Formula for room resonance

[Lee in Montreal]

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]

[1audiohack]

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]

Don´t 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]

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]

Hi Lee;

How big is this place?

[Lee in Montreal]

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]

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]

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?

[Lee in Montreal]

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.