Articles and whitepapers

airSOUND Single Point Stereo Technology - a unique solution to the problems of conventional stereo for CI (3/12/2007)

By Alan Johnson, Airsound LLP

airSOUND single-point stereo is a unique development from Airsound LLP, a new British technology company. Instead of discrete left and right speaker channels providing a true stereo image within a limited 'hot spot', airSOUND provides a uniform stereo signal from a single enclosure, with an arrangement of drivers reproducing the main signal information and the spatial signal information separately.

This 'single point' principle of reproduction originates from the earliest work on stereo sound. Its development to successfully reproduce high quality audio is the result of airSOUND patented technology. All of the technology, including airSOUND encoding amplifiers, is integrated within the single enclosure, enabling the simple connection of a standard left/right stereo signal.

An airSOUND enclosure radiates stereo sound throughout the room, without any on/off axis phase and frequency anomalies and other major physical limitations of conventional stereo. The high-quality, high-intelligibility signal provides significant performance advances over conventional stereo in all types of applications and environments. With airSOUND reproduction, the unique stereo performance is accompanied by a marked improvement in audio quality, particularly in products using low-cost, commodity components.

As a scalable technology, airSOUND can be applied to all forms of residential and commercial audio installation. Real stereo reproduction is available from single in-ceiling and in-wall enclosures of any size, from mounted cabinets, and high-definition compact audio enclosures for flatscreen TV, iPod dock units and entertainment products of all kinds.

A solution to the intrinsic problems of conventional stereo sound reproduction

The well-recognised constraints of conventional stereo include the phase and frequency imbalances outside of the fixed 'sweet spot', and the requirement to accommodate speakers far enough apart to create a proper sound field. This effectively makes conventional two-channel stereo an impractical form of reproduction in the majority of residential and commercial environments where audio systems are required to be installed. The inherent deficiencies resulting from the generation of a stereo sound field from separated speaker enclosures - timing discrepancies and frequency cancelling effects outside of the optimum listening position - are exaggerated still further by any increase in the degree of reflected sound reaching the listener, and are the cause of the poor sound quality that mars the performance of so many audio installations.

Single-point stereo reproduction has been the pursuit of audio engineers for years, given the potential advantages it offers in overcoming so many of the shortcomings of conventional two-channel reproduction. It is perhaps only surprising that it has taken more than 75 years to engineer since it was originally described by British inventor Alan Blumlein in his founding work on stereo sound. With his seminal patent, he suggested that the correct method of reproducing stereo sound may be the separate encoding of the signal and the spatial information. This methodology, which at the time resulted in the 'middle and side' (M/S) or 'sum and difference' stereo recording technique still favoured today by many classical recording engineers, failed to produce effective stereo reproduction at that time, due to inherent errors in encoding sound by this method. It is the work of inventor and principal partner in Airsound LLP, Ted Fletcher that has overcome these problems and resulted in airSOUND, a practical implementation based on Blumlein's original ideas so many years later.

Ted Fletcher, inventor and founder of airSOUND, holding an airSOUND prototype wallmount speaker.

A multi-patented development, airSOUND comprises a critical combination of speaker arrangement - normally a frontal mono 'main' signal speaker and two side firing 'spatial' signal speakers - enclosure design, and electronic filtering within the integrated encoding amplifiers.

An airSOUND cabinet accepts a normal left and right channel stereo input which is processed to produce discrete 'direct' and 'spatial' signals. These mix to produce an identically-balanced stereo soundfield throughout the room.

Performance and cost advantages for installation

By virtue of being a single point sound source, the audio path lengths to the ears of the listener are proportionally the same with respect to the loudspeaker unit, irrespective of their position in a room. This provides improved signal clarity by eliminating the path length phase distortion common to left / right loudspeaker arrangements. A single point system eliminates the frequency node and cancellation 'comb filter' effects resulting from separate left and right loudspeakers.

 
The limited 'sweet spot' listening position of conventional stereo - the only point at which a correct stereo phase and frequency balance is heard (left) - simply does not apply with airSOUND stereo (right).

An airSOUND loudspeaker system offers improved performance over conventional loudspeakers in several respects. Whether in a residential environment or a commercial audio installation, it is no longer necessary to have to attempt to position a pair of loudspeakers to optimise stereo reproduction at a given point. Equally, for surround sound installations, 5.1 channel coverage can be achieved with just single front and rear airSOUND enclosures and a sub; placement of front and rear enclosures is non-critical, and the surround sound field is identical at all points across the room.

Not only is the depth and width effect of the stereo soundfield apparent over a very wide listening area, height information that is 'lost' by phase errors in left/right channel reproduction can also be perceived.

Dissipation of the airSOUND stereo signal over distance is considerably less than with conventional reproduction. In a large installation requiring multiple enclosures, not only are two stereo speakers replaced by a single enclosure, but a far greater distance between the airSOUND enclosures is achievable than with conventional stereo, resulting in the maintenance of an even signal coverage without interference patterns between adjacent speakers.

airSOUND provides significant component and power efficiencies, with the reduced number of cabinets required to provide coverage over any given area. Furthermore, the main and spatial channels together require significantly less power draw than conventional two-channel systems: on average, the spatial channel requires only 20% rms power consumption of the main signal channel, representing an aggregate saving of 40% over conventional systems.

Licensed technology and designs

airSOUND technology licences are available to all manufactures of residential custom install and commercial AV equipment. The first product designs resulting from airSOUND technology licenses are already under development by hi-fi speaker, CE and MI manufacturers. The company provides considerable support in helping manufacturers bring airSOUND-based products to market, including the development of proof-of-concept prototypes.

For the CI and AV markets, airSOUND has developed a dedicated product design, which offers totally unique installation solutions, including the 'Walls of Sound' which will be unveiled at IS Europe in Amsterdam in January 2008. The design will be offered for license to CI and AV equipment manufacturers.

Alan Johnson is the Director of Business Development for Airsound LLP, a technology research company that specialises in the development and licensing of advanced audio reproduction techniques.

Tel 08456 521 219 / +44 1923 465 641
www.airsound.net