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Lee in Montreal
12-04-2012, 06:03 PM
I searched a lot and came up empty handed. I am lookig for the formula that uses the shortest distance between two parallel walls (floor/ceiling) as well as the longest distance to calculate resonance of a room. It is something with twice the shortest and three times the longest distance or something like that. Anyone can help?

MikeBrewster77
12-04-2012, 06:35 PM
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1audiohack
12-04-2012, 09:14 PM
Hi Lee;

In a nutshell the region where the acoustical performance of the space (small room) is mode dominated is bounded by the first mode of the space where f=.5C/RLD up to the highest where f=3C/RSD

C = speed of sound in your prefered metric, just use the same metric throughout.

RLD = Room Largest Dimension

RSD= Room Smallest Dimension

My measurement experience shows that modes are very narrow, usually only three to five Hz wide unless there is a pile up of more than one. Below .5/RLD the room has no contribution and above 3/RSD modes are pretty much statistically spaced.

Example, a room with an eight foot ceiling (RSD) and a 20 foot long wall RLD will be mode dominated between 28-424Hz. Here RTA will lie to you, EQ can't properly help you, absorption is your only weapon and your ears are your best tool.

Hope that helps,
Barry.

more10
12-05-2012, 01:48 AM
Donīt forget about cancellations. But these are dependant on speaker and listening position as well as dimensions. You will get cancellation when the path from speaker to listening position reflected in a wall/ceiling is half a wavelength longer than the direct path.

Lee in Montreal
12-05-2012, 05:24 AM
Thanks guys. I am renting a huge concrete space to do a party in January. There's a bit of treatment on the walls, but nothing on the ceiling (about 15 ft high). I have yet to think about the sound install, but am worried about resonnance. It will be much better when the place is packed with 300 people though... ;-)

1audiohack
12-05-2012, 07:27 AM
Hi Lee;

How big is this place?

Lee in Montreal
12-05-2012, 07:59 AM
Place is quite big. I don't have the measurements yet but ceilings seems to be 15 if not 18 feet tall. I expect a small range of resonance. I will rent 2 dozen sofas to help absorb resonance when the place is empty early in the evening. I will get exact dimensions when contract will be signed. I am going to check the place next week. My friends have seen it already.

http://www.facebook.com/UnionCommerciale/photos_stream

1audiohack
12-05-2012, 08:32 AM
No worries. I just wondered. My big shop is concrete on five surfaces and its been a fun adventure getting decent sound in here with no absorption, just the diffraction and diffusion of the equipment on the floor and pallet racks. It's coming around though. :^)

Mike F
12-08-2012, 08:44 PM
Place is quite big. I don't have the measurements yet but ceilings seems to be 15 if not 18 feet tall. I expect a small range of resonance. I will rent 2 dozen sofas to help absorb resonance when the place is empty early in the evening. I will get exact dimensions when contract will be signed. I am going to check the place next week. My friends have seen it already.

http://www.facebook.com/UnionCommerciale/photos_stream

Will you and Eaulive be rolling in the 4520`s?:D

Lee in Montreal
12-08-2012, 08:50 PM
I will get a pair of JBL 4550 and some 18" subs. JBL 2350 or 2390 for mids. I will bring the 4550 home after the party. Therefore my 4520s are for grab (empty) for cheap. I need the room.