GB2181620A

GB2181620A - Loudspeaker enclosure

Info

Publication number: GB2181620A
Application number: GB08525126A
Authority: GB
Inventors: Zbigniew Marian Zenkteler
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-10-11
Filing date: 1985-10-11
Publication date: 1987-04-23
Also published as: GB8525126D0; GB2181620B

Abstract

An enclosure for a loudspeaker assembly includes a sound deflector member 4 mounted on an internal wall of the enclosure. The deflector member has an inclined surface which deflects soundwaves 7 generated by the respective loudspeaker diaphragm away from the path of oncoming incident waves to inhibit the propagation of standing or resonant sound waves within the enclosure. Sound absorbing material 6 may be included in the enclosure. <IMAGE>

Description

SPECIFICATION Loudspeaker enclosures This invention relates to loudspeaker enclosures.

More especially, the invention concerns loudspeaker enclosures which include internally mounted deflectors positioned to deflect plane sound waves awayfrom their incident pathsto inhibitthe gener- ation of stationary or resonant sound waves within the loudspeaker enclosure.

A stationary or resonant sound wave is produced when a plane sound wave is reflected at normal inci dence from an interface formed by two different media; a reflected wave travels back into the incident medium and interfaces with the oncoming incident waves.

The internal walls of a conventional loudspeaker enclosure, and in particular a rectangular enclosure, invite repeated reflections of plane waves at normal incidence which give rise to sets of standing or reso nantwaveswithinthe enclosure. Although some of these resonance are not harmful to sound reproduction asthey augment output at lowfrequencies, other resonances, in particular ifthe frequency is above 1000 Hz, inevitably lead to distortion and are, consequently, detrimental to faithful reproduction of sound.

It is known to line loudspeaker cabinets with sound absorbing material in order to frustrate the formation ofstandingwaves. However, the residenttimeof such waves within the sound absorbing lining is insufficient to absorb pronounced resonances.

One object of the present invention isto inhibitthe creation of standing or resonant waves offrequency above approximately 1000 Hz.

Afurther object of the invention isto deflectsound waves travelling towards and normal to a wall of a loudspeaker enclosure away from the path of oncoming sound waves and into acoustic absorption material lining the walls of the enclosure.

According to the present invention in one aspect there is provided an enclosurefora loudspeaker assembly comprising a sound deflector member mounted on an internal wall ofthe enclosure and formed with a surface which is inclined with respect to sound waves incident thereon generated by a loudspeaker diaphragm of the assembly to deflect such sound waves away from the path of oncoming incidentwavesthereby to inhibit the propagation of standing or resonant sound waves.

More than one such deflector member may be provided, each positioned to receive and angularly def lett sound waves incident thereon. The angle of def lection ofthe inclined member(s) may be such as to direct incident sound waves into and along acoustic sound absorping material lining one or more walls of the enclòsure.

The or each deflector member may take the form of a pyramid, a cone ora parabola. In each case, the deflector member may be symmetrical or asymmetr- ical in construction. One or more members may be hollow in construction and may be spaced a small distance away from the respective internal wall ofthe enclosure. Where the deflector members are of hollow construction, they may be filled with sound absorption material.

In another aspect, the present invention provides a deflector member as described above for location within a loudspeaker enclosure at a position which lies within the path of sound waves generated by a loudspeaker diaphragm located within the enclosure.

The invention will now be described by way of ex ample only with reference to the accompanying dia- grammatic drawings in which: Figures 1 to 3 a re respectively front, side and plan elevational views in section of a simplified form of a conventional loudspeaker enclosure assembly illustrating the paths of travel of sound waves generated bya loudspeaker diaphragm; Figures 4, to 6are perspective views of alternative sound deflector members in accordance with the invention; Figures 7and 8are part sectional views illustrating the function of deflectors in accordance with the invention; and Figures 9to 11 are respectively end, side and plan views in section of loudspeaker enclosure assemblies in accordance with the invention.

As will be seen from Figures 1 to 3, in a conventional loudspeaker enclosure 1 the standing or stationary waves which contribute most to distortion of generated sound occur in the vicinity of the loudspeaker diaphragm 1 ofthe loudspeaker enclosure.

Those incident waves normal to the enclosure walls which are reflected backtowardsthe loudspeaker diaphragm to interfere with oncoming sound waves and which therefore create standing waves at high frequencies above approximately 1000 Hz, are indicated by the arrows3 in full line shown in Figures 1 to 3.

It is to inhibit the creation of such standing waves that sound deflector members in accordance with the invention are employed. Two typical deflector members 4 are illustrated in Figures 4 and 5.

The deflector member illustrated in Figure4consists ofthree inclined walls each triangular in shape upstanding from a triangular base, the apex of the upstanding walls being rounded. The assymetrical structure defined by the base and side walls is attached to one internal wall surface of a loudspeaker enclosure at a location which lies in the path ofthe incident sound waves eminating from the loudspeaker diaphragm of the enclosure. Other similarly shaped deflector members are positioned within the paths of other sets of sound waves emitted from the loudspeaker diaphragm.

The deflector member illustrated in Figure 5 is of similarconstructiontothatillustratedin Figure4excepting that the base is generally rectangular.

The deflector members 4 may be of solid construction; alternatively, they may be hollow, the interior being filled with a sound absorping material. The preferred heightofthese members have been found by experiment to lie between 1/4 and 1/5 ofthewave- length to be reflected.

The deflector member 5 illustrated in Figure 6 is of generally dome-like construction and is for mounting behind the loudspeaker diaphragm. The diame ter ofthe member5 is greater than the shadow cast by the diaphragm and is of solid construction to in hibitvibrational forces. The function of the member 5 isto deflect normal incident sound waves travelling from the diaphragm edge away from the path of subsequent oncoming sound waves. It has been found by experiment that the shape of deflector memberS illustrated interferes least with vertical oscillations within the enclosure which are beneficial to the recreated sound.

Experiments carried out using deflector members such as illustrated in Figures 4 to 6 have successfully demonstrated the effectiveness of the members in reducing the incidence of standing waves and, therefore, improving the quality ofthe recreated sound.

As illustrated in Figures 7 and 8, sound waves incident on the deflectors 4,5 were divided and redirected as indicated by arrows 7 into acoustic absorption material 6 lining the enclosure walls. Thus, in addition to inhibiting the creation of standing waves, the residenttime of the sound waves within the acoustic material was significantly increased, thereby enhancing its absorption effect.

The configuration ofthe deflector 4 is not nec essarilyas shown in Figures 4 and 5; indeed, any construction may be employed which provides a set of surfaces where the incident waves are reflected away from their incident paths to inhibit the creation of standing waves and so produce a diffused sound field in which random reflections prevail.

The size, shape and locations of the deflectors 4 will depend to a significant extent upon the geometry and type of loudspeaker enclosure in which they are placed. One example of a loudspeaker enclosure including deflector members 4, 5 in accordance with the invention is illustrated in Figures9to 11. As will be seen,the deflector members are sited at positions in which they lie in the paths of sound waves travelling from the loudspeaker diaphragm or from reflected sound waves travelling from other deflector members. The deflectors act not only to control harmonic distortion but also as low pass filters since a proportion of redirected waves offrequencies above approximately 1,000 Hztravel in directions parallel to the enclosure walls where they are absorbed by acoustical wadding attached to the walls.

It is to be understood thattheforegoing is merely exemplary of sound deflector members in accordance with the present invention and that modi ficationscan be made thereto without departing from the true scope ofthe invention.

Claims

1. An enclosure for a loudspeaker assembly comprising a sound deflector member mounted on an in ternal wall of the enclosure and formed with a surface which is inclined with respect two sound waves incident thereon generated by a loudspeaker diaphragm of the assembly to deflect such sound waves away from the path ofoncoming incidentwaves thereby to inhibit the propagation of standing or resonantsoundwaves.

2. An enclosure as claimed in claim 1 including a plurality of deflector members, each positioned to re ceive and angularly deflect sound waves incident thereon.

3. An enclosure as claimed in claim 2wherein the angle of deflection of at least one deflector member is such as to direct incident sound waves into and along acoustic sound absorping material lining one or more walls of the enclosure.

4. An enclosure as claimed inclaim2orclaim3 wherein at least one deflector member is in the form of a pyramid.

5. An enclosure as claimed in claim 2 or claim 3 wherein at least one deflector member is of conical construction.

6. An enclosure as claimed in claim 2 or claim 3 wherein at least one deflector member is of parabolic construction.

7. An enclosure as claimed in any one of the preceding claims wherein the or at least one deflector member is hollow in construction and is spaced a small distance away from the respective internal wall of the enclosure.

8. An enclosure as claimed in claim 7 wherein the or each hollow deflector member is filled with sound absorption material.

9. A loudspeaker enclosure as herein described with reference to Figures 1 to 3 ofthe accompanying drawings.

10. A loudspeaker enclosure as herein described with reference to Figures 4to 6 of the accompanying drawings.

11. A loudspeaker enclosure as herein described with reference to Figures 7 and 8 ofthe accompanying drawings.

12. A loudspeaker enclosure as herein described with reference to Figures 9 to 11 of the accompanying drawings.