24 l August 2013
www.psneurope.com
studionews UNITED KINGDON PMC measures up By Erica Basnicki
A NEWlaser-based acoustic measurement technique developed by the UK’s National Physical Laboratory (NPL) with the help of PMC loudspeakers was the focus of a recent event at the Teddington-based National Measurement Institute. Held on 3 July, the visit to the NPL came just two months after the Rapid Acousto-Optic Scanning (RAOS) technique was announced and allowed an invited group of trade press, including PSNEurope, to learn about the process. “A good analogy is comparing it to the Formula 1 industry, where they base a lot
of their work on aerodynamics,” said PMC project manager, R&D, Oliver Thomas. “They use computers to
simulate how the air flows around the car and then ‘proof’ that with their wind tunnel data – this is sort of like the wind
tunnel. As long as that ties up with what you’re predicting, everything’s going okay.” According to the NPL, RAOS
Dispersion patterns as measured through RAOS
removes the need for a physical measuring device and instead relies on the fact that sound waves affect the refractive index of the air they travel in. A laser passed through the air is affected to different degrees depending on the nature of the sound passing through the air at the same time as the laser. By accurately measuring the delay of a laser beam passing the device under test as it generates audio, a complete picture of the dispersion pattern of the device can be built up with ease. However, loudspeakers are just the beginning of what the
PMC’s Oliver Thomas and NPL’s Richard Jackett inside the hemi-anechoic chamber
research facility hopes RAOS can be applied towards. “We are nowhere near exhausting what we can do with loudspeakers, and that’s the thing we’ve looked at most,” said NPL’s Richard Jackett “I would love to be able to use this on characterising something other than sounds that have been generated from a loudspeaker, but there’s a lot of difficulties that have to be overcome with moving away from the loudspeaker as a source.” For PMC, the value of
RAOS is two-fold: to start, the company has been able to verify
existing loudspeaker design principles, “which is great because it’s all tallied up so far”, said Thomas. In addition Thomas says that PMC is “working on a few different things, which will come out in their own time”, and which will benefit from the laser measurement technique. “A lot of our time has been absorbed by background research at the NPL so far, so hopefully now we can start to apply that to a few more of the new speakers.”n
www.npl.co.uk www.pmc-speakers.com
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