AU658020B2

AU658020B2 - Coincident spatial loudspeaker

Info

Publication number: AU658020B2
Application number: AU28236/92A
Authority: AU
Inventors: Colin Arthur Preston
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-11-08
Filing date: 1992-11-09
Publication date: 1995-03-30
Anticipated expiration: 2012-11-09
Also published as: AU2823692A

Description

658020

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

0 Name of Applicant: COLIN ARTHUR PRESTON Actual Inventor: COLIN ARTHUR PRESTON Address for Service: H.R. HODGKINSON CO.

Patent Trade Mark Attorneys 26A Alfred Street MILSONS POINT NSW 2061 o* Invention Title: COINCIDENT SPATIAL LOUDSPEAKER Details of Associated Provisional Application: No: PK9362 dated 8 November 1991 The following statement is a full description of this invention, including the best method of performing it known to me: THIS INVENTION relates to the reproduction of audio programme and in particular the spatial aspects of such audio programme.

The spatial aspect of audio with which we are most familiar, utilising current recording, transmission and reproduction facilities, is stereophonic reproduction. Conventional stereo audio reproduction is achieved by the recording, e* transmission and reproduction of two discreet programme signals, generally referenced Left and Right. However 10 whilst the following description generally refers to spatial 0.0 effects based on Left/Right differentiation, it is not .intended that the invention be so limited and therefore any reference to Left and Right is meant to encompass any similar spatial relationship including Up/Down and Front/Back.

For the reproduction stage of conventional stereo, the Left and Right signals are separately amplified and are each fed to separate loudspeakers, which are spaced apart in the S listening area, generally facing the listener. Differences 4:..20 between the Left and Right programme in intensity, phase and timing create an auditory illusion of a stereo image between 9940 and around the loudspeakers, the effect being the creation of an apparent wall or plane of sound. However, the area in which a listener will perceive the desired stereo image is relatively small and those listeners who are positioned outside of this immediate area perceive only limited stereophonic information, or none at all, due to the so called precedence effect.

It would, therefore, be advantageous to provide a sound 3 reproduction system capable of reproducing a stereo image over a greater listening area. It would be especially advantageous if such a system could produce stereophonic effects from an essentially single source a single loudspeaker enclosure), so that the location of the listener with respect to the loudspeaker is not as spatially dependent as with conventional stereo arrangements requiring two loudspeaker enclosures.

Such a loudspeaker has now been developed and provides distinct advantages ovez conventional systems. At the very least, the invention provides an alternative to presently known sound reproduction arrangements.

SThroughout the specification reference to a "speaker enclosure" is intended to cover not only speaker arrangements that are housed within the one specific box like cabinet but also any other arrangements where speakers are grouped together to perform as a unit, whether in 4 separate adjoined enclosures or mounted on panels and the 4 like and therefore in the strictest sense not "enclosed".

.20 The term "speaker" itself is used to denote one or more .6000: acoustic drivers, each operable over a specific frequency range, together with their mechanical or electronic crossovers.

According to the invention there is provided a sound reproduction system capable of reproducing an audio programme including its spatial characteristics from a single location, in which the Left and Right audio programme signals of a conventional stereo source are processed into their sum (Left plus Right) and difference (Left minus Right) components for separate amplification. In order to reproduce the audio programme, the sound reproduction system comprises a single loudspeaker enclosure itself comprising at least two speakers, the speakers thus being positioned in essentially the same location so as to function effectively as a single source of sound, a first speaker of said at least two speakers having a broad angle of coverage facing forward in the loudspeaker enclosure and fed by the amplified sum (Left plus Right) of the audio programme signals, and a second speaker or speakers cf said at least two speakers creating a doublet polar pattern with a narrow angle of coverage for each half of the doublet, the second speaker or speakers being oriented perpendicular to the first speaker and fed by the amplified difference (Left minus Right) of the audio programme signals, :As mentioned above, in a conventional stereo recording, transmissioin and reproduction system, the signal is treated and reproduced as two discreet signals, namely Left and Right. According to the invention, the Left and Right S 20 electrical signals of a conventional sound source are passed through known electronic circuits to produce a summed or monophonic signal (Left plus Right) and a difference or ambience signal (Left minus Right), prior to amplification.

25 Preferably the second speaker or speakers, which provide the S•difference or ambience component, will be located in the .rear of the loudspeaker enclosure. The second speaker or speakers function effectively as a single source of sound, possessing a doublet polar pattern (also known as a Figure of 8 pattern) which is oriented not only perpendicular to the axis of the first speaker but also preferably sideways with respect to the listener (where conventional Left/Right differentiation is required), each half of the doublet polar pattern having a narrow angle of coverage.

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The second speaker or speakers as the case may be, are fed by the amplified difference of the stereo audio programme which generally represents the ambience or reverberant component thereof. Because the second speaker or speakers radiate sound that is in opposite phase/polarity on each side of the doublet at any given roment, ambiguous and misleading localisation cues fc the human ear are provided as a result. As a consequence, the second speaker or speakers can be difficult to locate as a source of sound, 10 and hence contribute to the spatial effect by providing the *0 said ambient or reverberant sound component.

0 The invention thus utilises an apparent single sound source, which in practice is a single loudspeaker enclosure or cabinet, capable of reproducing the sum (Left plus Right) and difference (Left minus Right) components of a suitably manipulated stereo sound source. As well as a "mono" speaker capable of reproducing the sum component, the enclosure contains a speaker or speakers producing a doublet polar pattern having a low or narrow coverage angle for each '20 lobe thereof. The doublet speaker or speakers must be m: capable of producing the said polar pattern having opposite S" absolute phase for each lobe thereof, located on either side of the speaker or speaker pair as the case may be be. The null or "dead" axis of the doublet sound source the :25 second speaker or speakers) will be preferably located in a plane which vertically bisects the first speaker and with particular advantage may be located immediately behind the first speaker.

The various embodiments of the invention thus require the use of acoustic drivers for use as the second speaker or speakers, which have the capacity either on their own or in tandem to produce the required doublet polar pattern. The doublet polar pattern can be created in a number of ways and the types of speaker arrangemei:t described below are capable of producing the required doublet polar pattern: An electrostatic driver element which produces a characteristic doublet polar pattern, Exposing both sides of a conventional moving coil cone type acoustic driver so that each side produces a rarefication and a compression alternately as the cone So vibrates, eo Placing two drivers back to back in a sealed cabinet (but allowing for porting and venting, if necessary) so that each speaker functions in opposite polarity to the other in a push-pull configuration). Both drivers could be driven by a single amplifier with the speakers wired in series or parallel but in opposite 0:.o polarity (out-of-phase). Alternatively, separate amplifiers could be used for each driver, with both 20 amplifiers being fed the same programme, but with each amplifier functioning in opposite polarity to the other, or

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A ribbon driver element, which like the electrostatic speaker, produces a characteristic doublet polar pattern.

Each driver required for the invention (both for sum and difference reproduction) is preferably positioned in the enclosure as close as physically possible to one another to minimise the size of the apparent source of sound i.e. to make the sound source as coincident as possible. By achieving a close proximity of individual sources within the loudspeaker cabinet, as far as is practical, the ability of the system to create an auditory illusion from the spatial components of the audio programme is in fact enhanced.

Furthermore, with advantage, it has been found that the performance of the combination is improved when individual drivers are separately baffled one from the other.

Thus, in accordance with the invention, by the process of summing and differencing the Left and Right signals together with the subsequent distribution of the sum and difference S. S signals to their respective speakers located in the same enclosure (baffled as required), it is possible to recreate .15 the differences in phase, time and intensity between the Left and Right audio programme channels of the original stereo source, thereby creating the auditory illusion of a stereo image from a single point source as represented by the speaker enclosure.

"20 In the same manner that the volume and balance of the Left and Right channels on a conventional stereo amplifier and S speakers can be controlled by the listener, the levels of S• the sum and difference amplifiers may be varied to suit the ~particular environment and the listener's taste.

In a second aspect of the invention, there is provided a "surround sound" configuration, which can be implemented with just two loudspeaker enclosures of the type defined above according to the invention, for example, with one in front of, and the other located behind the listener, to produce Left/Right and Front/Rear localisation.

8 Alternatively, the speaker enclosures can be located to each side of the listener, still giving Left/Right and Front/Rear localisation. In this latter arrangement for example, the speaker enclosures will be located to the left and right of the listener, facing inwardly. The "mono" driver of each enclosure carries Left or Right information in a manner similar to conventional two cabinet stereo systems, and the "difference" or doublet speakers reproduce Front/Rear information in conjunction with the "sum" or "mono" 10 speakers, to provide Front/Rear localisation.

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Thus, various combinations of the location of speaker enclosures according to the invention will result in a e variety of configurations to produce several different S. effective "surround sound" systems. In this regard for example, use may be made of speaker enclosures above or below the listener to create special spatial effects.

Furthermore, as required the speaker enclosure as

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herein described may be usefully combined with not only enclosures of the same type but also conventional speaker o• r 20 arrangements as well as other non conventional types. For example, in one such configuration an enclosure according to the invention may be positioned in front of the listener to 0000 give Left/Right horizontal spatial information, whilst a speaker enclosure having only a speaker or speakers of the second type to produce just ambient sound could be positioned behind the listener to provide additional ambient or reverberant information.

The invention will now be described by way of example only with reference to the accompanying drawings, of which: FIGURE 1: FIGURE 2: FIGURE 3: is a block diagram of sum and difference circuitry for use in the invention, is a perspective view of a first embodiment of a speaker enclosure according to the invention, is a top view of the first embodiment illustrated in Figure 2, is a perspective view of an alternative embodiment of the invention, is a top view showing the interior of the embodiment illustrated in Figure 4, and is a perspective view of a preferred speaker arrangement being another embodiment of the invention.

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FIGURE 4: FIGURE 5: FIGURE 6: Referring to Figure 1, there is illustrated a block schematic diagram for producing sum and difference et ~components from a conventional stereo source in which conventional Left and Right audio programme signals from a stereo source 1 are passed through an electronic circuit 2 Se to produce the summed or monophonic signal (Left plus Right), and also through a second electronic circuit 3 to produce the difference signal (Left minus Right). The sum and difference signals are then each amplified separately in respective amplifiers 4 and 4' and fedl to the appropriate corresponding speakers 5 and Referring generally to Figures 2 and 3, there is illustrated a first embodiment of the invention, in which it can be seen that a loudspeaker cabinet 6, of the open or panel variety, supports two speakers 7 and 8. Speaker 7 is a forward facing speaker with a broad angle of coverage fed by the amplified sum (Left plus Right) of the stereo audio programme. Speaker 8 faces sideways perpendicular to speaker 7 and has the capacity to produce a doublet polar pattern. It is fed by the amplified difference (Left minos Right) of the stereo audio programme. Speaker 8 could be a conventional moving coil cone type speaker with both surfaces of its diaphragm exposed, or alternatively, an •e e electrostatic or ribbon driver element. mhe loudspeaker system is positioned with speaker 7 facing the listener and S speaker 8 facing sideways to the listener in the horizontal 15 plane, for the recreatioa of conventional stereo *e S 6 reproduction.

Referring to Figures 4 and 5, the drawings show an alternative embodiment of a coincident spatial loudspeaker a, according to the invention. This embodiment comprises a 20 loudspeaker cabinet 9, which encloses three speakers 10, 11 and 12. Speaker 10 is a forward facing speaker with a broad an' e of coverage fed by the amplified sum (Left plus Right) •Vo* of the original stereo audio programme. Speakers 11 and 12 face sideways in the horizontal plane, are positioned back :25 to back, are wired in opposite polarity (out of phase), and are driven by the amplified difference (Left minus Right) of the original stereo audio programme, so that they produce a doublet polar pattern, Suitable baffles may be utilised to isolate the respective drivers one from the other. In use, the loudspeaker system is oriented so that speaker 10 is facing the listener and speakers 11 and 12 are facing sideways in the horizontal plane.

Figure 6 shows a particular arrangement in which a cabinet or enclosure 13 houses in total six speakers of which four (17, 18, 19 and 20) are visible in the particular perspective view. The enclosure 13 comprises a lower section 14 mounted on a stand 15, whilst an upper section 16 of lesser cross section is seated or mounted on the lower section 14 and will be generally integral therewith.

Speaker 17 is the main midrange and bass driver handling the sum (Left plus Right) component of the original stereo 10 source. It is housed in the upper portion of the lower "section 14 and is suitably baffled so as to occupy approximately one third of the available volume thereof.

The remaining speakers occupying the lower portion of S"section 14, namely speaker 18 and one of corresponding :15 performance mounted immediately opposite thereto (not illustrated), are able to handle the midrange and base requirements of the difference component (Left minus Right) of the original stereo audio signal. A suitable baffle will S" divide the lower portion of section 14 into equal volumes to facilitate the operation of the pair of speakers (18 and its twin).

0 S Similarly, the upper section 16 houses a forward facing S tweeter 19 to handle the high end of the audio spectrum of the sum component, whilst speaker 20 and its oppositely mounted twin (not illustrated) function in the same way as speaker 18 and its twin, but handle instead the high end of the audio spectrum for the difference component.

It will be readily apparent to those skilled in the art that various modifications may be made to the invention without departing from the true spirit and scope thereof. No 12 limitation with respect to the specific embodiments illustrated is intended or should be inferred.

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Claims

2. A sound reproduction system according to claim i, i wherein the second speaker or speakers of said at least two speakers, which provide the difference, are located in the rear of the loudspeaker enclosure.
3. A sound reproduction system according to claim 2, wherein the second speaker or speakers are located in a plane which vertically bisects the first speaker.
4. A sound reproduction system according tc claim 3,wherein the second speaker or speakers are located immediately behind the first speaker. A sound reproduction system according to any one of the preceding claims, in which the second speaker or speakers are oriented not only perpendicular to the axis of the first speaker but also sideways with respect to the listener.
6. A sound reproduction system according to any one of the previous claims, in which the second speaker or speakers creating the doublet polar pattern are selected from amongst the following: an electrostatic driver element, exposing both sides of a conventional moving coil cone type acoustic driver so that each side produces a V* t rarefication and a compression alternately as the cone :vibrates, placing two drivers back to back in a sealed cabinet so that each speaker functions in opposite polarity to the other, or to a ribbon driver element. o••oe S•7. A sound reproduction system according to any one of the preceding claims, in which each speaker is positioned in the enclosure as close as physically possible to one another to minimize the size of the apparent source of sound.
8. A sound reproduction system according to any one of the previous claims, in which individual drivers used for each speaker are separately baffled one from the other. difference amplifiers may be varied to suit the particular environment and the listener's taste. A surround sound reproduction system comprising one or more individual enclosures according to any one of the preceding claims in combination with one or more speaker enclosures, located to produce surround sound.
11. A surround sound system according to claim 10, in which one enclosure is located in front of, and another is located behind a listener, to produce Left/Right and Front/Rear localisation.
12. A surround sound system according to claim 10, in which one enclosure is located to one side of a listener, whilst a second enclosure is located to the other side to produce Left/Right and Front/Rear localisation.
13. A surround sound system according to claim 10, in which one enclosure is located to the front of a listener to produce Left/Right localisation, whilst a second enclosure having only a speaker or, speakers of the socond Sztype to produce just ambient sound is positioned behind the listener to provide additional ambient or reverberant information. So 14. A sound reproduction system substantially as described herein in conjunction with the drawings. Dated this 14th day of November, 1994 COLIP ARTH R PRESTON BY: Patent Attorneyfor the Applicant 'M ABSTRACT A sound reproduction system which is capable of reproducing stereo and other spatial effects from a single location is described. A loudspeaker enclosure comprises a first speaker having a broad angle of coverage, which faces forward and is fed by the amplified sum (Left plus Right) of a conventional stereo audio programme. The enclosure also comprises a second speaker or speakers capable of creating a doublet polar pattern with a narrow angle of coverage for each half of the doublet, the speaker or speakers being oriented perpendicular to the first speaker and fed by the amplified difference (Left minus Right) of the audio programme. Also described is a surround sound system o comprising one or more such loudspeaker enclosures. ae 0 as* 4 4 o S. *I S