Room Gain in Real Life

[richie00boy]

Has anybody got any real measurements of room gain?

Does it tend towards 6dB/oct or 12dB/oct?

Does it begin (+3dB) where the rooms longest dimension is equal to a half wavelength or whole wavelength?

[Jan Dupont]

First! You won't experience room gain at higher frequencies. Only in the bass area....

As to my knowledge, room gain +3dB only applies at full wavelenght.... And can easily be calculated

As to my knowledge you can use room gain to gain your bass output from the speakers as follows:
- Speaker up against a wall +3dB
- Speaker up against a wall in a corner +6dB
- Speaker up against a wall in a corner an on floor +9dB

[richie00boy]

That's not really room gain, that's loading into half/quarter/eighth space. The room gain I'm talking about is when the mode changes from wavelength reproduction to pressure mode. This gain rises as frequency goes down, hence my question on the slope. But thanks for the answer still

I've heard conflicting stories on the things I've questioned in my original post, hence the request for real, verified information.

[simon5]

Adire Audio did a room gain curve in a 50m^3 room (4m x 5.5m by 2.3m), it's around +5 dB octave when corner loaded, starting at around 300 Hz.

Page 4 of this document: http://www.adireaudio.com/Files/Vent...plications.PDF

[kelticwizard]

Here's a simulation of RobWells' sealed sub, Qtc = 0.75, according to WinISD:
http://www.diyaudio.com/forums/attac...amp=1081327935

Here is the measured response in the room:
http://www.diyaudio.com/forums/attac...amp=1081328162

So the room gain is substantial.

Here is the thread these are from:
http://www.diyaudio.com/forums/showt...440#post366440

[johninCR]

Richie,

Something you've got to keep in mind is that room gain is very dependant upon your room (it's volume, shape, dimensions, boundary construction, how well it is sealed, what kind of furniture you have in your room to absorb bass, etc.). Count on some gain in your design and then make the final tuning decisions based on actual in room response.

[richie00boy]

kelticwizard,

Thanks for that, it has given me some useful data to compare against my model.

jonhninCR,

I'm aware that there will be influencing factors like you mentioned, but I'm just trying to develop a generic, rough model.

[johninCR]

Why develop a "generic rough model" that could easily be off 10db or more in the lowest frequencies? Room dimensions, construction, and whether the room is open to another are much more than "influences". They are the primary factors along with frequency.

[Zaph]

I copied this from one of my projects:

Anechoic response curve, 1 speaker, on axis

In room response, 2 speakers

The room response image has 2 curves, one with no gating and one with a 4ms window. Describing the conditions: 2 meter equilateral triangle consisting of 2 speakers and a microphone. The offset tweeters are to the outside. The speakers are not toed in; they face straight ahead and as such are off axis to the mic. The room is 16 ft x 18ft. The speakers are on the 16 foot wall, mounted on 24" stands and the baffles are 28" out from the rear wall. The mic is level with the tweeters. There is no absorbtive material on the rear wall. Between the speakers is a 51" big screen TV, which the inside edge of the speakers cleared by about a foot. The room has a cathedral ceiling which, when facing the speakers from the mic location, goes from 8 feet on the left side to 13 feet on the right side. The right side front corner has a large opening leading to another room, and the right side rear corner has another opening leading to another room. The room is carpeted, contains a couch, a love seat and other pieces of furniture. The left side is moderately absorbant with blinds and curtains, and the right side (with the openings) is very reflective from a stone fireplace. Construction is traditional drywall. Whew. I think that covers it.

I think the important factors for the bottom two octaves, in order, are the room size, placement within the room and then openings to other rooms affect the very bottom octave. It's hard to generalize room response. Everything affects everything.

[tiroth]

Zaph,

How can you get that kind of data with a 4ms window? Shouldn't 250Hz be the lowest measurable point?

Kelticwizard,

Do you feel that RTA'd pink noise is the best measurement technique for the bottom octave? I've never been able to match 1/30 octave warbles to 1/30 octave pink noise RTA, and haven't any idea which is more accurate.