How do I stop my room from interfering with my speakers flatness?

[SunnyOctopus]

How do I do this? How do I figure out how to treat my room and how do I do it for cheap? (IE: Blankets and staplers, bed mattresses, etc.)

Could I put up a blanket at every point where I see the speakers reflection in a mirror to see improvement in frequency response? What about those little jigsaw pieces things they have on kid playgrounds and stuff? I have a million of those.

I currently have the speakers against the center of the long wall of my room with the subwoofer on the floor between the speakers. (the sub is localizable everywhere, but least localizable there.)

Could you guys teach me the secrets of room acoustic wizardry? I have a bed mattress on each of the shorter walls thinking they might do something. A rug covering the tiled floor. I am trying to get the best audio possible out of my bedroom, and I am willing to sleep on the floor to achieve this. I will post pictures and or room dimensions if requested.

Also: I am a poor, punk teenager with no job/money. Please help me.

 

[yepimonfire]

honestly i wouldn't worry about it much unless you actually have a room with excessive of reverb, do you have carpeted floors? unless you use ProLogicII or something like that to listen to music, a 100% dead room will sound awfully flat and lifeless. stereo listening needs some reflections. my advice to you is to worry about reducing bass issues first. also, you mentioned your setup was on the long wall of your room? if i understand you correctly thats not the best idea, in every room i have ever placed a setup in 100% of the time i got much better sound with speakers firing the long way into the room, and with the sub always placed about two feet off center aligned perfectly with the speakers (meaning not in front of them or behind them but at the same distance). as far as room treatment goes, i have found that the most effective way to improve sound is to put treatments behind and the the sides of the speakers, this stop reflections from interfering with the original sound leaving the speakers. honestly i would worry about speaker placement first, this will have a tremendous effect on your sound, good or bad.

 

[bpape]

Having a properly treated room and a complete dead room are two very different things.

Blankets, carpet, etc. are only going to address high frequencies which are already more absorbed than the rest of the band (air, furniture, curtains, people, etc. all absorb high frequencies) Most rooms DO have excessive decay times - especially in the lower mids through the bass region.

The secret to having a great sounding room is:

- Don't overdo it with thin, high frequency only absorbers
- Address your early side wall reflections
- Maintain symmetry left to right
- Don't sit right against a wall. That's the worst place for bass response.
- Don't put your sub in a corner. While it gives the most sheer output there, it's usually one of the worst places for smooth frequency response.
- Balance your absorption scheme to have a proper decay time curve for the room volume and usage that you have.

Bryan

 

[Alex2507]

- Address your early side wall reflections

I'm sure you know more about the pros and cons to this than I do but I have heard an argument against doing this. Any chance of you giving us the Cliff Notes version both sides of the argument and the reason for your position?

TIA,
Alex

 

[bpape]

Side wall reflections depend on a few things:

Closeness to the boundary

Off axis response of the tweeter

Distance difference (time) between direct and reflected sound.

If you don't want to kill the reflections, you can use diffusion instead. The idea is to not have a strong wavefront getting to you out of time if it's close as well as the wavefront being a completely different tonal balance than the direct sound.

Those that promote not absorbing reflections many times assume that the off axis response of the speaker is the same or similar to the direct sound. Most speakers don't perform that way. Tweeters can be as much as 20db different at 30 degrees off axis as they are in direct radiation.

Bryan

 

[Alex2507]

If you don't want to kill the reflections, you can use diffusion instead.

Ummm ... something else I read somewhere said that absorption panels tend to act more like diffusers because of the sound not hitting them straight on but at an angle (maybe that's only for small rooms). The sound absorption coefficients are obtained from tests with the speaker and mic directly ahead of the panel as opposed to the way they are positioned in real world applications. So ... your thoughts on this would also be appreciated.

Something else I have wondered about is the higher sound absorption coefficients for less dense and faced rigid fiberglass panels in the lower frequencies. Since we're focusing on them and trying to let the higher frequencies fly, why are they not used?

 

[bpape]

For bass control, as you get thicker, there is less reflection inside the material if it's less dense which relates to gas flow resistivity.

The faced material actually isn't giving you more at all frequencies, it simply provides a hump in the absorption depending on density of the material behind, thickness of the material behind, and mass of the facing.

Coefficients, if measured properly are measured with a rotating mic around a room with a large sample of the material laid on the floor. It measures both direct and indirect sound and waves are hitting the material at all angles.

Absorption NEVER acts like diffusion. Diffusion is scattering sound evenly in space and in time. Absorption does not do that. What CAN happen is that absorptive materials that are too dense and with very very shallow angles of incidence can allow higher frequencies to skip off of it like a rock skipping on water. It does not, however do anything in terms of scattering or changing it's distribution in the time domain.

Bryan

 

[Alex2507]

What does it all mean ?!?

Okay, we're right at the very edge of my understanding ... maybe a little past.

Thanks for the tutorial.

 

[jostenmeat]

I currently have the speakers against the center of the long wall of my room with the subwoofer on the floor between the speakers. (the sub is localizable everywhere, but least localizable there.)

Could you guys teach me the secrets of room acoustic wizardry? I have a bed mattress on each of the shorter walls thinking they might do something. A rug covering the tiled floor. I am trying to get the best audio possible out of my bedroom, and I am willing to sleep on the floor to achieve this. I will post pictures and or room dimensions if requested.

Also: I am a poor, punk teenager with no job/money. Please help me.

If it's easy enough to run an experiment, try putting them on a short wall instead. Ideal is to have the setup be lengthwise, I assume* so that modal intensity can be reduced.

Once you've done that, (and this is for pure performance for the dollar, with zero consideration to looks or convenience), try seating yourself about 38% from the front or back wall. (b pape has said that number can drop down to 33% with the inclusion of non-axial modes, but in that ballpark, after all your head won't be in a vice).

After that, play with your speakers without any inhibition. Even if they come out several feet into the room. If you found the perfect place, you can always just mark those spots somehow, and just pull speakers there for critical listening.

Well, just some ideas.

- Don't put your sub in a corner. While it gives the most sheer output there, it's usually one of the worst places for smooth frequency response.

Ah, thanks very much for saying this b pape, as maybe I'm not insane for not following the ubiquitous mantra of corner loading. I've never had luck with a corner loaded sub, ever, even in demo rooms. What I do read is that IF* (you know, a really big IF), the room has been properly treated, specifically for bass, then the corner loading can be used for lowering distortion, or increasing efficiency, without fears of modal issues.

I'm sure you know more about the pros and cons to this than I do but I have heard an argument against doing this. Any chance of you giving us the Cliff Notes version both sides of the argument and the reason for your position?

TIA,
Alex

The argument against doing this is to expand stereo width, I believe, with the side wall reflections. However, even those who argue for this will say that the speaker must have superb off-axis-response, as only then will the reflections have a chance of adding to what you hear in a positive way.

What I thought* I had read was that this was specifically with stereo, and that in mch situations, this doesn't really apply. However, I am talking outta my butt on this one, and might very well be wrong here.

Another situation where one may want to treat the sidewall, even with good offaxis, is when it's an asymmetrical room, with one wall much closer than the other, or something . . .

 

[yepimonfire]

i agree about the 38% from walls thing, in my rooms i have noticed, sitting too close to the front wall you hear standing waves from the wall behind, sitting dead center of the room, the standing waves from the front and back walls cancel out the resonating frequencies, (usually 40-80hz) sitting at 38% keeps you out of those problems. as far as corner loading, it is very useful when running two or four subs because this evens out room modes and destroys bass issues with interference of multiple standing waves, this is most useful when placing a sub in all corners.