room treatment

absolutely incorrect. additional subwoofers do not "cause more standing waves". the room dictates resonances; the subwoofers merely drive these resonances.

the "booming" is not a function of just the frequency response but also the decay times of the LF energy. in a resonance, the energy tends to persist. LF decay times must be controlled.




what you're attempting to describe is spatial polar lobing

What I was attempting to do is dumb it down for the non-audio engineers here.

what on earth is "early reflection point nulling"?

Mitigating or defeating first stage reflections, since direct sound in open space is accompanied by an echo <20ms. Ideally when a listening space is constructed, you can angle the surfaces of your side walls and plan for a sloped ceiling. Greater than 30 degrees angle, the early reflections will end up behind the listening position, avoiding foam material altogether from your B playback room (often used to woo customers in the studio that are listening to their mastered album in a more relaxed environment without all of the room treatments.)

As to the "what?" about micing speakers; measuring a speaker in an ideal environment with a set wave form, then taking measurements of the playback of that speaker in an in-ideal environment (such as a mildly treated home theater room) and then using equalization to match the wave forms (so they null against each other, or within a few percent) is going to give the easiest to attain semi-flat frequency response outside of more proper treatment. There is already plenty of hardware on the market that adjusts this for you, to "calibrate" your speakers, but it's never going to be as good as a properly treated room.

In a home environment, pillows on shelves are better than nothing and more wife friendly. The more surface absorption in a smaller room like the original poster, the better.

The layperson is not going to even be able to read an ETC graph, nor be able to figure out a Shroeder integral of the impulse response (correlating to the direct sound) without additional tools. I'd say a mirror is fine for a non-professional setup. Never mind moving around test materials for bad reflection spikes on said ETC graph. Though it might be entertaining looking at all of those spectral decays vs energy, even without an understanding of them.

Utilizing Owens Corning 703 is fine for his room, as long as it's stacked 4" thick. After first reflection points and enough bass trapping, the only issue he will face is likely 200-400Hz modal ringing.

Then of course there is the issue of relative level vs image shift that would have to be dialed in, if this were a professional installation (since we're on the subject of spectral decay.)

And then loss of momentum based on the subject you touched on -- absorption mechanisms of porous materials, and the loss involved with thermal conduction. Rule of thumb though, is as the thickness of a porous material (such as OC703/rockwool...) increases, the absorption of LF follows. 100mm profiled foam is going to have an absorption coefficient of ~0.25 (this is guessing, since you dissected my post so thoroughly, I'm sure you'll go nerd the math out) at 125Hz, versus ~0.2 on rockwool. Most recording areas get by just fine with either/or.

I'm surprised you didn't comment on the burlap reducing the HF absorption.

I'm not here to get into a flame war with your "clueless" crap. I'm here to help this poster, he asked what he could do "on the cheap", and I gave it to him. I'm not going to sit here and discuss Bazley models as if I were back in school writing a paper. Do you have any suggestions, or are you just here to flame people? Perhaps sheep wool? Relative flow resistance of it appears to be up to 15k MKS rayls m-1 at 4 inches thick. How about crushed up rubber in the walls? :rolleyes:
 
Mitigating or defeating first stage reflections, since direct sound in open space is accompanied by an echo <20ms.

echos are indirect signals arriving ~80ms after direct signal (ignoring gain for simplicity) - but yes, the high-gain early signals arriving with haas interval should be mitigated.

Ideally when a listening space is constructed, you can angle the surfaces of your side walls and plan for a sloped ceiling. Greater than 30 degrees angle, the early reflections will end up behind the listening position, avoiding foam material altogether from your B playback room (often used to woo customers in the studio that are listening to their mastered album in a more relaxed environment without all of the room treatments.)

+1 absolutely. the canted walls also allow the attenuation of the indirect signals without removing energy from the room (as would be with broadband porous absorption) - as the energy can be managed and reintroduced to the listening position via laterally arriving exp decaying diffused sound-field (if that is the target response).

As to the "what?" about micing speakers; measuring a speaker in an ideal environment with a set wave form, then taking measurements of the playback of that speaker in an in-ideal environment (such as a mildly treated home theater room) and then using equalization to match the wave forms (so they null against each other, or within a few percent) is going to give the easiest to attain semi-flat frequency response outside of more proper treatment.

you can't really eq non-minimum phase issues.


In a home environment, pillows on shelves are better than nothing and more wife friendly. The more surface absorption in a smaller room like the original poster, the better.

maybe as a "test" but i would not use pillows as a permanent solution. they're simply not broadband.

The layperson is not going to even be able to read an ETC graph, nor be able to figure out a Shroeder integral of the impulse response (correlating to the direct sound) without additional tools. I'd say a mirror is fine for a non-professional setup. Never mind moving around test materials for bad reflection spikes on said ETC graph. Though it might be entertaining looking at all of those spectral decays vs energy, even without an understanding of them.

i can agree there - but it's not terribly difficult to understand what the time-domain perspective represents.

Utilizing Owens Corning 703 is fine for his room, as long as it's stacked 4" thick. After first reflection points and enough bass trapping, the only issue he will face is likely 200-400Hz modal ringing.

4" oc703 with 4" air-gap ideally (for broadband indirect specular reflection attenuation). the pink fluffy (low gfr) material is what you want for sufficiently thick LF porous absorbers (corner porous bass traps). it's a more effective option *and lower cost (than utiliziing the expensive oc703/705)


And then loss of momentum based on the subject you touched on -- absorption mechanisms of porous materials, and the loss involved with thermal conduction. Rule of thumb though, is as the thickness of a porous material (such as OC703/rockwool...) increases, the absorption of LF follows. 100mm profiled foam is going to have an absorption coefficient of ~0.25 (this is guessing, since you dissected my post so thoroughly, I'm sure you'll go nerd the math out) at 125Hz, versus ~0.2 on rockwool. Most recording areas get by just fine with either/or.

the increased thickness (or additional air-gap) lowers the LF roll-off. again as you continue to increase thickness (to achieve greater LF absorption), one needs to utilize a material with *lower gas-flow resistivity. and this ignores the other aspect that the treatments must be large with respect to wavelength. 125hz is ~9ft. a 48"x24" batt of oc703 is not going to have much effect to a 125hz wave no matter the thickness.


Do you have any suggestions, or are you just here to flame people?

yeah - stick to the lower gfr material like pink fluffy for the corner bass traps and use the expensiev oc703 for broadband specular reflection absorbers (4" thick minimum ideally with 4" air-gap).
 
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