Wavefield synthesis: ‘souped-up’ surround sound

Wave Field Synthesis System in University of Salford’s Listening Room [1]

I’ve just been sent this great new photo from our research labs. Wave Field synthesis is arguably the most impressive surround sound system currently available. It isn’t something you’re likely to see outside a research laboratory, however, because of the large amount of equipment that is required. The above rig has over a hundred loudspeakers mounted in a rectangle surrounding the listener. What you can’t see, is the racks of amplifiers, convertors and digital signal processing equipment being used to send audio to the loudspeakers via huge thick cables. And the room is covered in acoustic treatment to reduce problems caused by sound reflections from the walls, floor and ceiling.

What makes wave field synthesis impressive is quite a few people can stand in the middle and get a real sense of where sound sources are. You can make things appear to be sounding from inside the rectangle, say a musician playing a flute, and listeners can walk all the way around this virtual sound source. This ability to stroll through the virtual sound field isn’t possible with many other 3D sound systems.

Below is a nice illustration of how it works from LIMSI in France. On the left is what happens when something makes a sound (e.g. a violin plays a note). Sound waves radiate out from the violin, and these can be pictured to be like ripples spreading out on the surface of a pond after a stone is thrown into the water.

Illustration of how wave field synthesis works [2]

On the right is the idea of wave field synthesis (WFS) to generate the sensation of the violin playing from a particular place. A line of loudspeakers re-creates the ‘ripples’ that the real violin would have made. In effect, the loudspeaker in the middle of the array starts playing the sound of the violin a little bit before the neighbouring loudspeakers to create a curved wavefront.

As with most spatial audio systems, it is probably most impressive when you get a sound source buzzing around your head. At Salford, we have a demo where a motorbike appears to drive right past you which is very cool. Colleagues at Salford have also used WFS to recreate the ancient sound of Stonehenge.

Sources

[1] Photo: www.gregharding.co.uk

[2] http://www.limsi.fr/Scientifique/aa/thmsonesp/IRV_web

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