WO1991009507A1

WO1991009507A1 - Manifold loudspeaker system

Info

Publication number: WO1991009507A1
Application number: PCT/GB1990/001956
Authority: WO
Inventors: Andrew John Fox
Original assignee: Andrew John Fox
Priority date: 1989-12-15
Filing date: 1990-12-14
Publication date: 1991-06-27
Also published as: AU6967791A; GB8928352D0

Abstract

A loudspeaker system especially for use in the mid/bass frequency range comprises a cabinet in which loudspeakers are mounted in mutually opposed points with an acute angle therebetween. The speakers may form respective mutually opposed banks. The enhanced sound quality without distortion or null zones, two such cabinets may be mounted side by side with a spacing between the centre points of the horns of the respective cabinets being 550-700 mm.

Description

MANIFOLD LOUDSPEAKER SYSTEM

This invention relates to loudspeaker systems intended primarily for large-scale public address purposes.

**. Various ways are know of enhancing the sound quality at high volumes in loudspeaker systems of the above type, intended for use in large concert halls, stadia and the like. The methods used vary with or depend on the proposed frequency range of the sound to be transmitted. Thus, frequency bands may be classified approximately as sub-bass (25-100Hz) ; bass (100-350Hz) ; mid-range (350Hz-1.6KHz) ; and high (1.6-7KHz, from 7 to 22KHz being considered as very high) .

The present invention has as its object the improvement or enhancement of sound quality in the approximate range 60-350Hz, that is, the range generally referred to as mid range/bass.

It is known to enhance sound output by acoustic coupling of loudspeakers. One way of achieving this in the mid range/bass frequency range is the so-called manifold system, in which pluralities of loudspeakers are mounted in a cabinet in such a way that individual pairs of speakers are opposed, all speakers being directed at a common intermediate point. Thus, for example, a total of eight speakers may be mounted in two banks of four, the banks being directly mutually opposed and the speakers in each bank being mounted in a rectangular or a diamond-shaped configuration so that a given speaker in one bank is opposed by a corresponding speaker in the other bank, all eight speakers being directed or focussed towards a point midway between the two banks. The effect of such -an arrangement is to provide a gain in volume of sound as perceived by the listener but a degree of distortion and phase cancellation also occurs, particularly at higher frequencies within the range.

According to the present invention, a loudspeaker system especially for use in the mid/bass frequency range comprises a cabinet in which loudspeakers are mounted in one or more mutually opposed pairs at an acute angle therebetween.

By "angle therebetween" is meant the angle subtended by the planes, which may be notional planes, in which the widest cross section of the speaker cones lie.

The acute angle should be between about 15 and 40 , preferably between about 25 and 30 , ideally about 28 . It has been found that an angle of about 28 is suitable for frequencies up to 300Hz and even up to 400Hz. At angles substantially outside the range 15 to 40 , the sound waves from each speaker of each mutually opposed pair become out of phase with resulting impairment of sound quality.

Where two or more opposed pairs of speakers are used, the respective opposed speakers are preferably mounted in co-planar fashion on a mounting panel with suitable apertures to receive the speaker cones. Preferably the or each mounting panel forms the front face of an enclosed box section within which the cone and driver of each speaker extends. The air trapped behind the speaker cones in the enclosed space is effectively pulsatingly compressed by vibrations of the material of the cone or cones, thus f rther enhancing the sound output. Desirably, the volume of the enclosed space is calculated and determined according to the dimensions of the loudspeakers, for optimum effect.

Optionally, according to a further aspect of the invention, the enclosed space behind the speaker cone may contain an expanded foam material such as a closed-cell urea formaldehyde foam. This tends to reduce or prevent the occurrence of structural resonance and is particularly appropriate for raid-range loudspeaker units.

It has been found that, using loudspeaker systems according to the invention, output may be increased by up to 5 decibellε without the distortion or phase cancellation produced by conventional systems.

In loudspeaker systems according to the invention, two or more cabinets may be mounted side by side to give a broader dispersion arc of sound. It has been found that, provided that certain dimensions are maintained in and between adjacent cabinets, it is possible to achieve a substantially perfect perceived sound dispersion, with respect to the horizontal coupling of the loudspeaker cabinets. Thus, the transmission of random noise through the loudspeaker results in a substantially flat frequency response across the entire arc of transmitted sound, with no perceived variation, distortion or null zones.

For example, a single cabinet may give a 60 distribution arc with a difference in gain between the mid-point and the sides of -6dB, whereas two cabinets positioned adjacent each other with their facing sides together may give a 120° distribution arc with no perceived difference in gain across the entire arc. In order to achieve the above effect, it has been found that the critical dimension is the spacing between the centre point of the horns of the respective cabinets, that is, from a point on the mid-line of the acute angle of one cabinet and approximately 2 cm in front of the front face, to the corresponding point on the other cabinet. This dimension may be in the range 550-700 mm, preferably 600-650 mm with a dimension of 622 mm appearing to give optimum results.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which:

Figure 1 is a cross-sectional view from above of a loudspeaker cabinet embodying a system according to the invention, and

Figure 2 is an exploded view of the loudspeaker cabinet of Figure 1.

Referring to Figure 1, a loudspeaker cabinet 11 has a back wall 12, side walls 13, 14 and a front wall 15. The back and side walls are preferably solid, formed for example from 24mm birch plywood, whereas the front wall is preferably an open frame covered with a fabric or gauze-like material. Inside the cabinet are mounted internal end walls 16, 17 and loudspeaker mounting boards or panels 18, 19. As shown, the panels subtend an angle € of 28°. A loudspeaker 20 is mounted in panel 18 and an opposed loudspeaker 21 is mounted in panel 19. Although only one speaker is shown per panel, further speakers could be included in opposed pairs, (see Figure 2) . The speakers 20 and 21, and any additional speakers, are focussed on a common intermediate point along a notional vertical line represented by point 22.

The parts 16-19 are also preferably formed from 24mm birch plywood and parts 13, 16, 18 and one half of 12 on the one hand and 14, 17, 19 and the other half of 12 form respective enclosed spaces, together with top and base parts, not shown.

Referring to Figure 2, the component parts, excluding the external fabric covering and therefore the front wall or face, of the cabinet of Figure 1 are shown as an exploded view. The same numbering as used in Figure 1 is used for like parts. The parts are assemblied on a base 22. The cabinet is divided into a lower portion for mounting the mid range/bass speakers in panels 18 and 19 and an upper portion separated by panel 23 and containing a mounting panel 24 for a mid-range speaker.

High frequency speakers are mounted in bracket 25 between the mid range/bass speakers and in the lower part of the lower portion of the cabinet. Brackets 26 and 27 are for mounting the left hand and right hand high frequency driver horns respectively.

In the illustrated cabinet, the front has a width of 637 mm, the back has a width of 380 mm, the depth (front to back) is 787 mm and the angle of each side is 9.27°.

Claims

1. A loudspeaker system especially for use in the mid/bass frequency range, the system comprising a cabinet in which loudspeakers are mounted in one or more mutually opposed pairs at an acute angle therebetween.

2. A loudspeaker system according to Claim 1, in wwhhiicchh tthhee aaccuuttee aarngle lies in the range of approximately 15 to 0 »⁽o

3. A loudspeaker system according to Claim 2, in which the acute angle lies in the range of approximately 25 to 30 .

4. A loudspeaker system according to any preceding claim, in which respective opposed loudspeakers are mounted on a mounting panel having a suitable aperture for receiving the speaker cone.

5. A loudspeaker system according to Claim 4 including two or more pairs of loudspeakers in which respective opposed groups of loudspeakers are mounted in co-planar fashion.

6. A loudspeaker system according to any preceding claim in which the or each mounting panel forms the front face of an enclosed box into which the cone and driver of each speaker extend.

7. A loudspeaker system according to Claim 6, in which the void of the box behind the speaker cone or cones contains an expanded foam material.

8. A loudspeaker system according to any preceding claim, in which two or more cabinets are disposed side by side.

9. A loudspeaker system according to Claim 8, in _$ which the spacing between the centre point of the horns

-ϊ of the respective cabinets is in the approximate range 550-700 mm.

10. A method of improving the perceived sound dispersion from a loudspeaker system, comprising positioning two or more loudspeaker systems according to any of Claims 1 to 7 in side by side arrangement with a spacing between the centre points of the horns of adjacent cabinets being in the range approximately 550-700 mm.