Example 1 and the circled areas in Figures 5 and 6).

A known method of minimizing such response irregularities in open speaker constructions is by using an acoustic damping material to generate friction in the pass-through to dampen the cavity resonance. For example, Figure 7 depicts an exemplary open tweeter construction analogous to the tweeter of Figure 4 but having a porous damping material 7.1 for restricting the movement of sound waves through the pass-through, Figure 8 depicts the open tweeter construction of Figure 4 having a perforated damping plate 8.1 for restricting the movement of sound waves through the pass-through, and Figure 9 depicts an alternative open speaker arrangement having a speaker diaphragm 9.1 mounted on a speaker housing 9.2 and porous damping material 9.4 for restricting movement of sound waves (and corresponding air flow) through the pass-through 9.3.

Whilst damping using these known prior art methods is effective for reducing the frequency response irregularities caused by Helmholtz resonation (see Reference Example 2 and Figure 10 around the 2000 Hz range), it also has the disadvantage that the damping effect occurs across the resonant frequency range of the diaphragm and is not therefore selective for the targeted Helmholtz resonance. In particular, reducing Helmholtz resonance using these damping methods causes significant friction at the desired extended lower frequencies of the diaphragm, creating a reduced response-efficiency (see Reference Example 2 and Figures 10 and 11).

Moreover, damping using such methods also results in a significant increase in harmonic distortion at lower frequencies (see Reference Example 2 and Figure 12).

Thus, there is a need to provide improved audio output devices that exhibit an extended low frequency response whilst minimising decreases in efficiency, frequency response irregularities, and harmonic distortion.

Accordingly, an aim of the present invention is to provide new and improved audio output devices that solve the problems described above. It is also an aim of the present invention to provide new and improved acoustic members for use in such audio output devices and methods of manufacture of such audio output devices and acoustic membeis.

SUMMARY OF INVENTION

Broadly speaking, the present invention provides new acoustic members that improve the quality of audio output devices, for instance by providing enhanced frequency-selective damping.

In a first aspect is provided an audio output device including: a) a speaker diaphragm including a front side facing the exterior of the device and a rear side facing the interior of the device; b) a speaker housing on which the diaphragm is mounted, the speaker housing at least partially enclosing the rear side of the diaphragm and including a pass-through that allows at least some sound waves generated by the diaphragm in use to exit the speaker housing; and c) an acoustic member located to be operable to restrict movement of at least some sound waves through the pass-through in use, wherein the acoustic member includes a substantially flattened body portion and a valve within the body, the valve being configured to open to facilitate the movement of at least some sound waves through the pass-through when in use.

The audio output device of the above aspect includes a pass-through in the speaker housing, which creates an open" speaker housing construction, thus helping to reduce the extent to which the enclosed air volume behind the speaker diaphragm impaits mechanical stiffness to the diaphragm in use, as described above.

Accordingly, the result is that the effective frequency response of the speaker diaphragm is extended to lower frequencies compared to analogous audio output devices having a closed speaker housing construction (i.e. having no pass-through in the speaker housing), as described above.

An acoustic member is provided, which operates to restrict movement of at least some sound waves through the pass-through when the device is in use. The valve provided within the body portion of the acoustic member opens in use to allow at least some sound waves to move through the pass-through. Inevitably, not all sound waves will move through the open valve when in use as some sound waves generated by the diaphragm will for example be absorbed and I or reflected by the acoustic member (e.g. by the body portion).

The acoustic member desirably ensures that the low-frequency extension of the diaphragm enabled by the pass-through in the speaker housing is maintained.

Furthermore, it also allows for damping of undesired resonances within the speaker housing and effective reduction of frequency irregularities, e.g. caused by Helmholtz resonance created by the presence of the pass-through, as described above.

However, the skilled person has also found that this novel construction surprisingly provides improved frequency response efficiency at lower frequencies whilst simultaneously providing decreased harmonic distortion compared to analogous prior art devices that use conventional damping materials, such as porous foam (see Example 1 and Figures 18-20).

Accordingly, the present invention provides audio output devices that deliver a desirable low frequency response, whilst minimising frequency irregularities, minimising decreases in response efficiency and minimising distortion at lower frequencies.

Audio output device In the above aspect, the audio output device may be any suitable device having the arrangement of features described.

In some embodiments, the audio output device is selected from the group consisting of a loudspeaker, a tweeter, headphones, and audio devices having bass-reflex, horn-loaded and transmission line topologies. In some embodiments the audio output device is selected from the group consisting of a loudspeaker and tweeter, such as a base-reflex loudspeaker and tweeter, for example a tweeter. For example, the tweeter may have the construction substantially as depicted in Figure 15. In other embodiments, the audio output device is a loudspeaker such as a base-reflex loudspeaker, for example, a loudspeaker having the construction substantially as depicted in Figure 22.

Speaker Diaphragm In the above aspect and embodiments, the speaker diaphragm may be any speaker diaphiagm known to the skilled person to be suitable for use in audio output devices.

The speaker diaphragm has a front side facing the exterior of the device (i.e. to project sound waves in the direction of the listener), and a rear side directed to the interior of the device.

The diaphragm is mounted on the speaker housing. In such mounting, the diaphragm profile may be sunk into the housing (such as depicted in Figure 17), or the diaphragm may protrude from the housing (such as in the embodiment of Figure 15).

Furthermore, the diaphragm may be mounted by direct attachment or by indirect attachment. Typically, the diaphragm is mounted by indirect attachment. In typical embodiments, the diaphragm is mounted on the speaker housing via a bridging member, such as a diaphragm suspension system (as in the embodiment of Figure 15).

In further embodiments, the speaker diaphragm is part of an electro-dynamic driver arrangement. Usually, such arrangements comprise a voice-coil coupled to the diaphragm, the voice coil being configured to interact with a magnetic field when an electric current is passed through the coil in use. The coil may be coupled to the diaphragm directly or indirectly.

The diaphragm is typically a membrane. Preferably, the diaphragm is lightweight, stiff and I or internally damped in order to provide optimum sound quality. The diaphiagm is shaped to provide a large surface area for efficient radiation of sound.

For instance, the diaphragm may have a dome-shaped, frusto-conical, flat or corrugated profile, such as dome-shaped or frusto-conical, e.g. frusto-conical.

Examples of dome-shaped or frusto-conical diaphragms are depicted in appended Figures 1 and 2, respectively. In particular embodiments, the diaphragm is dome-shaped, for example wherein the concave side of the dome faces the interior of the device.

The diaphragm may be composed of any suitable material that allows for the effective radiation of sound. Suitable materials include paper, aluminium, titanium, Kevlar, polypropylene, fabric, diamond, beryllium and Mylar, as well as various other synthetic materials. The use of paper has the advantage that it allows for the additional incorporation of fibers such as glass, carbon and I or other reinforcing fibers, which may improve the structure and function of the diaphragm. Fabric has the advantage of being lightweight and well internally damped.

Typical materials for making diaphragms having a frusto-conical profile include paper, aluminium, titanium, Kevlar and polypropylene. Typical materials for making diaphiagms having a dome-shaped profile include fabric, aluminum, titanium, diamond, beryllium and Mylar, as well as other synthetic materials.

Speaker Housing In the above aspect and embodiments, a speaker housing is provided on which the diaphragm is mounted, the housing at least partially enclosing the rear-side of the diaphragm and including a pass-through allowing at least some sound waves generated by the diaphragm in use to exit the speaker housing.

The speaker housing at least partially enclosing the rear-side of the diaphragm may be at least partially enclosed by a further speaker housing wherein sound waves which move through the pass-through in use enter a further enclosure provided by the further speaker housing.

The housing may be constructed from any material or combination of materials known to the skilled person to be suitable for use in such devices.

Acoustic Member An acoustic member in the above aspect and embodiments is located to be operable to restrict the movement of the sound waves through the pass-through in use, wherein the acoustic member includes a substantially flattened body portion and a valve within the body, the valve being configured to open to allow at least some sound waves to move through the pass-through when in use.

In some embodiments, the acoustic members of the present invention provide frequency-selective transmission of sound waves. The selective transmission of sound waves may for instance be the outcome of frequency-selective absorption of undesired resonances by the acoustic members within the device and I or by frequency-selective reflection of undesired resonances within the device by the acoustic members. Typically, the acoustic members provide frequency-selective damping of sound waves within the device.

Any suitable material may be used to make an acoustic member of the present invention. Many materials will have an inherent propensity to absorb and / or reflect acoustic resonances selectively according to frequency. However, by incorporating a valve into the body portion, the acoustic members of the present invention are able to enhance frequency-selective transmission of sound waves irrespective of the inherent properties of the material. Typically, the valve is configured to supplement a material's inherent frequency-selectivity by opening to allow the transmission of those frequencies more favourably transmitted by the material inherently.

In typical embodiments, the acoustic damping increases as the frequency of sound waves generated by the diaphragm in use increases. In some embodiments the acoustic damping decreases as the sound wave frequency generated by the diaphragm in use increases.

In some embodiments, the extent to which the valve opens is dependent on the air volume displacement within the speaker housing. In further embodiments, the extent to which the valve opens increases as the air volume displacement within the speaker housing increases. Typically, the opening of the valve is caused by the air volume within the speaker housing acting directly on the valve. It is known that the lower the sound wave frequency, the higher air volume velocity is required to maintain a given sound pressure level compared to higher frequencies (see Figure 21), thus resulting in a higher air volume displacement within the housing for lower frequencies. Accordingly, a result of this is that the acoustic member provides frequency-selective damping based on air volume displacement. For instance, in embodiments where the extent to which the valve opens increases as the air volume displacement within the speaker housing increases, the valve will open more for lower frequency sound waves than for higher frequency sound waves, thus damping lowerfrequencies less than higher frequencies.

In some embodiments, the extent to which the valve opens is dependent on the frequency of the sound waves generated by the diaphragm. In further embodiments, the extent to which the valve opens increases as the frequency of the sound waves generated by the diaphragm decreases. Typically, the opening of the valve is caused by the sound waves acting directly on the valve. A result of this is that the acoustic member provides frequency-selective damping of sound waves. For instance, in embodiments where the extent to which the valve opens increases as the frequency of the sound waves generated by the diaphragm decreases, the valve will open more for lower frequency sound waves than for higher frequency sound waves, thus damping higher frequencies more than lower frequencies. Selective damping of higher frequencies has the desirable effect of minimising damping and distortion in the extended lower frequency range of the device, whilst maintaining suitable damping of high frequencies.

In some embodiments, the valve is configured to open automatically during normal use to allow the sound waves to flow through the pass-through. This has the benefit of simplifying the operation of the device.

Typically, the valve is biased to a closed position. This improves the effectiveness of the device and ensures that the valve is returned to a closed position automatically when not in use.

The valve can be made out of any material. The choice of material will depend on the application. The surface area, absorption coefficient and F-modulus of the material In some embodiments, the valve is composed of a resilient material. This will, for example, assist with returning the valve to the closed position. Typically, the valve is biased to a closed position by virtue of the inherent resilience of the material, which avoids the use of additional resilient members, thus minimising the complexity of the valve. This property can also be used to assist with the function of providing selective damping of lower frequencies, since higher levels of air volume displacement within the speaker housing (associated with lower frequency sound waves) will exert a greater force upon the valve, thus opening the valve more than lower levels (associated with higher frequency sound waves), due to the counteracting resilient force of the valve material.

In some embodiments, the acoustic member includes a sound-absorbent material and I or a sound-reflective material. In some embodiments, the acoustic member includes a sound-reflective material. Typically, the acoustic member includes a sound-absorbent material. In some embodiments, the acoustic member is composed entirely of sound-absorbent material. In other embodiments, the acoustic member is composed entirely of sound-reflective material.

By adjusting the amounts of each material in the acoustic members of the invention, the frequency-selectivity of the acoustic member may be modulated.

Suitable sound-absorbent materials include fibrous materials, such as long-fibre wool, rock wool, fibre glass and bonded cellulose acetate fibre (BAF); open-cell-structured foams, such as polyurethane foam, polyester foam and polyether foam; felt; and mechanical absorbers, such as solid plates having a perforated surface.

Accordingly, in some embodiments, the sound-absorbent material is selected from the group consisting of fibrous materials, open-cell-structured foams, felt, mechanical absorbers, and mixtures thereof. In further embodiments, the sound-absorbent material is selected from the group consisting of long-fibre wool, rock wool, fibre glass, bonded cellulose acetate fibre (BAF), polyurethane foam, polyester foam, polyether foam, felt, a solid plate material having a perforated surface, and mixtures thereof. In still further embodiments, the sound-absorbent material is selected from the group consisting of long-fibre wool, rock wool, fibre glass, bonded cellulose acetate fibre (BAF), polyurethane foam, polyester foam, polyether foam and felt, such as from the group consisting of polyurethane foam, polyester foam, polyether foam and felt. Typically, the sound-absorbent material is felt. Felt has a good absorption for mid to high frequencies because of its porous structure. Its low E-modulus will also allow for suitable valve movement under higher air pressures (i.e. at lower sound wave frequencies).

Suitable sound-reflective materials will have a low absorption coefficient alpha. It is desirable that the sound-reflective material exhibits flexibility without fatigue, and most preferably is low in density. In the above embodiments, the sound-reflective material may be rubber. An acoustic member composed of rubber will have an absorption coefficient alpha close to zero for most frequencies and can thus be used in applications where reflection rather than absorption of frequencies by the acoustic member is desired when the valve is closed. For instance, in embodiments wherein the extent to which the valve opens increases as the wave frequency decreases, higher frequencies will be reflected by the acoustic member while lower frequencies are transmitted through the valve, thus providing a frequency dependent acoustic volume.

In some embodiments, the substantially flattened body of the acoustic member includes first and second opposing faces and a valve within the body, the valve being configured to open to allow at least some sound waves to move through the pass-through when in use. In some embodiments the first and second opposing faces are flat.

In some embodiments, the body portion is a pad or sheet of material.

In other embodiments, the valve includes a channel for the flow of sound waves through the body portion and one or more moveable valve members pivotally connected to the body portion operable to restrict the flow of sound waves through the channel in use.

For example, in particular embodiments, the substantially flattened body of the acoustic member includes first and second opposing faces; a channel for the flow of sound waves through the body portion between the first and second opposing faces; and one or more moveable valve members pivotally connected to the body portion operable to restrict the flow of sound waves through the channel in use.

The body portion may include one or more of the above channels. Typically, the body portion includes a single channel. The one or more channels are suitably proportioned to allow the passage of sound waves through the body portion. In some embodiments, a single channel is provided which is from about one tenth to about four fifths of the width of the body portion, such as from about one fifth to three fifths, for instance from about a quarter to about half of the width of the body portion, typically about half of the width of the body portion. In particular embodiments, the channel is approximately about 5-25 mm wide, such as about 7-15 mm, for instance about 10-13 mm, typically about 12 mm wide.

In some embodiments, the one or more valve members are integrally formed with the body portion. For instance, in some embodiments, the body portion and the one or more valve members are formed as a single piece.

Typically, from 1 to 10 moveable valve members are piovided on acoustic member of the invention for restricting the movement of sound waves through the channel, such as from 4 to 8 valve members. In some embodiments, 2, 3, 4, 5, 6, 7, 8, 9, or 10 valve members are provided, preferably 8.

In further embodiments, the acoustic member as described in any of the above aspects or embodiments is formed by providing one or more incisions through the body portion to provide one or more moveable valve members forming the valve.

Typically, a plurality of incisions is formed through the body portion to provide a plurality of moveable valve members forming the valve. In some embodiments the incisions bisect in the region of the centre of the body portion, such as at the centre.

For instance, in some embodiments a star-shaped incision pattern is provided, such as exemplified in Figures 13, 14 and 24-25. In other embodiments a grid-like incision pattern is provided, such as exemplified in Figure 23.

The acoustic members may be of any proportion or number suitable for the intended application. Typically, the proportions of the acoustic member will depend on the proportions of the device into which they are inserted in use. Typically, the acoustic members are of a suitable width to span a passage for sound waves within the device housing, such as the pass-through. For instance, in some embodiments, the acoustic member is from 10 mm to 50 mm wide, such as from 15 mm to 30 mm, for instance 20 mm to 25 mm, for example 24 mm. In some embodiments, the body portion of the acoustic member is from 1 mm to 10mm thick, such as from 1 mm to 5 mm thick, for instance 2 mm thick.

In some embodiments, the device includes a single acoustic member of the invention. In other embodiments, the audio output device includes a plurality of the acoustic members. In further embodiments, the device includes from one to six acoustic members, such as from two to four, for example two.

Any combination of the above embodiments may be provided. For instance, where more than one acoustic member is provided in devices of the invention, any combination of acoustic members may be provided. For example, two or more acoustic members may be identical and I or one or moie may be distinct (i.e. different to the other(s)). In some embodiments all of the acoustic members are identical. In other embodiments, each acoustic member is distinct (i.e. different to the other(s)).

When the device includes more than one acoustic member of the invention, the acoustic members are typically located such that each valve is able to operate unhindered. Typically, a first acoustic member is located at a position in the device upstream from a second acoustic member relative to the flow of sound waves from the rear side of the speaker diaphragm to the speaker housing exterior through the pass-through when in use. In some embodiments, a first acoustic member is located at a position closer to the diaphragm than a second acoustic member.

In some embodiments, at least one acoustic member is located in the pass-through.

In some embodiments two damping members are located in the pass through.

Typically, one of the damping members is located in the pass-through.

In further embodiments, an acoustic member is located at the velocity maxima of the sound wave frequency to be damped. This assists with providing improved frequency-selective damping. It is envisaged in some embodiments that the acoustic member may be moved within the device either automatically or manually to provide optimal damping properties, without deconstruction of the device. The manual input may be electronic or mechanical.

In the above aspects and embodiments, the one or more acoustic members may further include a frame attached to the body portion. Providing a frame for the acoustic member allows for ease of instalment of the acoustic members into acoustic devices. The frame may also suitably assist in providing rigidity to the acoustic member. The body portion may be attached to the frame directly or indirectly.

Typically, the frame is attached to the body portion by an adhesive, such as a glue.

In the above aspects and embodiments, the one or more acoustic members may further include a protective casing. For instance, each acoustic member may include a protective casing. The casing provides a more robust component that may be readily inserted into the devices of the invention. The casing may completely or partially enclose one or more acoustic members. Typically, the casing completely encloses one or more acoustic members. For instance, one or more acoustic members may be enclosed within a single casing. Preterably, each acoustic member is enclosed within its own casing. The casing may be of any suitable design provided it does not hinder the operation of the acoustic member. Typically, the casing does not substantially disrupt the flow of sound waves. For instance, in some embodiments, the casing is an open structure, such as a grille or mesh. Typically, the casing is a grille. Any suitable material or combination of materials may be used, such as selected from the group consisting of metals, plastics and combinations thereof.

In a second aspect of the invention is provided an acoustic member as described in any of the above aspects and embodiments.

In a third aspect of the invention is provided a vehicle including one or more audio output devices as described in any of the above aspects and embodiments and / or one or more acoustic members as described in any of the above aspects and embodiments. The vehicle may be any vehicle wherein an audio output device such as a speaker may be installed. Typically, the vehicle is a motor vehicle, such as a car.

In a fourth aspect of the invention is provided the use of an acoustic member as described in any of the above aspects and embodiments in a method of damping sound waves in an audio output device. The audio output device may be any device suitable for emitting sound waves. In some embodiments, the audio output device is a device according to the first aspect or any of its embodiments. In some embodiments, the audio output device is located in a vehicle as described in the above third aspect of the invention or its embodiments. In other embodiments, the method is for selectively damping low frequency sound waves.

In a fifth aspect of the invention is provided a method of manufacturing an audio output device according to any of the above aspects and embodiments including the step of providing an acoustic member as described in any of the above aspects and embodiments in the device at a location operable to restrict the sound waves through the pass-through in use.

In a sixth aspect of the invention is provided a method of manufacturing an acoustic member as described in any of the above aspects and embodiments including the step of making one or more incisions through the body portion to provide one or more moveable valve members forming the valve. As described above, typically from 1 to moveable valve members are formed, such as from 4 to 8 valve members. In some embodiments, 2, 3, 4, 5, 6, 7, 8, 9, or 10 valve members are formed, preferably 8. Typically, a plurality of incisions is formed through the body portion to provide a plurality of moveable valve members forming the valve. In some embodiments the incisions bisect in the region of the centre of the body portion. For instance, in some embodiments a star-shaped incision pattern is formed, such as exemplified in Figures 13, 14 and 24-25. In other embodiments a grid-like incision pattern is formed, such as exemplified in Figure 23.

In a seventh aspect of the invention is provided a method of manufacturing a vehicle as described in the above third aspect and embodiments thereof, including the step of installing an acoustic member as described in any of the above aspects and embodiments and I or installing an audio output device as described in any of the above aspects and embodiments into the vehicle.

It will be appreciated that the features of aspects and embodiments described above may also be present, alone or in combination with any of the features of other embodiments according to any other aspect of the invention.

GENERAL

The term "sound-absorbent material" refers to a material that absorbs more sound energy than it reflects.

The term "sound-reflective material" refers to a material that reflects more sound energy than it absorbs. Typically, a sound-reflective material will have an absorption coefficient alpha close to zero for most frequencies.

Materials encompassed by the term "felt" will be known to the skilled reader. For the avoidance of doubt, this term encompasses non-woven cloth produced by matting, condensing and pressing woollen fibres.

The term "low frequency" or "lower frequency" when used in the context of audio devices refers to the lower part of a frequency spectrum for a given audio output device and can be easily identified by the skilled person. For instance, in some embodiments, the term low frequency refers to the bottom 20% of the frequency response range for a given device, such as the bottom 10%. For instance, for 30 mm voice coil tweeters, the term low frequency typically refers to frequencies of 1000 Hz or less.

The term "high frequency" or "higher frequency" when used in the context of audio devices refers to the upper part of a frequency spectrum for a given audio output device and will be easily identified by the skilled person. For instance, in some embodiments, the term high frequency refers to the top 20% of the frequency response range for a given device, such as the top 10%. For instance, for 30 mm voice coil tweeters, the term high frequency typically refers to frequencies above 1000 Hz.

LIST OF FIGURES

Figure 1 shows a longitudinal cross-section of a known "closed" tweeter construction.

Figure 2 shows a longitudinal cross-section of an alternative known closed speaker construction.

Figure 3 shows a longitudinal cross-section of the closed tweeter construction of Figure 1 further including a damping sheet of felt 3.1 located on the top-plate.

Figure 4 shows a longitudinal cross-section of a typical known "open" tweeter arrangement wherein a pass-through is provided to allow air from the rear-side of the diaphragm to exit the speaker housing.

Figure 5 shows comparative data for known tweeters with a 30 mm diameter voice coil having either a closed construction (i.e. as in Figure 1) or an open construction (i.e. as in Figure 4). The graph plots sound pressure levels measured on an International Electrotechnical Commission (IEC) baffle against sound frequency. For avoidance of doubt, the top of the two plots at 500 Hz corresponds to the "open" configuration and the bottom of the two plots corresponds to the "closed" configuration.

Figure 6 shows comparative data for known tweeters with a 30 mm diameter voice coil having either a closed construction (i.e. as in Figure 1) or an open construction (i.e. as in Figure 4). The graph plots impedance measured on an IEC baffle against sound frequency. For avoidance of doubt, the top of the two plots at 500 Hz corresponds to the "open" configuration and the bottom of the two plots corresponds to the "closed" configuration.

Figure 7 shows a longitudinal cross-sectional view of a known "open" tweeter arrangement provided with porous material in the pass-through.

Figure 8 shows a longitudinal cross-section of a known "open" tweeter arrangement provided with a perforated plate to restrict movement of sound waves through the pass-through.

Figure 9 shows a longitudinal cross-section of a known "open" loudspeaker arrangement provided with a porous material located to restrict the movement of air through the pass-through.

Figure 10 shows comparative sound pressure level data measured on an IEC baffle for known tweeters with a 30 mm diameter voice coil having a) an open construction without damping material restricting the flow of sound waves through the pass-through (i.e. as in Figure 4, denoted as "open" in the graph legend); or b) an open construction having foam restricting the movement of sound waves through the pass-through (i.e. as in Figure 7, denoted as "foam" in the graph legend). The graph plots decibels levels against frequency and these data show that the use of foam material in the pass-through results in a decrease in efficiency at lower frequencies as indicated by a drop in sound pressure at lower frequencies. For avoidance of doubt, the top of the two plots at 500 Hz corresponds to "open" and the bottom of the two plots corresponds to "foam".

Figure 11 shows comparative impedance data measured on an IEC baffle for known tweeters with a 30 mm diameter voice coil having a) an open construction without damping material restricting the flow of sound waves through the pass-through (i.e. as in Figure 4, denoted as "open" in the graph legend); or b) an open construction having foam restricting the movement of sound waves through the pass-through (i.e. as in Figure 7, denoted as "foam" in the graph legend). The graph plots impedance against frequency and these data show that the use of foam material in the pass-through results in significant damping at lower frequencies indicated by a decrease in impedance. For avoidance of doubt, the top of the two plots at 500 Hz corresponds to "open" and the bottom of the two plots corresponds to "foam".

Figure 12 shows comparative harmonic distortion data measured on an IEC baffle for known tweeters with a 30 mm diameter voice coil having a) an open construction without damping material restricting the flow of sound waves through the pass-through (i.e. as in Figure 4, denoted as "open" in the graph legend); or b) an open construction having foam restricting the movement of sound waves through the pass-through (i.e. as in Figure 7, denoted as "foam" in the graph legend). The graph plots percentage harmonic distortion against frequency and these data show that the use of foam material in the pass-through causes a significant increase in harmonic distortion at lower frequencies. For avoidance of doubt, the top of the two plots at 500 Hz corresponds to "foam" and the bottom of the two plots corresponds to "open".

Figure 13 shows a perspective view of an exemplary acoustic member according to the present invention.

Figure 14 shows a longitudinal cross-section of the exemplary acoustic member of Figure 13 when in use.

Figure 15 shows a longitudinal cross-section of an exemplary tweeter according to the invention including two acoustic members.

Figure 16 shows a perspective cut-away view of the exemplary tweeter of Figure 15.

Figure 17 shows a longitudinal cross-section of an exemplary audio output device of the invention containing two acoustic members.

Figure 18 shows comparative sound pressure level data measured on an lEG baffle for a 30 mm diameter voice coil tweeter of the present invention as depicted in Figure (denoted as "acoustic valve" in the graph legend) compared to the data shown in Figure 10 for analogous known devices having: a) the construction of Figure 4 provided without damping material in the pass-through (denoted as "open" in the graph legend); or b) the construction as shown in Figure 7 provided with damping foam in the pass-through (denoted as "foam" in the graph legend). The graph plots decibels levels against frequency and the results are discussed in Example 1. For avoidance of doubt, the top of the three plots at 500 Hz corresponds to "open", the middle corresponds to the "acoustic valve" and the bottom corresponds to "foam".

Figure 19 shows comparative impedance data measured on an lEG baffle for a mm diameter voice coil tweeter of the present invention as depicted in Figure 15 (denoted as "acoustic valve" in the graph legend) compared to the data shown in Figure 11 for analogous known devices having: a) the construction of Figure 4 provided without damping material in the pass-through (denoted as "open" in the graph legend); or b) the construction as shown in Figure 7 provided with damping foam in the pass-through (denoted as "foam" in the graph legend). The graph plots impedance against frequency and the results are discussed in Example 1. For avoidance of doubt, the top of the three plots at 500 Hz corresponds to "open", the middle corresponds to the "acoustic valve" and the bottom corresponds to "foam".

Figure 20 shows comparative harmonic distortion data measured on an lEO baffle for a 30 mm diameter voice coil tweeter of the present invention as depicted in Figure (denoted as "acoustic valve" in the graph legend) compared to the data shown in Figure 12 for analogous known devices having: a) the construction of Figure 4 provided without damping material in the pass-through (denoted as "open" in the graph legend); or b) the construction as shown in Figure 7 provided with damping foam in the pass-through (denoted as "foam" in the graph legend). The graph plots percentage harmonic distortion against frequency and the results are discussed in Example 1. For avoidance of doubt, the top of the three plots at 500 Hz corresponds to "foam", the middle corresponds to "open" and the bottom corresponds to the "acoustic valve".

Figure 21 shows the air volume displacement (m3Is) required to maintain an arbitrary acoustic pressure at a given sound wave frequency (Hz).

Figure 22 shows a longitudinal cross-section of an exemplary base reflex loudspeaker of the invention containing two acoustic members of the invention.

Figure 23 shows both longitudinal cross-section and plan views of an acoustic member according to the present invention.

Figure 24 shows both longitudinal cross-section and plan views of an acoustic member as depicted in Figure 13 encased in a protective grille.

Figure 25 shows both longitudinal cross-section and plan views of an acoustic member of the invention.

Figure 26 depicts a longitudinal cross section of an acoustic member wherein the body portion is affixed to a frame using glue.

DETAILED DESCRIPTION

Specific embodiments of the present invention will now be described further, by way of example, with reference to the accompanying drawings.

Referring to Figure 15, an exemplary embodiment of an acoustic output device of the present invention is provided. The depicted device is a tweeter having an annular configuration and includes a typical domed speaker diaphragm 15.1. The diaphragm is mounted on the speaker housing via a suspension 15.2, which allows suitable vibration of the diaphragm in use. The diaphragm has a front side facing the exterior of the device, and so is configured to radiate sound waves away from the speaker body in the desired direction (e.g. to a listener) and a rear-side that faces the interior of the speaker housing.

The speaker housing 15.3 partially encloses the rear side of the diaphragm and includes a pass-through 15.4 allowing sound waves (and the corresponding displaced air volume) generated by the diaphragm in use to exit the speaker housing.

In order to allow a passage for sound waves to move from the diaphragm to the exterior of the speaker housing via the pass-through, the magnet 15.5 and top-plate 15.6 are suitably provided in an annular configuration. This configuration is more readily visualised in the perspective cut-away view of this device in Figure 16.

The device of Figures 15 and 16 is provided with two disc-shaped acoustic members 15.7 and 15.8 that are orientated to be perpendicular to the flow of sound waves through the speaker housing when in use, restricting the flow of at least some sound waves through the pass-through 15.4. Each acoustic member is proportioned to span the interior cavity created by the annular magnet 15.5 and top-plate 15.6.

Referring to Figure 17, an audio output device of the invention is described having a diaphragm 17.1, an elongated speaker housing 17.2, and two acoustic members 17.3 and 17.4 which restrict the flow of at least some sound waves from the diaphragm 17.1 to the exterior of the speaker housing through the pass-through 17.5 when in use. A first acoustic member 17.3 is located upstream from a second acoustic member 17.4 relative to the flow of sound waves from the rear side of the speaker diaphragm to the speaker housing exterior through the pass-through when in use. The acoustic members in this embodiment are located to coincide with the velocity maxima of the second harmonic sound wave in order to maximise the damping of this vibrational mode. The higher volume velocity generated by the quarter lambda resonance of the housing will open the valve for this frequency and in this way facilitate the transmission of these sound waves through the housing, resulting in lowered damping for frequencies related to this fundamental resonance.

Similar configurations of acoustic members of the present invention could find application in bass-reflex, horn loaded, or transmission line topologies or in audio devices having combinations of these topologies. In such applications, the radiated sound waves produced by the rear of the diaphragm are used to provide a positive effect on the lower frequency spectrum of the speaker. For instance, the acoustic members of the invention can then be used to selectively suppress unwanted resonances, whilst avoiding damping of the fundamental resonance of the speaker.

Figure 22 depicts an exemplary bass reflex loudspeaker housing construction in accordance with the invention having a diaphragm 22.1, a speaker housing 22.2, and two acoustic members 22.3 and 22.4 which restrict the flow of sound waves from the diaphragm 22.1 to the exterior of the speaker housing through the pass-through 22.5 when in use. A first acoustic member 22.3 is located upstream from a second acoustic member 22.4 relative to the flow of sound waves from the rear side of the diaphiagm 22.1 to the speaker housing exterior through the pass-through 22.5 when in use. The acoustic members in this embodiment are located in a vent 22.6 within the housing to minimize damping of the tuned frequency of the box (Helmholtz resonance) and maximize the damping of higher order modes that may occur in the vent.

Referiing to the specific embodiment of Figures 13 and 14, an acoustic member of the invention is depicted. The acoustic member is a flattened circular pad having a body 13.1 and a number of incisions 13.2 through the body centre. The incisions 13.2 intersect to form a star-shaped series of triangular valve flaps 13.3 defining the valve, which move when exposed to air volume displacement created by sound waves in the speaker housing generated by the diaphragm in use. The opening of these valve flaps 13.3 in use creates a channel 14.1 through the centre of the body 13.1. Suitably the pad is made of resilient material, such as felt. Suitably, the body 13.1 and valve flaps 13.3 are integrally formed from a single piece of material. When felt is used, the valve flaps will be inherently resilient and open automatically when subject to adequate air volume displacement in the speaker housing. Furthermore, because of this resilience, the valve members will open more during use as the air volume displacement within the speaker housing increases, thus damping lower frequencies less than higher frequencies. Figure 25 depicts an exemplary embodiment of an acoustic member of Figure 13 having a width (diameter) of 24 mm, a thickness of 2 mm and the incisions are 12 mm wide, thus defining a channel that is 12 mm wide at its widest point when the valve is open. Accordingly, the width of the channel in this embodiment is half the width of the acoustic member.

Figure 23 depicts an alternative acoustic member of the invention. The acoustic member is a flattened rectangular sheet having a body 23.1 and a plurality of incisions 23.2 through the body centre. The incisions 23.2 intersect in a grid-like arrangement to form a series of rectangular valve flaps 23.3 defining the valve, which move when exposed to air volume displacement created by sound waves in the speaker housing generated by the diaphragm in use. The opening of these valve flaps 23.3 in use creates a channel through the centre of the body 23.1. Suitably the sheet is made of a resilient material, such as felt. Suitably, the body 23.1 and valve flaps 23.3 are integrally formed from a single piece of material. When felt is used for example, the valve flaps will be inherently resilient and open automatically when subject to the air volume displacement in the speaker housing. Furthermore, because of this resilience, the valve members will open more during use as the air volume displacement within the speaker housing increases, thus damping lower frequencies less than higher frequencies.

Figure 24 depicts an acoustic member of the invention having a body portion 13.1 and valve flaps 13.3 as depicted in Figure 13 and further including a protective grille 24.1 completely encasing the body portion. The grille helps to provide a more robust component for ready installation into acoustic output devices. The grill is suitably proportioned to allow free movement of the valve flaps when in use.

Lastly, Figure 26 depicts an acoustic member of the present invention having a body portion that is attached to a frame using adhesive glue. The acoustic member may include the frame, which thus provides a convenient component for ready instalment into an acoustic output device, or the frame may be an integral part of the acoustic output device into which the acoustic member is inserted.

The above embodiments are described by way of example only. Other embodiments falling within the scope of the claims will be apparent to the skilled reader.

EXPERIMENTAL ANALYSIS

Reference example I

Figure 5 shows the relationship between the sound pressure level response and frequency for tweeters with a 30 mm diameter voice coil having either a closed (i.e. as in Figure 1) or open construction (i.e. as in Figure 4). Figure 6 shows the corresponding impedance data for the same open and closed tweeters used to provide the data for Figure 5.

These comparative data show that the resonance frequency for an open tweeter arrangement is notably extended to lower frequencies compared to a closed tweeter arrangement.

However, the circled area of figures 5 and 6 show a severe frequency response irregularity for the open speaker arrangement versus the closed speaker arrangement. This irregularity is the result of Helmholtz resonation in the operating frequency range of the tweeter created by interaction of the air volume behind the diaphragm (4.6 in Figure 4) with the air mass inside the pass-through (4.5 in Figure 4).

Reference example 2

Figures 10-12 show comparative data for tweeters with a 30 mm diameter voice coil having an open construction and provided either without damping material in the pass-through (i.e. as in Figure 4, denoted as "open" in the graph legend) or with foam in the pass-through (i.e. as in Figure 7, denoted as "foam" in the graph legend).

Figure 10 shows the relationship between the sound pressure level response and frequency for these tweeters, Figure 11 shows the relationship between the impedance and frequency for these tweeters and Figure 12 shows the relationship between percentage harmonic distortion and frequency for these tweeters.

These data show that provision of a foam material in the pass-through (Le. as in Figure 7) maintains the low frequency response extension exhibited by the open arrangement having no foam (Le. as in Figure 4) and suitably dampens the Helmholtz resonance associated with the open configuration in the absence of foam.

However, the foam-containing tweeter exhibits an undesirable decrease in efficiency at lower frequencies compared to the open construction without foam, indicated by a drop in sound pressure at lower frequencies in Figure 10.

This decrease in efficiency is likely to be the result of the significant damping at lower frequencies by the foam, as indicated by the decrease in impedance at lower frequencies in Figure 11.

Lastly, the presence of the foam also results in a significant increase in harmonic distortion at lower frequencies (Figure 12).

Example I

To show the improved properties of the present acoustic members in devices of the present invention, an exemplary tweeter having the general construction depicted in Figure 15 was prepared and tested.

Figures 18-20 show superimposed comparative data obtained for three different mm voice coil tweeter constructions. In particular, Figures 18-20 show the data obtained for a device of the present invention as depicted in Figure 15 (denoted as "acoustic valve" in the graph legend) compared to the data shown in Figures 10-12 for analogous devices having a) the construction of Figure 4, i.e. provided without damping material in the pass-through (denoted as "open" in the graph legend); and b) the construction as shown in Figure 7, i.e. provided with damping foam in the pass-through (denoted as "foam" in the graph legend).

Figure 18 shows that the device of the present invention provides increased sound pressure levels at lower frequencies (i.e. at around 1000 Hz and below) compared to the comparative device having foam in the pass-through. In other words, the response efficiency of the device of the invention is improved at lower frequencies compared to the comparative device having foam in the pass-through.

Additionally, Figure 18 also shows that the device of the invention shows significantly decreased frequency response irregularities compared to the comparative device having no acoustic member in the pass-through, providing a similar effect to the comparative device having a foam acoustic member in the pass-through (see for example the legion at approximately 1500-2000 Hz). This is particularly the case in the region of 2000 Hz to 3000 Hz, which is the approximate frequency of Helmholtz resonation in these 30 mm voice coil tweeters.

Figure 19 shows that the present invention desirably provides decreased damping (as indicated by increased impedance) at the lower frequencies (i.e. around 1000 Hz and less) compared to the foam filled device, whilst still providing adequate damping at the higher frequencies (i.e. above 1000 Hz). Thus, the low frequency response extension achieved by insertion of the pass-through in the housing is maintained at lower frequencies.

Lastly, it is clear from Figure 20 that the present invention provides a significantly improved harmonic distortion profile compared to the prior art devices, providing significantly lower distortion than both the open" and "foam" devices, especially at the desired low frequency end of the spectrum (i.e. 1000 Hz and less).

Conclusion

In summary, the data show that acoustic members of the present invention provide frequency-selective transmission of acoustic resonances within acoustic devices.

This thus allows for desirable modulation of acoustic resonances within audio output devices. By providing the acoustic members of the present invention in audio output devices having a pass-through, an extended low frequency response is achieved compared to analogous housing constructions provided without a pass-through. This extended low frequency response is achieved whilst minimising decreases in output efficiency, frequency response irregularities and harmonic distortion associated with

analogous devices of the prior art.

Claims

CLAIMS1. An audio output device including: a) a speaker diaphragm including a front side facing the exterior of the device and a rear side facing the interior of the device; b) a speaker housing on which the diaphragm is mounted, the speaker housing at least partially enclosing the rear side of the diaphragm and including a pass-through that allows at least some sound waves generated by the diaphragm in use to exit the speaker housing; and c) an acoustic member located to be operable to restrict movement of at least some sound waves through the pass-through in use, wherein the acoustic member includes a substantially flattened body portion and a valve within the body, the valve being configured to open to facilitate the movement of at least some sound waves through the pass-through when in use.
2. An audio output device according to claim 1, wherein the acoustic member provides frequency-selective transmission of sound waves.
3. An audio output device according to claim 1 or 2, wherein acoustic damping increases as the frequency of sound waves generated by the diaphragm increases.
4. An audio output device according to any previous claim, wherein the extent to which the valve opens is dependent on the extent of air volume displacement within the device housing in use.
5. An audio output device according to claim 4, wherein the extent to which the valve opens increases as the air volume displacement within the device housing increases.
6. An audio output device according to any of claims 4 and 5, wherein the opening of the valve is caused by the air volume displaced within the housing acting directly on the valve.
7. An audio output device according to any of claims 1-3, wherein the extent to which the valve opens is dependent on the frequency of the sound waves generated by the diaphragm.
8. An audio output device according to claim 7, wherein the extent to which the valve opens increases as the frequency of the sound waves generated by the diaphragm decreases.
9. An audio output device according to any of claims 7 and 8, wherein the opening of the valve is caused by the sound waves acting directly on the valve.
10. An audio output device according to any previous claim, wherein the valve is configured to open automatically during normal use to allow the sound waves to move through the pass-through.
11. An audio output device according to any previous claim, wherein the valve is biased to a closed position.
12. An audio output device according any previous claim, wherein the acoustic member is composed of a resilient material.
13. An audio output device according to claim 12, wherein the valve is biased to a closed position by virtue of the inherent resilience of the material.
14. An audio output device according to any previous claim, wherein the acoustic member includes a sound-absorbent material and I or a sound-reflective material.
15. An audio output device according to claim 14, wherein the acoustic member includes a sound-absorbent material.
16. An audio output device according to claim 14 or 15, wherein the acoustic member includes a sound-reflective material.
17. An audio output device according to any of claims 14-16, wherein the sound-absorbent material is selected from the group consisting of fibrous materials, open-cell-structured foams, felt, mechanical absorbers, and mixtures thereof.
18. An audio output device according to claim 17. wherein the sound-absorbent material is selected from the group consisting of long-fibre wool, rock wool, fibre glass, bonded cellulose acetate fibre (BAF), polyurethane foam, polyester foam, polyether foam, felt, a solid plate material having a perforated surface, and mixtures thereof.
19. An audio output device according to claim 18, wherein the sound-absorbent material is felt.
20. An audio output device according to any of claims 16-19, wherein the sound-reflective material is rubber.
21. An audio output device according to any previous claim wherein the substantially flattened body of the acoustic member includes first and second opposing faces; a channel for the flow of sound waves through the body portion between the first and second opposing faces; and one or more moveable valve members pivotally connected to the body portion and operable to restrict the flow of sound waves through the channel in use.
22. An audio output device according to claim 21, wherein the body portion includes a single channel.
23. An audio output device according to claim 21 or 22, wherein the channel is from one tenth to four fifths of the width of the body portion.
24. An audio output device according to claim 23, wherein the channel is about half of the width of the body portion.
25. An audio output device according to any of claims 21-24, wherein the body portion includes a plurality of valve members.
26. An audio output device according to any of claims 21-25, wherein the one or more valve members are integrally formed with the body portion.
27. An audio output device according to any of claims 21-26, wherein the body portion and one or more valve members are formed as a single piece.
28. An audio output device according to any previous claim, wherein the acoustic member is formed by making one or more incisions through the body portion to provide one or more moveable valve members forming the valve.
29. An audio output device according to claim 28, wherein the acoustic member is formed by making a plurality of incisions through the body portion to provide a plurality of moveable valve members forming the valve.
30. An audio output device according to claim 29, wherein the incisions bisect in the region of the centre of the body portion.
31. An audio output device according to claim 30 wherein the incisions form a star-shaped incision pattern or grid-like incision pattern.
32. An audio output device according to any previous claim wherein the acoustic member includes from 2 to 10 moveable valve members.
33. An audio output device according to claim 32 wherein the acoustic member includes from 4 to 8 moveable valve members.
34. An audio output device according to any previous claim, wherein the acoustic member is substantially as described in any of Figures 13, 14 and 23-26.
35. An audio output device according to any previous claim, including a single acoustic member.
36. An audio output device according to any previous claim, including a plurality of the acoustic members.
37. An audio output device according to claim 36, including two of the acoustic members.
38. An audio output device according to any of claims 1-34 and 36-37 wherein a first acoustic member is located in the device upstream from a second acoustic member relative to the flow of sound waves from the rear side of the speaker diaphragm to the speaker housing exterior through the pass-through when in use.
39. An audio output device according to any of claims 1-34 and 36-38, wherein a first of the acoustic members is located at a position in the device closer to the speaker diaphragm than a second of the acoustic members.
40. An audio output device according to any previous claim, wherein at least one acoustic member is located in the pass-through.
41. An audio output device according to any previous claim, wherein one or more of the acoustic members are located at the velocity maxima of the sound wave frequency to be damped.
42. An audio output device according to any previous claim selected from the group consisting of a loudspeaker, a tweeter, headphones, and audio devices having bass-reflex, horn-loaded and a transmission line topologies.
43. An audio output device of claim 42, wherein the device is a tweeter or base reflex loudspeaker.
44. An audio output device substantially as described in any of Figures 15-17 and 22.
45. An audio output device according to any previous claim wherein the one or more acoustic members further include a frame attached to the body portion.
46. An audio output device according to any previous claim wherein one or more acoustic members further include a protective casing.
47. An audio output device according to claim 46 wherein the protective casing completely or partially encloses one or more acoustic members.
48. An audio output device according to claim 47 wherein the protective casing completely encloses one or more acoustic members.
49. An audio output device according to any of claims 46-48 wherein the protective casing has an open grille or mesh structure.
50. An acoustic member as set out in any previous claim.
51. A vehicle including one or more audio output devices as described in any of claims 1-49 and / or one or more acoustic members as described in claim 50.
52. A vehicle of claim 51, wherein the vehicle is a motor vehicle.
53. Use of an acoustic member of claim 50 in a method of damping sound waves in an audio output device.
54. The use of claim 53, wherein the audio output device is a device according to any of claims 1-49.
55. The use of claim 53 or 54, wherein the audio output device is located in a vehicle as set out in claim 51 or 52.
56. The use of any of claims 53 to 55, wherein the acoustic member provides frequency-selective transmission of sound waves.
57. A method of manufacturing an audio output device according to any of claims 1-49 including the step of providing an acoustic member of claim 50 in the device at a location operable to restrict the movement of at least some sound waves through the pass-through in use.
58. A method of manufacturing an acoustic member according to claim 50 including the step of making one or more incisions through the body portion to provide one or more moveable valve members forming the valve.
59. A method of manufacturing an vehicle according to claim 51 or 52 including the step of installing an acoustic member of claim 50 and I or an audio output device according to any of claims 1-49 into the vehicle.