Systems and methods for delivering full-bandwidth sound to an audience in an audience space

Abstract

A system and method for delivering full-bandwidth sound to an audience in an audience space located in front of an acoustically reflective image screen (such as a plasma, LCD, LED, or OLED screen). The sound delivery system includes one or more high-frequency speakers for reproducing high-frequency components of sound associated with an image displayed on the acoustically reflective image screen, one or more low-frequency speakers for reproducing low-frequency components of sound associated with the image on the acoustically reflective image screen, a crossover for dividing a full-bandwidth audio input signal into a high-audio signal input and a low-audio signal input for the high-frequency speakers and the low-frequency speakers, respectively, the high-frequency speakers having an operating frequency range, the high-frequency speakers being located in front of the acoustically reflective image screen and tilted toward the image screen such that sound emitted by the high-frequency speakers in response to the high-audio signal input is reflected from the image screen.

Description

Technical Field

[0001] The present invention generally relates to the field of sound systems, and more particularly, to a sound system that produces sound that is spatially and contextually associated with an image displayed on an image screen. The present invention has a particular application in a cinema, where viewers sitting in front of a cinema screen watch a movie, documentary, or other content on the screen while listening to an associated soundtrack via speakers critically placed within the cinema space. However, it will be seen that the present invention can be applied to any application where sound associated with one or more images, whether moving or static, must be delivered to a viewer (whether one or more viewers) in such a way that the sound appears to come from the image or a general area of the image. Background Art

[0002] There is a long history of projecting movie images onto a projection screen that reflects the images back into a viewer space for viewing by the viewers. This is a typical cinema. In a typical cinema, the movie screen is essentially transparent to sound, and the soundtrack associated with the movie is typically played via speakers placed behind the projection screen. Additional speakers may be added to the sides of the viewer space for surround sound effects, but the main sound comes from, and importantly, the viewers will perceive the main sound as coming from the projection screen where the image is displayed.

[0003] With the maturation of new light-emitting screen technologies such as plasma, LCD, LED, and OLED, light-emitting screens have become practical and cost-effective in movie exhibition and are seen as a viable alternative to traditional reflective projection screens. (LCD screens are sometimes referred to as "transmissive" displays because the LCD layer of the screen transmits the light generated by the backlight.) These newer screen technologies have been widely used in applications such as home theaters and conference and seminar spaces. However, the difficulty with light-emitting screens is that they do not have any useful degree of transparency to sound. This creates a problem in creating the desired association of sound with image display in large screen applications. And it presents particular problems in cinema applications and meeting cinema standards for center channel sound, which is typically achieved using speakers behind the screen. A solution is needed for making the sound appear to come from the emissive screen (which does not require speakers to be placed behind the movie screen), but still achieving the goal of making the viewers believe that the sound is coming from the screen. Summary of the Invention

[0004] The present invention relates to a system and method for delivering full bandwidth sound to an audience in an audience space located in front of an acoustically reflective image screen, and in particular a relatively large acoustically reflective image screen. The image screen can be a self-emitting screen that generates its own image, such as a large plasma, LED or OLED screen, or a projection screen capable of reflecting sound at a higher frequency (e.g., above 500 Hz). The system and method of the present invention will enable full bandwidth sound to be delivered to an audience that is spatially and contextually associated with the image displayed on the image screen, and in particular will make it appear as if the full bandwidth sound is coming from the image screen. The system and method of the present invention replicates the experience of speakers behind a traditional screen in situations where it is not possible to place speakers behind the screen.

[0005] The system of the present invention includes two separate and spatially displaced sound sources, namely a high-frequency speaker for receiving and reproducing the high-frequency components of the sound associated with the image displayed on the acoustically reflective image screen, and a separate low-frequency speaker for receiving and reproducing the low-frequency components of the sound associated with the image. A cross-over divides the full bandwidth audio input signal into high-frequency and low-frequency components for driving the high-frequency and low-frequency speakers. It is contemplated that in most implementations of the present invention, more than one high-frequency speaker and more than one low-frequency speaker will be used, however, the present invention is not intended to be limited to the use of any particular number of high-frequency or low-frequency speakers.

[0006] According to the present invention, the high-frequency speaker(s) is / are located in front of the acoustically reflective image screen and tilted towards the image screen such that the sound emitted by the high-frequency speaker(s) in response to an audio signal input is reflected off the image screen. The high-frequency speaker(s) will have a directivity pattern that meets the following criteria: the directivity pattern is large enough so that the high-frequency speaker sound reflected from the image screen covers the audience space, but it is also small enough so that the direct sound from the high-frequency speaker does not extend into the audience space. On the other hand, the low-frequency speaker is located at or around the acoustically reflective image screen and is directed such that the low-frequency sound generated by the low-frequency speaker in response to an audio signal input is received by the audience as direct sound from the low-frequency speaker. Thus, when the combined sound reaches the audience, the audio experience of the audience associated with one or more images on the image screen is determined by combining the high-frequency components of the sound reflected from the image screen with the low-frequency components of the sound received directly from the low-frequency speaker. The cross-over from the low-frequency components of the sound to the high-frequency components preferably occurs in the range of about 350 to about 1000 Hz, however, it is contemplated that the cross-over may occur as low as about 150 Hz and as high as 1500 Hz.

[0007] To compensate for the difference in the lengths of the acoustic paths that the reflected and direct components of the sound must travel, a signal delay is placed in front of the (one or more) low-frequency loudspeakers. This delay will align in time the direct sound from the low-frequency loudspeakers reaching the audience space with the arrival of the sound from the high-frequency loudspeakers reflected from the display screen.

[0008] Preferably, one or more high-frequency loudspeakers will be located in front of the image screen at a distance not greater than the distance of the audience from the display screen and preferably at a distance roughly corresponding to the front row of the audience. This placement of the high-frequency loudspeakers will avoid the risk that any part of the audience will hear the reflected and direct sound from the high-frequency loudspeakers simultaneously.

[0009] In accordance with the method of the present invention, full-bandwidth sound is delivered to an audience in an audience space located in front of an acoustically reflective image screen that displays one or more static or moving images being viewed by the audience. The full-bandwidth sound delivered to the audience is spatially and contextually associated with the images displayed on the image screen. From a position in front of the image screen, the high-frequency components of the sound associated with the images displayed on the acoustically reflective image screen are directed towards the image screen such that the high-frequency components of the sound reach the audience only as reflected sound. From a different position, namely, at or around the acoustically reflective image screen, the low-frequency components of the sound associated with the images on the acoustically reflective image screen are directed towards the audience such that the low-frequency components of the sound reach the audience not as reflected sound but as direct sound, that is, the sound travels directly from its source to the audience. To time-align these two components of the full-bandwidth sound when they are combined and reach the audience, the low-frequency components of the full-bandwidth sound are delayed relative to the high-frequency components of the full-bandwidth sound. The listener perceives the combined and time-aligned frequency components of the full-bandwidth sound as coming from a single source spatially located in the screen area.

[0010] Thus, the systems and methods of the present invention solve the problem of creating a desired sound experience associated with an image display, such as a movie or video presentation, where an image screen that prevents traditional loudspeaker deployment behind the image screen is used. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is an elevation view of an exhibition room, such as a cinema, having a conventional sound-transmissive movie screen and loudspeakers behind the movie screen such that the audience receives full-bandwidth sound as direct sound.

[0012] Figure 2 FIG. 2 is an elevation view of the exhibition room as shown in FIG. 1, having an exemplary vertical plane arrangement of an acoustically reflective image screen and separate high-frequency and low-frequency loudspeakers in accordance with the present invention.

[0013] Figure 3 FIG. 3 is the same elevation view of the exhibition room showing an alternative vertical plane arrangement of the low-frequency loudspeakers.

[0014] Figure 4 This is the same elevation view of the exhibition room showing an exemplary straight - planar arrangement with two low - frequency speakers instead of one low - frequency speaker.

[0015] Figure 5 This is as Figures 2 to 4 shown in the floor plan of the exhibition room as explained therein, which shows the deployment of a single - center - channel high - frequency speaker and a single - center - channel low - frequency speaker in the horizontal plane.

[0016] Figure 6 This is as Figures 2 to 5 shown in the floor plan of the exhibition room as shown therein, which explains an exemplary horizontal - plane arrangement of three high - frequency and three low - frequency speakers according to the present invention.

[0017] Figure 7 This is a block diagram of an exemplary implementation of signal processing for driving separate high - frequency and low - frequency speakers of a system and method according to the present invention. Detailed Description

[0018] The embodiments of the present invention illustrated in the accompanying drawings show the implementation of the present invention in an audience space, such as a cinema having a light - emitting image screen (image screen). However, it will be understood that the present invention is not limited to video display of images. For example, a museum can use a speaker system according to the present invention to associate sound with a static image or a perspective view so that the sound appears to come from the image or perspective view. What is required is a surface that can reflect high - frequency sound energy to a sufficient extent so that an audience located in front of the surface can hear that component of the desired wider - bandwidth sound with reasonable clarity. The surface serves as an image screen. Thus, as used herein, "image screen" shall refer to any surface that displays a moving or static image by projecting an image onto the surface or by generating an image on the surface by any light - emitting technology, whether currently known or unknown.

[0019] Referring now to the drawings, FIG. 1 shows a building 10 having an exhibition room 11 with an audience space 12 in which an audience 13 is seated. FIG. 1 represents a movie screening room or a meeting room where there is a conventional acoustically transparent projection screen 15 onto which an image such as a movie image is projected by a projector 17 behind the audience, as depicted by the virtual projection light - cone lines 19. A speaker 21 (in this case a full - range speaker) is located behind the acoustically transparent image screen and is directed towards the audience. The sound emitted from the speaker behind the screen is emitted in a coverage (pointing) pattern depicted by the solid sound - cone lines 23, and it can be seen that the coverage pattern is wide enough to cover the entire audience, including the front row 14 of the audience. In this conventional sound - system design, the sound heard by the audience comes from behind the projection screen. As a result, the sound system achieves the desired result of spatially associating the sound with the image on the screen.

[0020] Note that in Figure 1, as shown in the following figure, the audience seating arrangement is a representative arrangement for illustrative purposes only. The seating arrangement may vary widely in configuration and size and may include balcony space. The selection and deployment of speakers will need to take into account these different audience seating configurations and audience sizes. Ideally, the speaker system design will provide uniform coverage over the entire audience space.

[0021] Figures 2 to 5 Building 10 is illustrated, whose exhibition room 11 is similar to the exhibition room shown in Figure 1. However, in this exhibition room, instead of a sound-transparent projection screen, there is an image screen 25 in the form of an image screen 25 that is not transparent to sound but reflects sound. Since the image screen provides little or no sound transparency, a sound system capable of spatially correlating full-bandwidth sound with the image on the screen viewed by the audience 13 cannot rely on speakers placed behind the image screen.

[0022] In Figures 2 to 5 the solution provided by the present invention is illustrated. As shown in these figures, two separate speakers 27, 29 (also referred to as "transducers" or "drivers") are physically displaced from each other, one at a distance in front of the image screen 25 and the other near the image screen. Neither is placed behind the image screen. The first of these two independent speakers, represented by the numeral 27 and located in front of the image screen, is a high-frequency speaker, sometimes referred to herein as a "tweeter". This speaker reproduces the high-frequency components of the audio program for the image displayed on the image screen and is tilted towards the image screen so that the image screen, which again has acoustic reflection, reflects the high-frequency components of the sound from this speaker back to the audience.

[0023] Figures 2 to 5 It is illustrated how a high-frequency speaker is deployed in front of the image screen to be equivalent to a high-frequency speaker having the same height and distance behind the image screen. This can be referred to as a "virtual" speaker because it does not physically exist but illustrates how to replicate the coverage of a speaker placed behind a conventional sound-transparent image screen from a speaker in front of an image screen that is not transparent to sound.

[0024] The virtual speaker is in Figures 2 to 5In the figure, it is depicted by the imaginary speaker 27p with a dashed line. The coverage of the actual speaker 27 is represented by the solid lines 31a and 31b, where the line 31a represents the travel of the direct sound from the speaker 27 to the image screen, and the line 31b represents the travel of the sound reflected from the image screen to the audience. The coverage of the sound traveling from the virtual speaker 27p behind the image screen is represented by the dashed line 33 behind the screen and the solid line 31b in front of the screen. It can be seen that in front of the image screen, the coverage provided by the virtual speaker 27p is equivalent to the coverage provided by the actual speaker 27. As will be further discussed below, importantly, the high-frequency speaker is directional and has a directivity pattern that conforms to certain limitations to achieve the desired coverage.

[0025] The second of the two required speakers, represented by the numeral 29, is a low-frequency speaker (sometimes referred to herein as the "woofer"). This speaker reproduces the low-frequency components of the audio program for the images displayed on the image screen. As Figure 2 seen, it is located directly above the image screen and points outward towards the audience so that the audience can directly receive the sound from this speaker from the speaker. The speaker 29 will excite the room reverberation, just as a woofer located behind the video projection screen does. Since the human ear has difficulty in localizing low-frequency sources, the low-frequency components of the audio program for the images can be easily associated with the screen images despite the fact that the speaker is not directly located behind the display screen.

[0026] It will be appreciated that one or more low-frequency speakers may be deployed at Figure 2 locations other than the location shown in Figures 3 to 4 An exemplary alternative for the deployment of the low-frequency speaker is shown in Figure 3 where Figure 2 two low-frequency speakers are shown, one (speaker 29) deployed above the image screen, as Figure 4 explained in the deployment of the low-frequency speaker as shown in

[0027] As described above, in addition to its location and pointing angle, the high-frequency speaker 27 must be directional. Within its operating frequency range, its directivity in the vertical and horizontal planes should be wide enough so that the sound reflected from the image screen covers the audience. However, its vertical directivity cannot be too wide so that it does not extend into the audience space, because being exposed to the direct sound in addition to the reflected sound is a highly distracting and unpleasant experience for anyone in the audience. Figure 3The cut-off angle, designated as "A" in the figure, meets this requirement. Ideally, the sound pressure level (SPL) generated by the high-frequency speaker will drop rapidly at this cut-off angle. Nor should it produce any significant side lobes that would cause any substantial direct sound leakage into the audience space.

[0028] The distance of the high-frequency speaker in front of the screen is a consideration in achieving the above objectives. Generally, the high speaker cannot be too close to the screen because it will be difficult to achieve the desired audience coverage and the speaker may visually block the view of the image screen. On the other hand, placing the high speaker too far from the screen may place some of the audience within the direct radiation pattern of the speaker. Preferably, as Figures 2 to 6 shown, the high speaker will be located at a distance in front of the image screen that roughly corresponds to the front row 14 of the audience 13; however, with suitable directivity and no significant side lobes, it can be placed behind this position.

[0029] Regardless of its location, the vertical and horizontal directivities of the high-frequency speaker used in the system and method of the present invention will generally be narrower than those of conventional behind-screen speakers. This is because the distance that the sound from the high speaker 27 has to travel to reach the audience is much greater than the direct path traveled by the sound generated by the behind-screen speaker. The required directivity can be achieved by a commercial horn speaker or a direct radiator line array, where the directivity is achieved through signal processing rather than the horn.

[0030] However, the required directivity cannot be achieved at low frequencies. Generally, it is impractical to achieve meaningful directivity from a speaker at frequencies well below 500 Hz. Providing spatially separated high- and low-frequency sound sources as described herein provides a solution to this problem. When implementing the system and method of the present invention, within limits, the crossover between the high speaker and the low speakers 27, 29 can occur above and below 500 Hz. Preferably, the crossover will occur somewhere in the range of about 350 Hz to about 1000 Hz; however, it is anticipated that an effective system can be achieved with the crossover occurring as low as 150 Hz and as high as 1500 Hz.

[0031] Finally, the present invention provides for delaying the sound generated by the low-frequency transducer so as to time-align the sound from the low speaker 29 with the sound from the high speaker 27, which has a longer travel path before reaching the audience. Amplitude and phase equalization can be applied to the signal inputs of the low and high speakers so that they add in phase in the range of the crossover frequency. Additionally, amplitude and phase equalization can be applied to the overall signal to account for boundary loading to synchronize the sound with the video and for other purposes.

[0032] Figure 6The system according to the present invention as viewed on a horizontal plane is explained. The system consists of three high-frequency directional speakers deployed in front of the image screen 25, namely the central channel high speaker 27 and the left and right channel speakers 27a and 27b. The deployment and the criteria of the directional characteristics of these three high-frequency speakers (which can be represented by their virtual cousins 27p, 27ap, and 27bp) are the same as those described above for the system with only a single high-frequency speaker. See Figures 2 to 5 . Figure 6 The system explained in Figures 2 to 5 is also seen to have three low-frequency speakers 29, 29a, 29b, which are deployed near the image screen. As in the exemplary system shown in

[0033] Figure 7 An exemplary implementation of signal processing that can be used in conjunction with the system and method of the present invention is shown. The audio input signal 40 is shown passing through a crossover 41, which divides the audio input into low-frequency and high-frequency components. The high-frequency component is sent as a high audio signal input via the high-frequency channel 43 to the high-frequency speaker 27, while the low-frequency component is sent as a low audio signal input via the low-frequency channel 45 to the low-frequency speaker 29. Each of these channels appropriately includes its own phase and amplitude correction, as represented by the phase correction blocks 47, 49 and the amplitude correction blocks 51, 53. Additionally, the signal processing in the low-frequency channel provides a delay function, where the low audio signal input to the low-frequency speaker 29 is delayed relative to the high audio signal input to the high-frequency speaker 27. As described above, the delay compensation in the low channel represented by the box 55 in Figure 7 corrects for the longer path that the sound from the high speaker must travel to reach the viewer.

[0034] It will be appreciated that Figure 7 the functions of the signal processing explained in Figure 7 can be implemented in a variety of different ways using analog circuits or digital signal processing.

[0035] Although the systems and methods of the present invention have been described in considerable detail in the foregoing specification and drawings, the present invention is not limited to such details. It will be apparent to those of ordinary skill in the art that variations of the described embodiments are possible without departing from the spirit and scope of the present invention as reflected in the following claims. The systems and methods of the present invention are also not limited to the applications described herein. Other applications, whether currently known or unknown, are possible or may be possible in the future, also without departing from the spirit and scope of the present invention as reflected in the following claims.

Claims

1. A system for delivering full-bandwidth sound to an audience in an audience space located in front of an acoustically reflective image screen, characterized in that, the acoustically reflective image screen displays one or more static or moving images viewed by the audience, and wherein the full-bandwidth sound delivered to the audience is spatially and contextually associated with the images displayed on the acoustically reflective image screen, the system comprising: one or more high-frequency speakers for reproducing the high-frequency components of the sound associated with the images displayed on the acoustically reflective image screen, one or more low-frequency speakers for reproducing the low-frequency components of the sound associated with the images displayed on the acoustically reflective image screen, a crossover for dividing a full-bandwidth audio input signal into a high-audio signal input and a low-audio signal input for the high-frequency speakers and the low-frequency speakers respectively, the high-frequency speakers having a working frequency range, the high-frequency speakers being located in front of the acoustically reflective image screen and being tilted towards the acoustically reflective image screen such that the sound emitted by the high-frequency speakers in response to the high-audio signal input is reflected from the acoustically reflective image screen, the high-frequency speakers all having a directivity pattern conforming to the following criteria: within the working frequency range, the directivity pattern is large enough in the horizontal direction so that the sound of the high-frequency speakers reflected from the acoustically reflective image screen covers the audience space, but small enough in the vertical direction such that the direct sound from the high-frequency speakers does not extend into the audience space, the high-frequency speakers provide the only high-frequency sound reaching the audience space that is associated with the images displayed on the acoustically reflective image screen, wherein the only high-frequency sound perceived by the audience that is associated with the images displayed on the acoustically reflective image screen is the sound from the high-frequency speakers reflected from the acoustically reflective image screen, the low-frequency speakers are located at or around the acoustically reflective image screen and are directed such that the low-frequency sound generated by the low-frequency speakers in response to the low-audio signal input is received by the audience as direct sound, and delay compensation in front of the low-frequency speakers for delaying the sound generated by the low-frequency speakers relative to the sound generated by the high-frequency speakers so as to align in time the direct sound from the low-frequency speakers reaching the audience space with the sound from the high-frequency speakers reflected from the acoustically reflective image screen.

2. The system according to claim 1, characterized in that, the crossover between the high-audio signal input and the low-audio signal input for the high-frequency speakers and the low-frequency speakers occurs between 150 Hz and 1500 Hz.

3. The system according to claim 1, characterized in that, the crossover between the high-audio signal input and the low-audio signal input for the high-frequency speakers and the low-frequency speakers occurs between 350 Hz and 1000 Hz.

4. The system according to claim 1, characterized in that, the high-frequency speakers are horn speakers having a directivity pattern conforming to the criteria.

5. The system according to claim 1, wherein, the high-frequency loudspeaker is a line array loudspeaker having a directivity pattern conforming to the standard.

6. The system according to claim 1, wherein, the high-frequency loudspeaker is located at a distance in front of the acoustic reflective image screen, and the distance is not greater than the distance between the front audience space and the acoustic reflective image screen.

7. The system according to claim 1, wherein, the low-frequency loudspeaker is located above the acoustic reflective image screen and is directed towards the audience space.

8. The system according to claim 1, wherein, the low-frequency loudspeaker is located below the acoustic reflective image screen and is directed towards the audience space.

9. The system according to claim 1, wherein, the low-frequency loudspeaker is located behind an opening in the acoustic reflective image screen and is directed towards the audience space.

10. A system for delivering full-bandwidth sound to an audience in an audience space in front of an acoustic reflective image screen, wherein, the acoustic reflective image screen displays an image for the audience to view, and the full-bandwidth sound delivered to the audience is spatially and contextually associated with the image displayed on the acoustic reflective image screen. The system includes: a directional high-frequency sound source located in front of the acoustic reflective image screen and directed towards the acoustic reflective image screen, such that the sound emitted by the high-frequency loudspeaker in response to a directional high-frequency audio signal input is reflected from the acoustic reflective image screen. The directional high-frequency sound source is located in front of the acoustic reflective image screen relative to the audience, such that the direct sound from the high-frequency loudspeaker does not extend vertically downwards into the audience space, the directional high-frequency sound source located in front of the acoustic reflective image screen provides the only high-frequency sound reaching the audience space that is associated with the image displayed on the acoustic reflective image screen. The only high-frequency sound perceived by the audience that is associated with the image displayed on the acoustic reflective image screen is the sound from the high-frequency loudspeaker reflected from the acoustic reflective image screen, a low-frequency sound source located at or around the acoustic reflective image screen and directed towards the audience space, such that the sound emitted by the low-frequency sound source in response to a low-frequency audio signal input is received by the audience as direct sound from the low-frequency loudspeaker, and a signal delay device for delaying the sound generated by the low-frequency loudspeaker relative to the sound generated by the high-frequency loudspeaker, so as to align the arrival of the direct sound from the low-frequency loudspeaker reaching the audience space with the arrival of the sound from the high-frequency loudspeaker reflected from the acoustic reflective image screen in time.

11. The system according to claim 10, wherein, the crossover between the high-frequency audio signal input for the high-frequency loudspeaker and the low-frequency audio signal input for the low-frequency loudspeaker occurs between 150 Hz and 1500 Hz.

12. The system according to claim 10, wherein, The crossover between the high-frequency audio signal input and the low-frequency audio signal input for the high-frequency speaker and the low-frequency speaker occurs between 350 Hz and 1000 Hz.

13. The system according to claim 10, wherein, the high-frequency speaker is located at a distance in front of the acoustic reflective image screen, and the distance is not greater than the distance between the audience and the acoustic reflective image screen.

14. A method for delivering full-bandwidth sound to an audience in an audience space in front of an acoustic reflective image screen, wherein, the acoustic reflective image screen displays one or more static or moving images viewed by the audience, and the full-bandwidth sound delivered to the audience is spatially and contextually associated with the images displayed on the acoustic reflective image screen, the method comprising: guiding the high-frequency component of the sound associated with the images displayed on the acoustic reflective image screen from a position in front of the acoustic reflective image screen to the acoustic reflective image screen such that the high-frequency component of the sound associated with the images displayed on the acoustic reflective image screen reaches the audience only as reflected sound, preventing the high-frequency component of the sound associated with the images displayed on the acoustic reflective image screen from reaching the audience space directly without first reflecting from the acoustic reflective image screen, guiding the low-frequency component of the sound associated with the images on the acoustic reflective image screen from a position located on or around the acoustic reflective image screen to the audience such that the low-frequency component of the sound reaches the audience as direct sound, and delaying the low-frequency component of the full-bandwidth sound relative to the high-frequency component of the full-bandwidth sound to temporally align the two components of the full-bandwidth sound when they are combined and delivered to the audience.

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