GB2458275A

GB2458275A - Horn loading arrangement for a co-axial two-way loudspeaker

Info

Publication number: GB2458275A
Application number: GB0804445A
Authority: GB
Inventors: Laurence Dickie
Original assignee: Turbosound Ltd
Current assignee: Turbosound Ltd
Priority date: 2008-03-10
Filing date: 2008-03-10
Publication date: 2009-09-16
Also published as: GB0804445D0

Abstract

The loudspeaker comprises first and second compression driver units 11, 12; the horn 1 comprises a flared outlet manifold 2. A first set of one or more passages 21-24 are arranged to direct acoustic energy from the first compression driver unit 11 to the entrance of the flared outlet manifold 2. A second set of one or more passages 31 are arranged to direct acoustic energy from the second compression driver unit 12 to the flared manifold2. The first and second sets of passages are configured such that the acoustic pathlength from said first compression driver unit to the outlet of the flared manifold is substantially the same as the acoustic pathlength from said second compression driver unit to the outlet of the flared manifold. Multiple such loudspeakers may be configured as an array (fig. 15).

Description

LOUDSPEAKER HORN

The present application relates to a horn for use with a loudspeaker and, in particular, a horn for a loudspeaker having two compression driver units.

In the field of high power sound reproduction, the transduction of electrical power to acoustic power is frequently achieved by the use of a compression driver. A compression driver is arranged such that the piston area is greater than the throat immediately adjacent to it. It should be appreciated, however, that the compression driver may further include a tapered duct immediately following the throat. The compression driver is arranged in order to effect an optimum match of impedances and hence maximise the power transfer. The compression driver is typically attached to a wave-guide of gradually increasing cross-sectional area, namely a horn.

In the field of high power sound reproduction, it is preferable for the system to have a relatively wide bandwidth so that a single unit may be used. However, achieving a wide bandwidth from a single type of horn, while also preserving a low distortion and high power handling, is difficult. Accordingly, it has previously been proposed to combine two or more devices, each covering consecutive frequency bands within a single enclosure. However, the provision of such a system has proven difficult because of interference of the sound produced by one device for a first frequency band and the sound produced by a second device for a second frequency band, particularly at the frequencies at which the two frequency bands overlap.

Accordingly, such previously proposed systems have required complicated driving electronics in order to divide the signal provided to each device in consecutive frequency bands and introduce a precise time delay to the signal provided to one of the devices in order to minimise the interference between sounds produced by the two devices at the same frequency without compromising the integrity of sound produced.

This has both been difficult and expensive to achieve.

Accordingly, it is an object of the present invention to provide a simplified system for high power sound reproduction.

According to the present invention, there is provided a horn for use in a loudspeaker that comprises first and second compression driver units, the horn comprising: a flared manifold a first set of one or more passages, arranged to direct acoustic energy from the first compression driver unit to an entrance of said flared manifold; a second set of one or more passages, arranged to direct acoustic energy from the second compression driver unit to said flared manifold; wherein said first and second sets of passages are configured such that the acoustic pathlength from said first compression driver unit to the outlet of the flared manifold is substantially the same as the acoustic pathlength from said second compression driver unit to the outlet of the flared manifold.

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The arrangement of a horn as above may be used to provide a loudspeaker in which, if both the compression driver units are driven simultaneously, the acoustic energy from each emerges from the output of the flared manifold simultaneously. As a result, interference between the acoustic energy derived from the first compression driver unit with the acoustic energy derived from the second compression driver unit may be minimised. Consequently, such a loudspeaker may have a significantly simplified control system. Specifically, such a loudspeaker may use passive filter networks to divide the signal frequencies between the first and second compression driver units, significantly reducing the complexity and cost of the loudspeaker.

The horn may be configured such that it has mounting locations provided for mounting each of the first and second compression driver units. When the compression dnver units are mounted to the horn, respective ducts may be defined between the respective compression driver unit and the horn. The passages of the first and second sets of passages may be connected to the respective ducts in order to receive acoustic energy from the compression driver units.

In a particular arrangement, the first compression driver unit may be mounted to the horn ahead of the second compression driver unit, namely closer to the outlet of the flared manifold. Providing the first compression driver unit in front of the second compression driver unit may enable a more compact loudspeaker to be formed.

The horn may be configured such that the compression driver units can be mounted such that they are substantially mutually coaxially aligned. Such an arrangement may facilitate the formation of a relatively compact combined loudspeaker and, in particular, may facilitate the formation of a combined loudspeaker having a minimal width in a direction transverse to the direction of propagation of acoustic energy provided by the loudspeaker. This may, in turn, facilitate the formation of loudspeaker units comprised of a plurality of such combined loudspeakers.

The horn may be configured such that the first compression driver unit is smaller than the second driver unit, namely the first compression driver mounting location may be configured to receive a smaller compression driver unit than the compression driver unit that the second compression driver mounting location is configured to receive. A loudspeaker including such a horn may, for example, have a first compression driver unit configured to provide acoustic energy of a relatively high frequency and have a second compression driver unit configured to provide acoustic energy of a relatively low frequency. In particular, for example, the first compression driver unit may be a High Frequency (HF) compression driver unit and the second compression driver unit may be a mid-range compression driver unit. As is well understood, a mid-range compression driver unit may, for example, produce acoustic energy in the range of from approximately 300 Hz to approximately 8,000 Hz and an HF compression driver unit may, for example, produce acoustic energy in the range of from approximately 2,000 Hz to approximately 20,000 Hz.

All of the passages of the second set of passages may be directly connected to the duct that is provided between the second compression driver unit, when it is mounted to the horn, and the horn. Accordingly, acoustic energy provided by the second compression driver unit may be divided into the passages of the second set of passages and directed to the flared manifold. The passages of the second set of passages may be configured such that they pass around the region of the horn in which the first compression driver unit is mounted and around the first set of passages. Accordingly, if the first compression driver unit is mounted in front of the second compression driver unit, the second set of passages may be connected to the flared manifold without interfering in any way with the arrangement of the first compression driver unit and the first set of passages.

The second set of passages may be arranged to open into the flared manifold. In particular, the passages may connect to a surface of the flared manifold at a location between the outlet of the flared manifold and the entrance of the flared manifold, at which the first set of passages are connected to the flared manifold. Accordingly, the acoustic energy derived from the first and second compression driver units may be combined within the flared manifold.

Each of the second set of passages may be sub-divided into sub-passages at the point at which the passages open into the flared manifold. Such an arrangement may improve the performance of the horn. Specifically, without the sub-division of the passages of the second set of passages at the opening into the flared manifold, the opening of the second set of passages into the flared manifold may disrupt the progress of the wavefront of the acoustic energy derived from the first compression driver unit. This may cause interference as well as a significant loss of the lower frequencies of the acoustic energy derived from the first compression driver unit as the acoustic energy diffracts around the corners of the openings of the second set of passages and down the passages of the second set of passages towards the second compression driver unit. The improvement provided by sub-dividing the passages of the second set of passages may be further improved by trimming the ends of the passage walls that sub-divide the passages such that they conform to the profile of the flared manifold. In a particular arrangement, it has been found that a cellular structure may be used to sub-divide the second set of passages. The diameter and shape of the sub-passages and the extent of the second set of passages that are sub-divided may be selected to provide optimum results.

The first set of passages may be arranged such that at least one passage for directing acoustic energy from the first compression driver unit to the flared manifold is sub-divided at a passage junction into two further passages. In fact, a plurality of such passage junctions may be provided within the first set of passages. Accordingly, the first set of passages may be configured such that a limited number, for example one or two passages, are directly connected to the duct adjacent the first compression driver unit, when it is mounted to the horn, and then successively divided into a plurality of further passages that open into the flared manifold. The provision of such a system may be beneficial because it provides a plurality of separate passages that may be independently configured, permitting independent control of the acoustic pathlength of each and therefore control of the wavefront output from the first set of passages into the flared manifold. However, only a limited number of passages need be directly connected to the duct adjacent the compression driver unit. This may be beneficial because the width of the duct may be relatively small, for example if the compression driver unit is an HF compression driver unit. In that case, it may be difficult to manufacture an arrangement in which a larger number of passages are directly connected to the duct, due to the difficulties in manufacturing passage walls of a sufficient thinness to divide the passages at the point at which they connect to the duct.

Each of the passage junctions in the first set of passages may be configured to divide acoustic energy from one passage into two further passages. This may assist in ensuring that the acoustic energy is divided evenly between passages at each junction for all frequencies.

The first set of passages may be arranged such that, regardless of which passage is considered, all of the acoustic energy directed from the first compression driver to the flared manifold, passes through the same number of passage junctions. Accordingly, if all of the passage junctions divide the acoustic energy from a passage into the same number of subsequent passages, for example two, then the acoustic energy is divided equally between each of the passages that open into the flared manifold, providing an even energy distribution across the entrance to the flared manifold.

Each of the passages of the first set of passages may be curved and the arrangement of the curvature of the passages may be selected in order to provide a required acoustic pathlength for acoustic energy directed from the first compression driver unit to the entrance of the flared manifold. For example, the curvature of each of the passages may be selected such that the acoustic pathlength is the same for all passages. The ability to independently control the pathlength for each of the passages ensures that it is possible to control the shape of the wavefront of the acoustic energy derived from the first compression driver unit as it enters the flared manifold and, in turn, the shape of the wavefront output from the flared manifold.

It will further be appreciated that the relative acoustic pathlengths of the second set of passages may similarly be controlled by independently adjusting the curvature of each of the passages, for example such that the shape of the wavefront of the acoustic energy derived from the second compression driver unit substantially matches the shape of the wavefront of the acoustic energy derived from the first compression driver unit at the outlet of the flared manifold.

It will be appreciated that the arrangement of the curvature of the passages of the first set of passages may also be selected to ensure that the acoustic pathlength from the first compression driver unit to the outlet of the flared manifold is substantially the same as the acoustic pathlength from the second compression driver unit to the outlet of the flared manifold, regardless of the relative positions in which the first and

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second compression driver units are mounted to the horn. Accordingly, the first and second compression driver units may be mounted to the horn at locations that are determined according to the convenience of manufacturing the horn and/or convenience of mounting the compression driver units to the horn rather than at locations that are dictated by the desire to minimise the difference between the acoustic pathlength from the first compression driver unit to the output of the flared manifold and the acoustic pathlength from the second compression driver unit to the output of the flared manifold.

At least one of the passages of the first set of passages may be curved such that, passing from one end of the passage to the other, the centre of curvature passes from one side of the passage to the other at least twice. Such an arrangement, which may be referred to as providing a meander or a wiggle in the shape of the passage, may allow a greater acoustic pathlength to be provided within a given region of space that is available for the passage than if a simpler shape with fewer changes of curvature were used.

The present invention also provides a loudspeaker unit comprising a horn as discussed above and first and second compression driver units mounted to the horn. As explained above, the first compression driver unit may, for example, be a High Frequency (HF) compression driver unit and the second compression driver unit may, for example, be a mid-range compression driver unit.

The present invention further provides a loudspeaker unit comprising a plurality of loudspeakers such as those discussed above, for example mounted in an array.

The present invention will now be described by way of non-limiting examples with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a loudspeaker including a horn according to the present invention; Figure 2 is a front elevation of a loudspeaker including a horn according to the present invention, oriented to face into the output of the horn; Figure 3 is a top elevation of a loudspeaker including a horn according to the present invention; Figure 4 is a cross-sectional view of a loudspeaker including a horn according to the present invention, depicting section A-A shown in Figure 3; Figure 5 is a cross-sectional view of a loudspeaker including a horn according to the present invention, depicting section D-D depicted in Figure 6; Figure 6 is a side elevation of a loudspeaker including a horn according to the present invention; Figures 7a, 7b, 7c and 7d are cross-sectional views of a loudspeaker including a horn according to the present invention, depicting section F-F, section G-G, section H-H and section 1-1 depicted in Figure 6, respectively; Figure 8 depicts a perspective view of a loudspeaker including a horn of a variation of the present invention; -10-Figure 9 depicts a front elevation of a loudspeaker including a horn of the variant depicted in Figure 8; Figure 10 depicts a top elevation of a loudspeaker including a horn of the variant depicted in Figure 8; Figure 11 depicts a cross-sectional view of a loudspeaker including a horn of the variant depicted in Figure 8, showing the section A-A depicted in Figure 10; Figure 12 depicts a cross-sectional view of a loudspeaker including a horn of the variant depicted in Figure 8, showing section D-D depicted in Figure 13; Figure 13 depicts a side elevation of a loudspeaker including a horn of the variant depicted in Figure 8; Figure 14 depicts an arrangement of a loudspeaker unit comprising loudspeakers having horns according to the present invention; and Figure 15 depicts an alternative arrangement of a loudspeaker unit comprising loudspeakers having horns according to the present invention.

Figures 1, 2, 3 and 6 depict a perspective view, a front view, a top view and a side view, respectively, of a loudspeaker including a horn according to the present invention. For the purposes of this description, it will be understood that a direction from the back of the horn to the front corresponds to the direction of propagation of acoustic energy output from the loudspeaker and that the loudspeaker described is oriented as shown in Figure 1. However, it will also be appreciated that the loudspeaker may, in use, be mounted at any desired orientation.

Figure 4 depicts a cross-sectional view of the loudspeaker through Section A-A depicted in Figure 3 and Figure 5 depicts a cross-sectional view of the loudspeaker through Section D-D depicted in Figure 6. As shown, the loudspeaker includes a horn I to which a first compression driver unit 11 and a second compression dnver unit 12 are mounted. The horn 1 includes a flared manifold 2 into which acoustic energy from the first compression dnver unit 11 and the second compression driver unit 12 is directed, when the loudspeaker is in use, in the manner that will be described below.

[he flared manifold further includes an output 3 from which the acoustic energy generated by the loudspeaker is output.

As depicted in Figure 4, when the first compression driver unit 11 is mounted to the horn 1, a first duct 13 is defined between the horn I and the first compression driver 11. A first set of passages 21,22 are provided in the horn I to direct acoustic energy from the first duct 13, namely acoustic energy generated by the first compression driver unit 11, to the entrance of the flared manifold 2. The entrance to the flared manifold 2 may, in particular, be slot-shaped having a relatively high aspect ratio.

Openings 23 from the first set of passages 2 1,22 open into the slot-shaped entrance of the flared manifold 2. These openings may be smaller than a half wavelength of the highest frequency sound that the horn is intended to propagate through the first set of passages. As shown in Figure 4, the slot-shaped entrance to the flared manifold 2 may be slightly curved depending on the desired vertical wavefront coverage angle.

However, it may alternatively be straight. -12-

As shown in Figure 4, immediately prior to the openings 23, the passages of the first set of passages may flare slightly. The area law of these passages may be selected to provide a smooth transition a the boundary with the first duct 13 and passing to the flared manifold 2. This may provide an improved frequency response of the horn 1.

As shown in Figure 4, in a particular arrangement, two passages 21 of the first set of passages are directly connected to the duct 13 adjacent the first compression driver unit 11. The acoustic energy received in these passages 21 is successively sub-divided into further passages 22 at passage junctions 24. Accordingly, the first set of passages 21,22 is arranged such that a relatively limited number of passages 21 are initially connected to the duct 13 but a plurality of passages output acoustic energy derived from the duct 13 into the flared manifold 2. In the particular arrangement depicted in Figure 4, for example, respective passage junctions 24 sub-divide each passage into two further passages. Furthermore, in the arrangement depicted, the passages are sub-divided into two at three stages, providing a total of sixteen passages that open into the flared manifold 2.

However, it will be appreciated that the present invention may be effected by variations of the arrangement of the first set of passages 2 1,22 depicted in Figure 4.

In particular, any suitable number of stages of sub-division may be provided, permitting, for example, the provision of 4, 8, 16 or 32 passages opening into the flared manifold 2.

Alternatively or additionally, although the arrangement depicted in Figure 4 is such that the passages of the first set of passages 21,22 are sub-divided the same number of times such that the acoustic energy output from each of the passages into the flared manifold 2 has passed through the same number of passage junctions 24, this need not be the case.

Alternatively or additionally, although the arrangement depicted in Figure 4 is such that two passages 21 are connected to the first duct 13, this need not be the case.

Instead, a single passage 21 or another, limited number of passages, may be connected to the first duct 13 in order to receive acoustic energy generated by the first compression driver unit.

Alternatively or additionally, although as depicted in Figure 4, each of the passage junctions may divide an associated passage into two further passages, this need not be the case. For example, one or more of the passage junctions may divide a passage into three or more subsequent passages.

Accordingly, any desired number of passages may be arranged to open onto the entrance of the flared manifold 2.

In addition, it will be appreciated that the arrangement of the first set of passages 21,22 is such that the acoustic pathlength from the first compression driver unit 11, when it is mounted to the horn, to an opening 23 into the flared manifold 2 (and -14-therefore from the first compression driver unit 11 to the outlet 3 of the flared manifold 2) may be selected independently of the equivalent acoustic pathlength for the other openings 23 of the first set of passages into the flared manifold 2.

Accordingly, by appropriate selection of the arrangement of the passages of the first set of passages 2 1,22, it can be ensured that the pathlength for each is the same, preventing interference between acoustic energy derived from each of the openings 23 of the first set of passages 2 1,22 on entry into the flared manifold 2.

As depicted in Figure 4, the arrangement of the first set of passages 2 1,22 in order to arrange the required acoustic pathlength is effected by selecting the curvature of the individual passages. In particular, by selecting the arrangement of a passage from the first duct 13 to an opening 23 into the flared manifold 2 such that, tracing the passage from one end to the other, the centre of curvature passages from one side of the passage to the other at least twice, namely includes two inflection points, introducing a meander or "wiggle" into the shape of the passage, a greater acoustic pathlength may be provided for a given volume of space available than if, for example, the passage were straight.

As shown in Figure 4, the first set of passages 21,22 may be arranged such that the passage junctions 24 are arranged at a location within a respective passage to be divided at which the passage is substantially straight. Furthermore, preferably, the passage junction 24 is arranged at a location such that the passage is straight immediately prior to the passage junction for a distance that is at least the wavelength of the highest frequency sound for which the passage is intended to transmit. For example, the first compression driver unit 11 may be a High Frequency compression driver unit, producing acoustic energy up to approximately 20 kHz, in which case the passages may be arranged to be straight for at least 17mm prior to a passage junction.

As depicted in Figure 5, the second compression driver unit 12 may comprise a conical driver diaphragm 16 and a so-called "bung" 15, namely a rigid separator mounted in front of the diaphragm 16. Accordingly, as shown, the bung 15 may be arranged between the diaphragm 16 and the first compression driver unit 11. In such an arrangement, the output of the second compression driver unit may be an annular duct 14. A second set of passages 31 are provided to direct acoustic energy from the annular duct 14, namely acoustic energy generated by the second compression driver unit 12, to the flared manifold 2.

As shown in Figures 7a, 7b, 7c and 7d, which are successive cross-sectional views depicted in Figure 6, the second set of passages 31 may be arranged to extend around the first compression driver unit 11, when it is mounted to the horn 1, and around the first set of passages 21,22. Accordingly, the arrangement of the second set of passages 31 does not interfere with the arrangement of the first compression driver unit 11 or the first set of passages 21,22, despite the fact that the first compression driver unit 11 may be mounted forward of the second compression driver unit 12. In particular, even if the first compression driver unit 11 is mounted immediately in front of the second compression driver unit 12, namely such that they are coaxially aligned -16-as depicted in Figures 4 and 5, the arrangement of the first compression driver unit 11 and the first set of passages 21,22 is not affected by the second set of passages 31.

Accordingly, it is not required, for example, for either compression driver unit 11,12 to have a form that permits the passage of acoustic energy from the other compression driver unit to pass through it to the outlet of the loudspeaker.

As shown in Figure 5 and Figures 7a, 7b, 7c and 7d, the second set of passages 3 1 may all be directly connected to the annular duct 14. However, if preferred, an arrangement similar to the first set of passages 21,22 may be provided for the second set of passages 31, namely directly connecting a more limited number of passages to the annular duct 14 and then sub-dividing at least some of those passages to provide the passages that are connected to the flared manifold 2.

As shown, the second set of passages 31 may be exponentially tapered. In order to improve acoustic impedance matching with the second compression driver unit 12, the total entry area to the second set of passages 31 may be limited to a fraction of the cone area, for example in the region of around one fifth. Furthermore, the second compression driver unit 12 may be configured such that the cross-sectional area of the space between the diaphragm 16 and the bung 15 increases smoothly from the apex to the rim at which the second duct 14 opens into the second set of passages 31 such that, at that point, it matches the total entry area of the second set of passages. As with the first set of passages, the width of the second set of passages 31 may be -17-limited to less than a half wavelength of the high frequency sound intended to propagate through the second set of passages.

As shown in Figures 2 and 5, the second set of passages 31 have outlets 32 that open into the flared manifold 2. In particular, the outlet 32 of the second set of passages 31 may open into the flared manifold 2 between the outlet 3 of the flared manifold 2 and the slot-shaped opening of the flared manifold 2 to which the openings 23 of the first set of passages 21,22 are provided. Accordingly, the acoustic energy derived from the first compression driver unit 11 and the acoustic energy derived from the second compression driver unit 12 are combined in the flared manifold 2.

In order to minimise the interference between the acoustic energy derived from the two compression driver units 11,12, the acoustic pathlength for the acoustic energy from each of the compression drivers 11,12 is set to be the same. Accordingly, the acoustic pathlength from the first compression driver unit 11 to the outlet 3 of the flared manifold 2 is set to be the same as the acoustic pathlength from the second compression driver unit 12 to the outlet 3 of the flared manifold 2.

It will be appreciated that the acoustic pathlength from the second compression driver unit 12 to the outlet 3 of the third manifold 2 is largely determined by the distance from the second compression driver unit 12 to the outlet 3 and the extent to which the second set of passages 31 must deviate from a straight line in order to pass around the first compression driver unit 11 and the first set of passages 21,22. However, as explained above, the acoustic pathlength from the first compression driver unit 11 to the outlet 3 of the flared manifold 2 may be readily adjusted as required to match the acoustic pathlength from the second compression driver unit 12 to the outlet 3 by adjusting the arrangement of the curvature of the first set of passages 21,22.

Accordingly, as explained above, the interference between the acoustic energy derived from the two compression driver units 11,12 may be minimised, permitting a relatively simple arrangement for dividing the driving signals for the first and second compression driver units 11,12. For example passive filter networks may be used, rather than requiring more complicated filters at the frequency crossover and/or providing time delays for the signal provided to one of the compression driver units.

The horn 1 of the present invention may be formed by first forming an inner section of the horn corresponding to the first set of passages 2 1,22. In particular, such an inner section may be formed in two parts that are subsequently combined together.

The two parts may be separated by a plane parallel to the cross-section depicted in Figure 4, namely Section A-A, permitting relatively straightforward forming of the two parts by injection moulding. Accordingly, each of the first set of passages 21,22 within the inner section of the horn is defined partly by the first part and partly by the second part, once the two parts are joined together. Subsequently, the remainder of the horn 1 is formed by injection moulding, using the inner section containing the first set of passages 2 1,22 that have already been formed as part of the mould. Once the horn 1 has been formed, the first compression driver unit 11 and, subsequently, the second compression driver unit 12 may be mounted to the horn 1.

Figures 8 to 13 depict a loudspeaker including a horn according to the present invention that is largely the same as that depicted in Figures 1 to 7 but includes an optional variation. In particular, as shown, at the point at which the second set of passages 31 open into the flared manifold 2, the second set of passages 31 are sub-divided into sub-passages 35. For example, a cellular structure may be inserted into the second set of passages 31, providing a plurality of passage waIls 36 that sub-divide each of the passages of the second set of passages 31.

The provision of the sub-division of the second set of passages 31 at the point at which they open into the flared manifold 2 may improve the performance of the horn.

Specifically, the provision of the openings 32 of the second set of passages 31 into the flared manifold 2 part way along the wall of the flared manifold, namely between the outlet 3 of the flared manifold 2 and the entrance to the flared manifold 2, at which the first set of passages 2 1,22 open into the flared manifold, may result in disruption of the progress of the wavefront of the acoustic energy derived from the first set of passages 2 1,22. This may result in interference, in addition, there may be a loss of the lower frequencies of the acoustic energy from the first set of passages 2 1,22, in particular caused by diffraction of the acoustic energy around the corners of the openings 32 of the second set of passages 31 and down into the second set of passages 31. The provision of the sub-divisions of the second set of passages 31 may reduce this.

As shown in Figure 8 to 13, the ends 32 of the passage walls 36 that sub-divide the second set of passages 31 may be trimmed to conform to the profile of the flared manifold 2, providing a further improvement.

In an example, the passages of the second set of passages may have a length of approximately 200mm and increase in width from about 10 mm at the annular duct 14 to approximately 28 mm at the flared manifold. In this case, the diameter of the sub-divided passages 35 may, for example, be approximately 2 to 3mm in order to provide a beneficial effect. The passage walls 36 that sub-divide the second set of passages 31 may, for example, have a wall thickness of approximately 0.2 mm.

As shown in Figure 12, any sub-division of the second passages 31 need not extend the full length of the second set of passages. Instead, a beneficial effect may be provided simply by the provision of the sub-divisions for a relatively short distance before the opening 32 of the second set of passages 31 into the flared manifold 2. It will be appreciated that this may facilitate manufacturing of the horn. For example, it may be sufficient for the sub-division of the second set of passages 31 to extend back from the openings 32 by at least the wavelength of the smallest wavelength sound that the first compression driver 11 is configured to provide. In the case of the first compression driver unit 11 being a High Frequency compression driver unit, for example, the smallest wavelength may be approximately 13 mm. However, it will be appreciated that, for example to facilitate placement and securing of the passage walls 36 used to sub-divide the second set of passages 31, a greater length may be used. In -21 -the example discussed above, the sub-divisions may extend approximately 35 mm into the passages of the second set of passages 31 from the openings 32 into the flared manifold 2.

Figures 14 and 15 depict alternative arrangements for combining loudspeakers using the horn according to the present invention to form loudspeaker units 40,45. As explained above, by appropriate selection of the configuration of the first and second sets of passages, it is possible to select the shape of the wavefront output from the horn. This flexibility permits the horn to be configured such that the radius of curvature of the emitted wavefront is as large as is desired. Such an arrangement is not possible, for example, if a single duct is used to connect a compression driver unit to a flared manifold.

As shown in Figure 14 and 15, the ability to control the shape of the wavefront output from the horn has the effect that it is possible to combine a plurality of loudspeakers together to form a single loudspeaker unit 40,45 with a required shape of the combined output wavefront 42,46, without the wavefronts from the individual loudspeakers interfering with each other. In addition a significant separation between adjacent loudspeakers is avoided. This is undesirable because it also leads to interference effects.

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Claims

CLAIMSI. A horn for use in a loudspeaker that comprises first and second compression driver units, the horn comprising: a flared manifold a first set of one or more passages, arranged to direct acoustic energy from the first compression driver unit to an entrance of said flared manifold; a second set of one or more passages, arranged to direct acoustic energy from the second compression driver unit to said flared manifold; wherein said first and second sets of passages are configured such that the acoustic pathlength from said first compression driver unit to the outlet of the flared manifold is substantially the same as the acoustic pathlength from said second compression driver unit to the outlet of the flared manifold.
2. A horn according to claim 1, further comprising first and second compression driver mounting locations, configured such that: when said first compression driver unit is mounted to the first compression driver mounting location, a first duct is defined adjacent said first compression driver unit by said first compression driver unit and the horn; and the first set of passages are configured to direct acoustic energy from said first duct to said flared manifold; and when said second compression driver unit is mounted to the second compression driver mounting location, a second duct is defined adjacent said second compression driver unit by said second compression driver unit and the horn; and the -23 -second set of passages are configured to direct acoustic energy from said second duct to said flared manifold.
3. A horn according to claim 2, wherein the first compression driver mounting location is arranged forwards of the second compression driver mounting location in a direction extending from the position of the compression driver mounting locations to the outlet of the flared manifold.
4. A horn according to claim 2 or 3, wherein the first and second compression driver mounting locations are configured such that, when the first and second compression driver units are mounted to the respective compression driver mounting locations, they are substantially mutually coaxially aligned.
5. A horn according to any one of claims 2 to 4, wherein the first compression driver mounting location is configured to receive a smaller compression driver unit than the compression driver unit that the second compression driver mounting location is configured to receive.
6. A horn according to any one of claims 2 to 5, wherein each of said second set of passages is directly connected to said second duct.

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7. A horn according to any one of claims 2 to 6, wherein each of said second set of passages extends around a first region of the horn that includes the first compression driver unit and the first set of passages.
8. A horn according to any one of the preceding claims, wherein the second set of passages open into the surface of the flared manifold, between the entrance of the flared manifold, at which the first set of passages open into the flared manifold, and the outlet of the flared manifold.
9. A horn according to claim 8, wherein each of the second set of passages is sub-divided into a plurality of sub-passages at the point at which the second set of passages open into the flared manifold.
10. A horn according to claim 9, wherein the ends of the passage walls that sub-divide the passages, at the end opening into the flared manifold, are arranged to conform to the profile of the flared manifold.
11. A horn according to any one of claims Ito 10, wherein said first set of passages comprises at least a first passage configured to receive acoustic energy from the first compression driver; and a passage junction that divides acoustic energy from the first passage into at least second and third passages.

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12. A horn according to claim 11, wherein said first set of passages comprises a plurality of passages and passage junctions configured such that acoustic energy from the first compression driver is received by one or two passages and divided into further passages that open into the entrance of said flared horn.
13: A horn according to claim 12. wherein each of said passage junctions is configured to divide acoustic energy from one passage into two further passages.
14. A horn according to claim 12 or 13, wherein said first set of passages is configured such that, regardless of the passage from which it is output into the flared manifold, all the acoustic energy passing through the first set of passages passes through the same number of passage junctions.
15. A horn according to any one of the preceding claims, wherein each of the first set of passages is curved; and the arrangement of the curved passages is selected such that the acoustic pathlength for acoustic energy directed from the first compression driver to the entrance of the flared manifold is the same, regardless of the passage.
16. A horn according to any one of the preceding claims, wherein each of the first set of passages is curved; and the arrangement of the curved passages is selected such that the acoustic pathlength from the first compression driver to the outlet of the flared manifold is substantially the same as the acoustic pathlength from the second compression driver to the outlet of the flared manifold.
17. A horn according to any one of the preceding claims, wherein at least one of said first set of passages is curved such that, passing from one end of the passage to the other, the centre of curvature passes from one side of the passage to the other at least twice.
18. A loudspeaker comprising first and second compression driver units and a horn according to any one of the preceding claims.
19. A loudspeaker according to claim 19, wherein said first compression driver unit is a high frequency compression driver unit and the second compression driver unit is a mid-range compression driver unit.
20. A loudspeaker unit, comprising a plurality of loudspeakers according to claim 19or20.
21. A horn, loudspeaker or loudspeaker unit, substantially as hereinbefore described with reference to the accompanying drawings.-27 -