Room gain

[Vikash]

I'm currently designing a sub which rolls off 8db from 100Hz to 20Hz but I want to alter the design to account for room gain. I'd like to use a generic transfer function that I could use to at least guess-attempt a flat in-room response.

Eg. 6db/octave below 80Hz, for a room approx. 4m x 3m x 2.5m?
I think even a crude approximation would be helpful.

Or since the transfer function is a result of the room dimensions (and volume?), does someone have a fomula to calculate it?

[kelticwizard]

Post #10 here gives a graph for average room gain. I will have to look up the original website I got it from, but here it is:
http://www.diyaudio.com/forums/showt...8719#post88719

One of our members, Serow, has made a file that can be added to Subwoofer Simulator, a loudspeaker modelling program written by our own F4ier, to display a louspeaker response with and without room gain. I'll dig up the post for Serow's file, if you like.

[kelticwizard]

Just for the heck of it, here is a simulation of a Peerless XLS 12" , (3.5 ohm Re), in a 1 cu ft box tuned to 25 Hz. 28.3 volts driven, (app 200 watts for a 4 ohm speaker). This simulation program is Subwoofer Simulator with Serow's room gain file added.

Upper green line is response with room gain.
Lower green line is response without room gainl
Orange line is impedance.
Purple line is cone excursion.

[Bill Fitzpatrick]

The effects of room gain will vary depending upon the location of the speaker and listener.

[Vikash]

According to that graph, a crude transfer function is 2db/octave, and my anaechonic design averages 3.3 db/octave below 100Hz which means that, although not perfect, it helps a bit in flattening out the overall FR.

KW, funnily enough, I'm designing for a 10" XLS and 1 passive.

Bill, I'm well aware, but better to have some approximation included in the design then none at all, as room gain will always be apparent.

I'd love a function on how to calcuate the gain based on dimensions...

[kelticwizard]

Absolutely. Which room the the sub is in, where in the room, and where the listener is in the room will have huge effects.

This is just an average. Any real world setup is likely to vary from that by quite a bit.

Anyway, this is F4ier's site to download Subwoofer Simulator:
http://www.geocities.com/f4ier/speaker.htm

This is Serow's post to download the room gain file:
How to: model room gain with Sub. Sim.

[sreten]

Post #10 here gives a graph for average room gain. I will have to look up the original website I got it from, but here it is:

Hi KC,

correct me if I'm wrong, but that graph and other similar graphs
are related to compact loudspeakers optimally sited in free space
away from walls, derived from an article by Martin Colloms.

http://www.stereophile.com/features/44/index3.html

Adire Audio use a different room gain curve, in their
subwoofer white papers from where I don't know.

sreten.

[kelticwizard]

Yes, it appears the ultimate source of that chart is Martin Colloms, as I just discovered.

Here is the link to the article:
http://www.speakerbuilding.com/content/1020/page_3.php

Here is another thread where this is discussed:
Room Gain

I know Pyle tech help uses a different chart as well-one which gives greater boost. But as is generally agreed, whatever you get is just an average anyway.

[kelticwizard]

Originally posted by Vikash

KW, funnily enough, I'm designing for a 10" XLS and 1 passive.


I'd love a function on how to calcuate the gain based on dimensions...

Ten inch or twelve inch passive?

You know, I have an article by Roy Allison here where he took one loudspeaker and put it in different rooms and measured the curves. I can scan it and send it to anyone interested.

[ThomasW]

Adire Audio use a different room gain curve, in their
subwoofer white papers from where I don't know.

I believe they use LspCAD to calculate room gain