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Title:
EXTENDED IMAGING SPLIT MODE LOUDSPEAKER SYSTEM
Document Type and Number:
WIPO Patent Application WO/1989/000802
Kind Code:
A1
Abstract:
Direct field sound, represented by the sum of left and right stereo input signals, is projected in a narrow dispersion pattern from a front radiating speaker (28, 32) and reverberant field sounds, represented by difference between left and right stereo input signals, is projected from speakers (26, 30) having a wide dispersion pattern. Direct field and reverberant field sounds are acoustically combined in space to create an improved representation of stereo sound.

Inventors:
KLAYMAN ARNOLD I (US)
Application Number:
PCT/US1988/002416
Publication Date:
January 26, 1989
Filing Date:
July 15, 1988
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
HUGHES AIRCRAFT CO (US)
International Classes:
H04R5/02; H04S1/00; H04S3/00; H04S5/00; (IPC1-7): H04S5/00
Foreign References:
US3849600A1974-11-19
FI35014C
US4594729A1986-06-10
Download PDF:
Claims:
CLAIMS
1. What is claimed is: A method of reproducing sound from left and right stereo signals comprising: combining left.and right stereo signals to form a sum signal representing sum of said stereo signals' and difference signals representing difference be¬ tween said stereo signals, radiating sound based on said difference signals in wide dispersion patterns over a frequency range, and radiating sound based on said sum signal in a limited dispersion pattern over said frequency range.
2. The method of claim 1 wherein said step of radiating sound based on said difference signals comprises radiating sound from mutually spaced locations.
3. The method of claim 1 wherein said step of radiating sound based on said difference signals comprises radiating sound in patterns having a dispersion of not less than about one hundred twenty degrees, and wherein said stepof radiating sound based on said sum signal comprises radiat¬ ing sound in a pattern having a dispersion of not more than about sixty degrees.
4. The method of claim 1 wherein said step of radiating sound based on said sum signal comprises radiating sound from a first location and wherein said step of radiating a sound based on said difference signals comprises radiating sound from locations at mutually opposite sides of said first location.
5. A method of reproducing sound from left and right stereo signals comprising: combining left and right stereo signals to form sum and difference signals respectively representing the sum and difference of said stereo signals, and acoustically combining said sum and difference signals to provide left and right acoustic signals, said step of acoustically combining including the steps of: radiating sound based upon said difference signals in wide dispersion patterns over a selected frequency range, radiating sound based on said sum signal in a narrow dispersion pattern over said frequency range, and directing at least parts of said radiated sound toward a common area.
6. The method of claim 5 wherein said sum signal com¬ prises a signal formed by L + R, where is said left stereo signal and R is said right stereo signal, and wherein said difference signals comprise a first dif ference signal (L R) and a second difference signal (R L) , and wherein said step of acoustically combining said sum and difference signals comprises positioning a speaker having a narrow dispersion pattern at a first location, energizing said first speaker with a signal that is a function of said sum signal, positioning second and third speakers at opposite sides of said first speaker, energizing said second speaker with said difference signal (L R) and energizing said third speaker with said difference signal (R L) .
7. The method of claim 6 wherein said step of radiating sound based upon said sum signal comprises radiating sound in a pattern having a dispersion of not more than about sixty degrees, and wherein said step of radiating sound based upon at least one of said difference signals comprises radiating sound in a dispersion pattern having a dispersion of not less than about one hundred twenty degrees.
8. A loudspeaker system for providing stereo sound from left and right stereo input signals comprising: a set of loudspeakers including a first speaker having a narrow dispersion pattern over a frequency range and second and third speakers having, wide dispersion patterns over said frequency range, means responsive to said stereo input signals for providing to said first speaker a sum signal representing the sum of said stereo input signals, and for providing to said second and third speakers difference signals representing difference between said stereo input signals.
9. The system of claim 8 wherein said first speaker, has a dispersion width of not more than about sixty degrees, and wherein at least one of said second and third speakers has a dispersion width of not less than about one.hundred twenty degrees.
10. The system of claim 8 wherein said first speaker is .a front radiating speaker having a dispersion width of not more than about sixty degrees.
11. The system of claim 8 wherein said first speaker is responsive to a sum signal (L + R) , where L is said left stereo input signal and R is said right stereo input sig¬ nal, wherein said second speaker is responsive to a dif¬ ference signal (L R) , and wherein said third speaker is responsive to a difference signal (R L) .
12. The system of claim 8 wherein said first speaker com¬ prises first and second narrow dispersion speakers each responsive to said sum signal, wherein said first narrow dispersion speaker is positioned adjacent said second speaker having a wide dispersion pattern, and wherein said second narrow dispersion speaker is positioned adjacent said third speaker having a wide dispersion pattern.
13. The system of claim 8 including a speaker cabinet, means for mounting said set of loudspeakers in said cabinet, said first speaker being mounted in said cabinet between said second and third speakers, said first speaker having an axis of radiation extending in a first direc¬ tion, each of said second and third speakers having an axis of radiation extending at a significant angle with respect to said first direction.
14. The system of claim 13 wherein each of said second and third speakers has a dispersion pattern of greater than 180°, and wherein said first speaker has a dispersion pattern of not more than about 60°.
15. The system of claim 8 wherein said set of loudspeakers is adapted to be mounted in an automobile having a dashboard and first and second sides, said first speaker being adapted to be mounted in a central portion of the dashboard of said automobile, said second and third speakers being adapted to be mounted at said first and second sides respectively.
16. The system of claim 8 wherein said set of loudspeakers is mounted adjacent to but spaced from the wall of a room, and wherein said second and third speakers are positioned on either side of said first speaker.
17. The system of claim 8 wherein said means for provid¬ ing to said first speaker a sum signal comprises providing a sum signal representing the sum (L + R) , where L and R respectively represent said left and right stereo input signals, and wherein said means for providing to each of said second and third speakers a difference signal com¬ prises means for providing a first difference signal (i R) and feeding said first difference signal to said second speaker, and providing a second difference signal (R L). and feeding said second difference signal to said third speaker.
18. The system of claim 17 including a theater having a front, a back, first and second sides and an audience seating area, said first speaker being responsive to a signal proportional to the sum signal (L + R) and being. positioned at a central portion of the front of said theater, said second speaker being responsive to said first difference signal (L R) and being positioned on one side of said first speaker at the front of said theater, said third speaker being responsive to said dif ference signal (R L) and being positioned on the other side of said first speaker at the front of said theater.
19. The system of claim 18 including a fourth speaker having a wide dispersion pattern positioned at one side of said theater rearwardly of the front of the theater and being responsive to said difference signal (L R) , and a fifth speaker having a wide dispersion pattern positioned at the other side of said theater and being responsive to said difference signal (R L) .
20. The system of claim 19 wherein said first mentioned stereo input signals are front stereo input signals LF and RF provided from a front sound system, and including a rear sound system providing rear left and rear right stereo input signals 1^ and RR, said first, second, third, fourth and fifth speakers being responsive to signals from said front sound system, said set of speakers including a first rear speaker having a narrow dispersion pattern and second and third rear speakers having wide dispersion patterns, said first rear speaker being responsive to a signal proportional to a sum signal (L + R)R representing the sum of the rear left and rear right stereo input sig¬ nals, said second rear speaker being responsive to a dif¬ ference signal (L R)R representing a difference between the rear left and rear right stereo input signals, said third rear speaker being responsive to a difference signal (R L)R representing the difference between the rear left and rear right stereo input signals, said first rear speaker being positioned at the center of the rear of said theater, and said second and third rear speakers being positioned at the rear of said theater on either side of said first rear speaker.
21. The system of claim 20 including first and second combined front and rear speakers each having a wide dis¬ persion pattern and positioned respectively on opposite sides of said theater, said first combined front and rear speaker being responsive to a combined difference signal (L R)F+R representing the sum of a difference signal of said front sound system and a difference signal of said rear sound system, and said second combined side speaker being responsive to a combined difference signal (R L)F+R representing the sum of a difference signal of said front sound system and a difference signal of said rear sound system.
22. A method of reproducing stereo sound from electrical "stereo signals that include components representing direct field sounds and reverberant field sounds comprising: employing said stereo signals to reproduce direct field sounds projected from a front radiating speaker system, and employing said stereo signals to reproduce reverberant, field sounds projected from a speaker system having a wide pattern of dispersion.
23. The method of claim 22 wherein said electrical stereo5 signals comprise left and right stereophonic signals and* including the step of providing sum and difference signals representing the sum and difference of said stereophonic input signals, said step of employing said stereo signals to reproduce direct field sounds comprising the step of feeding said sum signal to a front radiating speaker sys¬ tem having a limited angle of dispersion, and wherein said step of employing said stereo signal to reproduce rever 10 berant field sounds comprises feeding said difference signal to a speaker system having a wide pattern of dispersion. 1 24. The method of claim 22 including positioning said front radiating speaker system at a central location and positioning first and second speaker systems each having a wide pattern of dispersion on opposite sides of said 5 central location and energizing said first and second wide dispersion speakers with mutually opposite phase versions of said difference signal. 1 25. The method of claim 24 including positioning said speakers adjacent one wall of a room. l 26. The method of claim 22 including the step of radiat¬ ing direct field sounds from said front radiating speaker in a dispersion pattern having a width of not more than about sixty degrees and projecting said reverberant field 5 sounds from a speaker system having a wide dispersion pattern of a width not less than about one hundred twenty degrees. l 27. A method of reproducing sound from.left and right stereo signals comprising: combining left and right stereo signals to form sum and difference signals respectively representing the sum and difference of said stereo signals, providing first and second mutually spaced pairs of speakers, each pair comprising a speaker having a limited dispersion over a frequency range and a speaker having a wide dispersion over said frequency 0 range, energizing said limited dispersion speakers with said sum signal, and energizing said wide dispersion speakers with said difference signal.
24. 28 The method of claim 27 wherein one of said limited dispersion speakers is common to both pairs.
25. 29 The method of claim 6 including the step of adding a portion of said sum signal to said difference signals.
26. 30 The system of claim 10 wherein said first speaker is responsive to a sum signal (L + R) , where L is said left stereo input signal and R is said right stereo input sig¬ nal, wherein said second speaker is responsive to a dif ference signal (L R) plus a portion of said sum signal (L + R) , and wherein said third speaker is responsive to a difference signal (R L) plus a portion of said sum sig¬ nal (L + R) .
27. 31 The system of claim 8 wherein said set of loudspeakers is adapted to be mounted in an automobile having a dashboard, first and second sides, and a driver, seat between said first and second sides, and wherein said first speaker is adapted to be mounted adjacent one end of the dashboard, wherein said second speaker is adapted to be mounted at said first side at a distance from the. driver seat, and wherein said third speaker is adapted to be mounted at a distance from said driver seat substan tially equal to said first mentioned distance.
28. 32 The system of claim 31 including a second set of. loudspeakers comprising a fourth speaker having a narrow dispersion pattern and fifth and sixth speakers having wide dispersion patterns, said fourth speaker being adapted to be mounted on said dashboard adjacent a pas¬ senger seat position, said automobile having a passenger seat position, said fifth speaker being adapted to be mounted at said second side of the automobile at. a second distance from said passenger seat position, and wherein said sixth speaker is adapted to be mounted between said first and second sides at a distance from said passenger position substantially equal to said second distance.
29. 33 The system of claim 32 wherein each of said second, third, fifth and sixth speakers includes a tweeter, each of said tweeters being adapted to be mounted on said dash¬ board. ' 34. The system of claim 31 wherein said means for provid¬ ing to said first speaker a sum signal comprises providing a sum signal representing the sum (L + R) , where L and R respectively represent said left and right stereo input signals, and wherein said means for providing to each of said second and third speakers a difference signal com¬ prises means for providing a first combination signal in¬ cluding (L R) and portion of said sum signal (L + R) and feeding said first combination signal to said second speaker, and wherein said means for providing a difference signal to said third speaker comprises providing a second combination signal comprising a second difference signal (R L) plus a portion of said sum signal (L + R) and feeding said second combination signal to said third speaker.
30. 35 The system of claim 33 wherein said automobile in¬ cludes a rear shelf behind the rear passenger seat, and including a seventh speaker having a narrow dispersion pattern mounted at one side of said rear shelf and an 5 eighth speaker having a narrow dispersion pattern mounted on a second side of said rear shelf, a ninth speaker having a wide dispersion pattern mounted at said first side adjacent said rear passenger seat and a tenth speaker having a side dispersion pattern mounted at said second 10 side adjacent said rear passenger seat, and means responsive to said stereo input signals for providing said sum signal to said seventh and eighth speakers and for providing difference signals to said ninth and tenth speakers. l 36. In combination with an automotive vehicle having first and second sides, a dashboard and a seat having pas. senger and driver seat positions, an improved loudspeaker system for providing stereo sound from left and right 5 " stereo input signals, said loudspeaker system comprising: a first speaker having a narrow dispersion pattern over a frequency range mounted on said dash*., board adjacent said driver seat position, second and1 third speakers each having wide dispersion patterns 1° over said frequency range, said second speaker being mounted at a first distance from said driver seat position and said third speaker being"mounted betwee said first and second sides at a distance from said driver seat position substantially equal to said 15 first distance, and means responsive to said stereo input signals for providing to said first speaker a sum signal representing the sum of said stereo input signals and for providing to said second and third speakers dif 20 ference signals representing the difference between said stereo input signals. 1 37. The combination of claim 36 including a fourth speak¬ er having a narrow dispersion pattern over said frequency range mounted on said dashboard at a position adjacent said passenger seat position, a fifth speaker having a 5 wide dispersion pattern over said frequency range mounted at said second side at a second distance from said pas¬ senger seat position, and a sixth speaker mounted between said first and second sides at a distance from said pas¬ senger seat position equal to said second distance, means 10 responsive to said stereo input signals for providing said sum signal to said fourth speaker and for providing to said fifth and sixth speakers difference signals representing difference between said stereo input signals. l 38. The system of claim 37 including means for mixing a portion of said sum signal with said difference signal * before providing said difference signals to said second, third, fifth and sixth speakers. 1 39. The system of claim 37 wherein said automobile in¬ cludes a rear passenger seat and a rear shelf, and further including seventh and eighth speakers having narrow dis¬ persion patterns over said frequency range mounted 5 respectively at opposite ends of said rear shelf, and ninth and tenth speakers having wide dispersion patterns over said frequency range mounted respectively at said first and second sides of said automobile adjacent oppo¬ site ends of said rear passenger seat, means for providing 10 said sum signal to said seventh and eighth speakers and means for providing said difference signals to said ninth and tenth speakers. l 40. The combination of claim 39 wherein said second and third and fifth and sixth speakers each includes an individual tweeter, said tweeters being mounted on said automobile dashboard respectively adjacent individual ones of said second, third, fifth and sixth wide dispersion pattern speakers.
Description:
AMENDED CLAIMS

[received by the International Bureau on 27 January 1989 (27.01.89) original claims 1,5-8,22-24,26,29,31,34,35 and 37 amended; other claims unchanged (9 pages)]

1. A method of reproducing sound from left and right stereo signals comprising: combining left and right stereo signals to form a sum signal representing, sum of said stereo signals and difference signals representing difference be¬ tween said stereo signals, radiating sound based on said difference signals in wide dispersion patterns over a frequency range, and radiating sound based on said sum signal in a limited dispersion pattern over said frequency range.

2. The method of claim 1 wherein said step of radiating sound based on said difference signals comprises radiating sound from mutually spaced locations.

3. The method of -claim 1 wherein said step of radiating sound based on said difference signals comprises radiating sound in patterns having a dispersion of not less than about one hundred twenty degrees, and wherein said step of radiating sound based on said sum signal comprises radiat¬ ing sound in a pattern having a dispersion of not more than about sixty degrees.

4. The method of claim 1 wherein said step of radiating sound based on said sura signal comprises radiating sound

from a first location and wherein said step of radiating a sound based on said difference signals comprises radiating sound from locations at mutually opposite sides of said first location.

5. A method of reproducing sound from left and right stereo signals comprising: combining left and right stereo signals to form sum and difference signals respectively representing the sum and difference of said stereo signals, and acoustically combining said sum and difference signals to provide left and right acoustic signals, said step of acoustically combining including the steps of: radiating sound based upon said difference signals in wide dispersion patterns over a selected frequency range, radiating sound based on said sum signal in a narrow dispersion pattern over said frequency range, and directing at least parts of said radiated sound toward a common area.

6. The method of claim 5 wherein said sum signal com¬ prises a signal formed by L + R, where L is said left stereo signal and R is said right stereo signal, and wherein said difference signals compriεe a first dif- ference signal (L - R) and a second difference signal (R - L) , and wherein said step of acoustically combining said sum and difference signals comprises positioning a speaker having a narrow dispersion pattern at a first location, energizing said first speaker with a signal that is a function of said sum signal, positioning second and third

speakers at opposite sides of said first speaker, energizing said second speaker with said difference signal (L - R) and energizing said third speaker with said difference signal (R - L) .

7. The method of claim 6 wherein said step of radiating sound based upon said sum signal comprises radiating sound in a pattern having a dispersion of not more than about sixty -degrees, and wherein said step of radiating sound " based upό at least one of said, difference " signals ' comprises radiating sound in a dispersion pattern having a dispersion of not less than about one hundred twenty degrees.

8. A loudspeaker system for providing stereo sound from left and right stereo input signals comprising: a set of loudspeakers including a first speaker having a narrow dispersion pattern over a frequency range and second and third speakers having wide dispersion patterns over said frequency range, means responsive to said stereo input signals for providing to said first speaker a sum signal representing the sum of said stereo input signals, and for providing to said second and third speakers difference signals representing, difference between said stereo input signals.

9. The system of claim 8 wherein said first speaker has a dispersion width of not more than about sixty degrees, and wherein at least one of said second and third speakers has a dispersion width of not less than about one hundred twenty degrees.

10. The system of claim 8 wherein said first speaker is a

21. The system of claim 20 including first and second combined front and rear speakers each having a wide dis¬ persion pattern and positioned respectively on opposite sides of said theater, said first combined front and rear speaker being responsive to a combined difference signal (L -R) j - + R representing the sum of a difference signal of said front sound system and a difference signal of said rear sound system, and said second combined side speaker being responsive to a combined difference signal (R - L )F+R rep^sent-i- 111 ? the sum of a difference signal of said front sound system and a difference signal of said rear sound system.

22. A method of reproducing stereo sound from electrical stereo signals that include components representing direct field sounds and reverberant field sounds comprising: employing said stereo signals to reproduce direct field sounds projected from a front radiating speaker system, and employing said stereo signals to reproduce reverberant field sounds projected from a speaker system, having a wide pattern of dispersion. " -r,~ ---

23. The method of claim 22 wherein said electrical stereo signals comprise left and right stereophonic signals and including the step of providing sum and difference signals representing the sum and difference of said stereophonic input signals, said step of employing said stereo signals to reproduce direct field sounds comprising the step of feeding said sum signal to a front radiating speaker sys¬ tem having a limited angle of dispersion, and wherein said

step of employing said stereo signal to reproduce rever- berant field sounds comprises feeding said difference signal to a speaker system having a wide pattern of dispersion.

24. The method of claim 22 including positioning said front radiating speaker system at a central location and positioning first and second speaker systems each having a wide pattern of dispersion on opposite sides of said central location and energizing said first and second wide - J -~ϊ .-.ιn : dispersion speakers .with mutually opposite phase versions of said difference signal.

' 25. The method of claim 24 including positioning said speakers adjacent one wall of a room.

26. The method of claim 22 including the step of radiat¬ ing direct field sounds from said front radiating speaker ' ; in a dispersion pattern having a width of not more than about sixty degrees and projecting said reverberant field sounds from a speaker system having a wide dispersion pattern of a width not less than about one hundred twenty degrees.

27. A method of reproducing sound from left and right stereo signals comprising: combining left and right stereo signals to form sum and difference signals respectively representing the sum and difference of said stereo signals, providing first and second mutually spaced pairs of speakers, each pair comprising a speaker having a limited dispersion over a frequency range and a speaker having a wide dispersion over said frequency range, energizing said limited dispersion speakers with

said sum signal, and energizing said wide dispersion speakers with said difference signal.

28. The method of claim 27 wherein one of said limited dispersion speakers is common to both pairs.

29. The method of claim 6 including the step of adding a portion of said sum signal to saidTσlXfference signals.

30. The system of claim 10 wherein said first speaker is responsive to a sum signal (L + R) , where L is said left stereo input signal and R is said right stereo input sig¬ nal, wherein said second speaker is responsive to a dif- ference signal (L - R) plus a portion of said sum signal (L + R) , and wherein said third speaker is responsive to a difference signal (R - L) plus a portion of said sum sig¬ nal (L + R) .

31. The system of claim 8 wherein said set of loudspeakers is adapted to be mounted in an automobile having a dashboard, first and second sides, and a driver seat between said first and second sides, and wherein said first speaker is adapted to be mounted adjacent one end of the dashboard, wherein said second speaker is adapted to be mounted at said first side at a distance from the driver seat, and wherein said third speaker is adapted to be mounted at a distance from said driver seat substan- tially equal to said first.mentioned distance.

32. The system of claim 31 including a second set of loudspeakers comprising a fourth speaker having a narrow dispersion pattern and fifth and sixth speakers having

wide dispersion patterns, said fourth speaker being adapted to be mounted on said dashboard adjacent a pas¬ senger seat position, said automobile having a passenger seat position, said fifth speaker being adapted to be mounted at said second side of the automobile at a second distance from said passenger seat position, and wherein said sixth speaker is adapted to be mounted between said first and second sides at a distance from said passenger position substantially equal to said second distance.

33. The system of claim 32 wherein each of said second, third, fifth and sixth speakers includes a tweeter, each of said tweeters being adapted to be mounted on said dash¬ board.

34. The system of claim 31 wherein said means for provid- ing to said first speaker a sum signal compris 'eUs£/__Lp_rov yiydi ' ng a sum signal representing the sum (L + R) , where L and R respectively represent said left and right stereo input signals, and wherein said means for providing to each of said second and third speakers a difference signal com¬ prises means for providing a first combination signal in¬ cluding (L - R) and..portion of said sum signal (L + R) and feeding said first combination signal to said second speaker, and wherein said means for providing a difference signal to said third combination signal comprising a second difference signal (R - L) plus a portion of said sum signal (L + R) and feeding said second combination signal to said third speaker.

35. The system of claim 33 wherein said automobile in¬ cludes a rear shelf behind the rear passenger seat, and

including a seventh speaker having a narrow dispersion pattern mounted at one side of said rear shelf and an eighth speaker having a narrow dispersion pattern mounted on a second side of said rear shelf, a ninth speaker having a wide dispersion pattern mounted at said first side adjacent said rear passenger seat and a tenth speaker having a side dispersion pattern mounted at said second side adjacent said rear passenger seat, and means responsive to said stereo input signals for providing said sum signal to said seventh and eighth speakers and for providing difference signals to said ninth and tenth speakers.

36. In combination with an automotive vehicle having first and second sides, a dashboard and a seat having pas¬ senger and driver seat positions, an improved loudspeaker system for providing stereo sound from left and right stereo input signals, said loudspeaker system comprising: a first speaker having a narrow dispersion pattern over a frequency range mounted on said dash¬ board adjacent said driver seat position, second and third speakers each having wide dispersion patterns over said frequency range, said second speaker being mounted at a first distance from said driver seat position and said third speaker being mounted between said first and second sides at a distance from said driver seat position substantially equal to said first distance, and means responsive to said stereo input signals for providing to said first speaker a sum signal representing the sum of said stereo input signals and for providing to said second and third speakers dif- ference signals representing the difference between said stereo input signals.

37. The combination of claim 36 including a fourth speak¬ er having a narrow dispersion pattern over said frequency range mounted on said dashboard at a position adjacent said passenger seat position, a fifth speaker having a wide dispersion pattern over said frequency range mounted at said second side at a second distance from said pas¬ senger seat position, and a sixth speaker mounted between said first and second sides at a distance from said pas¬ senger seat position equal to said second distance, means responsive to said stereo input signals for providing said sum signal to said fourth speaker and for providing to said fifth and sixth speakers difference signals tΛ, • representing^difference between said stereo input signals.

38. The system of claim 37 including means for mixing a portion of said sum signal with said difference signal before providing said difference signals to said second, third, fifth and sixth speakers.

39. The system of claim 37 wherein said automobile in¬ cludes a rear passenger seat and a rear shelf, and further including seventh and eighth speakers having narrow dis¬ persion patterns over said frequency range mounted respectively at opposite ends of said rear shelf, and ninth and tenth speakers having wide dispersion patterns over said frequency range mounted respectively at said first and second sides of said automobile adjacent oppo¬ site ends of said rear passenger seat, means for providing said sum signal to said seventh and eighth speakers and means for providing said difference signals to said ninth and tenth speakers.

40. The combination of claim 39 wherein said second and third and fifth and sixth speakers each includes an individual tweeter, said tweeters being mounted on said

International Bureau

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)

(51) International Patent Classification 4 (11) International Publication Number: WO 89/ 00 H04S 5/00 Al (43) International Publication Date : 26 January 1989 (26.01

(21) International Application Number: PCT/US88/02416 (81) Designated States: AU, CH (European patent), (European patent), FR (European patent), GB (E

(22) International Filing Date: 15 July 1988 (15.07.88) pean patent), JP, KR, NL (European patent), SE ( ropean patent).

(31) Priority Application Number: 076,412

Published

(32) Priority Date : 21 July 1987 (21.07.87) With international search report. Before the expiration of the time limit for amendin

(33) Priority Countr : US claims and to be republished in the event of the re of amendments.

(71) Applicant: HUGHES AIRCRAFT COMPANY [US/

US]; 7200 Hughes Terrace, Los Angeles, CA 90045-0066 (US).

(72) Inventor: KLAYMAN, Arnold, I. ; 16821 Phelps Lane,

Huntington Beach, CA 92649 (US).

(74) Agents: SZABO, Joseph, E. et al.; Hughes Aircraft Company, Post Office Box 45066, Building C1/A126, Los Angeles, CA 90045-0066 (US).

(54) Title: EXTENDED IMAGING SPLIT MODE LOUDSPEAKER SYSTEM

(57) Abstract

Direct field sound, represented by the sum of left and right stereo input signals, is projected in a narrow dispersi pattern from a front radiating speaker (28, 32) and reverberant field sounds, represented by difference between left an right stereo input signals, is projected from speakers (26, 30) having a wide dispersion pattern. Direct field and reverbera field sounds are acoustically combined in space to create an improved representation of stereo sound.

FOR THE PURPOSES OFINFORMAHON ONLY

Codes used to identify States party to the PCTon the front pages ofpamphlets publishing international appli¬ cations under the PCT.

EXTENDED IMAGING SPLIT MODE LOUDSPEAKER SYSTEM

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to stereophonic speaker systems, and more particularly concerns an improved com¬ bination of speaker characteristics with speaker driving component signals to provide improved stereophonic sound.

2_j Description of Related Art

In reproduction of stereophonic sound, electrical signals generally representing left and right channel stereo input sounds are combined or processed and fed to left and right channel speaker systems or to various com¬ binations of speaker systems, with the goal of reproducing for the listener a sound that most realistically depicts sound heard during an actual, live performance. In at¬ tempts to achieve this goal, electrical stereophonic sig¬ nals have been combined and processed in various manners. Major efforts have been made in careful design and manufacture of recording, mixing and production equipment so that the electrical end product will reflect as closely as possible precisely what performing artists, engineers.

mixers or producers wish to convey to the listener. Sig¬ nals have been fed to speakers positioned in various loca¬ tions and in various groups, and speakers have been ener¬ gized by various combinations of stereo signals in further attempts to improve realism of the sound. Artificial time delays, reverberation techniques and deliberate reflec¬ tions from various walls have been employed, often at the expense of introduction of extraneous information of a type not originally present, thus actually changing the effect of the original performance. Yet, all the prior effort has not resulted in attainment of the goal of realistic reproduction of the sound of a live performance. The spatial acoustical field produced in a live per¬ formance varies in accordance with acoustics of the per-- formance area, and, importantly, in accordance with the type or nature of the performer or performers. For ex¬ ample, a solo vocalist or instrumentalist positioned at center stage will primarily provide sound known as direct field sound, that is radiated directly to the listeners' in the audience. However, where performers are spread across a wide stage, for example, as in a performance of a large choral group or a large symphony orchestra, significant portions of sound received by the audience are reflected from various parts of the theater so that the audience receives a mixture of direct field sound, radiated * , directly from the performers, . and sound known as rever¬ berant field sound, that is reflected from the walls of the theater. In the case of some sounds, such as the im¬ mense organ chords of a Saint-Saens organ symphony, the music resounds and reverberates from surfaces in all areas of the theater.

Various combinations of speaker systems, including those that reflect a majority of sound from a wall behind

the speaker, do not adequately reproduce all desired sounds with sufficient realism. Moreover, speaker systems arranged for one particular location or environment are not readily scaled up or down to operate in other environ- ments so that, for example, a speaker system designed for a living room environment is not properly operable in an automobile, theater, or even outdoors.

Accordingly, it is an object of. the present invention to provide a loudspeaker system that avoids or minimizes problems of prior systems and produces a spatial acousti¬ cal field which is more realistically representative of the live performance, and, moreover, is flexible in its application to different environments.

SUMMARY OF THE INVENTION

In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, direct field sounds are radiated from a front radiating speaker system and reverberant field sjounds are projected from a speaker system having a wider dispersion pattern. Accord¬ ing to a specific feature of the invention, a front radiating speaker system having a narrow dispersion pat¬ tern is energized from a signal representing the sum of left and right stereo input signals and a pair of com- panion speaker systems, having wide dispersion patterns, is energized from signals representing difference between left and right stereo signals. Direct field sound repre¬ senting a stereo sum signal, and radiated in a narrow dis¬ persion pattern, is combined acoustically with reverberant field sound representing difference signals, and radiated in a wide dispersion pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram illustrating a loudspeaker system embodying principles of the present invention; FIG. 2 schematically depicts an arrangement of speakers in accordance with principles of the present invention;

FIG. 3 illustrates a" modified speaker arrangement; FIG. 4 illustrates a single cabinet incorporating a set of speakers;

FIGS. 5, 6 and 7 illustrate still further arrange¬ ments and organizations of speaker systems; and

FIG. 8 shows a modification of the speaker arrange¬ ment particularly adapted for an automobile.

DESCRIPTION OF A PREFERRED EMBODIMENT Principles of the present .invention are based upon " a combination of control of (a)-, radiation of direct and reverberant field sounds and (b) the electronic processing of stereophonic left and right signals.

With respect to radiation of sound, the present in¬ vention takes advantage of the fact that a front radiating speaker system is effective for reproduction of direct field sound, but is relatively ineffective for reproduσ- tion of reflected or reverberant field sound. Further, an omnidirectional or wide dispersion speaker system is just the opposite, effective in reproduction of reverberant field sound, but ineffective for reproduction of direct field sound, which appears to be strangely disembodied, by an omnidirectional speaker system.

With respect to electronic processing of the stereophonic left and right signals L and R, it is known

that these signals may be broken down into their sum (L + R) and difference (L - R) or (R-L) components. It is also known that such components may be electrically remixed in various manners so as to reassemble the original stereophonic signals. For example, (L + R) + (L - R) = 2 L, and (L + R) + (R - L) * = 2 R. Further, in my prior co¬ pending application for Stereo Enhancement System, filed March 27, 1986, Serial No. 844,929, I describe various methods for specifically processing sum and difference signals (according to various frequency bands) and produc¬ ing stereo left and right channel output signals for ap¬ plication to a speaker system by various mixtures of processed sum and difference signals with the stereophonic left and right input signals. However, in no prior case has there been an attempt to obtain separate reverberant - field and direct field signals and to radiate sound based upon such signals in a manner that is optimum for the respective signal types. It has not been previously recognized that direct field sound and reverberant field sound can be separately projected from speaker systems respectively optimized for the particular type of sound, and that the sound types can then be acoustically recom¬ bined in space and transmitted to the ear-brain system of the listener. The sum of the stereophonic left and right signals, namely the sum signal (L + R) , . itself essentially repre¬ sents the direct field sound, namely that sound heard by the listener at a performance of a solo vocalist or in¬ strumentalist, positioned in the center of the theater stage. The difference signals, namely (L - R) and (R - L) , uniquely represent reverberant field sound which sig¬ nificantly include sound heard by the listener but which is reflected from or reverberating between the theater

walls. Direct field sound from a center stage soloist, for example, reaches the listener in a direct. line, whereas the reverberant field sound reaches the listener after various reflection in the theater. Thus, according to a feature of the present invention, a speaker system is set up to similarly provide direct field sound to the lis¬ tener via a direct path and reverberant field sound to the listener via direct or reflective paths, or a combination of both direct and reflective paths. Referring now to FIG. 1, there is shown a stereo, source 10 of left and right stereophonic input signals L and R which may be derived from a radio broadcast receiver, AM,FM or television, or from a stereo playback- system whether grooved record r magnetic, optical (laser * compact" disc) or the like. These stereophonic input signals L and R may be derived directly from the playback system or may be processed in some suitable arrangement, as for example, in the stereo enhancement system of my prior application above identified. Thus the signals; L and R of FIG. 1 may be derived from the mixer output-'sig¬ nals of the enhancement system of such prior co-pending, patent application. The signals L and R are fed to respective sum and difference circuits 12,14, which respectively provide the sum signal (L + R) and the dif- ference signal (L - R) , which are the sum and difference of the input signals L and R. These sum and difference- signals are fed to a multi-channel power amplifier 16, which also receives the output of an inverter 18 which in¬ verts the (L - R) signal to provide a second difference signal (R - L) . Thus the power amplifier provides as its output, amplified versions of the sum signal (L + R).,, which represents direct field sound of the stereo input, and the two difference signals (L - R) and (R - L) , which

represent the reverberant field sounds of the stereo in¬ put.

A set of speakers is provided to project sound based upon the three outputs of the amplifier 16. The terms speaker, speaker system or loudspeaker, loudspeaker system are used herein to denote systems having one or more electrical to acoustic transducers, each uniquely operable over a selected frequency range. For example, the term speaker may refer to a system having a woofer, tweeter and mid-range transducer or any group or combination thereof. FIG. 1 shows the set as being composed of three speakers, but greater numbers of speakers may be used, as shown in other drawings of the present application, and as described below. A first speaker 20 is energized with the sum signal (L + R) and projects its sound in a relatively - narrow dispersion pattern. Speaker 20 is a front radiat¬ ing speaker having a dispersion pattern of not greater than 60°. The difference signals (L - R) and (R - L) are fed to second and third speakers of the set, namely speakers 22 and 24, which are omnidirectional speakers or speakers having a wide dispersion pattern, which is a pat¬ tern of dispersion of at least 120°. Thus each of speakers 22 and 24 may have a dispersion pattern in the range of 120° to 360°, whereas speaker 20 has a dispersion pattern of not more than about 60°.

Speakers with wide dispersion patterns and omnidirec¬ tional speakers are known and readily available for use in the present invention. Wide dispersion is relatively easy to achieve below about 800 Hertz, but as wave lengths be- come shorter in relation to diameter of the radiating area of the speaker transducer, angular dispersion becomes nar¬ rower until at frequencies above about 3 Kilohertz, for cone type midrange speakers, and above about 10 Kilohertz

for dome type tweeters, the dispersion pattern becomes a narrow beam of sound. It has been found that higher frequencies require maximum angular dispersion to properly reproduce the reverberant field sound based upon dif- ference channel signals. Therefore many speakers do not have a dispersion pattern that is sufficiently wide, over the desired frequency band, to be suitable for projecting reverberant field sound. However, wide dispersion speakers for use in the present invention may be provided by using conventional techniques of wide dispersion horns or arrays of multiple transducers. Although a wide dis¬ persion horn will operate only over a discrete .band ..of frequencies and becomes physically large as cutoff frequency is lower, the horn operates quite satisfactorily at the higher frequencies, and dispersion angle may be made quite large with horns of reasonable dimension.

A dispersive element in the form of an uniquely shaped baffle is disclosed- in my co-pending application for Loudspeaker System with Conical Baffle filed r Serial No. . This * dispersive element may be used with most forms and sizes of speaker transducers,, and "is highly efficient, small and inexpensive to manufacture. Angle of dispersion may be designed into -the speaker and baffle, and thus a simple conventional cone-type speaker when used with such dispersive element may provide the wide dispersion pattern desirable for the reverberant field speakers, such as speakers 22 and 24 of FIG. 1. Ex¬ amples of other wide dispersion speakers are shown * in, U.S., Patents 4,580,654 and 4,348,549. Illustrated in FIG. 2 is an exemplary physical ar¬ rangement of a set of four speakers which illustrates, operation of the present invention. The speaker set shown in FIG. 2 comprises two pairs of speakers. For example a

left pair comprises a wide dispersion pattern speaker 26 and a narrow dispersion front radiating speaker 28. A right pair comprises a similar pair of speakers, including a wide dispersion pattern speaker 30 and a narrow disper- sion pattern front radiating speaker 32. Each of the wide dispersion range speakers 26 and 30 is energized with a difference signal, the left difference signal (L - R) being fed to speaker 26, and the right difference signal (R - L) being fed to speaker 30. Each of the front radiating speakers 28 and 32 is fed with the same sum sig¬ nal (L + R) . The arrows pointing away from the various speakers schematically represent the relatively narrow and relatively wide dispersion patterns. Sound projected from the wide and narrow dispersion pattern speakers is directed, at least in part, to a common area for acoustic recombination. Illustrated in FIG. 2, by boxes 34 and 36, is the acoustic recombination of the sounds from the speakers of the respective pairs. Thus, box 34 depicts acoustic recombination of the; (L - R) and (L + R) com- ponents from speakers 26,28 to provide the left stereophonic signal sound 2L. Similarly box 36 represents the acoustic combination of the right channel direct field and reverberant field sound from speakers 32,30, which respectively radiate sound based on the sum signal (L + R) and the difference signal (R - L) , which sounds provide, when combined acoustically, the acoustic equivalent of the right channel signal 2R. The arrangement is such that the listener may be in a wide range of locations without losing advantages of the improved realism of the sound. FIG. 3 illustrates a modified arrangement of speakers in which wide dispersion pattern speakers 38,40 are posi¬ tioned on either side of a centrally located narrow dis¬ persion pattern front radiating speaker 42, with speakers

38 and 40 being fed with the difference signals (L - R) and (R - L) respectively, and the center speaker, which is a direct radiating narrow dispersion pattern speaker that cooperates in common with each of the wide dispersion pat- tern speakers, being fed with the sum signal 2(L + R) . Again the direct field and reverberant field sounds of the speakers are 'acoustically combined by the listener. In one typical arrangement, the three speakers 38, 40 and 42 may be arranged in a line at the center of and along one wall of a room, being spaced at least one foot from the wall to allow for the reflection of the widely dispersed sound from speakers 38 and 40.

FIG. 4 illustrates a slightly modified version of the speaker arrangement of FIG. 3 wherein all three speakers are mounted in a single cabinet with direct front radiat¬ ing, speaker 42• being mounted directly between wide dis¬ persion speakers 38', 40'. The narrow and wide dispersion pattern speakers are .energized n the manner described in connection with FIG; 3." In the arrangement of FIG. 4 the center front radiating speaker 42' is provided with a dis¬ persion pattern of not more than about 60°, whereas each of the side speakers 38' and 40 is provided with a wide dispersion pattern in the order of about 270° as il¬ lustrated by the pattern of arrows in this figure. The central axes of the radiation pattern of the side speakers 38', 40' are substantially perpendicular to the central axes of the radiation pattern of the center speaker 42'.

The speaker arrangements of FIGS. 2, 3 and 4, which are arranged primarily for a living room or the like, may be modified as illustrated in FIG. 5 for use in an automobile. FIG. 5 shows a front radiating narrow disper¬ sion pattern speaker 50 energized by the sum signal 2(L + R) mounted at the center of the dashboard of an automobile

and flanked by wide dispersion pattern speakers 52 and 54 respectively energized with difference signals (L - R) and (R - L) and positioned either in opposite doors of the automobile at opposite sides of the driver, or in the respective extreme corners of the automobile dashboard. The direct field speaker 50 has a dispersion pattern of not more than about 60° and the reverberant field speakers 52,54 have wide dispersion patterns, of more than 180°.

FIG. 6 illustrates a speaker arrangement for a theater wherein a stage at the front of the theater sup¬ ports a screen 60, for example, and the audience is seated in areas indicated generally at 62,64. In such an ar¬ rangement a narrow dispersion pattern speaker 66, ener¬ gized by the sum signal 2(L + R) is mounted at the center of the stage, and wide dispersion pattern speakers 68,70, energized by difference signals (L - R) and (R - L) , are mounted on either side of the speaker 66 at opposite sides of the screen 60. Mounted on one side of the theater, such as the left side of the theater, is a pair of addi- tional wide dispersion pattern speakers 72,74 near the front and near the rear respectively of the left side of the theater, each energized with the difference signal (L - R) . On the right side of the theater, at front and back portions respectively, is mounted a second pair of wide dispersion pattern speakers 76,78, each energized with the difference signal (R - L) . The wide dispersion pattern speakers in the arrangement of FIG. 6 may have a disper¬ sion pattern of about 180°, whereas the front radiating direct field narrow dispersion pattern speaker 66 again has a narrow dispersion pattern of not more than about 60°.

In some theaters separate stereo sound systems are employed for the front and rear so that, in general, a

front system energized with front stereophonic left and right signals is provided at the front of the theater, and a rear system energized with rear stereophonic left and right signals is provided at the rear of the theater. Principles of the present invention are applicable to such a total immersion theater sound system, which includes both front and rear sound systems surrounding seating areas 62,64, in a manner illustrated in FIG. 7. Again a. narrow dispersion front radiating speaker 80 is energized by the sum signal 2(L + R) F , which is the sum signal; of the front stereo system, and is positioned at the center - of the front mounted screen 82. At opposite sides of the. theater, at the sides of the screen, are mounted wide dis¬ persion pattern speakers 84,86, energized with the front sound system difference signals (L - R) F and (R - L) F respectively.

At the rear of the theater, in the center, is mounted a second narrow dispersion ..front radiating speaker 88, energized with the sum signal 2CL -K*R) R of the rear sound system. On either side of speaker 88, at the opposite sides of the rear of the theater, are mounted wide disper¬ sion speakers 90,92, respectively energized with dif¬ ference signals (L - R) R and (R - L) R of .the rear stereo signals. In the exemplary system of FIG. 7 along each side of the theater are mounted three additional wide,dis--.. persion pattern speakers 94, 9δ,and 98 on one side, .and., wide dispersion pattern speakers 100,102 and.104 on the. other side, the speakers on each side being mounted, at ' front, back and center respectively of the theater sides. ; Speakers at the front of the theater sides, that, is speakers 98 and 104, are energized with the difference " signals (L - R) F and (R - L) F of the front sound system, whereas speakers at the rear of the sides, speakers 94 and

100, are energized with the difference signals (L - R) R and (R - L) R of the rear sound system. Speakers 96 and 102 at the center portions of the theater sides are ener¬ gized with signals representing a combination of the front sound system difference signals and the rear sound system difference signals. Thus speaker 96 is energized with the difference signal (L - R) F + R and speaker 102 is ener¬ gized with the difference signal (R - L) F + R where (L - R) F + R = (L - R) F + (L - R) R and where (R - L) F + R = (R - L) F + (R - L) R .

The speakers 88, 90 and 92 at the rear of the theater are all energized with stereophonic left and right signal sum and difference signals of the rear sound system, with center rear speaker 88 being energized with the rear sound system sum signal 2(L + R) R and the side speakers 90,92 at he. rear being respectively energized with the difference signals (L - R) R and (R - L) R of the rear sound system. In this arrangement of FIG. 7, as in the arrangement of FIG. 6, the narrow dispersion pattern speakers 80,88 have a dispersion pattern of not more than about 60°, whereas each of the other speakers has a wide dispersion pattern of about 180°.

The arrangement of FIG. 5, as described above, is a simplified version of the present system for use in an automobile. In use of this system for an automobile, as distinguished from use of the system in a larger area, such as a music room, living room, theater or the like, position of the speakers with respect to the listener be¬ comes important. Position of the listener with respect to the speakers is important in an automobile because of the very small area of the interior of the automobile, as com¬ pared to the area of a normal living room or theater. In such a situation, referring to the arrangement of FIG. 5,

for example r the driver of the automobile would be sitting . considerably closer to the left side of the car, and thus '. would be positioned very close to the speaker 52 in the left door and relatively further away from the speaker 54 _ in the right door. Accordingly,, sound from the much closer speaker 52 not only reaches the driver before the corresponding sound from the more remote speaker 54, but is less attenuated because of the .considerably shorter distance traveled. In such an arrangement, the driver will hear a sound that is less realistic, since it is. a combination of the direct field sound from narrow pattern speaker 50 and reverberant field sound primarily from the wide dispersion speaker 52. Of course a similar situation , occurs with the passenger, who hears the reverberant field sound from the right side speaker 54 at a much higher ;amplitude level than sound from the left side speaker 52

In order to avoid this limitation in the very close - confines of an automobile, principles of the invention may be applied to an automobile speaker arrangement, such as - is illustrated in FIG. 8. In this arrangement door * ' mounted speakers 110 and 112 are mounted in the left and right automobile doors, generally at a lowermost portion of the door in order to accommodate the vertically movable door window, and are of the reverberant field type having a wide, preferably 180° or more, dispersion pattern, as previously mentioned in connection with speakers 52 and 54 of FIG. 5. Thes≡fe speakers are fed with the difference - signals (L - R) and (R - L) respectively for speakers U0 . and 112 (which are modified with direct field signals (L + R) in a manner to be described below) . Instead of using * a single narrow pattern direct field speaker, as in the ar-. - rangement of FIG. 5, a pair of such speakers 114,116 is - employed, each mounted at a corner of the automobile dash-

board and pointed upwardly to direct sound to be reflected toward the listeners from the windshield. Speakers 114,116 are narrow pattern speakers, having a pattern width of about 60°, as previously mentioned. In this situation a second pair of reverberant field speakers 118,120 is mounted on a center console 122 that projects rearwardly from the dash, with speaker 118 being a wide dispersion pattern speaker of the type previously men¬ tioned, energized with the difference signal (R - L) , modified as described below, and pointed directly at and aligned with speaker 110. Similarly, speaker 120 is a wide dispersion pattern speaker energized with the dif¬ ference signal (L - R) (modified with an (L + R) component as will be described below) and positioned directly op¬ posite and pointed at the speaker 112.

The wide dispersion pattern speakers 110, 112, 118 and 120 are all mounted relatively low, and their high frequency components tend to be absorbed to varying de¬ grees, depending upon the acoustics of the automobile in¬ terior and the sound absorption qualities of the automobile upholstery. Particularly for plush upholstery other than vinyl or leather, high frequency sound of these speakers that are mounted at a relatively low position in the automobile tends to be absorbed. Thus " the wide dis¬ persion speakers 110, 112, 118 and 120 is each made with a cross-over network and provided with a tweeter to handle the wide dispersion radiation of the higher frequencies, employing a cross-over frequency in the order of about 1,000 Hertz. To this end there are provided wide disper¬ sion reverberant field high frequency tweeters 124,126,128, and 130 respectively coupled with cross-over networks of wide dispersion speakers 110,118,120, and 112 respectively. The tweeters are mounted as indicated on

portions of the dash horizontally adjacent the respective low frequency wide dispersion speakers with which they are associated, with tweeters 124 and 130 being positioned at rear corners of the dash pointing upwardly toward the windshield, and tweeters 126,128 being positioned on .the top of the dash again, also pointed upwardly at the * windshield, but- positioned adjacent respective associated low frequency wide dispersion speakers 118, 120. Of course the signals fed to " the low frequency wide disper- sion speakers 110,118,120 and 112 are also fed to the cor¬ responding tweeters, 124,126,128 and 130, respectively.

In the arrangement illustrated in FIG. 8 and * • described to this point, the driver, indicated at "D", hears direct field sound from narrow pattern speaker 114,. which is energized with a signal (L + R) , and a combina¬ tion of reverberant field sound from speakers 110 and 118, which are energized with the signals (L - R) and (R - L) (as modified by (L + R) as described below) . The high, frequencies of the reverberant field sound from speakers 124 and 126 are also heard by the driver. Similarly, the passenger on the right side of the car, identified -as -PI, . hears direct field sound from narrow pattern speaker 116, . energized by (L + R) and reverberant field sound from speakers 120,112 and tweeters 128,130. A. passenger (not shown) seated in the center of the front seat will hear direct field sound from both speakers;. 114,116, which produces an apparent source of direct field ' sound midway between the two. The center passenger also 1 hears the reverberant field sound from speakers 110,112:. and tweeters 124,130. Insofar as the center passenger is concerned, sound from the console mounted speakers- . 118,120, which are mounted very close to one another, and . from the tweeters 126 and 128, which are also mounted very

close to one another, is effectively cancelled because these speakers effectively radiate sound to the center passenger in the same space. Accordingly, the center pas¬ senger hears the image, which is a combination of direct field sound from speakers 114 and.116 and effectively hears only the reverberant field sound from the wide pat¬ tern side speakers 110,124 on the left and 112,130 on the right.

Because the sound from the direct field speakers 114,116 is pointed upwardly and reflected from the windshield, and the side door mounted speakers 110,112 are generally required to be mounted at a lower point on the door, there is a relatively large vertical distance be¬ tween the apparent source of direct field sound and the apparent source of reverberant field sound. Console mounted speakers 118 and 120 are similarly required by the physical constraints of the usual automobile to be mounted at a relatively low portion of the console. When the nar¬ row pattern speakers are energized with sum signal (L + R) , and the wide pattern speakers are energized only with the difference signals (L - R) and (R - L) , this dif¬ ference in elevations of direct and reverberant field sound provides an apparent separation of the.direct field sound, causing the latter to appear to emanate from a point higher than the reverberant field sound. The direct field sound is that of the soloist, for example, and the reverberant field sound is that of the background orchestra, all as previously described. In order to decrease the effect of this relative difference in eleva- tion which is imposed upon the system by physical con¬ straints of the automobile structural interior, a portion of the direct field sound, the signal (L + R) , is fed electrically to the wide dispersion pattern speakers.

which also receive the (L - R) and (R - L) components, respectively. In a particular example this portion of (L + R) is approximately fifty percent. However, according to principles of the invention, this portion may vary be- tween twenty-five and seventy-five percent of the direct field sound signal (L + R) , depending upon acoustics of. the automobile interior and particularly on the nature of the sound absorption qualities of the -interior upholstery. Thus, although the speakers 114 and 116 are fed with the direct field signal components L + R, just as previously described, speaker 110 actually receives a combination of- (L + R) and (L - R) , and, more specifically, the signal 1/2 (L + R) + (L - R) , and the speaker 112 actually, receives the signal 1/2 (L + R) + (R - L) . In other words, one-half of the sum signal is electrically added to each.difference signal. This addition of a part of the direct field sound component (L + R) to the wide rever¬ berant field speakers provides a greatly improved realism and apparent increase in realistic positioning of both the.. direct and reverberant field sounds. This addition of the L + R component to the wide dispersion speakers 110,118, 120 and 112 lowers the apparent position of the image of- the direct field sound source and decreases; dominance of the direct field sound source, which might otherwise tend. to occur.

For the rear passengers, identified as P2, P3 and P4, sitting in a back seat 134, narrow pattern- direct field- sound speakers 140 and 142 are mounted on opposite sides s . on a shelf behind the rear seat and pointed upwardly toward the car ceiling or sloping rear window. In forward, lower portions of the left and right rear doors are", mounted wide dispersion reverberant field speakers of broad frequency range, indicated at 146,148, facing toward

each other. Direct field sound speakers 140 and 142 add to the sound heard by all passengers in the car, including those in both front and back seats. Generally, as is well known, the rear speakers mounted on the shelf will provide improved low frequency sound because of their ability to use the automobile trunk as a resonant cavity. The wide dispersion pattern reverberant field speakers 118,120 mounted in the console are sufficiently loud to provide the desired effect for the passengers in the rear seat, who thus get the same effect from the center console mounted speakers. Thus passenger P2 will hear sound from both the front and rear direct field narrow pattern speakers 114,140 and will hear reverberant field sound (L - R) and (R - L) (as modified by a suitable percentage of (L + R) ) from wide dispersion pattern speakers 146, 124, 126 and 118. similarly passenger P4, on the right side of the rear seat, will hear direct field sound from the nar¬ row pattern speakers 116,142 and reverberant field sound from speakers 120,128,130,148, which provide the dif- ference signals (L - R) and (R - L) (both modified by an appropriate percentage of (L + R) ) . The center rear pas¬ senger P3 hears sound just as does the center passenger in the front seat, hearing an image from a point between the front direct field sound speaker pair 114,116 and an image from a point midway between rear mounted direct field speakers 140,142. The center back seat passenger also hears reverberant field sound from the side mounted rear speakers 146,148, but hears little sound from the console mounted wide dispersion pattern speakers 118,120. Wide pattern speakers 146,148 are also fed with a combination of one-half the sum signal with the difference signals, just as are all the wide pattern speakers.

The described speaker arrangements, in most listening

situations where the speakers are mounted in a room or area of reasonably large size, are independent of listener position, so that the significant advantages of the system may be enjoyed by a listener regardless of his position with respect to the speakers. This advantage of flexible listener position is somewhat diminished in the close con¬ finement of the interior of an automobile. For such a close space the speaker arrangement is preferably modified to suit the specifically predetermined listener position, which, of course, is dictated by the automobile seating arrangement.

The speaker systems described herein are tolerant of walls and other reflective surfaces because the front radiating speaker or speakers provide sound directly to the listener, whereas the wide dispersion pattern speakers -provide sound that is not adversely affected by reflection from walls of the room, inasmuch as such sound is heard as a reflection or reverberation in the live performance.

Furthermore, as can be seen from the exemplary speaker arrangements illustrated in FIGS. 4, 5, 6, 7 and 8, the speaker choice and arrangement can actually be designed to take advantage of various room sizes, situa¬ tions and the walls of the room, but is not dependent on such surfaces for its operation, nor is it dependent upon relative location of listener and speakers, except for the confining situation of an automobile where the listener is very close to the speakers, and the described special speaker arrangement is preferred. Accordingly the system is operable outside of any building where no reflective surfaces exist.

As previously mentioned, the described system is com¬ patible with and complementary to the stereo enhancement system described in the above-identified co-pending patent

application for Stereo Enhancement System. Desirable ef¬ fects of the enhancement system of such co-pending ap¬ plication are augmented by the use of the split mode sys¬ tem described herein in the place of ordinary loudspeakers. Although neither the. present invention nor that described in the co-pending application requires use of the other, use of the two together considerably en¬ hances operation of both.. As previously mentioned, the outputs L IN and L ouτ of the enhancement system of my co- pending application for Stereo Enhancement System may be employed as the inputs L and R of the system illustrated in FIG. 1. Alternatively, the sum, difference and invert¬ ing circuits and also the amplifier, if necessary or desirable, of the system of FIG. 1 may be readily inσor- porated into output portions of the enhancement system of my prior application so that such enhancement system would provide the sum and difference outputs (L + R) , (L - R) , and (R - L) , all based upon signals enhanced as provided in the system of my prior application. The loudspeaker arrangement illustrated and described herein provides almost complete freedom of listener posi¬ tion. Even in the close confinement of an automobile, all passengers and the driver will benefit from these advan¬ tages. This freedom of listener position is of particular importance in application of this system to a theater, where many listeners are seated in various different areas.