Last month we had the pleasure of an invitation to the University of Surrey, to attend a presentation and demonstration of some really interesting research on sound zones.
The team, headed by Dr Philip Jackson, was supported by Bang & Olufsen, and is a joint effort from the Centre for Vision, Speech, & Signal Processing, and the Institute of Sound Recording within the University.
As the presentation explained, the major goal of the project was to be able to deliver personal sound to an individual, and allow each listener control over their own sound source in a shared acoustic space.
This technology has fairly obvious advantages, such as allowing multiple people to listen to two or more sources in the home environment, or allowing selective informational audio to a car driver or museum attendant.
The team approached the problem in a much more practical and experimental way than other people had before them, as they had noticed that there was a lot of material written on various proposed methods to create a sound zone system, but very little practical comparisons of systems in the real world and in real rooms. The team also took on the project in a collaborative way, using their two working groups, but also divided the work load into their respective specialities, the engineering team working on the technical implementation, and the subjective sound quality team making sure that the project fulfilled its potential.
The team established that there were two general methods to controlling zonal sound images, dubbed “energy control” and “least squares plane-wave”. Both of these methods had advantages and disadvantages, and so the team developed a technique that allowed a good compromise between the level of contrast between the sound sources, amount of power required into the system, and the naturalness of the listening experience (planarity of sound waves).
The result of this was startling, and was excellently demonstrated in their spherical test rig, in which two sound zones were prepared. When the user pressed the button to play the sound files, two separate music tracks played, and despite the fact that the sound zones were set only a meter apart, it was very difficult to hear the sound that was not intended for your zone, while hearing the intended source quite clearly.
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While there were some engineering compromises in the system (this example required 60 speakers) the concept works, and we are looking forward to seeing more developments in the future. For further reading, please head to the University of Surrey Project Page.
