# Another corner trap question...



## chas (Jan 28, 2007)

I'm building some corner bass traps from 703, cut into wedges for a "superchunk" style trap. For WAF purposes it will only be a four foot stack of wedges capped with an oak corner shelf.

For WAF purposes it will also be up off the floor above the baseboard (the bottom will be about 6 inches from the floor). I realize I'm missing that floor/corner intersection point, but the bottom of the trap will be open (wedges sitting on 2X2's screwed to the wall) so I'm hoping that will catch some of the corner waves.

Will I lose much performance having it elevated above the corner?


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## bpape (Sep 14, 2006)

SOunds like you're doing as much as you can to stay within the parameters you have to work with. On the floor would be better but 6" isn't bad. 

Bryan


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## chas (Jan 28, 2007)

Thanks Bryan. Maybe once she gets used to it in the corner I can wrap a few more wedges in burlap and just shove them under the trap so they can be easily removed if needed...


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## chas (Jan 28, 2007)

Speaking of extra wedges - would it help if I stuck a 3-wedge stack in the four upper wall/ceiling corners of the room? These would each be a six-inch wedge of 703 with a 24 inch wide face. Just wondering if it is too little to have any effect.


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## Glenn Kuras (Sep 7, 2006)

chas said:


> Speaking of extra wedges - would it help if I stuck a 3-wedge stack in the four upper wall/ceiling corners of the room? These would each be a six-inch wedge of 703 with a 24 inch wide face. Just wondering if it is too little to have any effect.


**** yes that would help.. 

Glenn


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## chas (Jan 28, 2007)

Great...thanks Glenn!


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## Guest (Jan 31, 2007)

chas said:


> I'm building some corner bass traps from 703, cut into wedges for a "superchunk" style trap. For WAF purposes it will only be a four foot stack of wedges capped with an oak corner shelf.


Do you absolutely NEED the shelf on top? To be honest, you are better to leave the absorption surface exposed at the top of the trap, rather than covering it up with something that is not acoustically transparent.

It is not *only* thickness and mass that affects how much absorption you will get, but also the amount of actual absorption material that is exposed to the room.

You do need a certain amount of mass and thickness to deal with the lower frequencies, but after a point you want to aim for a greater amount of exposed surface.

TBH, I'm not entirely sure that a gap of few inches below the trap is going to give you less performance. It may actually give you more, because it gives you a little extra exposed absorption surface. But I'm only guessing on this point, as I haven't had a chance to test the differences with this particular trap design.

And I'll add my vote as well for putting some traps in the upper corners as you suggest. That will definitely offer you some benefit -- again, preferably keeping as much of the absorption surface exposed as possible, rather than covering it with wood. I think if you were to put the wood on one surface of a smaller trap like that it would have a particularly detrimental effect (more so than with a larger trap, because you get an even smaller ratio of exposed surface to covered surface on the small trap). Further, you end up creating additional corners when you put wooden end caps on these traps! Better to be absorbing from as many directions as possible, rather than just focusing on absorbing in the horizontal directions!

Better yet would be to treat the whole corner from floor to ceiling with a superchunk-type trap . . . and it might even look nicer to do it that way than having a break in the middle, with a big trap on the bottom and then another trap on top. If you build it right and use a covering fabric that matches closely with the colour of the walls, it may actually be less noticeable as being an "object", and my look more like a natural part of the room design.

Perhaps, if you have room, you could throw some plants on stands, or a small indoor tree, in front of the traps. Or you could put some kind of lattice with a climbing vine-type plant across the front of the trap (though it's best to keep a lattice as light/sparse as possible, rather than having wider wooden slats across the face of the trap). Just a few possible ideas for accomodating WAF while maximising the amount of acoustic treatment you can install into your room


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## chas (Jan 28, 2007)

Thanks for the ideas Scott. The wife wasn't too crazy about the floor to ceiling idea, and liked the idea of a shelf which is how I ended up with my plan. I hadn't actually talked to her about the extra chunks in the upper corners....I thought that might be something I could squeeze in later, but your right about one large color-matched column blending in better. Of course that would cost me another case of 703....

If I do go with the shelf, what if I leave a gap between the top of the fiberglass and the bottom of the shelf (the gap will be covered with burlap like the rest of the front anyway)?


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## Guest (Jan 31, 2007)

chas said:


> I thought that might be something I could squeeze in later, but your right about one large color-matched column blending in better. Of course that would cost me another case of 703....


It would be well worth it, though, for the additional improvement you'd get.



> If I do go with the shelf, what if I leave a gap between the top of the fiberglass and the bottom of the shelf (the gap will be covered with burlap like the rest of the front anyway)?


Tough to say for sure, as with the difference between gap/no gap at the bottom.

Is the plan to actually put something on the shelf, or is it just supposed to look like a shelf that you *could* put something on?

If you MUST put the end cap/shelf on there, you might consider cutting a series of parallel slits in the shelf, preferably at least 1/2" to 1" wide, so that all but the outer inch or so of the triangle ends up being like a grid of sorts, so it will let sound pass through it. You want the slits to be big enough to easily let through a decent amount of sound pressure, but obviously not so big that something would fall through if you set something on it.

From there, I'd say it's better if you don't put anything on the shelf, though you could probably put something relatively small on the shelf, or something that doesn't significantly impede the openings. Or you could hang a small plant or some kind of sconce or whatever above it. Main thing is to try to keep it as open as possible.

Another idea, if you don't want to see the slits in the shelf, is to make an appropriately sized triangular fabric "place mat" to put on the shelf. And perhaps, if you are going to put something like a potted plant or something on the shelf, you might put the plant on a small stand of sorts, to leave a little breathing space between the bottom of the pot and the shelf.

Maybe you'll have a few better ideas of your own.

I'll add a (very) quick and dirty sketch here so you can get an idea what I'm talking about.


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## bpape (Sep 14, 2006)

I was kind of thinking the same thing. If you have a scroll saw and are handy (or want to hire it out to a woodworker looking for a fun project), you could potentially make the top shelf a decorative thing. Think about the old scrolled woodwork on speaker fronts, or a floor HVAC grille.

Maybe something like this:

http://www.signaturehardware.com/product3040?tr=sh&Prod=144307

with a cloth backing on it? Wouldn't have to be quite so intricate but you get the idea. You could even do a school logo, your monogram initial, etc. 

Bryan


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## Guest (Jan 31, 2007)

That's a cool suggestion too, Bryan.  Surely one could come up with a design to fit just about any decor.

On another subject, I've been meaning to point out:



> I am serious... and don't call *my* Shirley.


I hate to break it to you, but your Shirley's actually the one who's been calling ME!  :bigsmile:


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## chas (Jan 28, 2007)

Those are some great ideas guys! I'm pushing my limited wordworking skills just making the frames for the fabric covers, but the slatted or scrolled shelves would look _really_ nice.

I might just hold off on the shelf for now and cap it with a burlap covered wood frame like the front. This would leave it open to sound on top and I can always add a slatted or scrolled shelf later OR remove the cap and continue the stack to the ceiling at some point in the future.


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## bpape (Sep 14, 2006)

Doh! I need to go change that - thanks Scott.

Bryan


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## Guest (Feb 1, 2007)

bpape said:


> Doh! I need to go change that - thanks Scott.


Yes . . . all this and free poofreading services as well.  :bigsmile:


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## bpape (Sep 14, 2006)

I owe you a beer at RMAF this year  

Bryan


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## Guest (Feb 3, 2007)

Would that corner trap be better or worse with the back of the trap open with fabric covering it only, or with plywood covering the back?

Thanks


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## Ethan Winer (Jul 21, 2006)

vfrjim said:


> Would that corner trap be better or worse with the back of the trap open with fabric covering it only, or with plywood covering the back?


Rigid fiberglass straddling a corner should never have a rigid back, if that's what you're asking.

--Ethan


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## Bob_99 (May 8, 2006)

Ethan,

I'm not sure if vfrjim is referring to panels or superchunks but to clarify, when you say straddling, that refers to panels. Since the edges of superchunks are against the wall, it should be ok to back them with plywood, correct? My apologies if this was obvious to everyone.

Bob


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## bpape (Sep 14, 2006)

If you're doing triangular chunks and it is going to fit right into the corner then a hard backer wouldn't be a problem. 

Bryan


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## Guest (Feb 6, 2007)

I was referring to triangle chunks and to me, Ethan said to leave them open and NOT to back them.


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## Ethan Winer (Jul 21, 2006)

Bob_99 said:


> Since the edges of superchunks are against the wall, it should be ok to back them with plywood, correct?


Sure, but not for traditional panels straddling a corner with an air space behind.

--Ethan


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## Guest (Feb 12, 2007)

Ethan, I have treated my entire 2 channel room (11'x13' room) with 703 panels:
(all panels are suspended from the wall the same thickness as the fiberglass)
(3) 2'x4' 1" panels on each side wall
(2) 2'x4' 2" panels on the front wall (left & right of the equip rack)
(1) 3'x6' 1" panel directly behind the equip rack (covering a window
(4) 1'x8' 2" panels angled on each wall/ceiling area
(2) 1'x8' 2" panels in the front corners (floor to ceiling)
(1) 2'x8' 1" panels suspended over the listening chair

Now for my 2 questions:

1) I have to treat the back of the room. It is difficult because there is an entry door in one corner and a set of bi-fold doors on the other corner. I wanted to make traps attached to the wall like in your bass trap diagrams with sealed plywood, but it going to be a pain. I may just make some moveable panels (open back) and they can be placed in the corners when I as listening.....probably 3" thickness, floor to ceiling. Is this as effective as the sealed plywood traps?

2) My room was sounding so great. Last night I acutually hung the 2'x8' over the listening chair and I lost a LOT....I mean a LOT of bass. My bass was always really tight. I don't understand why the panel on the ceiling would cause me to lose that much bass. I am probably going to take it down. 
Any ideas on why that would reduce the bass that much?

Thanks, Mark


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## bpape (Sep 14, 2006)

It would probably be best to start your own thread. But for some quick answers...

What you probably did was to kill some of the vertical mode which usually falls from 70-90Hz in most standard height rooms. Have you taken any measurements to see if you just got rid of a big peak that you're just used to or if you really lost something?

You have a lot of thinner absorbtion in the room but not much thick for the bottom end. That should be better balanced. The corner panels and straddling panels should be at least 4" thick.

As for the rear, I'd get the rest balanced out first before doing anything there.

Bryan


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## Guest (Feb 12, 2007)

Thanks Bryan, a new thread probably would have been more appropriate. 

Thanks for the input. Mark


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## Ethan Winer (Jul 21, 2006)

Mark,

I agree with Bryan that corner traps need to be four inches thick.

> I may just make some moveable panels (open back) and they can be placed in the corners when I as listening.....probably 3" thickness, floor to ceiling. Is this as effective as the sealed plywood traps? <

Sure, as long as they're thick.

> Last night I acutually hung the 2'x8' over the listening chair and I lost a LOT....I mean a LOT of bass. My bass was always really tight. I don't understand why the panel on the ceiling would cause me to lose that much bass. <

Sometimes adding absorption makes the response worse, though the logic is slightly complicated. The quote below is from THIS article on my company's web site.

--Ethan



> Finally, I'll explain an interesting problem that happens when relying on low frequency response only for assessing the effect of placing bass traps. Sometimes moving a trap to a better location, or even adding another bass trap, can appear to make the response worse even though this is not really the case. The low frequency response at any given location in a room is the sum of the direct sound from the loudspeakers plus a large number of competing reflections from all of the room's surfaces. Some combinations create peaks, and some create nulls, but sometimes a reflection that would have made a null combines with one that would have made a peak. So together the result is somewhere between the two.
> 
> If a trap reduces a reflection that had negated a null caused by a different reflection from somewhere else, the null will then appear. The null-causing reflection was always present but was partially cancelled by another reflection that has now been trapped. This is another reason that ETF's waterfall plots are the best way to assess the improvement by adding or positioning bass traps. With this type of graph, adding traps will always show the ringing being reduced, even if the raw response happens to be worse where you measure.


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## Guest (Feb 12, 2007)

Thanks Ethan, 

I bought a Radio Shack analog meter and a Rives Audio Test CD 2. I am still trying to figure it all out.

To be honest, while this whole project has been a lot of fun, there are times when I feel like I should just be satisfied with the status quo. But, I guess that is the nature of this hobby.....always trying to acheive that perfect sound, that perfect room, that perfect look. 

I have been trying to learn/study acoustics for many months now.......and it is painfully obvious that the more I learn....the more I realize how little I know.

Mark


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## Bob_99 (May 8, 2006)

Mark,

I know exactly what you mean! There is a lot to learn but if it stops being fun, then it's time to sit back and just enjoy what you have. Also understand that it will never be perfect so just aim for the best that works for you. It is amazing though what a huge difference a little treatment can make.


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## bpape (Sep 14, 2006)

Ding! Give the man a prize 

Bryan


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## Ethan Winer (Jul 21, 2006)

Mark,

> I bought a Radio Shack analog meter and a Rives Audio Test CD 2. I am still trying to figure it all out. <

I love Richard Rives Bird because, like me, he's a big booster of acoustics and room treatment. But that test CD is not very useful. The best way to test a room is with the REW program you can download in this very forum for free. If you don't have a computer connected to your system, there's a series of tones at 1 Hz spacing you can download from the Acoustics Info section of my company's web site and burn onto a CDR.

> always trying to acheive that perfect sound, that perfect room, that perfect look. <

I know a lot of audiophiles who constantly futz with their setup, always unhappy. Or maybe they just like to keep spending money. This usually stops once they discover the joys of a properly treated room. Me, I _hate_ buying things and rewiring stuff. It's not even difficult for me to get behind my receiver!

--Ethan


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## bpape (Sep 14, 2006)

OK Ethan - you just failed your audiophile entrance exam...  Playing with the setup, trying new things, etc. is half the fun.

Bryan


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## Ethan Winer (Jul 21, 2006)

bpape said:


> OK Ethan - you just failed your audiophile entrance exam...  Playing with the setup, trying new things, etc. is half the fun.


LOL. Well, okay, I _did_ recently try diffusion at the side wall first reflection points.

I subscribe to the philosophy that if it ain't broke, don't fix it. :banana:

--Ethan


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## bpape (Sep 14, 2006)

Exactly. But it's kind of like a car nut. I can get back and forth just fine in my car without a better exhaust, better intake, better filtering, better tires, new performance chip, etc. It ain't broke - but it runs a whole lot better with the new parts 

Bryan


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## Ethan Winer (Jul 21, 2006)

bpape said:


> it runs a whole lot better with the new parts


You didn't know that my room and setup are already perfect?

:R

--Ethan


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