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Locating Room Modes/ Maximum Pressure
Old 14th July 2016
  #1
Gear Addict
 

Locating Room Modes/ Maximum Pressure

Hi folks,

I'm about to go about installing two large limp mass membrane bass traps on my back wall and was hoping for some guidance before I start the process as I want to get this right.. I realise this is a slightly precarious situation in that even if the boxes are built well, without being placed just right for the incident waves they may do very little or nothing.
I have used an online room mode calculator to determine the problem modes.. sure enough after running REW, they show up.
Now that I know what I am chasing, my question is in regard to finding exactly where these waves are happening and where on the walls they are hitting, if I can find these points my thinking is to centre the membranes at their maximum pressure points.
How can I achieve this process without the use of an SPL meter?? Is there a sure fire way of finding these points? I do have some DPA omni mics that could help here..
Thanks for reading and appreciate any input on the matter!
Old 14th July 2016
  #2
Lives for gear
 

If you know what modes they are, then you will already know in theory where they will be at highest pressure. To verify, I use a sine generator (in my DAW) playing the modal frequency, and walk around the room to hear the peaks and nulls. For absolute accuracy, you could use an SPL meter to verify areas of highest pressure, but I find my ears are accurate enough in this case. With the axial modes, it's really no mystery where their pressure zones lie, however.
Old 14th July 2016
  #3
Gear Maniac
 

I could just complete what DPower says. With the axial modes, the whole wall involved, so the position should be flexible.
Old 14th July 2016
  #4
Gear Guru
 
Glenn Kuras's Avatar
If the problem is forward to back then cover as much of the back wall as possible. You won't nail it with just on 2'x4' panel.
Old 14th July 2016
  #5
Lives for gear
 
akebrake's Avatar
 

Nice built in tools

Quote:
Originally Posted by PartHunter View Post
.... How can I achieve this process without the use of an SPL meter?? Is there a sure fire way of finding these points? I do have some DPA omni mics that could help here..
You've got excellent SPL meter, Generator and also FFT and RTA meters included in REW. Try them, they are really fun!

OK, you don't get absolute levels but you can compare levels easily.
And if you adjust the calibration for normal speech at 1 ft for approx 70 dB SPL your in the ball park.

Cheers

Voice Level and Distance
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