Diablo-RCU, I will agree on the compression factor. As for composites being quieter than wood I don't have any experience of being able to compare wood against composite on a test stand or some other method.
I'd be interested in testing if some one would care to donate some props to be returned after the testing.
I currently test my engines 30"over concrete and measure the noise levels in a 360 degree circle with digital and analog meters.
FWIW