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silvertone
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Diffusers or Absorbers behind the speakers?

I'm in the process of treating my listening room's acoustics. After doing some research, it looks like some are of the opinion that one must 'kill' the first reflections by placing sound absorbers right behind the speakers. Others prefer to put diffusers right behind them. Which approach is right? I'm definately going to put diffusers (3 Furutech panels) on the wall behind the listening couch, heavy curtains (velvet) on the side walls to cover up glass windows. I have relly high ceilings, about 15 feet. Any feedback will be appreciated.

Thanks,

mrlowry
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Re: Diffusers or Absorbers behind the speakers?

What kind of speakers do you have? How far from the front wall are they? That might influence people's answers. Personally I almost always lean towards diffusion rather than absorption for one very simple reason, it's really easy to over do absorption and it can really destroy the sound. People tend to do a little and then say,

silvertone
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Re: Diffusers or Absorbers behind the speakers?

Thanks a lot for the reply. I have Paradigm S8's, these go down deep in the bass, but since I moved to this house the bass has completely dissapear. Everything sounds bright, just awful. I have the speakers about 4 feet from the back wall (into the room), problem is there's glass windows behind them. I guess I'll start by putting two diffuser panels right behind them, and the velvet curtains. I'll see how things start sounding at that point. Do you have a specific product in mind for the bass traps?? Again, thanks for your tips.

mrlowry
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Re: Diffusers or Absorbers behind the speakers?

Do you have your speakers firing down the long dimension of the room or across the short dimension? The best bass that a room has to offer is almost always obtained by firing down the long dimension of a room it gives the bass wave more distance to propagate. Is your listening position directly against the back wall? If so try moving it forward temporarily, see what happens. If you have a rectangular room figuring out where the bass problems are is fairly simple. Here is the formula:

1130/2X=F1 (1130 is the speed of sound at sea level through air, 2X is one of the room dimensions multiplied by 2, F1 is the first resonant mode .)

You would calculate each room dimension with this formula. As an example a room that has a 10 foot depth would be 1130 divided by 2 multiplied by 10. This would be 57 hz. This is only THE FIRST resonant mode of ONE dimension. To calculate the other modes of that dimension you would add 57+57 which equals 114 to calculate the next mode you would just keep adding 57 to the last number so the next mode would be 171. You would stop at 200 hz. Now do that for the other two dimensions of the room. The frequencies that will give you the most problems are ones that are close together or identical in more than one dimension. This is why you don

Yiangos
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Re: Diffusers or Absorbers behind the speakers?

You could allways experiment with egg crates.When you are happy with the results,go get some good stuff !

Jan Vigne
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Re: Diffusers or Absorbers behind the speakers?

You say you are in the process of treating your room but don't indicate you've done anything to improve the sound by way of speaker placement. Maybe I've just misinterpreted what is happening but trying to reduce brightness in order to increase bass performance is heading you in the wrong direction.

If you haven't done a comprehensive speaker set up, I would suggest you first try something that costs nothing but time. Read about speaker set up and try several of the described methods. Many times the answer for any given room lies in combining aspects of several set up procedures. Each set up process aims for something different and experimentation is the key to good sound. The best speaker set up is done with a few tools; a tape measure, some masking or drafting tape, a laser pointer and a level. If you find the proper location for your speakers places them in awkward positions for normal life, mark the spot in an inconspicuous manner and move the speakers to and from the location for listening. If you have carpeting on the floor, I usually suggest a slightly different color of thread looped through two corner locations of the speaker to mark the spot. If you haven't done spikes and stabilization of the speaker, start with getting the speaker right. When thinking about set up, remember your listening position is part of what affects the sound quality you hear. Moving your listening chair a few feet can make large differences in what you perceive, and this is especially true if your room has standing waves of any intensity (which most rooms do to some extent).

Normally, a room works best with a combination of absorption, diffusion and controlled reflection. If you haven't read any articles to give you a good handle on how to set up room treatments, spend some time studying before you head off to spend money. A cheap experiment in absorption is loosely wadded up newspaper inside cardboard boxes. Use these in the corners of the room to act as temporary bass traps. Remember a monople speaker is treated differently than a bipolar design when you think about room treatment. Almost all monople speakers will benefit from dampening the first reflection point in the room. When you experiment with absorption of mid and high frequencies, keep in mind that any "home brew" material you use will almost always be reflective at some frequencies and absorptive at others. Treat the two largest parallel surfaces which are the floor and ceiling. If room reflections are the real problem and you want a cheap fix, set your system up on the diagonal of the room. The longer distances between direct and reflected signals will diminish the signal strength of the reflected sound.

http://www.gcaudio.com/resources/howtos/index.html

http://www.harman.com/wp/pdf/Loudspeakers&RoomsPt3.pdf

http://www.soundstage.com/audiohell/audiohell200111.htm

http://www.tnt-audio.com/casse/waspe.html

http://www.nsmaudio.com/brochures/basicstsetup.html

http://forum.ecoustics.com/bbs/messages/5/1664.html

http://forum.ecoustics.com/bbs/messages/1/263652.html

silvertone
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Re: Diffusers or Absorbers behind the speakers?


Quote:
If room reflections are the real problem and you want a cheap fix, set your system up on the diagonal of the room. The longer distances between direct and reflected signals will diminish the signal strength of the reflected sound.

Great suggestion! I had thought about this, I'll give it a shot. In my case though, if I orient the speakers this way then the kichen space would be behind me not a wall. I think this will def. get rid of some reflections. Thanks everybody for the suggestions. I don't think I'm getting carried away with the intial treatment, the velvet curtains are for sure going in to cover the glass windows, and I'm ordering two Furutech panels to start, these will go right behind the speakers. At that time I'll evaulate the sound and measure the response. Next, I'll probably put absobers right behind the speakers and move the Furutech's to different locations and re-measure. Now, I'm lazy in that I don't want to scroll through different tones and graph the response by hand, I think there's a software tool out there with mic built in which automatically graphs the response. Anybody knows the name of this application/hardware? I vaguely rememember reading about it long time ago, I think it was an add on application to a PDA.

cyclebrain
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Re: Diffusers or Absorbers behind the speakers?


Quote:

At that time I'll evaulate the sound and measure the response. Next, I'll probably put absobers right behind the speakers and move the Furutech's to different locations and re-measure. Now, I'm lazy in that I don't want to scroll through different tones and graph the response by hand, I think there's a software tool out there with mic built in which automatically graphs the response. Anybody knows the name of this application/hardware? I vaguely rememember reading about it long time ago, I think it was an add on application to a PDA.


Moving your speakers around to change relections will also influence how they excite room modes. Trying to step through frequencies and measure levels does not work well. Better is to use pink noise and a spectrum analyzer setup like the Trueaudio free download. Even better yet is to use an impulse based test signal. I have tried positioning my speakers in various positions and listening to them I would think they sounded great.Then later would put on a certain disk that would excite a room mode and sound awful. Using test software has helped get a good setup much quicker.

cyclebrain
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Re: Diffusers or Absorbers behind the speakers?


Quote:
You could allways experiment with egg crates.When you are happy with the results,go get some good stuff !


Though many diffusors out there look like an eggcrate, they are very different. A modern commercial diffusor is designed using many close tolerances each playing a part in the diffusor's bandwidth and dispersion.

Yiangos
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Re: Diffusers or Absorbers behind the speakers?

Hiya

Yes,i know that.All i meant was,experiment with eqq crates, see how many and where they need to go,then purchase the expensive stuff (real diffusers).
I have a question regarding these things.I understand there is no simple answer to this unless measurementsare done etc but i am going to ask anyway. My main system is in a dedicated listening room and i do not have any acoustic problems.I moved my old system which was eating dust ib a storage room,down to the living room.The acoustics there is not bad except from some standing wave problems.My loudspeakers do not "develop" mid-bass and lower-bass the way they should.If i stand behind the speakers,there is too much bass actually.From what i read,bass traps is not supposed to actually eliminate bass in areas where excessive bass is produced but actually cure situations like mine,where the front and rear waves interact with each other and procude a null,thus,less bass than the normal.
I am not saying this is the only purpose for a bass trap but will it work in my situation ?In a few words,will a bass trap actually give more bass ?

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