# Any benefit of Bass Trappings not in corners?



## Guest (Dec 11, 2006)

I've thought about adding bass trappings for quite some time in my Home Theater. Actually my room is somewhat of a multipurpose room in that it also doubles as a billiards room in the back half of my theater area, and a nice adult beverage area off to one side.

So the wife isn't really into large pieces of anything placed in any of the corners. It dawned on me this weekend that I could hide some owens corning panels underneath the 4' x 8' billiard table and could also hide some behind my 55" mits rear projection unit, and no one but me would even know anything was there.

But neither of these places is in a corner, so I'm thinking that it would be of little to no value.

Expert (and even non-expert) opinions welcomed.


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## brucek (Apr 11, 2006)

> and even non-expert) opinions welcomed


That's me for sure. I would think that in the same way if you hung curtains on all the walls, the sound would be damped because of the loss of reflective surfaces, the corning panels would provide the same result. This would be more for higher frequencies would it not?

brucek


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## Bob_99 (May 8, 2006)

Steve,

I'm not an expert but I just treated my listening area and unfortunately you can't change the physics of sound. For bass trapping, you need to get as much of the wall/wall corners and wall/ceiling corners. Then, deal with the first reflections points. I understand the dilemma of making it look good but unless you want to tear the room apart and build it to hide the treatment, then you just have to try and find something acceptable. My wife has been really outstanding in letting me put panels up and I only had to let her paint whatever she wanted. I may have to pee in a purple bathroom but my listening area sounds pretty good.

Bob


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## Guest (Dec 12, 2006)

Bob_99 said:


> For bass trapping, you need to get as much of the wall/wall corners and wall/ceiling corners.


This is what I figured to be the case. Particularly since in my room there are 2 corners where I can hear a substantial loudness increase. It sounds as if the bass accumulates in these corners, must be that physics thing.:bigsmile: 

So with that in mind, I have an HVAC soffit, boxed out in drywall, that runs down the middle of the room, dropped about 9 inches below the height of my drop ceiling and about 14-16 feet long. I wondering if a small base trap at this soffit/ceiling junction would be of value? I think if I did it properly it could blend into the environment fairly easily, but I'm also thinking this small of an area may not be too much of a problem area for bass accumulating.

One of my challenges is that the room sounds pretty good as is. I have a pad and carpet over the concrete floor, an Armtrong acoustic tile drop ceiling and some pretty thick drapes on the 2 windows. So I'm not displeased with the sound quality at all, just trying to tweak it to be even better. Of course my wife thinks I'm nuts as is, so trying to convince her "bass traps" are essential is fighting an uphill battle.:dumbcrazy:


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## Bob_99 (May 8, 2006)

Steve,

The soffit down the middle probably won't do much for the bass but, if I understand your layout correctly, I think that it gives you a great opportunity by considering running fake soffits down the left and right side of the wall/ceiling corner. If you fill the fake soffits with OC703 or equivalent, you should get some really good bass trapping. It will also make the the room look symmetrical and not look out of place (if done correctly). For the front corners, have you considered something like GIK tri-corner traps? They look nice and can easily fit in without being too intrusive. You should also consider measuring the room to see what your decay time looks like. The bottom line though, is this: whatever sounds good to you, is what you are trying to achieve :yes: . Do the treatment if it's something that you will enjoy. Personally, I was totally impressed with my results. After I first installed my system, my wife told me that she couldn't tell the difference between my new surround system and a fifteen year old Technique stereo system :duh:. Then one day after I treated the room and while we were watching a movie, she told me that the system really sounded good :bigsmile: . This totally came out of the blue and I practically soiled myself when she said it :holycow: . 

Bob


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## yphs_mst (Nov 11, 2006)

Hello Steve,

If half back of the area is used for other thing, I don't think we need to worry that much on that area (if I understand it correctly). The point between the home theater and the billiard area can be separated be .. say draperies ? I guess putting bass trap like doubling the wall with thin gypsum board near the listening area would work if that's possible. If bass is really a big problem at the listening spot, trapping can be made by cutting PVC at certain length if you know what frequencies the problems are.

Hadi


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## brucek (Apr 11, 2006)

> trapping can be made by cutting PVC at certain length if you know what frequencies the problems are.


Can you explain this further? 

brucek


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## bpape (Sep 14, 2006)

The absorbtion behind the TV is in the wall/floor corner. It's not a lot but better than nothing. Under the pool table will give you a little but but again, not a lot and will actually filter somewhat as it's in the center of the room. It will be more effective at the 2nd, 4th, etc. harmonics of the mode for the dimension it's centered in.

Would the significant other allow something that looked like Wainscoat on the bottoms of the walls? If so, you could build some wood faced membrane absorbers that would work over a couple of octaves in the bottom end and be pretty effective.

Bryan


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## scott (Dec 11, 2006)

i have read that you can take a concrete form (sonno tube) plug it and fill it with sand for base trapping. of courase it would work in the corners where your wife doesn't want anything, but you could turn it into a kind of pillar to display something of hers! like...baby i want to build you a place to show off your angle figures. that stuff works for me all the time,it's months before she figures out that i somehow benefited from it!


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## yphs_mst (Nov 11, 2006)

> trapping can be made by cutting PVC at certain length if you know what frequencies the problems are.
> 
> Can you explain this further?


It's bassically taking the principle of an open-closed tube, match the resonance with a certain frequency and putting it on the node.

by using L=1130/4f (where L is the length of the PVC in feet), and f is the frequency (the diameter of the PVC shouldnt be bigger than 7 inches) we can get the PVC length. Put fiberglass near the opening of the PVC (not on the close end). By putting that on the node (where the frequency is the problem), you'll trap that frequency.

The more fiberglass you put (filling it until the closed end), you'll have a wider bandwidth.

Does that make sense ? My friends have tried this. It works well to trap low frequency, it's just the PVC rings a little bit (around 2-4KHz), it has to be damped at the end.

Hadi


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## Ethan Winer (Jul 21, 2006)

Scott,

> i have read that you can take a concrete form (sonno tube) plug it and fill it with sand for base trapping. <

Sorry, no, that's a myth. A tube filled with sand won't help even a tiny bit.

--Ethan


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## Guest (Dec 14, 2006)

Thanks for all the feedback.

My latest thoughts are perhaps constructing freestanding, floor to ceiling, traps for 3 or 4 of my corners. I thinking of making them from a wooden skeleton, plywood or mdf, using Owens Corning 705 panels, shoot for 4 inches? thick. I would attempt to make them attractive on the face with perhaps some speaker grill cloth, or other material. 

What I probably would not want to do is attach them to the wall corners, rather just slide them in as tight as possible into the corner. Goal would be 2 ft width at the widest portion/front. Any thoughts?

I'd try to attach some photos of my theater but I don't see any way to add an attachment.


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## Ethan Winer (Jul 21, 2006)

Steve,

> I thinking of making them from a wooden skeleton, plywood or mdf, using Owens Corning 705 panels, shoot for 4 inches? thick. <

Sure.

--Ethan


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## Guest (Dec 15, 2006)

I poked around on the site and figured out I can post photos in a different area. So here's a link to a few photos of my room:

http://www.hometheatershack.com/photopost/showphoto.php/photo/215

I'm thinking I can occupy 4 of the corners as follows, fireplace corner with a 4 ft wide trap, full corner behind the bar with 2 ft wide trap, short corner behind the bar where the fridge is with 2 ft wide trap, and the corner where the pool cues sit with 2 ft wide trap.

So if my math is right that gives me about 70 sq ft of trapping that face the room in these corners as my ceiling is about 7 1/2 ft high. Is that a number that is significant enough to be worth the effort and new cosmetic appearance that would result?

If I go through with making these units would it be better to pack them full of the 705 and not leave air space behind the corner units, or is the airspace beneficial? 

Would a mix of say 2 inches of 703 and 2 inches of 705 be better than just 705?

Thanks for all the expert help, I've been a long time member at hometheaterspot and avscience but am enjoying the shack a great deal!


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## Ethan Winer (Jul 21, 2006)

Steve,

> So if my math is right that gives me about 70 sq ft of trapping that face the room in these corners as my ceiling is about 7 1/2 ft high. Is that a number that is significant enough to be worth the effort and new cosmetic appearance that would result? <

Yes!

> If I go through with making these units would it be better to pack them full of the 705 and not leave air space behind the corner units, or is the airspace beneficial? <

Solid is best, but there are diminishing returns. So you'd do better using the same amount of material to cover more total surface.

> Would a mix of say 2 inches of 703 and 2 inches of 705 be better than just 705? <

No. At least not for bass trapping.

--Ethan


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## scot (Dec 26, 2006)

I have found that the corners are virtually useless for damping in my room. Seriously. 

It is L-shaped, which might be part of the issue but my guess is that any normal non custom constructed converted home theater will be somewhat similar. I have 4 home made (and ugly as sin) bass tubes using insulation I compressed with chicken wire and covered with burlap. They sat in the corners forever. I started doing measurements with my new behringer mic and REW, and found I had 20+db dips at just under 60, 80 and 120hz. Walking around the room I could hear it get REALLY loud, then really quiet, so based on that I moved my sub around until I got what looked like the best application, then placed the tubes in the "loud" spots. With just one moved into a loud spot, it pushed up my db reading 6db. 

Just so you understand how I checked that, I set the REW playing a constant tone at that specific freq ( 56.4) and watched the number. Put the tube where it was loud in the room, and it went from 60db to 66. I removed it, back to 60, put it back, back to 66. 

Put a few more tubes in other loud spots, and gained another 2 or so each one. Then I noticed while moving one if I had it above my head the reading shot up to about 74, which is getting close to where it should be. This is 8ft up, in the middle of the room, so it is hard to imagine I could actually put something there, but...

I think the moral of the story here is that you need to figure out where to put the absorbers based on your room. The first reflection points are obvious, but reality is too complex to just say "here here here and here" for second, third, fouth etc.


If your corners are in a null (like mine) then the absorbers will do squat there.


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