Compensate QTC (Room Gain) Sealed Subwoofer Build

[Vitus]

I'm in the midst of attempting to build my first ever subwoofer.

It'll be a sealed enclosure where my goal is to measure my room gain, then compensate the build Qtc to achieve the final Qtc once placed in the room.

I've read that the final Qtc can change, and most likely will change, once you place the subwoofer in the room.

Hence my understanding of aiming for a build Qtc is quite useless if the room alters the final Qtc once installed.

I think I know how to measure the room gain, a near-field and a far-field measurement, preferably at listening position and/or sweet spot, if you will, compare the two SPL results by looking at the scale.

However, what to do with the given/generated dB difference?

How do you add the difference into the build Qtc to calculate the final Qtc in the room?

Thanks, as always.

 

[bentoronto]

Except in tightly sealed cars, there is not enough gain through pressurization in a domestic room with drywall finishes to bother thinking about.

But the room environment can greatly affect results in lots of other ways and ways that are specific to the setting and often not predictable with any useful degree of accuracy.

 

[The Lord Flashheart]

There is a simple way to test in cars which ought to be applicable here, open the doors and windows to test if pressurisation is going to be a factor.

 

[Vitus]

There is a simple way to test in cars which ought to be applicable here, open the doors and windows to test if pressurisation is going to be a factor.

Hello,

The original question was not concerning cars, but a normal living room with a home theater installation.

Thanks for your tip, I think bentoronto's answer is fully adequate here.

 

[ctrlx]

vitus, you should do acoustic tests.

bentoronto, can you provide some acoustic tests to backup your statement?

 

[Vitus]

vitus, you should do acoustic tests.

Yeah, I realized yesterday I need a microphone, ordered the UMIK-1.

 

[The Lord Flashheart]

Hello,

The original question was not concerning cars, but a normal living room with a home theater installation.

Thanks for your tip, I think bentoronto's answer is fully adequate here.

I fear clarity has been the victim of brevity, you can test for pressurisation in a simple manner by playing the same tone in your living room twice, once with the doors and windows sealed and once without.

 

[Vitus]

I fear clarity has been the victim of brevity, you can test for pressurisation in a simple manner by playing the same tone in your living room twice, once with the doors and windows sealed and once without.

Yeah, well, I have a big archway in the room, impossible to cover.

 

[The Lord Flashheart]

The room is open to the elements by means of an unobstructed archway?

 

[Vitus]

The room is open to the elements by means of an unobstructed archway?

My right main tower is about 1 meter away from the archway, all the speakers are pointing towards the sweet spot, so the right speaker is toed in 15ish degrees, my room is not wide enough to accomodate the full Dolby placement guidelines, 15 or so degrees is the widest possible stereo image I can create.

I have my subwoofers closer to the screen than my towers, otherwise the channel separation would be quite small/narrow.

I can't do anything about the archway, not going to cover it up.

Why do you ask, would there be more of a room loss than gain in this case?

 

[The Lord Flashheart]

Because for truly low frequency effects, as you want from home cinema and I want to reproduce the lowest notes of organs, depends on room volume, shape and even whether you have the windows open.

Have a read through REL’s guide to setting up the subs and compare to the Dolby method: High and Low Level Tuning Guide – REL Acoustics

 

[Vitus]

Because for truly low frequency effects, as you want from home cinema and I want to reproduce the lowest notes of organs, depends on room volume, shape and even whether you have the windows open.

Have a read through REL’s guide to setting up the subs and compare to the Dolby method: High and Low Level Tuning Guide – REL Acoustics

Thanks, I'll experience with corner placement to see the effects.


Cheers.

 

[bentoronto]

...bentoronto, can you provide some acoustic tests to backup your statement?

Sorry ctrix, you've the logic wrong. The obligation to demonstrate an effect is on the proponents of pressurization, not on the skeptics.

The topic of "room gain" has been discussed at great length at this forum many times and I have stated the consensus: it's just wishful thinking based on - as ever - applying elementary school Laws of Physics and wannabee engineering in an effort to over-simplify the real world.

Rather unsophisticated to talk about opening windows and other tests that modify all kinds of factors besides pressure. As I mentioned in my earlier post, when you have drywall, the walls are rubbery and ordinary domestic rooms are far from sealed, no matter how thick the paint coat. Even the most solid seeming floors are essentially floating to allow for expansion changes.

 

[Vitus]

Sorry ctrix, you've the logic wrong. The obligation to demonstrate an effect is on the proponents of pressurization, not on the skeptics.

The topic of "room gain" has been discussed at great length at this forum many times and I have stated the consensus: it's just wishful thinking based on - as ever - applying elementary school Laws of Physics and wannabee engineering in an effort to over-simplify the real world.

Rather unsophisticated to talk about opening windows and other tests that modify all kinds of factors besides pressure. As I mentioned in my earlier post, when you have drywall, the walls are rubbery and ordinary domestic rooms are far from sealed, no matter how thick the paint coat. Even the most solid seeming floors are essentially floating to allow for expansion changes.

+1 I think.