Pegboard good for corner bass trap?

[smokapot]

I am thinking of using four foot wide pegboard from floor to ceiling in the corners of my live room.
I will pack it full of fiberglass (the fluffy stuff) as tight as i can.

I will also bend the pegboard convex as a diffuser.

Does this sound right ?

[Brainchild]

Are you going for a perforated-panel resonant absorber? If you are, then a couple of things:

1. The cavity behind the pegboard will have to be sealed airtight (basically, you'd have to create a triangular column that is airtight except for the perforations).
2. The measurements of the board thickness, hole spacing, hole diameter, cavity volume and fiberglass characteristics will all have to be carefully calculated and measured in order for you to get absorption at the frequency you're looking to absorb. The average store-bought pegboard isn't very helpful at serious bass frequencies. Which brings up another point:
3. The panel will pretty much only absorb a relatively narrow band of frequencies if the perforated-panel design is what you're going for.

If you're just wanting to create a porous absorber that won't absorb too much high-frequency content, you could just face whatever insulation you use with something as thin as paper or foil (a la the frk facing on 700-series or equivalent).

Whatever you choose to do, you won't want to just pack the insulation in as tight as possible. You'll want the fiberglass to be a definite known, consistent density.

Bending the board won't really create a diffusion effect (but the peg holes will, at least around their effective frequency). It will disperse the sound energy horizontally , but without knowing the other dimensions of your room and what other objects are in there, you can't really predict how that will affect the room's overall sound. It could create more problems in certain spots.

[Weasel9992]

Originally Posted by smokapot

I am thinking of using four foot wide pegboard from floor to ceiling in the corners of my live room.
I will pack it full of fiberglass (the fluffy stuff) as tight as i can.

I will also bend the pegboard convex as a diffuser.

Does this sound right ?

It'll do somethin'. I couldn't tell you what the results will be exactly other than the fact that it will be pretty reflective above 500Hz or so and that the pegboard will make it work along a narrower bandwidth, but it'll work. One issue I can foresee is the difficulty in making all the corners identical; there will probably be significant variations in how densely the fiberglass is packed and the curvature of the pegboard just to name a couple of things.

Frank

[smokapot]

thanks guys

Im trying to control the boom in the room and not kill the highs.

The room is 25'-6" x 22'-6" with 9'-0" ceiling (center flat with sloping sides) mostly nonpararell walls.

Its about 4500 cubic ft.

I am planning on a hanging ceiling made from 2x4's that holds fiberglass insulation (about 12") and covered in fabric (going for broadband absorbtion). leaving the slopes bare with some treament if needed

One end of room diffused the other deadend.

Wood floor "floated" on a thin foam pad (not nailed down)

Along the long walls I will put some broadband 2'x4'x 4" panels spaced out.

Basically there is speaker cabs and a drumset in the room.

One goal is to not need a vocal booth which I use 1" 703 panels and moving blankets now.

[jayfrigo]

The typical commercially available pegboard usually has a hole density too high for good low-bass trapping. Without measuring and calculating it all, or figuring box depth, off the top of my head I'd estimate you are more likely to get peak absorption at around 4-500Hz rather than the deeper bands.

Perforated panel traps can be great, but you need to calculate and build from scratch. Probably the easiest perforation material is thin plywood. Use denser wood for the cavity. Also, the cavity indeed needs to be airtight, and it's usually better (for typical design goals) to half-fill rather than completely stuff the cavity. The suggested curvature also throws a monkey wrench into the calculations. It will likely broaden it a bit, reducing the maximum attenuation, and to figure out the likely center frequency, you'll have to use some geometry and calculate the average depth. It won't be exact, but close enough to use for hole density criterium.

[smokapot]

Would I be better off just dumping the pegboard and use fabric ?

[Brainchild]

It sounds like you would be better off just going fabric, judging from the description. If you're leaving part of the ceiling and (it sounds like) a good bit of the side walls bare, absorbing 4' in the corners isn't going to kill the liveliness of the room. Especially if you're going with diffusion on one end wall.
Yeah...that's what I would do. Dealing with bending that pegboard (and securing it, and all that) just seems like an unnecessary headache.

[kooz]

Originally Posted by smokapot

Would I be better off just dumping the pegboard and use fabric ?

SuperChunkin? probably, man. quicker, easier and more predictable results. hundreds if not thousands of corners out there are like this, so there has to be a good reason for it. I know many of my issues disappeared when I did it. Roxul RockBoard is da stuff!

[Tomer1]

Consult with the handy "Porous Absorber Calculator" to predict your planing for a the device which won't result in a narrow band device but more of a natural low pass filter-
Large perforation area+large diameter holes.

Using a perfboard does not mean you no longer need fabric,
I would still use fabric as safty measure to keep the fibers under control,
attach it to the back side of the panel.
Using just fabric,even thick with a a very dense pattern will still result in alot of high freq absorption.

To me it doesnt sound like a waste of time,
If you have a requirement ,stick to it.

[smokapot]

I'm gonna go for it and hear what happens.

There is gonna be a lot of absorbtion throughout the room so maybe it wont be bad, plus I can add more. Shouldn't take me long to do, I'm only doing three corners.

The forth corner is an angled wall (2x4 with half inch sheetrock on each side)with a door to the pass through/computer room. Is the computer room acting like a bass trap ?

Probably a dumb question I know.

Tomer, did you mean high pass filter or low pass? wouldn't this thing cut the lows more than the highs?

[silverdisk]

I think its a good idea to try at least and tell us if it sucks Seriously though, it would be great if you could get some before/ after room measurements happening...... but maybe thats beyond what you want to get into at this point. I agree with the others that it should do something. However im not so sure as to the stringent requirement of sealing it and acheiving only a narrowband performance even though thats what gives time tested results. Across the corners and curved like you said it will do some of these things, vibrate like a panel and absorb like a poly, absorb some like a helmholtz but higher up, some of the deep powerfull stuff will pass right through it into the insulation, it will re-radiate sound in a semi circle, it will reflect upper stuff, but in a more diffused pattern than flat wall or corner. I had non sealed non insulated polys in 4 corners at one time and it was nice stuff. Sorry for the long useless post

[smokapot]

I got one done last night, really was easy to curve.
I just used two pieces of strapping and just popped it in so the fiber is being held in place.

Looks good.....

Maybe I will post some pics if I can stop being such a lazy ass.

Not sure what its doing to the sound, it sounds more empty than the other corner. when I stick my head in the plain corner I can hear bass build up from kik drum. I dont hear the same build up where the trap is, but I cant stick my head in as far becuse of the trap.

Anyone know what would change if I drill more holes or plug them for that matter?

Thanks for the replys

[jinksdingo]

It'll do something but I'd go for regular corner traps myself.

Your idea works well in home theatre where they bend a thin fabric covered
ply in a semi circle half tube and stuff it with insulation. It doubles as a diffuser and a mid bass trap. That is what I'd do with your pegboard if you really have to use it.

As mentioned the corner traps will absorb more down low.

[Brainchild]

Yeah I'd love to see some pictures; I'm having a hard time picturing the strap situation.

To answer a couple of questions from one of your earlier posts smoka, the computer room would act as a bass trap if you covered the doorway in some kind of fibrous absorption. Since the air has a lot of freedom to flow through the doorway, the velocity of bass waves would be high through the doorway, so fibrous absorption would be very effective there. I actually use the same kind of approach in part of my room where, in one corner, there's this useless 2'x3' space. I put a 3'-wide wall of fiberglass in front of it, so I get a free 2' of rear space behind the absorber.

I think what Tomer meant by "low-pass filter" is that the pegboard is rejecting the high frequencies (reflecting them back into the room) while passing the low frequencies (where they are absorbed by the insulation).

You don't really have any Helmholtz action going at all if the rear of the cavity is not sealed. The size of the holes would have to be minuscule in order for resonant absorption to occur without a sealed rear cavity.
Instead, adding or removing holes would pretty much just decrease or increase - respectively - the amount of high frequency reflection you're getting into the room. As far as bass absorption, that will be essentially unaffected by the number or size of holes in board that thin and light (at least for the lowest frequencies; I'm not sure how low the reflectivity of the board would go).

[smokapot]

Thanks Brainchild.

The pegboard is held in place by two strips of wood
(strapping 3/4" x 2 1/2")

When the board is bent there is tension and the board kinda "snaps" into place (between the strapping) squeezing the fiber and holding it tight.
No need to screw the pegboard down and very easy to take out later if it sounds like hell in there when I'm done.

Way easier than I thought it would be.

[J.P.]

Can bass frequencies pass through a material like 1/4 plywood or do they bounce off of it? I was thinking about the previous post here about peg board which I like the look of. I have a design in mind using cotton panels and peg board, or at least a perforated plywood. The Front panel would be perforated not so much for diffusion but for the purpose of changing the ratio of reflective vs. absorptive surface for high and mid range frequencies. I wasn't sure if the use of a hard front panel would impede bass absorption though. Thanks.

[avare]

Originally Posted by J.P.

Can bass frequencies pass through a material like 1/4 plywood or do they bounce off of it?... I... purpose of changing the ratio of reflective vs. absorptive surface for high and mid range frequencies. I wasn't sure if the use of a hard front panel would impede bass absorption though. Thanks.

The effect of ratio and solid panel size is related to the reflection/passing through of frequencies. It is heavy on the math, but I know of no shot form, Shultz's work linked below.

Acoustical Usus of Perforated Panels


Solidly perforated,
Andre

[PaulP]

Originally Posted by avare

It is heavy on the math, but I know of no shot form, Shultz's owrk linked below.

Acoustical Usus of Perforated Panels

A great read and the math isn't so bad. Thanks for this.

One question : for the use of perforated sheets in tuned resonant absorbers
(p. 24) I take it the enclosure should be sealed ? The text doesn't exactly
specify, other than :

In this application, the perforated metal is used in combination
with a trapped layer of air, in order to modify the acoustical
performance of the absorptive material. This is done by setting up an
acoustical resonance condition, which concentrates the sound
absorption into a particular frequency range of special interest.

I take it 'trapped' means in a sealed enclosure.

Now to try and locate perforated metal sheets, sparsely and otherwise...

Paul P

[avare]

Originally Posted by PaulP

I take it 'trapped' means in a sealed enclosure.

I am glad you found it of value. When saying heavy on math I was thinking of people hear who are afraid of equations with 2 variables!

Yes, it means sealed enclosure.

Polynomially trapped,
Andre