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post #1 of 38 Old 02-04-2013, 05:44 AM - Thread Starter
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I want to start a project for building some bass traps to help with the sound quality of my home theater room as I am getting ready to order several new subs, and also a MiniDsp to EQ everything.

I am quite new to the acoustical side of this, but I am open to any and all suggestions on building these bass traps!

First off, what material should be used to co struct these? I know about OC703 and OC705, but I am not sure what the traps should be constructed out of? Also, are ""pressure based resonate absorbing" traps the best way to go?

Any help for this newb would be great!
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post #2 of 38 Old 02-04-2013, 05:52 AM
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Quote:
Originally Posted by Martycool007 View Post

I want to start a project for building some bass traps to help with the sound quality of my home theater room as I am getting ready to order several new subs, and also a MiniDsp to EQ everything.

I am quite new to the acoustical side of this, but I am open to any and all suggestions on building these bass traps!

First off, what material should be used to co struct these? I know about OC703 and OC705, but I am not sure what the traps should be constructed out of? Also, are ""pressure based resonate absorbing" traps the best way to go?

Any help for this newb would be great!

One key parameter for the design of a bass trap is the space available for the trap. The general rule is that the deeper the trap, the less dense absorbing matiral.

"pressure based resonate absorbing" Are indicated when space is short and you have only a narrow band resonance to correct.

Stepping back a bit and looking at the big picture, ideally you would first set up a measuring facility for yourself and find out some details about the problem that you are trying to cure.
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post #3 of 38 Old 02-04-2013, 01:14 PM
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I googled "bass absorption wavelength. First hit was this. http://www.recordingreview.com/blog/recording-studio-construction-acoustics/why-your-bass-traps-dont-work/
I didn't watch the video or read in detail. I noticed it contains the 1.4 wavelength effective thickness number I remember bumping into a number of times when I was coming to the conclusion I wasn't going to fool with bass traps for my home recording space.

If the quarter wavelength concept is at least a reasonable working assumption, you can go here http://www.sengpielaudio.com/calculator-wavelength.htm to see the wavelength of troublesome frequencies. 100 Hz is a little over 11 feet, so you need just under 3 feet of absorption. Forty Hz is 28 feet so you need a 7 foot deep absorber (or at least seven feet of space with the absorber (still fairly thick) spaced off the wall to capture the 40 Hz waves that hit the absorber.

If you know the frequencies that are problematic in the room and can put trapping in the right target area, using "tuned" helmholz or limp membrane, etc. trapping is a lot less space inefficient.
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post #4 of 38 Old 02-04-2013, 01:18 PM
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So my brilliant idea of just wrapping my whole house with forty feet of pink insulation had some merit after all!

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post #5 of 38 Old 02-04-2013, 01:26 PM
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Quote:
Originally Posted by Martycool007 View Post

are "pressure based resonate absorbing" traps the best way to go? Any help for this newb would be great!

Pressure traps are not the first choice for most rooms, though they are useful in some situations. This should help:

Acoustics FAQ

Follow-up questions here are welcome.

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

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post #6 of 38 Old 02-04-2013, 01:44 PM
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Originally Posted by JHAz View Post


If you know the frequencies that are problematic in the room and can put trapping in the right target area, using "tuned" helmholz or limp membrane, etc. trapping is a lot less space inefficient.

Constrained layer absorbers which are for example two layers of drywall with Green Glue in-between can absorb low frequencies and be very space efficient.

http://www.greengluecompany.com/faq
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post #7 of 38 Old 02-04-2013, 06:49 PM
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Quote:
Originally Posted by arnyk View Post

Constrained layer absorbers which are for example two layers of drywall with Green Glue in-between can absorb low frequencies and be very space efficient.

http://www.greengluecompany.com/faq

a cool one I saw when looking at studio options was to use a flexible panel like masonite, and bend it into curved surfaces between studs at whatever spacing seems reasonable. Bass trapping plus reasonably effective high frequency diffusers. But a beeatch to tune . . .
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post #8 of 38 Old 02-04-2013, 07:19 PM
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Quote:
Originally Posted by Martycool007 View Post

I want to start a project for building some bass traps to help with the sound quality of my home theater room as I am getting ready to order several new subs, and also a MiniDsp to EQ everything.

I am quite new to the acoustical side of this, but I am open to any and all suggestions on building these bass traps!

First off, what material should be used to co struct these? I know about OC703 and OC705, but I am not sure what the traps should be constructed out of? Also, are ""pressure based resonate absorbing" traps the best way to go?

Any help for this newb would be great!


I built corner traps using OC 703 for my listening attic. I'd be happy to share my build notes, send a PM my way if you're interested.

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post #9 of 38 Old 02-05-2013, 05:45 AM
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Quote:
Originally Posted by JHAz View Post

Quote:
Originally Posted by arnyk View Post

Constrained layer absorbers which are for example two layers of drywall with Green Glue in-between can absorb low frequencies and be very space efficient.

http://www.greengluecompany.com/faq

a cool one I saw when looking at studio options was to use a flexible panel like Masonite, and bend it into curved surfaces between studs at whatever spacing seems reasonable. Bass trapping plus reasonably effective high frequency diffusers. But a beeatch to tune . . .

Are you saying that the Masonite diffuser was also a constrained layer absorber? If so, that has to be the coolest idea I've heard for weeks. They would probably have to be curved before the green glue set, but once set up, they might stand by themselves.

BTW check out Toole's comments about polycylindrical diffusers. One standing alone is cool, a row of them is not so cool.
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post #10 of 38 Old 02-05-2013, 06:48 AM - Thread Starter
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Ok so being that I live in a rental, I can't add any green glue or new wall boards. I am, however interested in possibly using OC-703 or OC-705 in the corners with two 2" panals stacked to form one 4" panal tacked into the corners with a decent airspace in between them and the wall. Which is better for low frequency absorbion, OC-703 or OC-705?

I am also thinking of building some ceiling and wall absorbion panals out of two 2" inch thick OC-703 panala that are stacked to form 4" inch panals with a 4" air gap, for both additional Low Frequency control and also better mids and highs as well.

Does this sound like a good plan? Localhost? Dragonfly? Arnyk? Ethan? Ect...
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post #11 of 38 Old 02-05-2013, 08:08 AM
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Originally Posted by Martycool007 View Post

Ok so being that I live in a rental, I can't add any green glue or new wall boards.

If you are allowed to hang pictures, green board/masonite or thin dry wall "sandwiches" are still possible.
Quote:
I am, however interested in possibly using OC-703 or OC-705 in the corners with two 2" panals stacked to form one 4" panal tacked into the corners with a decent airspace in between them and the wall. Which is better for low frequency absorbion, OC-703 or OC-705?

Optimal density is inversely proportional to the thickness of the panel. A 2" panel probably wants to be 705, a foot-thick corner trap may want to be made from thermal insulation. Always put your air space against the wall.
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I am also thinking of building some ceiling and wall absorption panels out of two 2" inch thick OC-703 panala that are stacked to form 4" inch panals with a 4" air gap, for both additional Low Frequency control and also better mids and highs as well.

I would have to run that past the free Chris Whealy's spread sheet but you probably have Excel so here's the URL: http://www.whealy.com/acoustics/Porous.html
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post #12 of 38 Old 02-05-2013, 08:18 AM
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Quote:
Originally Posted by arnyk View Post

If you are allowed to hang pictures, green board/masonite or thin dry wall "sandwiches" are still possible.

Are you saying one can make a pair of drywall panels, say, 2x4 feet in size, glue them together with green glue, hang the assembly on the wall and get some beneficial effect?

That is something that might just have the WAF I need. I'd just call it a 3D picture frame.

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post #13 of 38 Old 02-05-2013, 08:25 AM
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Originally Posted by JD in NJ View Post

Quote:
Originally Posted by arnyk View Post

If you are allowed to hang pictures, green board/masonite or thin dry wall "sandwiches" are still possible.

Are you saying one can make a pair of drywall panels, say, 2x4 feet in size, glue them together with green glue, hang the assembly on the wall and get some beneficial effect?

Yes. But I'd go for something larger, maybe 4 x 4 or 2 x 8.
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That is something that might just have the WAF I need. I'd just call it a 3D picture frame.

If you used the thinnest drywall, the whole sandwich might only be 1 inch thick. Not much of a 3D effect, eh? ;-)
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post #14 of 38 Old 02-05-2013, 08:35 AM
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So I take it the thickness of the 'bread' in this little sandwich isn't particularly critical?

Would two 2x4 panels have the same effect as one 4x4 or 4x8 panel, or is important to have solid panels of sufficient size? Does tuning the size of such a panel help to tune the frequencies being absorbed?

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post #15 of 38 Old 02-05-2013, 08:49 AM
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Quote:
Originally Posted by arnyk View Post


BTW check out Toole's comments about polycylindrical diffusers. One standing alone is cool, a row of them is not so cool.

poly's offer good spatial dispersion (size dictates bandwidth) but no temporal unless used in an array. so you are still at the mercy of a specular return from the poly (albiet lower in gain thus less con/destructive interferene).

no one (no competent user, that is) deploys polys in an array/row without proper modeling (BEM). that's another case of operator error.
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post #16 of 38 Old 02-05-2013, 09:02 AM
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Originally Posted by JD in NJ View Post

So I take it the thickness of the 'bread' in this little sandwich isn't particularly critical?

The green glue layer has to be thick enough to create a layer with enough resilience to do a good job of absorbing energy.

read here:

http://www.greengluecompany.com/benefit/how-to-use-it

and here

http://www.greengluecompany.com/sites/default/files/Green_Glue_Compound_Installation_Guide_-_English.pdf
Quote:
Would two 2 x 4 panels have the same effect as one 4 x 4 or 4 x 8 panel, or is important to have solid panels of sufficient size? Does tuning the size of such a panel help to tune the frequencies being absorbed?

I've got to remind myself that the usual rule of thumb is that a given area of coverage implemented as a collection of smaller panels is generally more effective than an equal area implemented as collection of fewer larger panels. That's particularly true of porous absorbers if the edges are left untreated and themselves porous.

The current frequent policy of stiffening the edges of porous absorbers with resin for aesthetic and structural reasons probably reduces that benefit.

But, a stiff ridge sticking out of a wall is probably still a bit of a diffuser and as such it still has more benefits than nothing.

I think the operative principle is that acoustic treatments tend to have a bit of a halo effect. ;-)

The trick is to spread them out enough so the halos just touch.
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post #17 of 38 Old 02-05-2013, 09:04 AM
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Quote:
Originally Posted by Martycool007 View Post

Ok so being that I live in a rental, I can't add any green glue or new wall boards. I am, however interested in possibly using OC-703 or OC-705 in the corners with two 2" panals stacked to form one 4" panal tacked into the corners with a decent airspace in between them and the wall. Which is better for low frequency absorbion, OC-703 or OC-705?

I am also thinking of building some ceiling and wall absorbion panals out of two 2" inch thick OC-703 panala that are stacked to form 4" inch panals with a 4" air gap, for both additional Low Frequency control and also better mids and highs as well. .

marty, for the LF corner porous absorbers - here is a very simple design you can do that will not result in any damage to the room to place/install.

- cut two pieces of plywood (home depot can do this for you) 2' x 2' square or whatever the maximum real estate you can afford to give up.
one sheet/piece will represent the top of the structure/absorber and the other will represent the bottom.
- take four small wood studs (does not have to support much weight so you do not need to use very thick pieces of wood) and screw or nail these into each corner of the plywood face. it will look like a small dining table with four legs. flip it upside down and nail/screw down the other plywood section to the studs.

if you have a ~8ft+ ceilings, then it is best to make 2x 4ft absorbers for each corner - which would then be stacked on top of each other floor-to-ceiling. cut the length of the wooden support studs to whatever is needed based on ceiling height.

you can now fill this empty 2' x 2' x 4' "container" loosely with pink fluffy fiberglass insulation. please take care to align the insulation in the same orientation (stack the layers neatly). do NOT compress the insulation; fill it loosely.

wrap the rectangular structure (now filled loosely (uncompressed) with pink fluffy attic insulation) in 6mil plastic (can be found in the paint section of the hardware store). the plastic will contain the fibres and reflect some specular energies back into the room (you only care about LF absorption for this specific treatment). staple the plastic sheeting to the wood studs. for looks, you can also wrap the absorber in your choice of fabric - but not necessary for functionality.

repeat until you have constructed the required amount of 2'x2' (x4' tall) LF porous absorbers. stack to floor/ceiling and place in any other available corners (2D/3D corners).
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post #18 of 38 Old 02-05-2013, 09:10 AM
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Quote:
Originally Posted by arnyk View Post

I've got to remind myself that the usual rule of thumb is that a given area of coverage implemented as a collection of smaller panels is generally more effective than an equal area implemented as collection of fewer larger panels. That's particularly true of porous absorbers if the edges are left untreated and themselves porous.

when you space multiple absorbers apart, you are exposing more edges and thus have increased losses due to edge diffraction. for this application, you do not want to do this - as wavelengths smaller than the gap will still reflect from the areas and impede the listening position. to minimize the removal of too much specular energy from the room, the panel should be constructed just large enough to meet the wavelength criteria as well as to provide attenuation across the entire listening position(s).
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post #19 of 38 Old 02-05-2013, 09:17 AM
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Originally Posted by JD in NJ View Post

So I take it the thickness of the 'bread' in this little sandwich isn't particularly critical?

Would two 2x4 panels have the same effect as one 4x4 or 4x8 panel, or is important to have solid panels of sufficient size? Does tuning the size of such a panel help to tune the frequencies being absorbed?



What are you trying to do? Absorb? Low bass, high bass? Reflections?
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post #20 of 38 Old 02-05-2013, 09:19 AM
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What are you trying to do? Absorb? Low bass, high bass? Reflections?

Me? I'm trying to learn. smile.gif

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post #21 of 38 Old 02-05-2013, 10:29 AM
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Me? I'm trying to learn. smile.gif

Quote:
Originally Posted by Ethan Winer View Post

Pressure traps are not the first choice for most rooms, though they are useful in some situations. This should help:

Acoustics FAQ

Follow-up questions here are welcome.

--Ethan


Open Ethan's link above and read the document he produced, it's easy to comprehend. The next step is measure your listening space.
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post #22 of 38 Old 02-05-2013, 02:00 PM
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Originally Posted by K Shep View Post

Open Ethan's link above and read the document he produced, it's easy to comprehend.

This tutorial is much shorter and simpler, though it doesn't mention pressure-based traps which is why I didn't link to it originally:

Acoustic Basics

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post #23 of 38 Old 02-05-2013, 02:38 PM
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Quote:
Originally Posted by Ethan Winer View Post

This tutorial is much shorter and simpler, though it doesn't mention pressure-based traps which is why I didn't link to it originally:

Acoustic Basics

--Ethan


It was my experience that after I treated my room with first and second reflection panels and corner bass traps that using bass management which is a type of EQing my room greatly improved, measurements showed the improvement. But the article doesn't promote EQing. Is that because we would rather treat the room first then EQ in the next step?
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post #24 of 38 Old 02-06-2013, 07:05 AM - Thread Starter
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Quote:
Originally Posted by localhost127 View Post

marty, for the LF corner porous absorbers - here is a very simple design you can do that will not result in any damage to the room to place/install.

- cut two pieces of plywood (home depot can do this for you) 2' x 2' square or whatever the maximum real estate you can afford to give up.
one sheet/piece will represent the top of the structure/absorber and the other will represent the bottom.
- take four small wood studs (does not have to support much weight so you do not need to use very thick pieces of wood) and screw or nail these into each corner of the plywood face. it will look like a small dining table with four legs. flip it upside down and nail/screw down the other plywood section to the studs.

if you have a ~8ft+ ceilings, then it is best to make 2x 4ft absorbers for each corner - which would then be stacked on top of each other floor-to-ceiling. cut the length of the wooden support studs to whatever is needed based on ceiling height.

you can now fill this empty 2' x 2' x 4' "container" loosely with pink fluffy fiberglass insulation. please take care to align the insulation in the same orientation (stack the layers neatly). do NOT compress the insulation; fill it loosely.

wrap the rectangular structure (now filled loosely (uncompressed) with pink fluffy attic insulation) in 6mil plastic (can be found in the paint section of the hardware store). the plastic will contain the fibres and reflect some specular energies back into the room (you only care about LF absorption for this specific treatment). staple the plastic sheeting to the wood studs. for looks, you can also wrap the absorber in your choice of fabric - but not necessary for functionality.

repeat until you have constructed the required amount of 2'x2' (x4' tall) LF porous absorbers. stack to floor/ceiling and place in any other available corners (2D/3D corners).

Ok, thanks for that reply Localhost! Finally some good advise and specific information about actually building the bass traps.

Let me know if this sounds like a good plan on my soon to be completed room treatments....?

First I plan on building a ceiling cloud/absorbion panal out of OC-703, using two 2" inch thick panels stacked together to form a single 4" inch thick by 6 foot long by 6 foot wide for my 12 by 20 room leaving a 4" inch air gap between the cloud and the actual ceiling.

Then I plan on building some absorbion panels out of 2 inch thick OC-703 stacked together to make 4" inches thick with a 4" inch air gap. Although unlock the ceiling panal, I will not put these up until have measurements from REW in order to see where the panels need to be placed along the walls.

I will treat the rear wall that is 12' feet wide with two of the wall panels that I described above but at a bigger dimension of 4' by 4'.

Does this sound ideal?
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post #25 of 38 Old 02-06-2013, 08:00 AM
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You're getting some good advice.

I'm a big advocate of ceiling treatment, very little downside (hit on spaciousness), and it oftentimes overlooked.

I'd like to add to examine the corners,...and add in bass trapping until it's no longer aesthetically acceptable. You can always employ a ~6mil plastic facing on the traps, if there becomes a scenario whereby an un-acceptable amount of MF/HF is damped. Typical residential spaces can use and benefit from an extraordinary amount of trapping.

Do you have any corners whereby a massive amount of trapping can be placed? If you're really serious, give up all you can and go for it. We all realize there are limitations, but determine what you can forfeit and go for it.

Go here, and you can check it all out, however go about 3/4 of the way down and begin reading the rules of thumb and check out the links.


This is how it's done. eek.gif

Here is a decent example of some corner absorption.

This quote "In all cases if you have less than 4" you use rigid, if you have 8" or more you use fluffy, unless you need rigid for structure." is found in that page of info. There's exceptions, but it's good advice.

One thing is certain, the subjective result of adequately taming the decay characteristics, and smoothing the LF response, is without question quite significant.


With Ethan, local, et al, you'll be fine.

Best of luck

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post #26 of 38 Old 02-06-2013, 10:55 AM
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Another option for corner broadband bass traps:
http://www.avsforum.com/t/1312693/diy-construction-methods-of-hang-able-acoustic-panels-not-fixed-frames/120#post_22131618
Quote:
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Hi guys,

I've been following a number of the acoustics threads here for a while, though I haven't been very active on the AVS forums. Mike suggested that I share some of my work on room acoustics with everyone here, so here are my corner bass traps:

I followed a similar construction technique that Mike posted for his corner bass traps, but made mine from pink fluffy R-19 instead and wrapped the fabric around the outside of the threaded rod. Here is the photo journey:

My traps are 24x24x34 inch triangles, are about 3.5 feet tall, and probably weigh less than 10lbs each. Since I need access to one of the corners for a doorway, I made them stackable and moveable. I started by cutting triangles, drilling holes for the threaded rod, and inserting T-Nuts for the sides that stack on one another:
287

Then I cut 23" squares of insulation, cut them diagonally for triangles, and clipped off the corners so they fit snugly between the threaded rods:
390


A wire mesh made from separated Cat5 wire goes between each layer to keep the insulation from sagging over time. The numbered arrows indicate the direction of winding the wire to support the insulation. A bead of solder keeps the wire from unwinding. Each layer of insulation is about 5" thick.
400

Here is the first one all stacked up. You can see the supportive wire mesh wrapped around the threaded rod on each side:
516

And then with the Kraft paper glued to the front with spray adhesive:
529

Then, turn the trap upside down to affix the cloth wrapping - a two-pack of curtains from the giant W for $15. Each pack is enough for two traps.
400

The cloth is stapled to the underside of the top plate to prevent sagging over time:
291

When the fabric is fully secured to the top panel, turn the trap right side up again and pull the fabric around to the back. Trim off the excess and then just pull it tight and use a desk stapler to hold the fabric together in the back:
550

The staples produce a few ripples in the sides, but you won't see those once you put it in the corner. The front looks nice and clean:
528

Here is a closer shot of two of them stacked together:
600

And finally, the entire back half of the theater. With a few bean bag chairs up front, we can comfortably seat 10-12 people. The colors are a little off from a combination of CFL and flash lighting:
326

Below are the before and after REW plots. The purple trace is the original measurement with no traps and no EQ. The yellow trace is the difference made by the bass traps alone. The traps took 5dB off of the room-induced peak at 45Hz without sacrificing anything else in the audible range:
329

This is the original waterfall plot made by REW - no traps, no other corrections - just a mess with room modes at 45Hz and 90Hz:
443

And here is the waterfall plot after ONLY the traps are put in place. I was surprised by how much of a difference the traps made in the decay:
447

After several days of tweaking the parametric equalizer with the traps in place and a first order high-pass filter in place, here is my "final" room response curve - flat from 7Hz to 100Hz, plus/minus 3dB :'( The peak at 105Hz won't ever really happen because the preamp crosses the LFE channel at 60Hz.
449

And the "final" waterfall plot - nice and smooth. If I adjust the waterfall graphing limits in REW, the entire response curve is down by 20dB within the first 100-120ms with the exception of a 2-3dB narrow bump at about 23Hz. I am really pleased with this result:
443

It sounds great! The EQ and high-pass filter reduce (but don't eliminate) the incidence of amp clipping, but still provide enough punch to cause visitors to literally jump up from the couch :P

All of my other projects are on my web page, which I think is linked in my signature.

Eric
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post #27 of 38 Old 02-06-2013, 01:49 PM
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But the article doesn't promote EQing. Is that because we would rather treat the room first then EQ in the next step?

Yes, exactly. EQ is useful only to reduce the level of peaks. It can't counter deep nulls which are common, and often are the larger problem in small rooms.

--Ethan

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post #28 of 38 Old 02-07-2013, 05:47 PM
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Eric your pre response looks almost like mine! You using multi-subs?

Acoustic Frontiers: design and creation of high performance listening rooms, home theaters and project studios for discerning audio/video enthusiasts.
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post #29 of 38 Old 02-08-2013, 07:41 AM
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Eric your pre response looks almost like mine! You using multi-subs?

Nyal - Eric Posted in my DIY acoustics treatment thread, and I shared here so others can see easy way to make movable corner traps.
Back when I made them origianlly, it was not widely know to use pink fluffy above a certain depth, so I used OC705 in mine, have advised people since to use pink fluffy for the deep corner traps, which Eric did.
Eric is running dual IB manifolds in his HT just below the screen, we became web friends via the IB cult, here is more info and pict of his set-up.
Eric's Home Theater & DIY Audio Projects
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post #30 of 38 Old 02-09-2013, 12:54 AM
 
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Originally Posted by Martycool007 View Post

are "pressure based resonate absorbing" traps the best way to go? Any help for this newb would be great!

Pressure traps are not the first choice for most rooms, though they are useful in some situations. This should help:

Acoustics FAQ

Follow-up questions here are welcome.

--Ethan

Hey Ethan thanks for all those utubes out there.. and your post on acoustics very good informative post thanks

my 1st home made absorber

6 inches of roxul safe n sound

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