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spm_gl · 27th June 2009

We are talking particle velocity, because that is the energy we can actually absorb.
At 1/4 wavelength, the particle velocity is highest, at 1/2 wavelength it is zero again. So a porous absorber is most effective at depth = 1/4 wavelength.
Take 100Hz, WL=3,4m, most energy at 0.85m. But for 200Hz, 0.85 is half wavelength, so no particle displacement, no energy to dissipate, no absorption.
So if our absorber is too thin, placing it away from the wall makes a comb-filter.
Edit: This is, of course, for 90° incident angle.

27th June 2009	#18
spm_gl Gear addict Joined: Apr 2009 Location: Spreewald, near Berlin / Germany Posts: 316	We are talking particle velocity, because that is the energy we can actually absorb. At 1/4 wavelength, the particle velocity is highest, at 1/2 wavelength it is zero again. So a porous absorber is most effective at depth = 1/4 wavelength. Take 100Hz, WL=3,4m, most energy at 0.85m. But for 200Hz, 0.85 is half wavelength, so no particle displacement, no energy to dissipate, no absorption. So if our absorber is too thin, placing it away from the wall makes a comb-filter. Edit: This is, of course, for 90° incident angle. __________________ --- Spreemusik --- Jan Fuchsmann, Audio Engineer Our new Blog: http://blog.spreemusik.com Last edited by spm_gl; 27th June 2009 at 06:07 PM.. Reason: confusing...