GB2391739A - Speaker enclosure attenuates rear waves through destructive interference of the divided and then recombined wavefront - Google Patents

Abstract

A speaker enclosure is provided for attenuating rear waves generated by at least one speaker mounted in the enclosure. The speaker enclosure includes an interference configuration means for directing section of the rear wave front generated by the speaker or speakers along different path lengths to recombine destructively in one or more interference chambers. In one aspect of the invention, a plurality of conduits 7,8 of a plurality of lengths are provided. Each conduit has a first end which receives a fraction of the rear waves generated by the speaker or speakers and a second end for directing the rear waves to the interference chamber. In one embodiment, means for pressure equalization with ambient external pressure 14 are connected and baffles filled with acoustic damping material 16 are provided. In one embodiment, the second ends of the conduits are in opposed relationship whereas in another embodiment, the second ends of the conduits are in parallel relationship (see fig. 3 and fig. 6).

Description

239 1 739

( 1 A Sneaker Enclosure The present invention generally relates to speaker enclosures and more particularly the present invention relates to a speaker enclosure that attenuates rear waves.

Speakers typically comprise paper cones or diaphragms suspended at their open ends in encompassing rigid frames or baskets by way of annular elastomeric rings or roll surrounds or edge suspensions. The apexes or closed ends of the cones are supported at or spaced from their apexes by way of elastomeric suspension discs or spiders attached to the baskets which in cooperation with the roll surrounds, are intended to allow the cones to move or vibrate substantially along their axis in forward and backward motions relative to the baskets. The described suspension arrangement is intended to allow the cones to move as freely as possible in order to more accurately reproduce sounds.

Moreover the spiders hold voice coil forrners in fixed positions in relation to the cones such that movement of the voice coils are substantially communicated to the cones. Permanent ring magnets rigidly mounted at the rear of the baskets usually surround the voice coil and support non-ferrous or soft iron central cores (which cannot be permanently magnetised) connected to the permanent magnets, around which the voice coils are movably situated such that variable magnetic fields induced by currents passing through the voice coils are intensified by the soft

iron cores and which varying fields react with the relatively strong permanent magnetic fields of

the permanent magnets thereby generating electromechanical forces resulting in physical movements or vibrations of the voice coils and the coupled cones to which they are connected thereby reproducing sounds or noises.

The vibrations generate alternate pressures on one side and simultaneous rarefactions on the other side of the cones which are immediately followed by the converse, namely rarefactions on the said one side and pressures on the other. These air pressures and rarefactions are generally referred to as front waves, which emanate from the open ends of the cones and rear waves which emanate form the apex ends of the cones, the rear waves being generally regarded as 180 degrees out of phase in relation to the front waves Ed may also be regarded as complementary opposite to each other. It is understood that the human ear may have difficulty in distinguishing between the rear waves and front waves.

( 2 When sounds or noises are reproduced through speakers without enclosures, for example, simply suspended in free air, the front waves and rear waves move away radially from their side of origin of the cone and seek to find the shortest paths around the edges of the cones towards the other sides of the cones. It is understood that frequencies lower than those associated with the distance Dom the apex of the cones to the edges of the cones have no difficulty in finding the shortest paths. However higher frequencies have more difficulty in finding the shortest paths because the cone size is relatively large compared to their wavelengths.

In this manner the rear waves and front waves substantially or effectively recombine and only a weak sound is audible to listners in its vicinity even when the speakers are driven at high powers.

It is noted that only relatively small masses of air are disturbed in this free air state as compared to other arrangements, such as when baffles or enclosures are used (described below). Hence only small sounds or noises are audible namely those which escape recombination.

In this free air state the cones are not as inhibited in their movement as compared to when they are housed in enclosures or have baffles (described below). Primarily the greatest impediments to cone movements in free air are those of the resilience or elasticity of the roll surrounds or spiders. In this free air state relatively large cone excursions from their quiescent resting positions are readily obtained since only small mechanical motive forces are required to overcome the delicate suspension arrangements of the speaker driver namely the roll surround and spider. Consequently relatively small currents in the voice coils readily produce the desired cone movements.

In this free air state, on the one hand, speakers behave very well from an electrical point of view because cone excursions more accurately follow the signal currents and therefore reproduce sounds more accurately with low voice coil currents, low heat dissipation in the voice coils and low power consumption. On the other hand the end result, namely the sounds produced, are of very low volume and severely degraded in quality due to recombination.

However when speakers are housed in suitable baffles or enclosures the front waves and rear waves are more separated and consequently much louder sounds are audible, particularly lower frequencies. It is understood that larger masses of air are being moved in this case and therefore the voice coils will need to draw more current in order to perform this additional work burden of

( 3 moving larger air masses both in front of and behind the cones. lt is also understood that larger voice coil currents are not desirable for a variety of reasons, for example, larger power supplies and additional cost are required; or the voice coils may burn out if excessive currents occur because heat dissipation in the voice coils increases with current.

Known enclosure designs commonly seek to manipulate the rear waves in a variety of ways, for example, a simple box with openable side doors which increases the effective baffle thereby separating the front and rear waves (and reduction in recombination); sending the rear waves down long conduits within enclosures in order to attenuate the amplitudes of the various sounds; filling the enclosures with sound absorbing materials to attenuate the unwanted rear waves.

In other known designs it is desirable to eliminate as much as possible the rear waves so that its cancellation effect on the front waves is much reduced or ideally eliminated. For example sealed enclosures known collectively as an infinite baffle type of design; enclosures filled with sound absorbing material in attempts to absorb the entire rear waves or at least to dampen them. These designs commonly suffer interference due to resonance's of the enclosures. Typically such enclosures will resonate noticeably at low frequencies, in sympathy with certain harmonic frequencies of the sounds reproduced through these enclosures often resulting in noticeable low frequency booming sounds.

Commonly such enclosures are deliberately tuned to resonate at very low frequencies so as not to interfere too much with the sound being replayed or to enhance bass frequencies which may require boosting. Even though an enclosure may be entirely sealed this resonant booming may still be heard. Moreover since such designs target low frequencies they are typically large or heavy or made from dense materials, which may be expensive or difficult to cut. Size, weight or cost typically increase with the desired power output of the speaker drivers or speaker enclosures or power supplies.

Another more significant effect of this booming relates to standing waves generated at or around the resonant frequencies of the enclosures. Standing waves within an enclosure are thought to impede the free movement of speaker cones particularly at or near the frequencies or harmonics of the standing waves. The result of this is that the voice coils must perform more work at these frequencies to overcome the impeding standing waves and therefore will require higher voice coil currents at those frequencies. It is known that the transient or frequency responses of speaker

( 4 drivers fitted into enclosures are typically quite different from that of their free air transient or frequency responses. Typically impedance peaks occur around the resonant frequencies of the enclosures. Other designs seek to modify the rear waves and deploy them usefully to combine with the front waves, for example, bass reflex designs which have flutes for phase shifting or delaying certain targeted low frequencies which frequencies are enhanced by the design or resonant frequencies of the flutes, the flutes being connected with openings on the enclosures such that when the targeted enhanced low frequencies emerge they are at least in phase with those of the front wave.

For example US 3993162, US4592444 and US4509192 disclose speaker enclosures that use conduits to redirect the rear wave for output in phase with the front wave. It is understood that when phase shifted or delayed sound is mixed with unaltered sound the overall sound quality may be considered to be degraded since strictly speaking the sounds are not of the same origin, however the human ear may not notice this particularly at low frequencies unless the phase difference is large.

It is an objective of the present invention to attenuate the rear waves generated by a speaker in a speaker enclosure or cabinet.

According to one aspect, the present invention provides a speaker enclosure for attenuating rear waves generated by at least one speaker mounted in the enclosure. The speaker enclosure includes an interference configuration means for directing sections of the rear wave front generated by the speaker or speakers along different path lengths to recombine in one or more interference chambers.

In one embodiment pressure equalization means is connected to the interference configuration means to equalize the pressure in the interference configuration means to ambient external pressure. The pressure equalization means can be connected to the interference configuration means in a region where the sections of the rear wave front interferingly recombine.

An aspect of the invention provides a speaker enclosure for the mounting of at least one speaker for generating sound. The speaker enclosure comprises at least one interference chamber, and a plurality of conduits of a plurality of lengths. Each conduit has a first end for interfacing with a rear face of a speaker to receive a fraction of the rear waves generated by the speaker. The

( 5 plurality of conduits are arranged to receive substantially all of the rear waves generated by the or each speaker. Each conduit has a second end connected to an interference chamber for directing the fraction of rear waves to interfere in the interference chamber.

In one embodiment the or each interference chamber includes a port for pressure equalization with ambient pressure external to said speaker enclosure. This enable both static and dynamic pressure equalization. In one embodiment a baffle is connected to the or each said port and the or each baffle is filled with acoustic damping material for damping sound output from said port.

This reduces the escape of high frequency residual noise from the pressure equalization port.

In an embodiment of the present invention the total cross sectional area of the conduits is substantially equal to the area of the diaphragm or diaphragms of the speaker or speakers. This ensures that there is no pressurization down the conduits caused by displacements of the diaphragm. In embodiments the enclosure can be adapted to mount a plurality of speakers. In one such embodiment the first end of each conduit is arranged for interfacing with the rear face of a speaker to receive substantially all of the rear waves generated by the speaker. In an alternative embodiment two speaker drivers can be arranged to share a single conduit, each speaker having its own mounting aperture to the conduit.

In one embodiment the first end of each conduit is arranged for interfacing with the rear face of a speaker to receive a fraction of rear waves generated by the speaker, and the plurality of conduits are arranged to receive substantially all of the rear waves generated by the speaker. Thus in this single speaker arrangement the rear wave from the speaker is divided into portions for each conduit In a preferred arrangement the or each interference chamber is arranged at a position rearward of a mounting position of the or each speaker.

In an embodiment of the present invention in which the enclosure is adapted to mount a single speaker, the first end of each conduit is arranged for interfacing with the rear face of the speaker to receive a fraction of rear waves generated by the speaker, the plurality of conduits are arranged to receive substantially all of the rear waves generated by the speaker, and a single

interference chamber is arranged in a position rearward of a mounting position of the speaker for receiving the rear waves from the conduits. This provides and efficient and compact design.

In a preferred embodiment of the present invention each interference chamber is formed by extending the second ends of a plurality of the conduits. Thus the interference chamber need not be a distinct components but can instead be a region provided and ends of the conduits remote from the or each speaker.

In an embodiment of the present invention, the or each interference chamber is arranged connected to the second ends of the conduits such that the second ends of one or more pairs of the conduits are in substantially opposed relationship. Thus in this arrangement the interference is produced between wave fronts traveling in opposite directions.

In another embodiment the or each interference chamber is arranged connected to the second ends of the conduits such that the second ends of one or more pairs of the conduits are in substantially parallel relationship. Thus in this arrangement the interference is produced between wave fronts traveling in the same direction.

In one embodiment of the present invention the conduits comprise at least one pair of conduits having different lengths and the or each pair of said conduits are connected to a interference chamber. In an alternative embodiment of the present invention the conduits comprise a plurality of pairs of conduits and each conduit in a pair has a different length. Each pair of conduits are connected to a interference chamber.

In and embodiment of the present invention the first end of each said conduit is formed as a manifold for coupling to the rear face of a speaker.

Since baskets commonly have four openings, an embodiment is envisaged such that each basket opening communicates exclusively with its own conduit. It is understood that although even numbers of conduits are readily accommodated, an odd number of conduits may also be employed. For example, three conduits comprising one short conduit and two longer conduits

can be used. The lengths and end points of these multiple conduits could be varied or terminated accordingly at suitable locations for recombination regions.

Another aspect of the present invention provides a speaker arrangement comprising the speaker enclosure and at least one speaker mounted in the speaker enclosure. The or each speaker is coupled to the interference configuration means to provide for the attenuation of the generated rear waves.

Another aspect of the present invention provides an audio system comprising the speaker arrangement and an audio signal generating means for generating audio for output to the or each speaker arranged in the enclosure.

Embodiments of the present invention can significantly reduce standing waves in the enclosure produced by rear waves thereby enabling better performance from the speaker or the transient or frequency responses of the speaker to be closer to that of their free air transient or frequency responses respectively.

Embodiments of the present invention can also reduce the current requirements of speaker voice coils and consequently the power supply ratings required.

Embodiments of the present invention also enable light materials or materials which are devoid of significant resonant frequencies to be used in the construction of enclosure. Due to the reduction of standing waves, the enclosure may be made from light materials which do not suffer greatly from the effects of resonance. Fortunately several of such light materials, for example, polystyrene exhibit excellent desirable qualities such as excellent soundproofing, low cost, low weight and ease of cutting or working.

Embodiments of the present invention further enable injection moulded or low cost or easily worked materials to be used in the construction of enclosure.

Embodiments of the present invention also enable small speakers to have improved effective power or performance equivalent to much larger conventional types.

l In use speakers are fitted to the enclosure and the rear waves, sounds or noises emanate from the speakers and travel along at least two effectively different paths through the conduits. The effect of this is that sounds that traveled along one path through the conduits, in a first direction, collide with sounds which travelled along another path in a second direction. The said first and second directions can opposite to each other or substantially parallel. The effect of such collisions results in substantial or effective destructive recombination of both sounds which together formed the rear wave. Surprisingly recombination readily takes place. It is noted that the enclosure appears to function without the creation of significant standing waves and the associated degradation electrical or performance characteristics. It is thought that although two colliding sounds may be of slightly different origin, namely if one sound channel path length is shorter than another sound channel path length then the former sound is of slightly more recent origin, they are nevertheless thought to be regardable as being sufficiently similar for substantial destructive recombination to take place.

Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic crosssectional diagram of a speaker enclosure in accordance with the first embodiment of the present invention; Figures 2a, b, c and d are schematic cross-sectional diagrams of a speaker enclosure in accordance with a second embodiment of the present invention; Figure 3 is a schematic crosssectional diagram of a speaker enclosure in accordance with a third embodiment of the present invention; Figure 4 is a schematic crosssectional diagram of a speaker enclosure in accordance with a fourth embodiment of the present invention; Figure 5 is a schematic crosssectional diagram of a speaker enclosure in accordance with a fifth embodiment of the present invention; and Figure 6 is a schematic crosssectional diagram of a speaker enclosure in accordance with a sixth embodiment of the present invention.

Referring to Figure 1, which is a cross-sectional diagram of a first embodiment of the present invention, a cabinet I houses a speaker 2 comprising a speaker coil arrangement 3, a diaphragm 4 which is driven by the speaker coil arrangement 3, and a speaker basket S for supporting the diaphragm 4. The speaker basket 5 is provided with apertures 6 to allow the rear wave generated by the diaphragm to exit therethrough.

Thus when the speaker 2 generates sounds, a desirable front wave is generated in conjunction with an undesirable rear wave which exits through the apertures 6 in the basket 5.

In this embodiment a pair of conduits 7 and 8 are arranged to interface to the rear of the speaker 2 in order to conduct the generated rear wave. The conduits 7 and 8 are arranged diametrically opposed to extend along a length of the speaker enclosure I. Each conduit 7 and 8 is arranged to receive half of the rear waves generated by the diaphragm 4. This is achieved by a partitioning wall arrangement comprising an interfacing wall 9 for the first conduit 7 and an interfacing wall I O for the second conduit 8. Thus in this way all of the rear waves generated by the diaphragm 5 are conducted down the conduits 7 and 8: each conduit taking half of the rear wave.

The total cross-sectional area of the conduits 7 and 8 is equal to the area of the diaphragm. This ensures that the pressure fluctuations forming the rear waves which are generated by displacements of the diaphragm 4 are not constricted down the conduits 7 and 8. Thus each conduit 7 and 8 has a cross-sectional area equal to substantially half of the area of the diaphragm 4. Each conduit 7 arid 8 is of different length to provide different path lengths for the portion of the rear wave carried thereby. In this compact design each conduit 7 and 8 wraps around 180 around a central partition I t so that ends 7a and 8a of conduits 7 and 8 respectively meet in an opposed manner to form an interference chamber region 12 where the portions of the rear waves carried by each conduit 7 and 8 combine destructively due to the different path lengths that they have travelled. At the ends 7a and 8a of the conduits 7 and 8 in order to avoid the ends 7a and 8a pointing directly at each other, thereby providing the possibility of sound being directed down an opposed end 7a and 8a, a deflecting portion 13 is provided on the partition I 1 to deflect the sound and to thus enhance interference. In the region of the interference chamber at the ends 7a and 8a of the conduits 7 and 8, a port 14 is provided to facilitate a pressure equalization between

external ambient pressure and pressure within the conduits 7 and 8. This pressure equalization can provide for static, pressure equalization e.g. due to barometric changes, and dynamic pressure equalization due to mass displacement of the diaphragm 4.

The port 14 is connected to a dame 15 which is filled or at least partly filled with sound absorbing material 16. Thus the baffle which has an opening 17 to the atmosphere can attenuate residual sound such as high frequency sound which remains after interference within the interference chamber region 12. The baffle 15 can comprise an elongate and convoluted conduit to enhance the attenuation.

Within the enclosure 1 the remaining space not taken up by the conduits 7 and 8, the speaker 2 and the baffle 15 is filled with sound absorbing material. Conveniently, the enclosure can be constructed from an injection moulded material. For example, the enclosure can comprise an external casing and an injection moulded internal structure. The injection moulded internal structure can comprise two halves which can be placed together within the casing of the cabinet.

A suitable injection moulded material is polystyrene since it has low weight, low cost and is easy to manufacture.

A second embodiment of the present invention will now be described with reference to Figures 2a, 2b, 2c and 2d. Figure 2a is a cross section XX through Figure 2b. Figure 2b is a cross section YY through Figure 2a. Figure 2c is a cross section ZZ through Figure 2a. Figure 2d is a cross section WW through Figure 2a.

This embodiment is similar to the first embodiment described with reference to Figure I except that no pressure equalization port is provided. This embodiment is suitable for use with speakers which provide low displacement and thus the conduit arrangement is less susceptible to large dynamic pressure variations.

The speaker enclosure 20 comprises a speaker 21 housed within the enclosure 20. A first conduit 22 and a second conduit 23 are coupled to receive the rear waves generated by the speaker 21 in a similar manner to the first embodiment of the present invention. Conduits 22 and 23 are of different lengths and extend around a partition 24 so that they turn through 180 to meet at an interference chamber region 25 at a position behind the speaker 21. The interference

chamber region 25 is formed by a deflecting member 26 for deflecting the rear wave portions carried by the conduits 22 and 23 and a bulbous region 27 in the enclosure 20.

Thus this embodiment of the present invention operates in a similar manner to the first embodiment of the present invention to provide for a destructive interference region to attenuate the rear waves generated by the speaker 21.

In this embodiment the conduits 22 and 23 are conveniently of rectangular cross section. The conduits can, however, be of any suitable cross section such as circular, oval or elliptical.

A third embodiment of the present invention will now be described with reference to Figure 3.

In this embodiment of the present invention a speaker arrangement comprises two speakers 30 and 31 which are arranged to be driven in phase. Thus each speaker generates a rear wave. The rear wave generated by each speaker is coupled to a respective conduit 32 and 33 respectively.

Each conduit 32 and 33 has a different length and the ends of each conduit 32a and 33a meet in an interference chamber region 34 to provide for the destructive interference of the rear wave for attenuation of the rear wave To enhance interference and to reduce standing waves a deflector 35 is provided to deflect the rear waves output from the ends 32a and 33a of the conduits 32 and 33. Adjacent to the interference chamber region 34 there is provided a port 36 for pressure equalization. A baffle 37 is connected to the port 36 and the baffle 37 is partially filled with sand-absorbing material 38 for absorbing residual sound which is not destructive cancelled within the interference chamber region 34. The baffle 37 and port 36 provide for dynamic and static pressure equalization between external ambient pressure and the pressure within the conduits 32 and 33.

Thus in this embodiment of the present invention, the total rear waves generated by the in phase speakers 30 and 31 is attenuated within the interference chamber region 34. Each conduit 32 and 33 receives half of the total rear wave generated by the in phase speakers 30 and 31. Each speaker 30 and 31 is provided with its own rear wave attenuating conduit 32 and 33. The cross sectional area of each conduit 32 and 33 is equal to the area of the diaphragm in each respective

speaker 30 and 31. This avoids the conduits 32 and 33 providing for resistance to displacements by the respective diaphragms.

In this embodiment of the present invention, each of the speakers 30 and 31 are arranged to generate sound in the same direction. Thus each conduit 32 and 33 has a 90 bend so that the ends 32a and 33a of the conduits 32 and 32 meet in an opposed relationship to form the interference chamber region 34.

A fourth embodiment of the present invention will now be described with reference to Figure 4.

This embodiment of the present invention is similar to the third embodiment of the present invention except that two speakers 40 and 41 provided within the speaker enclosure are arranged to produce sound in phase but in opposite directions. Each speaker 40 and 41 is provided with a respective conduit 42 and 43 for receiving rear waves. The ends 42a and 43a of the conduits 42 and 43 meet in an opposed relationship to form an interference chamber region 44. A deflecting portion 45 is provided to deflect sound within the interference chamber region 44 towards a port 46 provided for pressure equalization. A baffle 47 is connected to the port 46 and is part-filled with sound absorbing material 48 for damping residual sound remaining after the destructive interference within the interference chamber region 44.

Thus this embodiment of the present invention is similar to the third embodiment of the present invention except that each of the conduits 42 and 43 is straight and does not include a 90 bend.

A fifth embodiment of the present invention will now be described with reference to Figure 5.

In this embodiment ofthe present invention, a speaker enclosure 58 houses two speakers 50 and 51. The speakers are arranged to be driven in phase and to generate sound in the same direction.

Each speaker 50 and 51 is coupled to a respective conduit 52 and 53. The conduit 52 is of longer length than the conduit 53. The conduits 52 and 53 are arranged to wrap round through 180 around a partition 54. In this way the ends of the conduits 52a and 53a meet in an opposed relationship toform an interference chamber region 55 at a position rearward of the speakers 50 and 51. A deflecting portion S9 is provided on the partition 54 to deflect sound emanating from the ends 52a and 53a of the conduits 52 and 53. A port 56 is provided in the wall of the enclosure 58 for pressure equalization in the region of the interference chamber region 55.

Acoustic absorbing material 57 is provided adjacent to the port 56 for absorbing any residual acoustic vibrations which were not cancelled in the interference chamber region 55.

Thus in this embodiment of the present invention a compact arrangement is provided in which conduits turn through 180 , and each speaker 50 and 51 is connected to its own conduit 52 and 53 respectively. In this embodiment of the present invention the conduits 52 and 53 initially have a cross-sectional area equal substantially to the area of the diaphragm of the speakers 50 and 51. The cross-sectional area is however reduced along the conduits 52 and 53.

The sixth embodiment of the present invention will now be described with reference to Figure 6.

Figure 6 is a schematic cross-sectional diagram through a speaker enclosure 60. The speaker enclosure 60 houses a speaker 61 having a diaphragm 62 driven by a speaker coil arrangement 63. In this arrangement, two conduits 64 and 65 are provided coupled to each receive half of the rear wave generated by the diaphragm 62. Each conduit 64 and 65 extend away in opposed directions from the speaker 61 and then turn around the central former 66 so that the ends 64a and 65a of the conduits 64 and 65 come to lie in a substantial parallel arrangement to form an interference chamber region 67. The length of the conduit 65 is greater than the length of the conduit 64 and thus the sound traveling down the conduit 64 and 65 destructively interferes in the interference chamber region 67.

A port 68 is provided into the interference chamber region for pressure equalization between the external and the internal pressure and the internal pressure within the conduits 64 and 65. A baffle 69 is connected to the port 68 and is partially filled with sand absorbing material 70 to acoustically damp residue sound which would otherwise escape through an external port 71.

Thus in this embodiment of the present invention, the portions of the rear wave conducted through the conduits 64 and 65 is brought into interference in a substantially parallel manner in the interference chamber region 67.

Although in the embodiments illustrated above, each speaker is provided with a single conduit or a pair of conduits which terminate in an interference chamber region, a speaker can be provided with more than two conduits which terminate in more than one interference chamber region. For exermple a speaker can be provided with a multiple number of conduits having different path

lengths which terminate in a single interference chamber region. The multiple conduits can be arranged to be in pairs where each pair has a conduit of short length and a conduit of long length.

The pairs of conduits can be the same or of differing lengths. Alternatively, any number of conduits can be used with each conduit having a different path length. In a further embodiment of the present invention, multiple interference chamber regions can be provided. Each chamber region can be fed by a pair of conduits, multiple pairs of conduits, or a plurality of conduits of different lengths.

Thus where a speaker is provided with multiple conduits to receive the generated rear wave, a manifold arrangement can be provided for coupling the parts of the rear wave into respective conduits. Because by virtue of this invention, the rear wave is significantly attenuated, this enables use of very light enclosure materials. For example, polystyrene is used throughout in the described embodiment above. This has the advantage of low cost, low weight, ease of manufacture, and small size.

Moreover it has been noticed that use of this invention results in a noticeable reduction in heat dissipated in the voice coil. Additionally it has been noticed that speaker drivers used in the described enclosure also behave as if they were not in an enclosure, specifically their transient response is much closer to their free air optimum. This results in more accurate sound reproduction. This is thought to be due to the destruction of the rear wave. Another significant consequence of the described invention is that a much smaller speaker in the described enclosure can perfo'Tn similarly to a much larger speaker in a much larger conventional enclosure.

Although the present invention has been described with reference to specific embodiments, it will be apparent to a skilled person in the art that modifications lie within the spirit and scope of the present invention.

Claims (18)

Claims

1. A speaker enclosure for mounting at least one speaker and for attenuating rear waves generated by at least one speaker, said speaker enclosure comprising an interference configuration means for directing sections of the rear wave front generated by the speaker or speakers along different path lengths to interferingly recombine.

2. A speaker enclosure according to claim 1, wherein said interference configuration means comprises: at least one interference chamber; and a plurality of conduits of a plurality of lengths, each conduit having a first end for interfacing with a rear face of a said speaker to receive a fraction of rear waves generated by said at least one speaker, said plurality of conduits being arranged to receive substantially all of the rear waves generated by said at least one speaker, each said conduit having a second end connected to a said interference chamber for directing the fraction of rear waves to interfere in said interference chamber.

3. A speaker enclosure according to claim 2, wherein the or each interference chamber includes a port for pressure equalization with ambient pressure external to said speaker enclosure.

4. A speaker enclosure according to claim 3, wherein including a baffle connected to the or each said port, the or each baffle being filled with acoustic damping material for damping sound output from said port.

5. A speaker enclosure according to any one of claims 2 to 4 for the mounting of a plurality of speakers, wherein said first end of each conduit is arranged for interfacing with the rear face of a said speaker to receive substantially all of the rear waves generated by said speaker.

6. A speaker enclosure according to any one of claims 2 to 4, wherein said first end of each conduit is arranged for interfacing with the rear face of a said speaker to receive a fraction of rear waves generated by said speaker, and said plurality of conduits are arranged to receive substantially all of the rear waves generated by said speaker.

7. A speaker enclosure according to any one of claims 2 to 6, wherein the or each interference chamber is arranged at a position rearward of a mounting position of the or each speaker.

8. A speaker enclosure according to any one of claims 2 to 4 for mounting a single speaker, wherein the first end of each said conduit is arranged for interfacing with the rear face of said speaker to receive a fraction of rear waves generated by said speaker, said plurality of conduits are arranged to receive substantially all of the rear waves generated by said speaker, and a single said interference chamber is arranged in a position rearward of a mounting position of said speaker for receiving the rear waves from said conduits.

9. A speaker enclosure according to any one of claims 2 to 8, wherein each said interference chamber is formed by extending said second ends of a plurality of said conduits.

10. A speaker enclosure according to any one of claims 2 to 9, wherein said at least one interference chamber is arranged connected to said second ends of said conduits such that said second ends of one or more pairs of said conduits are in substantially opposed relationship.

11. A loud speaker enclosure according to any one of claims 2 to 10, wherein said at least one interference chamber is arranged connected to said second ends of said conduits such that said second ends of one or more pairs of said conduits are in substantially parallel relationship.

12. A speaker enclosure according to any one of claims 2 to 11, wherein said conduits comprise at least one pair of conduits having different lengths, the or each pair of said conduits being connected to a said interference chamber.

13. A speaker enclosure according to any one of claims 2 to 12, wherein said conduits comprise a plurality of pairs of conduits, each said conduit in a said pair having a different length, each pair of said conduits being connected to a said interference chamber.

14. A speaker enclosure according to any one of claims 2 to 13, wherein said first end of each said conduit is formed as a manifold for coupling to the rear face of a said speaker.

15. A speaker enclosure according to claim I, including pressure equalization means connected to said interference configuration means to equalize the pressure in said interference configuration means to ambient external pressure.

16. A speaker enclosure according to claim 15, wherein said pressure equalization means is connected to said interference configuration means in a region where the sections of the rear wave front interferingly recombine.

17. A speaker arrangement comprising the speaker enclosure according to an preceding claim and at least one speaker mounted in said speaker enclosure, the or each speaker being coupled to said interference configuration means.

18. An audio system comprising a speaker arrangement according to claim 17 and an audio signal generating means for generating audio for output to said at least one speaker.