GB2256773A - Loudspeaker uinit - Google Patents

Abstract

A loudspeaker unit for reproducing stereo sound has a single body from which first and second drive units 20, 22 emit diagonal intensifies of mid and high frequency sound from audio mirrors 16, 18. The intensities face away from the listener so that sound is reflected from the walls of room before reaching the listener. Each drive unit 20, 22 is vertically directed and sound therefrom is reflected into the room at offset sound mirrors 16, 18. The room acoustics are used to give the illusion of a wide stereo stage. <IMAGE>

Description

LOUDSPEAKER UNIT This invention relates to a loudspeaker unit for reproducing stereophonic sound by reflection from a wall or walls or, in portable form, radiated directly towards the listener.

It is known to provide pairs of loudspeaker units for individual sound channels in a common body particularly in the field of portable stereophonic sound reproducers. However, these loudspeaker units are used for direct listening and not in reflection and do not incorporate audio mirrors.

In one aspect, the present invention provides a loudspeaker unit for reproducing stereophonic sound which comprises a single body and first and second drive units in the body for individual stereophonic channels for emitting treble sound with the main intensities thereof being in different directions other than parallel or perpendicular.

The invention also relates to the use of a speaker unit as aforesaid for reproduction of stereo sound emitted from the unit, in which treble sound from the individual channels is emitted in a direction facing away from an intended listening direction, the individual sound channels being reflected from different locations of a wall or walls before reaching the listener. Both channels may be first reflected from a single wall or they may be reflected initially at different walls e.g. at the corner of a room. The perceived positions from which sound comes are virtual images of the sound source produced when the sound undergoes its first and or second reflections.

The result is to produce spaced-apart virtual sound sources for the individual channels, the apparent sound distribution from the individual channels generally corresponding to the sound distribution in the same channels from the actual loudspeaker unit.

Thus the positions from which the sound seems to come which are defined by the virtual images are much further apart than the positions where the drive units occur in the body of the loudspeaker unit giving the effect or illusion of a wide stereo stage. With this arrangment both the left and right sound channels can be reproduced from within a single enclosure, and the acoustics of the room in which the sound is reproduced can be used to give a wide stereo stage.

The angle between the main intensity directions of the respective channels is a large acute angle e.g. from 60 to 90 degrees and preferably about 90 degrees.

The drive units which produce the beams of sound are treble units and reproduce at least intermediate frequencies above 5kHz where the reflection of sound begins to be predictable by geometrical acoustics.

They may each comprise concentric diaphragms for relatively low and relatively high frequencies which may be individually driven or which may be a parasitic tweeter arrangement e.g. as disclosed in patent application number 9111775.4 filed 31 May 1991 in the United Kingdom. The treble unit may also be used for the production of bass sound but separate bass speakers can also be provided. There may be one or two such bass speakers which may radiate sound direct into the room or via a sound mirror which diffracts sound into the room even at frequencies below 5kHz with change in direction.

Each loudspeaker unit comprises a drive unit or speaker which emits sound in a generally vertical direction and an acoustic reflector disposed at a spacing from the speaker for redirecting sound therefrom into a generally horizontal direction, the reflector having a generally conical surface facing the speaker with the apex of the cone nearest the speaker and with the center of the speaker offset from the axis of the conical surface so as to define a preferential direction of mid range and high frequency sound leaving the speaker (see Patent GB-B-2188811).

The use of such a generally conical sound mirror, particularly where the mirror is concave when viewed in profile to produce a controlled distribution sound in the vertical direction is particularly advantageous when used in association with an offset single concentric drive unit e.g. of the parasitic tweeter type.

The invention also provides a portable player for tape cassettes and/or compact discs optionally also incorporating a tuner and in which individual sound channels to produce stereophonic sound are reproduced by drive units the sound from which is deflected into a generally horizontal direction by audio mirrors.

Preferably the audio mirrors are of the aforesaid generally conical or part conical shape including a sector of a conical surface. In such a sound reproducing apparatus the individual loudspeaker units which are present in the player may be directed so that the higher frequency sound distributions diverge from the player, converge from the player or are generally parallel. Where the sound intensities are divergent the player will be intended for use in reflection as aforesaid, and the face of the player on which the controls appear may be opposite to that from which the main sound intensities are radiated.

Various forms of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figures 1 and 2 are respectively a diagrammatic plan and a partly cut away elevation of a first form of loudspeaker unit; Figures 3 and 4 are respectively a diagrammatic plan and a cut away elevation of a second form of loudspeaker unit; Figure 5 is a rear perspective view of a third form of the loudspeaker unit; Figure 6 shows diagrammatically a pattern of treble sound from a loudspeaker according to the invention reflected at a corner of a room; Figure 7 shows diagrammitically a pattern or treble sound from a loudspeaker unit according to the invention reflected first at an end wall and then at side walls of a generally rectangular room;; Figures 8 and 9 are respectively a perspective view and a diagrammatic plan of a first form of portable player for tape cassettes and/or compact discs incorporating a loudspeaking unit according to the invention; and Figure 10 is a diagrammatic plan of a second form of portable player for tape cassettes and/or compact discs incorporating a loudspeaker unit according to the invention.

In the drawings a loudspeaker unit 10 comprises a main body 12 which supports a treble drive housing 14 above a pair of sound mirrors 16, 18 which reflect treble sound into a room or other listening environment. The housing 14 contains a pair of downwardly facing drive units 20, 22 for the individual sound channels from which intermediate and/or high frequency sounds are radiated onto mirrors 16, 18 and thence horizontally into the room. The drive units 20, 22 which may be circular or elliptical have their centers offset from the apexes of the conical reflectors 16, 18 so as to direct beams of sound at angular directions about 90 degrees apart with the beams of sound being diagonally outwards with reference to the line joining the centers of the sound mirrors.

Each sound mirror which is located below the drive unit so that sound is directed downwards onto the floor of the room where the speaker is used is concave in profile as disclosed in European patent application number EP-A-0409360 in order to cause the reflected sound to diverge in a vertical direction and increase the range of positions where a stereo image is perceptible. The use of an offset conical mirror and drive unit is described in patent GB-B-2188811 the disclosure of which is incorporated herein by reference. Although the drive units for treble are directed downwardly in the embodiment shown they could be directed upwardly with the positions of the mirrors 16 and 18 reversed, although that arrangement is less preferred.

The individual sound channels also pass via a suitable cross-over network (not shown) to bass speakers 26, 28 which direct sound downwardly onto a sound mirror 30 which is shared between them. The positions of the drive units 26, 28 are less critical because low frequency sound tends to be radiated omni-directionally, although the mirror 30 produces a degree of diffraction of the sound towards the horizontal direction, particularly at frequencies about 800 Hz.

The drive units 26, 28 could alternatively face towards the listener.

The treble drive units 20, 22 are housed within individual compartments bounded by flexible membranes 21 and 23 which serve to prevent cross-talk and to damp sound from the back face of each drive unit as disclosed in our UK application number 9013640.9.

Alternatively or additionally absorbent as a channel separator is provided in the form of a sound-damping member or wall which is directed in a front-two-rear direction midway between sound mirrors 14, 16 to limit unwanted cross-talk. In particular, such cross-talk can arise by sound from the drive unit 22 being reflected at the mirror 16 and correspondingly sound at the drive mirror unit 24 being reflected at the mirror 18.

The arrangement is figures 3 and 4 is similar to figures 1 and 2 except that the drive units 20, 22 face opposite sides of a common sound mirror 40.

The arrangement of figure 5 is similar to that of figure 4 except that both sound channels are reproduced through a single bass speaker 42 from which sound is radiated omni-directionally from a concentric sound mirror 44.

The reflection of sound from a unit 10 into a corner of a room is shown in figure 6 and the apparent or virtual stereo sources are at positions 50, 52 resulting from sound first reflected at walls 54, 56.

The net effect is to produce a wide but nevertheless directional intensity of sound from the individual channels into the room from virtual sources 50, 52 particularly at high frequencies. Because each channel is preferentially first reflected from one wall of the room with significantly less reflection from the other wall, good channel separation is achieved. Figure 7 shows the effect of a unit 10 radiating diagonally opposed sound intensities at least at the mid and high frequencies towards an end wall 60 to produce for example a first virtual source 10a by first reflection at the end wall 61 and second widely spaced virtual sources 62, 64 by second reflections from the side wall 65, 66 so that the individual channels of high frequency sound seem to come from the widely spaced sources 62, 64 or from the opposite walls of the room.

Although the stereo image may be less clearly perceived than sound direct from speakers it is nevertheless agreeable and effective for some listeners. Furthermore because of the omni-directional radiation of low frequency sound and the reflection of the mid to high range frequencies there can be some compensation for the group delay of low frequency sound. Alternatively an optionally adjustable delay unit (e.g. a charge coupled device or a travelling-wave filter) could be used to delay bass sound so that bass direct from the unit 10 more closely approaches or coincides with reflected sound from the virtual sources 10a or 62, 64.

Figure 8 diagrammatically shows a portable tape or disc player unit 70 comprising a disc player 72, tape player 74, 76, a radio tuner 78 and amplifier not shown, stereo sound signals from all of which are fed to drive units 80, 82. The sound from these drive units is directed downwardly relative to the normal orientation of the reproducer 70 onto sound mirrors 84, 86 which are semi-circular when viewed in plan and of concave profile as shown. These mirrors produce a relatively wide distribution of sound in a horizontal plane and a controlled spread of sound in a vertical plane. The drive unit 80, 82 may be fixed or movable relative to the sound mirror 84, 86 and for example in figure 9 they may be movable between the solid and phantom positions. When in the position that presented by the solid lines the drive units and mirrors 80, 84 and 82, 82 produce sound intensities direct diagonally outwardly of the unit 70, whereas when they are in the position shown in phantom they produce sound intensities that are diagonally inwards.

An alternative structure is shown diagrammatically in figure 10 in which the drive units 80, 82 are disposed above quadrant rather than half conical sound mirrors, the sound mirrors 90, 92 still being concave when viewed in profile. With this arrangement the sound passes diagonally outwards from the unit, and the controls may be located on a face of the unit opposite to that from which sound is radiated.

Claims (21)

1. A loudspeaker unit for reproducing stereophonic sound comprising a single body and first and second loudspeaker means mounted in the body wherein the loudspeaker means are arranged to emit intensities of sound at mid/high frequency which are angled relative to one another.

2. A unit according to claim 1 wherein the emitted intensities converge.

3. A unit according to claim 1 wherein the emitted intensities are directed parallel to one another.

4. A unit according to claim 1 wherein the emitted intensities diverge.

5. A loudspeaker unit according to any preceding claim wherein the loudspeaker units each comprise a drive unit and a sound mirror that reflects sound into the room in a direction other than that in which the sound is emitted from the drive unit.

6. A speaker unit according to any preceding claim in which each loudspeaker unit comprises a drive unit or speaker which emits sound in a generally vertical direction and an acoustic reflector disposed at a spacing from the speaker for redirecting sound therefrom into a generally horizontal direction, the reflector having a generally conical surface facing the speaker with the apex of the cone nearest the speaker and with the centre of the speaker offset from the axis of the conical surface so as to define a direction of the sound leaving the speaker.

7. A speaker unit according to claim 6 wherein first and second drive units for respective sound channels have a common audio mirror.

8. A speaker unit according to claim 6 wherein first and second drive units for respective sound channels have individual sound mirrors.

9. A speaker unit according to any preceding claim wherein a flexible member is provided behind each drive unit for damping sound emitted from the concealed face of the unit.

10. A speaker unit according to any preceding claim wherein a sound-absorbent material is provided between the loudspeaker means to reduce unwanted cross-talk.

11. A speaker unit according to any preceding claim, further comprising at least one bass speaker.

12. A speaker unit according to any preceding claim, comprising two bass speakers.

13. A speaker unit according to claim 11 or 12 wherein sound from the or each bass speaker is deflected into the room via a sound mirror.

14. A speaker unit according to any preceding claim wherein incorporated into a portable player for tape cassettes and/or compact discs optionally also incorporated a radio.

15. A speaker unit substantially as hereinbefore described with reference to or as illustrated in figures 1 and 2 or figures 3 and 4 or figure 5 or figures 8 and 9 or figure 10 of the accompanying drawings.

16. Use of a speaker unit as claimed in any preceding claim to reproduce stereo sound emitted from the unit in a direction facing away from an intended listening direction, individual sound channels being reflected from different regions of a wall or walls before reaching the listener.

17. Use according to claim 16 wherein both channels are initially reflected from a single wall.

18. Use according to claim 11 wherein both channels are initially reflected at a corner of a walled listening space.

19. Use according to claim 16 wherein spaced apart virtual images of the individual sound channels are produced at a single reflection.

20. Use according to claim 16 wherein spaced apart virtual images of the individual sound channels are produced on two successive reflections.

21. Use of a speaker unit as claimed in claim 16 to reproduce sound emitted from the unit in a direction facing towards the listener.