Room Treatment Idea

[seti]

My room has a terible echo and I don't like the foam stuff you can buy. While I was at home depot and in the carpet section I noticed the mat that goes underneath was fairly thick. I had a friend with me who works in a fabric shop and she was telling me how people are using fabric on walls instead of wallpaper and she could get me a good deal. Do you think it could work to put the carpet under padding on the walls and then the fabric over that? It's just an idea but was wondering what you guys thought.

this stuff looks good for absorbing sound wouldn't need underpad...

http://www.distinctivefabric.com/pics.php?id=3TONEFUR1

lol maybe not

[sfogg]

What some people do in dedicated rooms (wouldn't last in a typical room) put up furring strips at the top bottom and middle of the room horizontally. Then treat the bottom half of the walls with 1" Insulshield and the top half with polyster batting. This is covered with Gilfords of Maine acoustic cloth usually with a different color on the top half compared to the bottom half. The furring strings and cloth edging is covered with crown molding and a chair rail.

Looks great and is supposed to sound very good. But the walls are literally covered in fabric about an inch off the actual wallboard so it makes outlets and light switches have to be extended and with kids in a common room I doubt it would last.

This is how all the walls are treated in the pictures here...

http://www.designcinema.com/gallery1.htm

Lots of work to do it but it does look great at the end.

I didn't have the room to do this in my theater so I went with the foam tiles. Since it is a dedicated room and the lights are usually turned down the look doesn't bother me but others might disagree.

Shawn

[Colin]

your walls probably have fiberglass batting, but they could be filled more and be deader, especailly if you can get through the header in the attic and blow in more insulation, the interior walls don't have anything inside them...

[sfogg]

Colin,

Putting fiberglass between the studs of his walls won't do anything for a slap echo. The whole reason he is getting the echo is the sound is bouncing off the drywall. You control that with treatments in the room.

Shawn

[Colin]

too true, claps start at 125Hz and continue throughtout the rest of the upper spectrum with their energy centered at 1-2kHz, this area is attenuated by foam wall treatments, though I think the batts or wall insualtion might do better, many foam treatments only affect the upper 4-5kHz and above frequencies, RealTraps MiniTraps work, but they are large panels, so I though the interior wall solution might help more, might be only two walls...

[sfogg]

"many foam treatments only affect the upper 4-5kHz and above frequencies,"

What products are you looking at that are only effective that high? 2" acoustic foam wedge panels are reasonably effect from about 300hz and up. 4" panels have reasonable absorption to about 125hz. With either panels spacing them off the wall will increase their effectiveness too.

"so I though the interior wall solution might help more, might be only two walls."

It does nothing for slap echo. The whole reason for the echo is because the sound is reflecting off the walls. If the sound is reflecting off the walls what is behind the wall isn't going to help.

Trust me, I recently built my room with double staggered stub walls (6" thick instead of 4"... so they had more then normal insulation in them) and once the drywall went up the room had horrible slap echo in it... as expected. After the foam went in you can clap almost anywhere in the room and hear just about no echo at all.

Shawn

[seti]

Interesting hadn't thought of insulating inside the walls. That room could use all the insulation it can get as it is the hardest room to heat or cool. The house was built in 1890 so I am not sure how it was constructed but I did mention this to my brother who is a contractor and he was sure I would have to drill lots of holes at the top of the walls and fill it in that way.

If I did two walls which two should I do? Behind and infront of the Belles?

I was hoping that a combo of foam and fabric on the walls could help as I have seen the fabric covered walls done before and it looked pretty cool. The addition of the foam would add some instalation complications but nothing I couldn't figure out. If I can just cut the echo in half I would be happy.

[DrWho]

Though absorbtion will probably get rid of the echo, you might end up with an eery dead sounding room if you use too much. Diffusion really is the better way to get rid of these echos and keep the room lively sounding. That said, diffusion tends to look a lot uglier unless you're building it into the design of the room. Can you think of any kind of decor or something acceptable that would change the shape of your walls? Like old roman pillars or tapestries with large extravagant moulding? I'm not sure what look you're going for, but getting rid of the large parallel walls is the first step in defeating echo and keeping the room live. Even putting extra furniture or bookshelves in a room goes a long way in diffusing the sound.

Could you build large curved panels (similar to the masonite panels, but it doesn't have to be masonite) into the wall and cover them with fabric? You could even paint the curves the same color as your wall too if you wanted. I have seen pictures of a few rooms that do this and it looks really cool. I'll see if I can find some links.

[Colin]

bookshelves-

on both sides of the reflective walls...

[sfogg]

"Though absorbtion will probably get rid of the echo, you might end up with an eery dead sounding room if you use too much."

That is true for 2 channel listening. Typically you want a live end, dead end. You make the front of the room up near the speakers dead and leave the back of the room fairly live to add ambiance/life to the playback.

When you listen to music in surround sound you are pulling the ambiance right out of the recording and reproducing it from the proper directions so for the most part the less 'extra' ambiance the room adds the better.

Shawn

[Erik Mandaville]

Don't clap!

[DrWho]

The eery sounding deadness I'm talking about is when you walk into the room with nothing playing. It seriously is a very hard thing to get used to.

I think you could argue that the "live end dead end" still applies to surround sound, just that you've now got a more complex situation with at least 3 sets of "live and dead ends" to accomplish. However, I've read that you want the front of the room live and the back of the room dead...I wonder if both approaches aren't considered standard.

The studio acoustics guides that I've read all try to minimize the early reflections to the listener, but do try to keep a natural room reverberation so that it continues to sound natural (a studio that sounds too dead means the mixer is going to try and make the recording more alive, which will then sound over produced in a room that isn't dead sounding). I know studio acoustics is a slightly different approach, but it's the only place where I've seen absorbtion consistently overdone. Absorbtion in moderation really is a good valid method, but it's better to underdo it than overdo it.

[sfogg]

"The eery sounding deadness I'm talking about is when you walk into the room with nothing playing. It seriously is a very hard thing to get used to."

My room does that too but since it is a dedicated room it isn't an issue. Anytime we are in there something is playing. I've have numerous comments from people walking in the first time that 'it feels like a theater' which it does. Even though it is tiny in comparison, I think that comes from lack of reverb as well as the lighting.

"However, I've read that you want the front of the room live and the back of the room dead...I wonder if both approaches aren't considered standard."

That is the first time I've seen that suggested for a surround system. I left a little life in the rear of the room but not much. I did that partially for asthetics and partially because the surrounds are very close by so I wanted a little bit of reflections for more fill.

"The studio acoustics guides that I've read all try to minimize the early reflections to the listener, but do try to keep a natural room reverberation so that it continues to sound natural"

That is a different animal then surround. They are typically mixing for 2 channel distribution, so it does make sense that they have live end dead end setups.

"Absorbtion in moderation really is a good valid method, but it's better to underdo it than overdo it."

For 2 channel listening I agree.

Shawn

[colterphoto1]

DrWho writes:

"The studio acoustics guides that I've read all try to minimize the early reflections to the listener, but do try to keep a natural room reverberation so that it continues to sound natural (a studio that sounds too dead means the mixer is going to try and make the recording more alive, which will then sound over produced in a room that isn't dead sounding). I know studio acoustics is a slightly different approach, but it's the only place where I've seen absorbtion consistently overdone. Absorbtion in moderation really is a good valid method, but it's better to underdo it than overdo it."

Mike, you just described my approach in my living room. The angles of the speakers insure that there are absolutely minimal early reflections, ie NO sidewalls for ANY of the four main Cornwalls (except maybe the rear right, which has one wall five feet away) and the rooms walls and other surfaces are a mixture of 20% very hard (plaster ceiling) 20% very soft (double padded carpet) and 60% warm (wood paneling with no backing plaster so it can flex)

Michael

[WMcD]

I have a similar problem in the main room. When I sneeze, the echo sounds like science-fiction sound effects.

I had made some poly cylindrical reflectors for the office out of foam core and they seemed to help. I don't know where that posting is, but there were some photos.

I couldn't put too much of a bow in them because foam core will snap. In the mean time I've discovered that foam core without the paper covering is very much more flexible. It is like the difference between uncooked spaghetti and al dente. It is hard to believe the paper contributes that much to the stiffness, but true.

It may be that all you have to do is wet the paper until it is soft, rather than remove it. I'm still experimenting.

Right now I'm considering polycylinders for home. I have some of the masonite. You can find some plans and comments in the Dope From Hope which I previously posted. Search in Technical Questions.

The Master Handbook of Acoustics states you can stuff them with fill and it makes them a bit more effective. This is based upon a Russian book on acoustics.

PWK said to cover 10 percent of the wall area. My thought is that 20 percent might be more realistic.

I made my previous ones of a size to allow me to glue an art print to it. Monet on a curved surface is not half bad.

Gil

[DrWho]

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On 2/27/2005 11:08:46 AM sfogg wrote:

My room does that too but since it is a dedicated room it isn't an issue. Anytime we are in there something is playing. I've have numerous comments from people walking in the first time that 'it feels like a theater' which it does. Even though it is tiny in comparison, I think that comes from lack of reverb as well as the lighting.

That is a different animal then surround. They are typically mixing for 2 channel distribution, so it does make sense that they have live end dead end setups.

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I would wager that your room has the proper amount of absorbtion then, and really isn't that eery dead sound I'm trying to describe. With the room silent, do you feel like you have to shout when trying to have a normal conversation? What you describe sounds to me like the noise floor in your room is extremely low (kinda like Artto's place) and there are few resonances in the room. I can guarantee that there's reverb though, it's just a question of how long it is

And I just wanted to point out for the record that the studios I was referring to are all surround studios. I wish I had a scanner so that I could upload the pics from my textbooks. Every wall is splayed so that there are no early reflections arriving at the mix position (including the cieling). The only surface that allows for early reflections is the floor which is almost always wooden. There are a bunch of psychoacoustic theories that try to explain why it sounds more natural that way, but the important thing is that it sounds unnatural to have absolutely no reflections at all (otherwise we should just listen on headphones and be done with it). The back of the room typically uses a ton of absorbtion so that the signal from the mains doesn't bounce off the rear wall and interfere with the info from the surrounds. I would think this would be a concern in a playback situation as well. I notice it a lot in my home because I've got over 60 feet to the first real wall behind me...the echo from the mains is very distracting. In a room where the listening position is closer to the back wall, this echo will start to sound more like a smearing of the sound because it will be arriving sooner, though a certain level of smearing could also be percieved as a fuller sound as well.

In referece back to Shawn's system, the more live rear end is probably helping to make the surrounds sound larger (whereas a dead end would make them sound smaller). I think it's important to note the complexity of the matter and that acoustics really is an art of compromise. If it were completely science, then we would already know what the ideal room is and every studio and every major listening environment would be built that way.

Btw, do you have any pics Shawn? and what components are you running? (I didn't see anything in your profile). It sounds like you got a rockin system over there.

[sfogg]

" What you describe sounds to me like the noise floor in your room is extremely low (kinda like Artto's place) and there are few resonances in the room."

That is a good point about the noise floor, that definitely contributes to it too. The room is very quite as it was built in the basement using staggered studs (different studs for the outside of the wall then the inside) on 2x6 top/bottom plates with drywall on the outside and double drywall on the inside. The ceiling is also double drywall on its own studs secured to the side walls alone. Other then the poured cement basement floor the room isn't attached to the rest of the house at all to keep it as isolated as possible. The door is a heavy DIY affair using 3/4" Maple plywood front and rear spaced apart with 1x6s and sealed using a couple of different Zero International products. As far as treatments do the front wall is all 4" acoustic foam. Side walls at the front are 3" foam that transitions down to 2" then to bare walls. Ceiling is entirely covered in 2" foam and the rear wall and the side walls have a strip of 4" foam (on the rear wall) that extends on the side walls using 2" foam at slightly above ear level. The floor is carpeted.

" I can guarantee that there's reverb though, it's just a question of how long it is "

That is true of course but it is short. I don't have the measurements in front of me but I have checked it with ETF as well as spending entirely too much time clapping down there. It was pretty funny but after I got the treatments done at certain points if I clapped I'd still get a slightly ringing in the room. Took me a couple of minutes to realize it was because the hand clap was causing the 511B horns to ring on their own from across the room. A little damping on them took care of that though.

"In a room where the listening position is closer to the back wall, this echo will start to sound more like a smearing of the sound because it will be arriving sooner, though a certain level of smearing could also be percieved as a fuller sound as well."

Get it close enough and because of the Haas effect it won't have nearly the same effect as when the echo is very delayed such as your example of your rear wall.

" I think it's important to note the complexity of the matter and that acoustics really is an art of compromise. If it were completely science, then we would already know what the ideal room is and every studio and every major listening environment would be built that way."

It is also a matter of preference too of course as two different people may very well have two different preferences in sound.

"Btw, do you have any pics Shawn? and what components are you running? "

I posted some in the long home theater thread here showing the construction and it after it was completed. Front speakers are modified 2-way LaScalas using 511B horns w/Altec 902B drivers and Al K's ES600 crossovers. L/R subs are DIY units using a pair of JBL Sub1500 drivers (Revel Ultima Sub 15 driver) in 6'^3 sealed cabinets. For an LFE sub I have a ServoDrive ContraBass but haven't moved it into the system yet. Sides and rears as RS-3IIs. My L/R amp currently is a modded St-70 and the center channel is a similarly modded MKIV. L/R subs are driven by a Crown K2 and the surrounds by Adcom 535II. Pre-Pro is a Lexicon MC-12B with the v4 room correction software/hardware in it. A Denon 2900 is my main source for CD playback as well as DVD-A/SACD and it is also SDI modded for video.

The system also doubles as a theater which has a JVC G10U projector with ISCO II lens projecting onto a 8' wide Carada Brilliant White 2.35 AR screen in a constant height setup. The screen is hung from the ceiling so that I could have the acoustic treatment behind it as well as a mini-split AC system. Lumagen HDP Pro video processor handles deinterlacting and scaling. OTA HDTV, D-VHS, Pioneer LD, and a Kenwood Soverign 400 disc DVD changer and Entre system is used to catalog my DVDs for library style playback. The changer is also SDI modded for direct digital video feed to the Lumagen.

Shawn