What to put on the wall behind my speakers?

tboooe · « **on:** 12 Sep 2006, 11:52 pm »

Hi, I have read conflicting results about how to treat the wall behind my speakers. Some people recommend doing nothing. Other recommend absorption. And still others recommend diffusion. Can someone please shed light on this matter? I am utterly confused. I would also appreciate any product recommedation as well.

Thank you in advance.

Levi · « **Reply #1 on:** 13 Sep 2006, 01:00 am »

If money is not an object, RPG it.

tboooe · « **Reply #2 on:** 13 Sep 2006, 01:03 am »

Quote from: Levi on 13 Sep 2006, 01:00 am

If money is not an object, RPG it.

Hi, thank you for the reply. By RPG you mean use their diffusion products? Anything in particular?

thanks again...

Levi · « **Reply #3 on:** 13 Sep 2006, 01:14 am »

There are so many types of RPG Diffusor System. I am guessing you will need an imaging tool the ABFussor.

Analyse your system's needs then check RPG Website and decide which tools you need.

Glenn K · « **Reply #4 on:** 13 Sep 2006, 01:08 pm »

A lot is going to depend on room, speaker type and what the room is used for. If you list those things then I am sure we can let you know what might work best for you.

Glenn

woodsyi · « **Reply #5 on:** 13 Sep 2006, 01:30 pm »

Quote from: tboooe on 12 Sep 2006, 11:52 pm

Hi, I have read conflicting results about how to treat the wall behind my speakers. Some people recommend doing nothing. Other recommend absorption. And still others recommend diffusion. Can someone please shed light on this matter? I am utterly confused. I would also appreciate any product recommendation as well.

Thank you in advance.

Perhaps if you give us a few more details like the room size, layout, speaker make and model, speaker placement and what kind of music you like, we can better assist you. You absolutely need absorption if you have dipole speakers but you can can go many ways with box speakers. God only knows the stuff I have tried. I personally like absorption behind the front speakers and diffusion behind my listening position. BTW, would you please beat SC for once!!!!!!!!

tboooe · « **Reply #6 on:** 13 Sep 2006, 01:31 pm »

Quote from: Glenn K on 13 Sep 2006, 01:08 pm

A lot is going to depend on room, speaker type and what the room is used for. If you list those things then I am sure we can let you know what might work best for you.

Glenn

Thanks Glenn. My 2 ch only system is in our living room which we converted to a type of music parlor with our grand piano and guitars. The overall appearance of the room is very important. I have BW 802d speakers. The room itself is about 15ft wide and 22 ft long. My system is setup on the 15ft wall. The speakers are 4ft from the front wall and only 2.5ft from the side walls (i cant really change this). I sit about 15 ft away. The ceiling is 9ft above where the stereo is but this changes to vaulted ceilings after about 7ft measured from the front wall. Behind me opens up to the rest of our house. There is a staircase (3 staggered walls) and a large hallway. Because I of this I think I have a lot of good diffusion behind me. I hope this clarifies things.

By the way, usc is GOING DOWN THIS YEAR!!!!!!!!!!!!!!!!!!!!1

woodsyi · « **Reply #7 on:** 13 Sep 2006, 01:40 pm »

Is the piano behind your listening position against the back wall? Are there any acoustic treatments there currently? What do you have between the speakers and the listening sofa -- a coffee table? Carpeted or hardwood? Paneled, drywall or wood? Flat or domed ceiling? Anything else I missed.

Addendum: We are cross posting. Would you characterize your sound as live or dead at the moment?

bpape · « **Reply #8 on:** 13 Sep 2006, 02:53 pm »

My guess is that with all the instruments in there that are specifically designed to resonate, it's probably got a huge decay time.

With 802 D's and for 2 channel, I'd probably agree with woodsyi about absorbtion on the front wall and diffusion on the rear. The question now is where are the speakers placed so we can get an idea of whether or not you have serious SBIR issues that need to be addressed with panels behind the speakers and directly beside the speakers on the side wall.

Bryan

tboooe · « **Reply #9 on:** 13 Sep 2006, 03:58 pm »

Quote from: woodsyi on 13 Sep 2006, 01:40 pm

Is the piano behind your listening position against the back wall? Are there any acoustic treatments there currently? What do you have between the speakers and the listening sofa -- a coffee table? Carpeted or hardwood? Paneled, drywall or wood? Flat or domed ceiling? Anything else I missed.

Addendum: We are cross posting. Would you characterize your sound as live or dead at the moment?

Hi, the piano is behind the listening position. I do not have any treatments yet. There is only a very low cocktail ottoman (about 15" high) that is leather between the listening position and speakers. The floor is carpeted and the walls are drywall. The ceiling is flat at 9ft then it transitions to about vaulted ceiling about 1/3 of the way into the room (from the front wall where the speakers are).

I think the sound is pretty lively. I actually do not have anything to complain about. I just want to make sure I am getting the most out of my setup. The one weakness of the system is soundstage. I do get a good sense of width or depth. Because the speakers are so close to the sidewalls I am thinking that I need to treat the 1st order reflections. I have no idea why I do not get a good sense of depth in my system. Another problem is soundstage height. When I listened to my speakers at the dealer, the sound seemed like it was originating from a position about 2-3 ft above the speakers which I like. My sound is right at speaker height.

thanks in advance for the help!

tboooe · « **Reply #10 on:** 13 Sep 2006, 04:00 pm »

Quote from: bpape on 13 Sep 2006, 02:53 pm

My guess is that with all the instruments in there that are specifically designed to resonate, it's probably got a huge decay time.

With 802 D's and for 2 channel, I'd probably agree with woodsyi about absorbtion on the front wall and diffusion on the rear. The question now is where are the speakers placed so we can get an idea of whether or not you have serious SBIR issues that need to be addressed with panels behind the speakers and directly beside the speakers on the side wall.

Bryan

Bryan, the room is arranged in this order (from the front wall): speakers >> listening position >> piano and guitars.

I think I have a problem with 1st order reflections since the speakers are so close to the side walls.

Ethan Winer · « **Reply #11 on:** 13 Sep 2006, 06:36 pm »

> I have read conflicting results about how to treat the wall behind my speakers. Some people recommend doing nothing. Other recommend absorption. And still others recommend diffusion. Can someone please shed light on this matter? <

To my way of thinking, the front wall is third place in the list of things to worry about. Unless you have loudspeakers that send sound equally out the rear. Most important are the first reflection points on the side walls and ceiling. Second is the wall behind you. Last is the wall behind the speakers. Note that this speaks to direct reflections only. You still need bass trapping.

Also, I'm not so worried about having musical instruments in the same room. In my home studio I have an acoustic guitar and a cello out in the room (too lazy to put them away), and I've never noticed a problem. If you notice your piano and guitar ringing obviously when music stops, then you can address that.

--Ethan

bpape · « **Reply #12 on:** 13 Sep 2006, 11:52 pm »

Not saying they're a problem - just that they'll add to extending decay time.

As for speakers being close to side walls, the early reflections would not be as much of my concern as the SBIR issues from same. Pretty much all rooms need to deal with early reflections off the side wall (disputed by some but proven over time by many smarter than I am). THe issue becomes how much, how thick, how deep they should go, etc.

Bryan

jimlevitt · « **Reply #13 on:** 18 Sep 2006, 07:00 am »

Quote from: Ethan Winer on 13 Sep 2006, 06:36 pm

>
To my way of thinking, the front wall is third place in the list of things to worry about. Unless you have loudspeakers that send sound equally out the rear. Most important are the first reflection points on the side walls and ceiling. Second is the wall behind you. Last is the wall behind the speakers. Note that this speaks to direct reflections only. You still need bass trapping.

--Ethan

Ethan: where does the front wall rate in your heirarchy if one does have loudspeakers that send sound equally out the rear? Mine do in the bass and mid. The wall behind the speaker is sheetrock, with a window located behind each speaker as well. Do dipoles require some trapping on the wall behind them?

Bryan: since you just heard the Nomad Ronin, which is dipole at least in the midrange, what are your thoughts on this?

Thanks,

Jim

bpape · « **Reply #14 on:** 18 Sep 2006, 11:02 am »

Well, I'll caveat it and say it depends on the usage. In a multi-channel environment, the front wall needs to be dead. In a 2 channel environment, it's debatable - but still usable if you prefer.

I'll say that the most important place is on the side walls for those reflections. After that, the back wall is a decent place but again more for dealing with modal issues rather than purely for reflections - unless you're sitting very close to the rear wall.

As for back being an earlier reflection than the front, that's true - from about 1kHz up. Lower than that, the waves propogate more and more like a sphere so that they're actually bouncing off the front wall first. This is also why they can be so destructive in terms of SBIR and why I personally choose to damp it at least in places, with something much thicker than standard reflection control. Think more 2-4" thick directly behind the speaker.

In the case of an open baffle like the Ronin, I'd likely either use diffusion up high behind it (some still like absorbtion) and absorbtion down low - OR - faced absorbtion that will leave most of the mids/highs untouched and just absorb bass.

Bryan

Ethan Winer · « **Reply #15 on:** 18 Sep 2006, 05:24 pm »

Jim,

> where does the front wall rate in your heirarchy if one does have loudspeakers that send sound equally out the rear? <

I don't understand why speakers would be designed that way, but I know some are. When this has come up in the past - more than a few times - I have always suggested asking the speaker manufacturer. I have also asked people to come back and post what the manufacturer said. So far not one person has ever done that! So I advise you to do the same. Please ask your speaker maker what they recommend and let us know what they say. My gut feeling is it's best to absorb those reflections. If not by treating the entire front wall, at least the portion right behind the speakers.

--Ethan

bpape · « **Reply #16 on:** 18 Sep 2006, 05:28 pm »

Well, actually, we had the Ronin's designer and builder in the room with us while we were listening. He seemed pleased that there were some shelves, albums, etc. and a 3D (pseudo-skyline) on the wall behind/between the speakers.

He said basically to treat these the same way as you would Maggies or something similar. They did indeed seem to couple to the room the same way.

As for why, I'll just say that these were some of the most effortless, easy to listen to speakers I've heard in a long time.

Bryan

jimlevitt · « **Reply #17 on:** 18 Sep 2006, 07:35 pm »

Ethan:

Here's what Siegfried Linkwitz (Linkwitz Riley crossovers, Audio Artistry speakers, Linkwitz Orion and Pluto speakers) has to say:

"Often concern is expressed over the fact that the rear radiation from a dipole is out of phase with the front radiation, and that thus any sound reflected from a wall behind the speaker would cancel sound coming from the front of the speaker. Cancellation can only occur when direct and reflected sounds are exactly of opposite phase (180 degrees) and of the same strength. Since direct and reflected sounds travel paths of different length, they undergo different amounts of phase shift. Thus, the phase and magnitude conditions for cancellation are given only at certain frequencies, if at all. At some other frequencies direct and reflected sounds will add. The same also applies to a monopole speaker in front of a wall. The only difference is in the frequencies for which addition and subtraction occur. The best remedy is to move the speaker away from the wall, or to make the wall as sound absorptive or diffusive as possible."

You can find a wealth of information at the Linkwitz Lab site, starting with this page and proceeding from there:
http://www.linkwitzlab.com/rooms.htm

Jim

Ethan Winer · « **Reply #18 on:** 19 Sep 2006, 01:31 pm »

Hi Jim,

> Here's what Siegfried Linkwitz (Linkwitz Riley crossovers, Audio Artistry speakers, Linkwitz Orion and Pluto speakers) has to say <

That's interesting, and it sounds like he's saying it's okay to absorb or diffuse the reflected sound, thus discarding the part that comes from the rear. So essentially, the rear radiation from this type of speaker is a byproduct, not a design goal. To my way of thinking that's the only approach that makes sense. Thanks.

--Ethan

woodsyi · « **Reply #19 on:** 19 Sep 2006, 01:47 pm »

I don't know about Orion or other dipole speakers but it was a big improvement when I put absorbers behind a pair of Soundlab full electrostats in a 22x26 room. Everything depends on room size/shape and speaker arrangement. What I found in my room of 16x24x7.5 is that bass traps and early reflection treatments are essential. A diffusive panel on the back wall really clears the mid range up. I would generalize and say that bass traps, mid/high absorbers and mid/high diffusers deployed strategically in a room according to your needs gets you the best sound.