Compensate QTC (Room Gain) Sealed Subwoofer Build

Vitus

Member
2020-02-13 6:04 am
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.
 
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

Member
2020-02-13 6:04 am
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?
 

Vitus

Member
2020-02-13 6:04 am
...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.
 
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Vitus

Member
2020-02-13 6:04 am
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.