Room gain

[Raka]

I have some small question (yes, one more, but when you see my new speakers you'll be green of envy )

Could I rely on the room gain to achieve a flat FR? I mean, my main design is a BR that has a small mountain starting at where the baffle losses do. This way (boosting acoustically the curve from the driver) I don't need passive components to achieve a flat FR in real life. From the top of the mountain I have a 12db steep curve until the port, that makes it 24dB. My question is: Could I simply use maths and supperpose the three curves: the box output, the baffle loss and the room gain? If I can, I get a nice flat response up to decent low bass without equalizing.

BTW: How the he** can have my center pioneer poor AV speaker a f3 of less than 60H with a sensivity of >90dB if it is small??

[paulspencer]

It's hard to rely on room gain if you don't know what it is. You also have room modes to deal with. As I understand, it's hard to count on room gain to improve your frequency response down low, unless you have measuring capacity to determine your room gain. Also it will vary based on where you are in the room. In my room I get a large boost at the rear wall, but if I step forward 1.5m, the bass disapears.

You can try to model your room using a simulation package such as LspCAD or others. Also some people have published general attempts at estimating room gain. My guess is that you can guess 3 - 6 db / octave gain below 50 Hz as a good starting point, but I'm certainly no expert on this.

[Raka]

Yes, I forgot the room modes on purpose, because I think I can manage this with speakers position (not totally obviously, but the better you could)
I meant the theorical output without modes. I saw here a graph that starting at 250Hz (+1dB) up to 30Hz (+6dB) shows a linear gain response. If so, a closed box (that is, a 6dB steep down line) starting to roll of properly, will expose a flat response (without modes and without baffle step losses) up to very low, without equalizing. I'm I right?

[roddyama]

Originally posted by Raka
Yes, I forgot the room modes on purpose, because I think I can manage this with speakers position (not totally obviously, but the better you could)
I meant the theorical output without modes. I saw here a graph that starting at 250Hz (+1dB) up to 30Hz (+6dB) shows a linear gain response. If so, a closed box (that is, a 6dB steep down line) starting to roll of properly, will expose a flat response (without modes and without baffle step losses) up to very low, without equalizing. I'm I right?

The FR roll off of a typical closed box is 12db/octave. From 30Hz to 250Hz is 3 octaves so your getting a 2db/octave boost. It would take some extra tweaking of the alignment and speaker placement to get back to a flat FR. It possible, but not quite that straight forward.

[tg3]

Raka,

You might find the Room Response Calculator from the FRD to be useful.

Room Response Calculator

[paulspencer]

I'm looking into room gain for a subwoofer I'm designing at the moment. You may find this interesting:

http://members.optusnet.com.au/~pete..._roomgain.html

Please note: you need to account for your room as it will be different. This is just an example of different results - LspCAD, FRD calculator and some generic examples which don't relate to my room.

As these are simulations I can't vouch for their accuracy either. Don't rely too much on room gain to improve bass response.

[advance]

Could I simply use maths and supperpose the three curves: the box output, the baffle loss and the room gain?

Of course, it is possible. In my experience without taking room gain into consideration the bass is often too prominent. However, use all simulations and maths concerning room gain with some common sense.

Reading

Roy F. Allison, The Influence of Room Boundaries on Loudspeaker Power Output, JAES, June 1974
Roy F. Allison, The Speaker and the Listener, Stereo Review, August 1976

Floyd E. Toole, Loudspeakers and room - Working together, Harman International Industries
Floyd E. Toole, Maximizing Loudspeaker Performance in Rooms, Harman International Industries
Floyd E. Toole, Getting the Bass Right , Harman International Industries

Software

http://melhuish.org/audio/Xlbox.xls (by Thorsten Loesch)
http://www.pvconsultants.com/audio/reflection/rrc.htm (by Yavuz Aksan)
http://members.chello.se/jpo/bassand...room_beta2.xls (by jpo@chello.se)

Example

http://home.tiscalinet.ch/cooltune/B...coustics01.htm
http://home.tiscalinet.ch/cooltune/B...Speakers01.htm
http://home.tiscalinet.ch/cooltune/P...s/Menhir01.htm


Hope this helps.

advance