GB2583075A

GB2583075A - Manifold for a loudspeaker

Info

Publication number: GB2583075A
Application number: GB1904652.3A
Authority: GB
Inventors: Kinsella Edward
Original assignee: Em Acoustics Ltd
Current assignee: Em Acoustics Ltd
Priority date: 2019-04-02
Filing date: 2019-04-02
Publication date: 2020-10-21
Also published as: GB201904652D0

Abstract

The manifold comprises at least a first, a second and a third longitudinal outer wall 33a, 33b, 33c wherein the first and second outer walls 33a, 33b each comprise at least one circular inlet opening 34; the third outer wall 33c comprises at least four exit openings 37; wherein each inlet opening 34 is connected to one or more exit openings 37 by a curved path 40 through the manifold, wherein each curved path 40 is interwoven with the adjacent curved path 40 such that the distance from the inlet opening 34 to the exit opening 37 of each curved path 40 is substantially the same length.

Description

MANIFOLD FOR A LOUDSPEAKER

The present invention relates to an improved manifold for a loudspeaker system and an improved loudspeaker unit. For example, the present invention relates to loudspeakers used for sound systems to deliver audio to arenas, concert halls, places of worship and outdoor events. The system of the present invention also has industrial applications.

It is known that when a sound source is small with respect to the wavelength of the sound waves emitted, the sound waves propagate spherically from the point source in space. To improve the directional control of the sound source, a horn or similar enclosure may be used to control the radiating direction of the sound waves. However, this will only be effective if the horn mouth perimeter is comparable in size to the wavelength of the sound. The broad range of possible wavelengths is such that a horn to control lower frequencies may need to be impractically large (20Hz to 20,000Hz equating to approximately 1740cm to 1.7cm in horn circumference).

A known technique to improve directional control is to construct a 'line source_ or 'line array_, which has been found to achieve a high degree of directivity by creating a continuous or pseudo-continuous source that is large with respect to the wavelengths concerned. Successful implementation of a line array requires isophase emission of sound from the device in the vertical plane, such that the sound wave will be at the same point in phase regardless of its point of emission in the vertical plane.

Contemporary sound reinforcement requires the generation of high sound pressure levels in order to provide the desired sonic impression at considerable distances; for example, when the sound is to be broadcast across a stadium. This requires the use of sound sources known as compression drivers, which have an electromagnetically operated circular diaphragm that is axial to the sound exit of the device. The radiating area of the diaphragm is typically six to seven times the area of the sound exit.

The 'compression ratio_ of the compression driver provides optimal acoustic loading to the horn or waveguide, with which the driver is used, to produce the required acoustic output.

In order to meet the requirements of large-scale events it is known to group loudspeakers together in a line array system. However, there remains a need to improve sonic performance to ensure that line array systems provide clarity, detail and consistent performance at all sound pressure levels (SPL).

A problem that has been identified with line array systems is air overload distortion. At typical sound pressure levels that we experience, air pressure changes as a wave passes, which causes local temperature changes giving rise to distortion of the sound wave, that can reasonably be ignored.

However, in high-powered horn loudspeakers, the pressure levels can make these distortion artefacts significant. Typically, pressure levels of around 160dB can be present at the exit of a compression driver unit and at these pressure levels these contributing factors to the distortion must be considered to avoid excessive degradation of the intended signal.

US patent publication 5,163,167 discloses a sound waveguide to transform a planar circular isophase wave surface, i.e. a membrane of a loudspeaker, into an isophase planar rectangular wave surface. The solution proposed by US 5,163,167 is to make the path lengths from the entrance to the exit of a manifold approximately equal in length using a shaped internal body.

However, it has been found that such systems have a limited power density for a given height of a loudspeaker stack.

US patent publication 9,571,923 discloses dividing the acoustic paths from the acoustic input to the acoustic output so that the width of the path is a specific proportion of the wavelength of the highest frequency of the input signal. This attempts to make the paths that the sound waves travel more uniform, but again the configuration only allows for the drivers to be stacked in a single plane, which again limits the power density that can be achieved for a given height of loudspeaker stack.

These previously disclosed devices and methods are limited because, for a given size of acoustic source, the number of sources per unit height is physically limited by the point at which their outer diameters touch each other. Source output power is related to diameter and so there is a limit to the power density available per unit height of the rectangular exit.

US patent publication 6,394,223 discloses stacking of drivers, which are acoustically coupled to the throats of the loudspeaker system, but the arrangement requires longer path lengths between the driver and the waveguide. Air overload distortion, as discussed above, is proportional to, amongst other things, horn or path length. Paths of longer lengths increase the overload distortion of the sound delivered.

The present invention sets out to provide an improved loudspeaker unit, including an improved manifold for a loudspeaker unit, which alleviates the problems described above.

In one aspect, the invention provides a manifold for a loudspeaker unit comprising at least a first, a second and a third longitudinal outer wall wherein: the first and second outer walls each comprise at least one circular inlet opening; the third outer wall comprises at least four exit openings; wherein each inlet opening is connected to one or more exit openings by a curved path through the manifold, wherein each curved path is interwoven with the adjacent curved path such that the distance from the inlet opening to the exit opening of each curved path is substantially the same length.

Preferably, the manifold is shaped substantially as a triangular prism.

Preferably, the geometry of each curved path is identical.

Preferably, the length of each curved path is about three wavelengths at the highest frequency of sound transmitted to minimise air overload distortion.

The 'length_ of the curved path is understood to be the core path length.

The path length of each of the interwoven paths of the present invention are relatively short, which further minimises air overload distortion, because the distance the sound wave travels at any given pressure is proportional to the degree of distortion.

Preferably, each circular inlet opening is divided into two to form two semicircular inlet openings.

It is understood that in the context of the present invention, a 'manifold_ refers to a space with several openings to allow sound waves to enter and leave. 'Interwoven_ is understood to refer to an alternating arrangement wherein each curved path meshes or rests against the adjacent curved path/s, such that they are curved together; preferably, wherein the direction of each alternating path is in an opposing direction to the adjacent path.

The present invention is a significant improvement because it is configured to create multiple paths of equal length and identical geometry, to convert a spherical wave front at the inlet opening/driver exit to a planar one at the sound exit, but also to allow the geometric nesting of the acoustic devices in a more confined space. That is, the manifold paths 'mesh_ in an arrangement that means that the paths are geometrically identical to each other and any minor deviation from the ideal of equal path lengths is identical for all ports such that the output response is significantly more uniform.

Preferably, the manifold comprises four circular inlet openings, eight interwoven curved paths and eight exit openings.

The proposed device can be scaled in multiples of two inlet openings/compression driver sound sources and allows for any length of desired array to be configured by adding pairs of inlet openings, with a first inlet opening on a first outer wall and a second inlet opening on a second outer wall. The compact arrangement and geometry of the interwoven curved paths can be scaled up or down as required, whilst achieving the improvements in sound output.

Preferably, the or each circular inlet opening in the first outer wall is offset from the or each adjacent circular inlet opening in the second outer wall with respect to their position along the length (x) of the wall.

Length_ is understood to refer to the longest dimension of the wall.

Preferably, the curvature of each path through the waveguide is geometrically minimised. The compression driver positions are set by their being as close to each other as physically possible within physical limits. Given that the position of the central rectangular exit is fixed, the boundary conditions are now set for the path(s). They simply take the shortest, least curved route possible without clashing with each other, and maintaining a minimum wall thickness of around 3mm of material.

The curvature of the path is minimised as far as practical to allow the path to pass around and be interwoven with, i.e. to interleave with, the adjacent path so that the boundary wall between adjacent paths is not too thin and the path length is minimised to reduce distortion. This balance is precisely engineered to arrive at the geometry of the present invention. The circular inlet openings are configured to be compatible with standard compression driver geometry.

Preferably, the width and/or cross-sectional area of the curved path at the or each inlet opening is less than the width and/or cross-sectional area of the curved path at the or each exit opening.

Preferably, the ratio of the cross-sectional area of the curved path at the or each inlet opening to the cross-sectional area of the curved path at the or each exit opening is about 4:7.

Preferably, the cross-sectional area of the curved path at the or each inlet opening is about 1000mm2. Preferably, the cross-sectional area of the curved path at the or each exit opening is about 1750mm2.

Preferably, the cross-sectional area of the curved path through the manifold increases along the path from the inlet opening to the exit opening. Thus, as the sound propagates through the manifold, this provides better impedance matching to the horn, so that maximum power is delivered. Furthermore, the pressure of the sound wave reduces as is propagates and expands along the path/port, which helps to significantly reduce the air overload distortion.

Preferably, the manifold further comprises an enclosure or housing.

In a second aspect, the present invention provides a loudspeaker unit comprising a manifold as previously described and at least one pair of compression drivers, wherein a compression driver is connected to the or each circular inlet opening on the first and on the second outer walls of the manifold, such that the sound waves emitted from the or each compression driver enter the manifold through each inlet opening.

Preferably, the first driver in each pair is offset from the second driver in the pair with respect to their position along the length (x) of the longitudinal wall to which they are fixed.

Preferably, the loudspeaker unit comprises four compression drivers and the manifold is comprised of eight inter-woven curved paths and eight exit openings in the third face of the housing.

The waveguide/manifold of the present invention allows for higher power density because of the improved geometry of the device. The improved shape of the housing makes use of the z-dimension to offset the sources. For example, the triangular prism shape of the housing in which the manifold is contained allows for the improved geometry, where the axis referred to when looking at the manifold from the third wall at the exit openings refers to the z-axis, i.e. the direction into the device and the y-axis is the direction transversely across the exit openings. The x-axis is used to refer to the length of each wall; the 'length_ being understood to be the longest dimension of the wall. It is understood that in use the x-axis is the height of the housing and multiple units can be stacked one on top of each other.

The configuration of the present invention allows the density of the acoustic sources to be close to double that which can be achieved with known arrangements, whilst path meshing avoids problems associated with long path lengths. Furthermore, the geometry of the present invention allows for an infinite repeatability in multiples of two (compression driver) sources for any desired total array length. This is achieved by offsetting the sources.

Whilst the present invention can be said to have near double the current power-density, it is equivalent to say that distortion is lower for a given output level. This is because having double the source density, means each source must only provide half as much output for the same total, reducing the overload distortion.

Preferably, the drivers are arranged as close to each other as reasonable manufacture will allow.

The power units/ drivers of the present invention tesselate more efficiently and allow for the units to nest together. Thus, for a given height of loudspeaker, the power density is significantly increased whilst the paths are all identical so that the acoustic performance is an improvement over known loudspeaker systems. The geometry of the present invention allows for a more densely packed vertical arrangement. It has also been found that the present system has lower distortion and that the loudspeaker system can be run at the same level with less work from the driver. In contrast to known systems, the overall path length through the waveguide between the driver exit/inlet opening and the sound exit is kept as small as possible to minimise any possible distortion. That is, because of lower distortion the sound pressure level (S PL) that is required is significantly reduced. In comparison to known systems, if the present invention were running at the same SPL as a known system, the present invention would operate with up to 3dB less distortion.

For the purposes of clarity and a concise description, features are described herein as part of the same or separate embodiments; however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

The invention will now be described by way of example with reference to the accompanying drawings, in which: -Figure 1 is a first perspective view of the loudspeaker unit of the present invention; Figure 2 is a plan view looking at the exit openings of the loudspeaker unit of the present invention; Figure 3 is a side perspective view looking at the compression drivers at the inlet openings of a preferred embodiment of the present invention; Figures 4 is a side perspective view looking at a first outer wall and two of the four compression drivers of the preferred embodiment of the present invention; Figure 5 is a plan view of the outer wall and exit openings of the manifold of a preferred embodiment of the invention; Figure 6 is a cross-sectional view along the line A-A, shown in Figure 5, showing a slice through the manifold of a preferred embodiment of the present invention; Figure 7 is an end plan view of the manifold of the present invention; Figure 8 is a cross-sectional view along the line E-E, shown in Figure 7, showing a slice through the manifold of a preferred embodiment of the present invention; Figure 9 is a is a plan schematic view looking through the exit openings of the loudspeaker unit of the present invention to show the interwoven channels within the manifold; Figure 10 is a perspective view showing two pairs of interwoven channels within the manifold; and Figure 11 is a schematic illustration to show the route of each inlet opening to the outlet openings shown in Figure 5.

Referring to Figure 1, a preferred embodiment of the manifold 36 and the loudspeaker unit 30 of the present invention is shown. The housing 31 of the manifold 36 is a triangular prism shape having substantially triangular end plates 32 and three rectangular side walls 33. In alternative embodiments any one or more corners of the triangular end plates 32 are squared or rounded so that the shape of the main housing 31 is a truncated triangular prism shape.

In use, the housing of the manifold is contained within a cuboidal loudspeaker enclosure (not shown), which is made of multi-laminate plywood.

Referring to Figures 1, 3, 7 and 10 the first and second rectangular side wall 33a, 33b, each have two circular driver inlets 34, which are each acoustically coupled, in use, to a compression driver 35. In the embodiment shown, the loudspeaker unit 30 comprises four driver inlets 34 (shown in Figure 10) and four compression drivers 35.

Referring to Figures 1 and 5, the third rectangular wall 33c comprises the outlets 37 of the waveguide or manifold 36 connecting the inlet ports (not shown) to the exit outlets 37 of the loudspeaker unit 30. For the embodiment shown, which has four inlet ports, there are eight exit ports 37 through which sound is emitted.

Referring to Figures 2, 5 and 6, the exits 37 of the manifold 36 are substantially rectangular and of equal output area. However, it is understood that in alternative embodiments, the exits 37 could be a different shape; for example, square.

Referring to Figures 3 and 4, a compression driver 35 is connected to each of the four inlet ports (not shown). In the embodiments shown in these figures there are four inlet ports 34 and four compressions drivers 35, arranged in pairs. Each compression driver 35 is paired with a second compression driver 35 on an adjacent wall 33a, 33b. In alternative embodiments of the loudspeaker unit 30, there are only two inlet ports 34 and four exit openings. Referring to Figures 3 and 10, a first inlet port 34 is on the first rectangular wall 33a and attached to a first compression driver 35a and a second inlet port is on the second rectangular wall 33b and attached to a second compression driver 35b.

As shown, in Figure 3, the rectangular walls 33a, 33b are angled with respect to each other. The longitudinal position of the second inlet in each pair, which is attached to a compression driver 35b, 35d, is offset from the respective longitudinal position of the first inlet in the pair, which is also attached to a compression driver 35a, 35c. The longitudinal position of the inlet 34 is understood to refer to the positioning of the inlet/driver 34/35 along the longest (x) dimension/length of the rectangular side wall 33 to which it is attached.

Referring to Figures 5, 6, 8, 9 and 10, the waveguides or paths 40 are arranged within the manifold 36, such that the acoustic path lengths between the inlet port that is acoustically coupled to the compression driver 35 and the exit outlet 37, are all substantially equal. The geometry of each curved path 40 is also carefully configured to be substantially identical although their direction from the inlet to the outlet may be different to allow them to be interwoven.

As shown in Figures 8, 9 and 10 the curved paths 40 of the waveguide are curved with a width that uniformly increases along their length from the driver inlet 34 to the exit outlet 37. That is, the cross-sectional area of the path increases along the path from the driver inlet 34 to the exit outlet 37. As shown in Figure 9, the curved paths 40 mesh with each other and are interwoven so that, as shown in Figure 10, the alternate paths are geometrically identical and are mirror images of each other with a plane of symmetry equidistant between the two exit outlets 37.

Referring to Figures 1 to 11, the air overload distortion is minimised by the configuration of the present invention. The degree of distortion has been found to be proportional to the distance the pressure wave travels at a given pressure. The cross-sectional area of the paths 40 through the manifold 36 of the present invention increases as the sound propagates through the manifold 36. This has been shown to provide better impedance matching to the horn and the pressure of the wave reduces as it expands along the curved path 40. The meshing of the curved paths 40 allows for the paths 40 to be relatively short. By way of example, the path length is approximately three wavelengths at the highest frequency of interest, which has been found to minimise air overload distortion.

Referring to Figures 7, 8, 9 and 10, the circular driver inlet 34 for each compression driver is divided into two to form two semi-circular driver inlets 34a, 34b for each compression driver. The semi-circular driver inlets 34a, 34b of the manifold 36 are split by a dividing wall 38 formed where two adjacent paths 40 meet, with the centre line that is formed by the dividing wall 38 being substantially parallel to the end plate 32 of the housing 31.

Figure 8 is a cross-sectional slice along line E-E, shown in Figure 7, from the driver inlet 34 to the exit outlet 37 of the manifold 36. Looking into the manifold 36 through the circular driver inlet 34, two symmetrical paths 40 are formed wherein the plane of symmetry is substantially parallel to the centre line of the inlet. The cross-sectional area of the path 40 at the driver inlet 34 is less than the cross-sectional area of the path at the exit outlet 37.

Referring to Figures 6, 7, 8, 9 and 10 the waveguide through the manifold 36 comprises multiple inter-woven paths 40. The curve of each path 40 is carefully configured to pass around the neighbouring paths 40, so that the boundary between the paths 40 through the manifold is not too thin and the overall path length between the driver inlet 34 and the exit outlet 37 are as small as possible to minimise distortion.

In the preferred embodiment, comprising four compression drivers 35 and eight exit outlets 37, the geometry of the paths 40 is described with reference to Figures 5, 6, 9, 10 and 11.

Figure 5 shows a view of the exit face of the unit, comprising exit openings 37a, 37b, 37c, 37d, 37e, 37f, 37g, 37h. Figure 5 and Figure 11 show the paths to the exit openings 37a-h from the respective driver inlet, with the symmetrical, inter-woven arrangement of the paths 40 being as set out in the table below, with the inlet openings P1, P2, P3, P4, P5, P6, P7, P8 shown in Figure 11 and the exit openings 37a-h shown in Figure 5: Inlet opening Exit opening P1 37a P3 37b P2 37c P4 37d PS 37e P7 37f P6 37g P8 37h Referring to Figures 3, 8, 9, 10 and 11, in use the compression drivers 35 each produce a point source of sound, which enters the manifold 36 as a spherical sound wave through the circular driver inlet openings 34. Referring to Figure 10, the sound waves received at each driver inlet opening 34 are divided to follow two geometrically identical curved paths of identical length. The sound waves exit the system at the exit outlets 37 of the manifold 36, with lower distortion and a substantially uniform output response.

In further embodiments of the present invention, the entire manifold is curved to achieve different dispersion patterns. Rather than providing acoustic exits that are all coincident with the longitudinal axis it is possible to curve the array of exit ports, so that the exits are arranged along a convex wall, which is outward of the inlet ports.

Within this specification, the term "about" means plus or minus 20%; more preferably, plus or minus 10%; even more preferably, plus or minus 5%; most preferably, plus or minus 2%.

The above described embodiment has been given by way of example only, and the skilled reader will naturally appreciate that many variations could be made thereto without departing from the scope of the claims.

Claims

Claims 1. A manifold for a loudspeaker unit comprising at least a first, a second and a third longitudinal outer wall wherein: the first and second outer walls each comprise at least one circular inlet opening; the third outer wall comprises at least four exit openings; wherein each inlet opening is connected to one or more exit openings by a curved path through the manifold, wherein each curved path is interwoven with the adjacent curved path such that the distance from the inlet opening to the exit opening of each curved path is substantially the same length.
2. A manifold for a loudspeaker unit according to claim 1, wherein the manifold is shaped substantially as a triangular prism.
3. A manifold for a loudspeaker unit according to claim 1 or claim 2, wherein the geometry of each curved path is identical.
4. A manifold for a loudspeaker unit according to any of claims 1 to 3, wherein the length of each curved path is about three wavelengths at the highest frequency of sound transmitted.
5. A manifold for a loudspeaker unit according to any preceding claim, wherein each circular inlet opening is divided into two to form two semicircular inlet openings.
6. A manifold for a loudspeaker unit according to any preceding claim, wherein the manifold comprises four circular inlet openings, eight interwoven curved paths and eight exit openings.
7. A manifold for a loudspeaker unit according to any preceding claim, wherein the or each circular inlet opening in the first outer wall is offset from the or each adjacent circular inlet opening in the second outer wall with respect to their position along the length of the wall.
8. A manifold for a loudspeaker unit according to any preceding claim, wherein the width and/or cross-sectional area of the curved path at the or each inlet opening is less than the width and/or cross-sectional area of the curved path at the or each exit opening.
9. A manifold for a loudspeaker unit according to any preceding claim, wherein the ratio of the cross-sectional area of the curved path at the or each inlet opening to the cross-sectional area of the curved path at the or each exit opening is about 4:7.
10. A manifold for a loudspeaker unit according to any preceding claim, wherein the cross-sectional area of the curved path at the or each inlet opening is about 1000mm2.
11. A manifold for a loudspeaker unit according to any preceding claim, wherein the cross-sectional area of the curved path at the or each exit opening is about 1750mm2.
12. A manifold for a loudspeaker unit according to any preceding claim, wherein the manifold further comprises an enclosure or housing.
13. A loudspeaker unit comprising a manifold according to any preceding claim and further comprising at least one pair of compression drivers, wherein a compression driver is connected to the or each circular inlet opening on the first and on the second outer walls of the manifold.
14. A loudspeaker unit according to claim 13, wherein the first compression driver in each pair is offset from the second compression driver in the pair with respect to their position along the length of the longitudinal wall to which they are fixed.
15. A loudspeaker unit according to claim 13 or claim 14, wherein the loudspeaker unit comprises four compression drivers and the manifold is comprised of eight inter-woven curved paths and eight exit openings in the third face of the housing.