AU2004202113A1 - Depth render system for audio - Google Patents

Description

Complete Specification Standard Patent 17 May 2004 Date: Inventors: Zeljko Velican Title: DEPTH RENDER SYSTEM FOR AUDIO Applicant: Zeljko Velican The following statement is a full description of this invention, including the best method of performing it known to me.

DEPTH RENDER SYSTEM FOR AUDIO Field of the Invention The present invention relates to sound reproduction systems for the presentation of depth or distance information.

Background of the Invention In the past, efforts to present depth or distance dimensions in sound reproduction have concentrated on directional clues combined with direct to reverberant sound ratios and known source scaling to give the feeling or impression of depth. This has resulted in surround sound systems where loudspeakers are distributed around the perimeter of a listening environment and often in locations equidistant from a single listening position referred to as the sweet spot in the art. Further efforts to improve the perception of depth have used modified spectral response and amplitude of signals in one or more electro-acoustic transducers such as loudspeakers or headphones based on the Head Related Transfer Function (HRTF), as known in the art, or acoustic cross-talk cancelling for a listener in an attempt to create the impression of sound directions other than where the electro-acoustic transducers is placed.

This has been combined with direct to reverberant sound ratios and reverberation effects to give the impression of a suitably sized acoustic space with implied distance or depth information.

Yet other efforts to present depth or distance dimensions have used time delayed audio signals in one or more apparatus corresponding to distances of different objects by giving the impression or illusion of a reverberant space and direct to reverberant sound ratio giving the feeling of distance or depth.

In all cases, the approach has been to present the illusion of distance or depth and no approaches or apparatus in the art have directly used the ability of the hearing apparatus of the human head to directly determine distance by interaural processing and frequency selective trigonometry, as this ability has not been widely understood in the art.

Limitations of prior art approaches include restricted listening locations where the effects work, unnatural acoustic image behaviour or breakdown of the effect when the listener turns or moves, lack of effectiveness for a wide range of listeners because of HRTF differences, complex signal processing, and critical loudspeaker placement. Where headphones have been used, the acoustic image behaviour has been unnatural when turning or moving, the reproduced sound effect has been replicated rather than correctly presented for multiple headphone wearers and so the format is not able to be a shared environment.

Many listeners find the headphone device is invasive and inconvenient, stopping natural conversing between listeners.

Summary of the Invention The object of the present invention is to provide a more effective system of sound reproduction for depth presentation than is known in prior art, and this is achieved by means of a novel loudspeaker placement scheme. The main characterising feature of the invention is the arrangement of loudspeakers of similar form and controlled radiation pattern in a radial pattern relative to a listening position and fed with differing signals corresponding to sounds from spatially separated locations. The arrangement of the present invention is not to be confused with dual cone, triple cone, 2-way or 3-way coaxial electro-acoustic transducers where each electro-acoustic transducer is designed to operate in a different frequency range.

The principles behind the invention are: to create a genuine radial sound field that corresponds to the sound field of a source environment as distinct from the depthless field of a surround sound system; to spread out the elements of a sound field by means of relative signal levels from two or more loudspeakers as is done in stereo for example; and to engage the natural ability of human ears to triangulate the location of sound sources.

A further objective of the present invention is to significantly broaden the sweet spot of a listening environment. In the present invention this is achieved by default in that the sound images created are viewable from different angles and different locations apart from a nominal listening position.

Description of the Invention Preferred embodiments of the present invention will now be described with reference to the following drawings: Figure 1 shows a layout of a depth render set comprising two loudspeakers according to the present invention.

3 Figure 2 shows a layout of a depth render set comprising three loudspeakers according to the present invention.

Figure 3 shows a depth render arrangement comprising four depth render sets according to the present invention.

Figure 4 shows a staggered alignment variation of the present invention.

For the sake of clarity a radial line of loudspeakers relative to a listening position is referred to as a "Depth Render set".

In one form of the invention, a loudspeaker system for the presentation of an acoustic image having depth or distance dimensions, to a listener comprises: at least one set of loudspeakers, with similar frequency response and well defined polar spectral characteristics, arranged in a substantially radial alignment relative to a listening position such that at least one loudspeaker is close to the listening position and at least one loudspeaker is distant from the listening position, provision for a separate signal source for each loudspeaker corresponding to sounds from spatially separated locations, and a sound level alignment that causes the sounds to spread out in distance relative to the listening position.

Ideally the intervening distances between the listening position and subsequent loudspeakers are of similar size. However considerable variation of the intervening distances is possible before the effectiveness of the depth render arrangement becomes unsatisfactory.

The sound level alignment may be achieved quite efficiently by trial and error.

In a two loudspeaker alignment, for example, the level of say the close loudspeaker may be varied until the sounds spread out to the listener's satisfaction while listening to program material. Another option is to follow a rule of thumb that each loudspeaker is set at the same level measured from the listening position. Ideally levels are pre-set in the recording media so that simple built in test tones may be used to set loudspeaker levels.

In a preferred embodiment the loudspeakers are high accuracy point sources and the loudspeakers closer to the listening position are arranged so as not to block the radiation from the loudspeakers more distant from the listening Sposition. The arrangement may be achieved by making the closer loudspeakers of small size and/or placing them at a lower or higher level than the more distant ones. The simplest system would consist of just one pair of loudspeakers, one behind the other with the distant one typically twice as far away from the listening position as the closer one. An example of a Depth Render set comprising two loudspeakers 2, 3 and their typical positioning relative to a listening position 1 is shown in Figure 1. In the arrangement of Figure 1, the distant loudspeaker 3 is typically twice the distance from the listening position 1 as the closer loudspeaker 2. An example of a Depth Render set comprising three loudspeakers 2, 3, 4 and their positioning relative to listening position 1 is shown in Figure 2. In the arrangement of Figure 2 the distances to the second 3 and third 4 loudspeakers from the listening position 1 are respectively typically twice and three times the distance of the first 2 from the listening position 1. The signals fed to each loudspeaker of a Depth Render set are normally derived from recordings of sounds occurring at spatially separated locations. Signals for Depth Render sets may also be simulated by creating a relative time separation between different components of the relative signals to the loudspeakers of a Depth Render set. Phase and frequency profiles may also be varied to enhance the suitability of simulated signals. The simulation of signals is not a characterising feature of the present invention but it forms part of the scope of the invention.

The invention may be implemented as a single Depth Render set to provide a localised three dimensional field in front of the listening position.

The three dimensional field may be expanded by employing a stereo arrangement of Depth Render sets.

Depth Render sets may also be arranged in three or more different directions to provide a surround effect. A four set depth render arrangement is shown in Figure 3, where it can be seen that loudspeakers 2 are closer to the listening position 1 than loudspeakers 3 and the radial pattern is obvious.

While single or multiple Depth Render sets are aligned to radiate away from a nominal listening position, it is important to understand that the listener may move away from the listening position so as to experience the three dimensional field from a different angle.

In a further embodiment virtual loudspeakers may be created using pairs of loudspeakers consisting, for example, of one loudspeaker near floor level and preferably flush with the floor and one loudspeaker above listening height, possibly suspended from the ceiling. Such an arrangement creates a virtual loudspeaker somewhere between if the same signal is fed to both loudspeakers. If signal levels are equal, the virtual image will be typically half way between. Alternatively a virtual loudspeaker may be created by a left and right pair of loudspeakers as would occur with stereo loudspeakers if both were fed with identical signals. Alignment is less critical in the vertical plane and it is possible to achieve satisfactory results with just a single misaligned loudspeaker in the vertical plane.

As an example using a virtual loudspeaker, the present invention could be implemented using a virtual speaker consisting of a loudspeaker in the floor and a ceiling mounted loudspeaker in place of the close loudspeaker of a Depth Render set. However for a less critical but still effective result either one of the vertical pair could be eliminated. Ceiling mounted loudspeakers may be mounted in the ceiling or suspended from the ceiling.

In the horizontal plane alignment is more critical, because human ears are on a horizontal plane. However even in the horizontal plane considerable misalignment is possible before the result becomes unsatisfactory. For example a misalignment of 30 degrees in the case of a single Depth Render set will sustain a satisfactory depth effect but with a different perspective than a perfect alignment.

A further consequence of the suitability of virtual loudspeakers is that the radial lines of loudspeakers may consist of a real and a virtual loudspeaker on the radial line. Accordingly an acceptable depth render arrangement could be created by two circles of loudspeakers, one circle being typically twice the radius of the other. The loudspeakers of one circle may then be staggered at angles half way between the angles of the loudspeakers of the other circle.

They would create virtual loudspeakers that were in line with loudspeakers in the other circle. Figure 4 provides an example of a depth render arrangement where staggered positioning of loudspeakers produces a radial alignment pattern by means of virtual loudspeakers. With regard to Figure 4, each adjacent pair of the four loudspeakers 3 may be represented by a virtual loudspeaker at the centre of the pair (not shown). The virtual loudspeakers so formed would be in radial alignment with loudspeakers 2 relative to the listening position 1.

In a near field example of the present invention three Depth Render sets each radiating in a direction substantially 120 degrees from the others are attached to a seat in a listening room where a listener would normally sit. The closer loudspeaker of each Depth Render set may be say 150 mm from the listener's head. The distant loudspeaker of each Depth Render set may be say 300mm from the listener's head.

In another form a Depth Render set may be constructed as a single enclosure for near field listening.

The present invention may be implemented in a vehicle by installing one or more loudspeakers close to the listening positions, such as in the front of the dash or on the steering wheel or in the head lining or visor, and one or more loudspeakers well forward of the listening positions such as in the dash near the windscreen, the close and well forward loudspeaker(s) being fed with signals corresponding to sounds from spatially separated locations.

The main practical consideration for the provision of a depth render arrangement according to the present invention is how to get around the problem of loudspeakers in inconvenient locations. One solution to this problem is to locate the loudspeakers under-floor and to feed the sound into a room through ports or floor grills. The floor grills may be flush mounted and strong enough to bear the weight of foot traffic.

Finally it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

Zeljko Velican 17t' May 2004

Claims (11)

1. A loudspeaker system for the presentation of an acoustic image having distance dimensions to a listener comprising: at least one set of loudspeakers, with similar frequency response and well defined polar spectral characteristics, arranged in a substantially radial alignment relative to a listening position such that at least one loudspeaker is close to the listening position and at least one loudspeaker is distant from the listening position, provision for a separate signal source for each loudspeaker corresponding to sounds from spatially separated locations, and a sound level alignment that causes the sounds to spread out in distance relative to the listening position.

2. A loudspeaker system according to claim 1 wherein more than one set of loudspeakers are arranged in a substantially radial alignment relative to a listening position and each set of loudspeakers is aligned in a significantly different direction.

3. A loudspeaker system according to claims 1 and 2 wherein at least one of the loudspeakers in a set location is replaced by two other loudspeakers, one replacement loudspeaker being near floor level below the set location and the other replacement loudspeaker being above head height above the set location.

4. A loudspeaker system according to claims 1 and 2 wherein at least one of the loudspeakers in a set location is replaced by two other loudspeakers, one replacement loudspeaker being to the left of the set location and the other replacement loudspeaker being to the right of the set location.

A loudspeaker system having at least one set of loudspeakers according to claims 1 and 2 wherein the loudspeakers of the at least one set are constructed into a single enclosure.

6. A floor constructed with port holes and under-floor space specifically to adapt a loudspeaker system according to claims 1 and 2.

7. A loudspeaker system according to claims 1 and 2, wherein the loudspeakers are attached via a mounting structure to a seat at the listening position.

8. A loudspeaker system according to claims 1 and 2 installed in a vehicle, wherein at least one loudspeaker is mounted close to and forward of the 8 listening position(s) and at least one loudspeaker is mounted well forward of the listening position(s).

9. A loudspeaker system for the presentation of an acoustic image having distance dimensions, to a listener comprising: a close set of loudspeakers and a distant set of loudspeakers relative to a listening position such that the distant set are at staggered angles relative to the close set, provision for a separate signal source for each loudspeaker corresponding to sounds from spatially separated locations, a sound level alignment that causes the sounds to spread out in distance relative to the listening position.

A loudspeaker system according to any of the preceding claims wherein the separate signal source for each loudspeaker includes a modified or simulated signal which appears to come from a spatially separate location.

11. A loudspeaker system according to any one of the preceding claims wherein each loudspeaker is a close approximation to a point source.