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Author Topic: Calculating Room Modes?  (Read 2217 times)

John Bailey

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Calculating Room Modes?
« on: June 22, 2007, 07:49:22 pm »

Hi Guys,

I'm wondering if anyone can help me to calculate the necessary data correctly for a room.  A very good Producer friend of mine is building a new control room, and can't afford the big bucks to hire a consultant, so I'm trying to help him avoid some pitfalls before they start forging ahead with the building (I'm in Toronto, he's in the US).  I make records.  Plenty of em', but I'm not an acoustician.

The control room will essentially be limited to an 18' width, approx 27' (maximum) length, and a variable ceiling height (around 10' would be fine, but could be as high as 14' if necessary).

I've downloaded a fantastic Excel spreadsheet for calculating room modes, mode density, and mode distribution on a Bonello Graph.

I've read a whole bunch on this board, and I'm trying to understand the practical application of the Bonello criteria in terms of ratios, etc....

He would like to angle the front wall in on a 45deg angle on each side (I suggested a 30deg angle).  Even though the longest axial dimension around the room is unchanged, should the dimensions in the room-mode calculation be adjusted for the reduced volume in the room?

For instance, if they angle the front wall in at about 54" from each side on a 45deg angle, they would reduce the overall square footage of the room by 40.5 sq ft, and therefore reduce the volume of the room from 4860 to 4455 cubic feet (assuming it was 27' in length).

Any help on this would be hugely appreciated!

Cheers from Toronto...
John Bailey
Toronto, Canada


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Re: Calculating Room Modes?
« Reply #1 on: June 22, 2007, 07:54:02 pm »

When we calculate modes in an irregular rectangle (ceiling angled down, corners cut in the front as you are suggesting), I would normally calculate Max, Min and Average dimensions in a suitable room mode calculator. If they all look acceptable, then you're good to go!

One thought, perhaps the angled walls at the front (30 deg sounds better to me as well) could be trapped with porous absorption? There is no practical advantage to doing these angles in "hard" construction unless you are building In-Wall speaker soffit walls... I might suggest cutting these corners and installing some deep trapping covered with stretched fabric!!

Good luck... Carry on calculating!!
Francis Manzella - President, FM Design Ltd.
                 - Managing Director, Griffin Audio

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