Accounting for Room Lift

[Trapshooter]

When considering a new design, how much consideration should be given to room lift? Should one intentionally design a droop in the response to account for room lift?

[jamikl]

My understanding Trapshooter is that what you ask is correct. There is a chart somewhere, I think by Martin Colloms, that shows the room lift for an "average" British sitting room. As he was probably higher paid than a lot of people in that country his view of what is an average sized room could be a bit larger than what we see on TV programs. I certainly hope that it will have some effect on the speakers I am working out at the moment.

I think this is a good question and am surprised that you have no replies as yet. Perhaps it is not esoteric enough to involve those knowledgeable people who get involved in threads that go on forever, go nowhere and never reach any form of consensus that could be useful to those of us who " don't know as much!"
jamikl

[Brett]

Presenting, 'The Colloms Curve'.

[Shaun]

Originally posted by Brett
Presenting, 'The Colloms Curve'.

This curve is all but useless, as the boundary reinforcement will change, depending on where the speakers are placed and, as has been pointed out above, the size of the room. DIY allows one to tailor a speaker's frequency response to suit the room.

See here http://www.pvconsultants.com/audio/reflection/rrc.htm

[Brett]

Originally posted by Shaun


This curve is all but useless, as the boundary reinforcement will change, depending on where the speakers are placed and, as has been pointed out above, the size of the room. DIY allows one to tailor a speaker's frequency response to suit the room.

See here http://www.pvconsultants.com/audio/reflection/rrc.htm

I agree, I just posted what the other person asked for. I measure rather than rely on something generic like that.

[Shaun]

I somewhat regret having said "useless", as it at least gives a general idea of how low frequencies are reinforced. But still, actual response of a specific room and placemnt therein will likely be very different.

[Brett]

Originally posted by jamikl
There is a chart somewhere, I think by Martin Colloms, that shows the room lift for an "average" British sitting room.

Originally posted by Shaun
I somewhat regret having said "useless", as it at least gives a general idea of how low frequencies are reinforced. But still, actual response of a specific room and placemnt therein will likely be very different.

The quote above is all I've ever taken the curve to mean, ie I agree with you that it's an indicator only and each room and speaker position will give a different response. Cheers

[macka]

Phillips did a compehensive study a long time ago that was published in their diy handbook.

There are a set of known response permutations depending on the location of the loudspeaker in an X, Y, Z set of co ordinates.

What I did was look at those published data curves and the modified the Colloms curve based on where the woofer in my design was likely to be located and saved in Bassbox 5.1 as a room curve.

What I found was that by tuning a particular driver with banana curve a certain set of Fs and QTS I was able on paper to get a smooth response with extension from the room where the box was near the front wall and the woofer about 2 feet off the floor.

Bassbox 5.1 has an extended tuning that does this as a custom design. The result is a Fb tuning close to the Fs and a somewhat larger box.

Typically a maximally flat QB3 response will peak in the 50- 100 hertz region (reflect) unless it is placed 1 metre from the front wall and raised off the floor.

This is not always a convenient location in a domestic setting.

[Shaun]

Originally posted by macka
Typically a maximally flat QB3 response will peak in the 50- 100 hertz region (reflect) unless it is placed 1 metre from the front wall and raised off the floor.

This is not always a convenient location in a domestic setting.

Dunno the situation there in OZ, but over here the average-sized house is getting more and more compact. Seems to me the most common (forced) placement is close to the front wall, often with one speaker in a corner.

[Inductor]

Had to change my 10"/58L speakers from BR to closed enclosure because of that, after a long time simulating BSC. I think I can use BR when PA'ing outside. I had them on the floor away from walls and I din't use the inductors/xovers yet as it was just a first test. That Martin Colloms curve makes a lot of sense.