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Old 11th April 2010   #1
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Interesting patent - QRD with imbedded Helmholtz resonators
Here's a recent US patent (April 21, 2009) for a wavy QRD out of laminated wood
with adjustable cylindrical Helmholtz resonators imbedded behind the wells :
And I just noticed that "QRD" and "Skyline" are registered trademarks of RPG.

Paul P
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