Room Gain ?

Jeff_Wi · 05-16-2005, 10:11 PM

I was just wondering, when it comes to a home setup, how much room gain is realistic with a corner-loaded sub? Does room size play a factor? I have a really small room, so I would figure a decent gain similar to that of a vehicle.

Wayne A. Pflughaupt · 05-16-2005, 11:47 PM

Room gain is not related to corner loading. The former refers to low frequency boost and extension that smaller rooms get for “free.” It’s true that corner loading generally maximizes a sub’s output and extension. However, you can have the sub away from a corner and still get the benefits of room gain that you wouldn’t get if the sub was in the same location in a large room. Basically the main benefit of a smaller room is that you can get away with using a smaller and/or less powerful sub.

So yes, you’ll get better extension and output in a smaller room, but it’ll be nothing like what you get in a car, since that is a tiny acoustical space.

Regards,
Wayne A. Pflughaupt

Jeff_Wi · 05-17-2005, 01:09 AM

Quote:

Basically the main benefit of a smaller room is that you can get away with using a smaller and/or less powerful sub.

Interesting, so does that mean you need a sub with lower extension if it is used in a larger room? I know a more capable sub is needed for higher spl's, but I am only referring to extension. Also, is it common for the bass to be muddy in small rooms? I have noticed that the bass seems to be muddy/boomy in bedroom sized rooms. Has anybody else experienced this?

Edward J M · 05-17-2005, 05:15 AM

Yes, there is a difference between boundary gain and room gain.

Boundary gain comes from moving from full space (no boundaries), to 1/2 space (one boundary), to 1/4 space (2 boundaries), to 1/8 space (three boundaries - corner loaded like a floor and two walls).

In theory each boundary adds 6 dB, but rooms are "lossy" and it generally ends up being maybe 4 dB per boundary. The ceiling (although much farther away) might add 1-2 dB too.

So if you went from full space (say suspended from a crane or in an anechoic chamber), to 1/8 space (corner loaded with a ceiling), you might see a 12-14 dB gain in absolute volume.

Room gain is a 2nd order (in theory) transfer function which occurs at/below the 1/2 wavelength corresponding to the longest diagonal (corner to corner) dimension in the room. So if your longest diagonal is 15 feet (small room), you should start seeing room gain at: 15 feet x 2 = 30 feet = ~37 Hz.

Again, most rooms are not perfectly rigid, nor are they 100% enclosed, so you won't usually see a 2nd order transfer function - 6-9 dB/octave would be more typical.

Regards,

Ed

ChrisWiggles · 05-22-2005, 02:04 PM

Quote:

Interesting, so does that mean you need a sub with lower extension if it is used in a larger room? I know a more capable sub is needed for higher spl's, but I am only referring to extension. Also, is it common for the bass to be muddy in small rooms? I have noticed that the bass seems to be muddy/boomy in bedroom sized rooms. Has anybody else experienced this?

The room's frequency response in the bass frequencies will be pretty directly related to the distribution of modes for the three main dimensions. There will be some other more complicated modes, but are less dominant. A smaller room will have usually more severe problems with bass modes, but this does serve to "boost" the bass in the room. However, this causes terrible problems with bass frequency response. Proper bass absorption and placement will help, along with room dimensions that are carefully chosen to spread out the modal distribution evenly.

Small rooms also will also have their lowest mode at higher frequencies. Rooms have a sort of lowest "boosted" frequency, and the larger the room, the longer the waveleneght, the lower the freq. So small rooms will "roll-off" in response at a higher frequency, which can be difficult to overcome. Larger rooms will remain flatter in response to a lower frequency, generally.

They key to good bass in small rooms is lots of bass absorbtion, or your response will be all over the map, and buddy. It will be boosted, sure, but it will sound like a mess. Larger rooms just tend to make this a little easier to achieve.

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Jeff_Wi · 05-22-2005, 07:18 PM

Quote:

They key to good bass in small rooms is lots of bass absorbtion, or your response will be all over the map, and buddy.

What is a good way to add bass absorption in a small room, especially if it is quite small?

ChrisWiggles · 05-22-2005, 07:22 PM

typo: and muddy

All the same physics applies to waves, so broadband bass absorption/bass traps are great. Resonating absorbers and such can help target problem frequencies in more advanced design. All the usual. Thick fiberglass panels is the easiest way to make bass traps, put em across corners and such.



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