How much room gain can I expect? - Home Theater Forum and Systems - HomeTheaterShack.com

Old 01-23-10, 01:37 PM Thread Starter
Shackster
Reese

Join Date: Jan 2010
Location: Dallas
Posts: 44
How much room gain can I expect?

Not sure if this is the right forum to ask this question.

My immediate listening area is approx 300 ft^2 but it also part of an open first floor that is over 1200 ft^2.

I have limited space and a large ported subs will probably not work. How much if any room gain I can expect at lower fequencies from a sealed box tuned at 36 hz f3?
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Old 01-23-10, 03:26 PM
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Matt

Join Date: Feb 2007
Posts: 355
Re: How much room gain can I expect?

cabin gain all depends on how 'tightly sealed' the room you are pressurizing is; if your listening area is not walled off, you would probably be dealing with cabin gain from the 1200ft^2 area, so the frequency that the cabin gain would start would be lower (than a 300ft^2 area)...

basically the cabin gain in a perfectly sealed volume is 12 db/oct gain as you decrease in frequency, however wall flex and air leaks (open doors and non rigid walls) will eat into the 12 db/oct... so you may get 6-9 db/oct starting at a certain frequency in reality; I believe you need to know the volume of the area in question, not the square footage to figure out the frequency the cabin gain starts

Addition: i should have also mentioned, the cabin gain of a room is going to happen independent of the type of sub-woofer you have... even if you had no sub-woofer there would be cabin gain, it is just a characteristic of the frequency response of a room

Another way to think about it, the cabin gain frequency (where the effect starts) is the transition point where you are no longer producing 'sound waves', you are pressurizing and de-pressurizing the room (I find that to be the most intuitive way to think about it)

Last edited by Chester; 01-23-10 at 03:35 PM.
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Old 01-24-10, 01:00 PM
Elite Shackster

Join Date: Aug 2008
Posts: 7,142
Re: How much room gain can I expect?

If you just want a rough figure to work with then you can work to about 6db gain. Its only a rough figure/guideline though, as posted above it will vary depending on your sub and your room.
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Old 01-24-10, 09:52 PM Thread Starter
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Reese

Join Date: Jan 2010
Location: Dallas
Posts: 44
Re: How much room gain can I expect?

I'm guessing that with my open floorplan, I wil not get much gain.

I was originally thinking of using 2 - 12" daytons (3.5 ft^3, 36hz, f3), but I am now leaning towards a ported version (7 ft^3, 22hz, f3).

I think the ported version will be better suited the large open area.
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Old 01-25-10, 12:53 PM
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Josh

Join Date: May 2007
Location: Louisville, KY
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Re: How much room gain can I expect?

Also figure that the gain will start at the 1/2 wave length of the longest dimension in your room.
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Old 01-25-10, 05:24 PM
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Dylan

Join Date: Apr 2009
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Re: How much room gain can I expect?

Quote:
Ricci wrote: View Post
Also figure that the gain will start at the 1/4 wave length of the longest dimension in your room.
I'm not exactly following what your saying there, Josh. Could you explain more?
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Old 01-25-10, 09:46 PM Thread Starter
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Reese

Join Date: Jan 2010
Location: Dallas
Posts: 44
Re: How much room gain can I expect?

Not exactly sure either but I found this wavelength conversion applet

http://www.onlineconversion.com/freq...wavelength.htm

My backwall is 40ft from speakers so I guess the 1/4 wave is 6 hz????
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Old 01-25-10, 10:41 PM
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Dylan

Join Date: Apr 2009
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Re: How much room gain can I expect?

Quote:
Reese wrote: View Post
Not exactly sure either but I found this wavelength conversion applet

http://www.onlineconversion.com/freq...wavelength.htm

My backwall is 40ft from speakers so I guess the 1/4 wave is 6 hz????
If I'm understanding correctly what your saying, it looks like you used Megahertz, and not hz. If it was 6hz, and not 6mhz, the frequency wavelength would be 41,000,000 feet (according to that website).
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Old 01-26-10, 09:55 AM Thread Starter
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Reese

Join Date: Jan 2010
Location: Dallas
Posts: 44
Re: How much room gain can I expect?

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Old 01-27-10, 09:21 AM
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Josh

Join Date: May 2007
Location: Louisville, KY
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Re: How much room gain can I expect?

Quote:
sub_junkie wrote: View Post
I'm not exactly following what your saying there, Josh. Could you explain more?
Basically below the lowest 1/2 wave support in your room is where you will enter pressure vessel gain (like what you get in a car) and you can figure on about 6db octave of gain from below that point, or maybe more depending on your room construction among other things. Figure if you have a length of 25ft then a 50ft soundwave will correspond (about 22.5hz). Estimating these things off of just dimensions is highly sketchy though because the room construction, resonances in the walls, floors, HVAC and other things can all affect the low bass response and the strength of the resonances or nulls.

If you have a room that is basically a simple square or rectangle, with no windows and is a cement slab with cinder block walls then you may get a good idea by using some of the calculators available online. On the other hand if you have cathedral ceilings with an open floor plan, oddly shaped room, wood sub floor and studs with drywall, plus a bunch of windows and doorways, things are way more complicated and the best way would be to simply measure it IMO.
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