Resonator help needed

I'm trying to make a brick rear wall into a resonator /diffuser by drilling holes into the cavity behind. (Spanish brick 500x200x45,Cavity 35mm) Using a loudspeaker port designer on internet (treating each brick as a separate box) tuning to 244 (the worst room mode peak) I get a 23mm port diameter needed. When I calculate with smaller holes (with the same area as the port)over the whole brick and using f=200root(p/dt) from the acoustics handbook I get 129Hz. t (hole length) has a correction factor of t=t+0.8hole diameter(inches) p=perforation% d=air cavity Any suggestions as to the best approach?

GC, I think trying and measuring. Do one single stone. Knock on it with your fist (something soft). Measure the generated sound with whatever narrow-banded measurement tool. Note that this effective length correction 0.8 can deviate somewhat (somewhat lot). E.g.: http://www.diracdelta.co.uk/science/sou ... ource.html Somehow I'm surprised that you're only left with one single relative high frequent disturbing frequency (244 Hz). I rather should try to find out first where that's coming from, in how far this is a mode or some boundary interference. Once you drilled these holes they're there. :) My belly tells: be careful here .... My belly often knows more than my brain (:? what's left of it). For whatever it's worth: http://www.phys.unsw.edu.au/jw/Helmholtz.html

Thanks Mr Eric Are you worried a little that the wall will fall down... Filling you in a little we have built a small studio from scratch. John Sayers kindly gave us a rough plan and we have a brick soffit wall consisting of 3 angled 1.5m walls and angled side walls. We trapped the soffits behind and there are 3 large -still sealed- 50% stuffed cavities behind to tune to the worst room modes. Rear Control Room wall has a corner trap too. We are working on the Control Room at the moment. After bricking off the rear corners the 244Hz has moved to 175Hz as far as I can see from ETF. While bricking up the corners I thought of the rear wall idea. My plan was to build a diffuser for the centre and damp as little as possible. Ceiling will be angled slot resonator past the centre. After rockwooling the previous studio from floor to ceiling I realized (after a time) that it did little to the bass end and killed everything else including the recordings. I get around 800ms RT60 - bellying up in the mids. Worth a try drilling ? I thought a thin layer of foam over the holes will help broaden the q of the resonators. Wall area with cavity is approx 2x2m.