R/E/P > Acoustics in Motion

Steering advice for small room treatment


Michael Jaspers:
Hello All,
I've been working my way through the Everest acoustics book, with the intention of treating my office at work so that I can use my office as a decent place to mix audio.  I'm a church sound guy with an office.  I cannot change the structure, but can add treatment.

Dimensions are:
10'3" W
15'7" L
9'3" H (drop in ceiling)

I have a dual-FFT analyzer(Smaart) with TF and IR measurement capability and a Josephson measurement mic. 
So far, all I've done is taken a couple IR measurements with sampling to 256k, with pink noise as a stimulus and using a studio monitor (aimed into a corner).  The studio monitor has a FR of 80Hz-20kHz (Tannoy Active (Reveal; dark teal color)).  I placed my microphone at ear height for the mix position and did the measurement. 

I have a peak at 73Hz and another wide-band peak from 100Hz-200Hz.  My measurement had a 40dB S/N ratio and the RT with my stimulus (band limited to 80Hz)is about 250ms.

At this point, I am uncertain what to do.  I need absorption to be effective to 100Hz, which seems rather easy with some dense mineral fiber in corners, and the perhaps a resonator for the 73Hz problem?  Since my walls are parallel I thought that alternating panels of absorption and quadratic-residue diffusers, using the prime = 13 so as not to overdamp, but with good effectiveness to the middle frequencies.

I only need to maintain effectiveness to the response of my monitors (80Hz).  Sorry for the long post. TIA!


You don't necessarily need a resonator to take care of the 73Hz problem.

Identify which mode it is, play with spacing the Rockwool from these walls and see if you can get this 73Hz resonance down at least.

If not, then I would suggest membranes rather than a resonator anyway - works better. And in a way they're more forgiving as well.

I assume you have nulls as well?

Michael Jaspers:
Yes, I have nulls in between the 73Hz-100Hz area, then narrow band problems from the low mids on up.
What do you mean by "membrane?"
I've been thinking about this more as well, and I *think* I need to take measurements as to my monitoring positions as well.  The room modes terminate in corners, obviously, and were easy to spot because of the 1/8 space loading and resultant peaks in response, but the corner firing method doesn't seem the most accurate for HF-MF response problems due to the shorter wavelengths.  I'm just a newb, though, so any advice is welcome.

I've been doing research as to where I can find rockwool/OC70*/Johns Manville superduct and even tried sourcing "safe insulation" and am having trouble finding a good source right now...but that is secondary to identifying my acoustic problems.

Don't know Smaart, can Pink Noise make an Impulse Response measurement?
If you can do an IR, export it as a WAV. Then anyone can read it using their own software.
FuzzMeasure and Room Eq Wizard here.
I would be more worried about nulls than peaks, however clever treatment should hit both.
Try a Signal Generator. There is a great one which follows the cursor in REW. Signalsuite is also good.
You need fine resolution, not digital jumps. Tune to the loudest resonance. Hold it there. Move about the room finding nulls and peaks.
You could mark them on the floor with coloured masking tape and SPL numbers if you have a meter. There is of course an SPL meter built in to REW also.  If you do a few more resonances you will end up with a map.
This map will tell you where not to sit, where not to place speakers. It will also tell where to place traps, where to sit or place speakers for a wanted boost. Positions of listener and speakers is incredibly powerful, particularly for the price :-)
You can try this out virtually using the Wall Bounce Calculator here  http://www.irishacoustics.com/index.php/acoustics/acoustic-resources/

The corner stimulus thing obviously doesn't deal with SBIR, so do measure with one, the other, then both speakers running.
There is a measurement quick start here http://www.gearslutz.com/board/studio-building-acoustics/469574-basic-acoustic-measurement-primer-v2-1-a.html
Perhaps I should do a rewrite for here?


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