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Need a Limp-Mass Membrane. Reverb & Delay Plugins
Old 4th November 2008
  #31
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Quote:
Originally Posted by [email protected] View Post
I think so...

so the fact that the plastic isn't breathable isn't exactly what makes it benefical, it's the thin-ness of a boundary that effects the fiberglass on one "membrane"...allowing the surface to act as a complete unit?

because my covering has too much mass and doesn't utilize the benefits of a membrane, not only am I not recieving the benefits of a "surface as a unit", but also not allowing the airflow to reach any of my insulation optimally.

SO what if I were to utilize a membrane under the covering I already have?

"less confused but trying to spend less money",

-John
I'd love to save you some money man, but it's probably not gonna happen. Right now, were you to add a membrane under the non-breathable fabric, you'd accomplish nothing. I'm not sure it would make anything worse, but it wouldn't make it better either. Plus, by the time you get the fabric off to add the membrane, you might as well replace it. The important thing in your specific case is to allow more gas flow to the absorption layer to allow it to work as efficiently as it should.

Frank
Old 4th November 2008
  #32
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Quote:
Originally Posted by Weasel9992 View Post
I'd love to save you some money man, but it's probably not gonna happen. Right now, were you to add a membrane under the non-breathable fabric, you'd accomplish nothing. I'm not sure it would make anything worse, but it wouldn't make it better either. Plus, by the time you get the fabric off to add the membrane, you might as well replace it. The important thing in your specific case is to allow more gas flow to the absorption layer to allow it to work as efficiently as it should.

Frank
regretfully understood.

For the record, it is breathable..just not as much as say a t-shirt
Old 4th November 2008
  #33
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Quote:
Originally Posted by [email protected] View Post
regretfully understood.

For the record, it is breathable..just not as much as say a t-shirt
Hahaha...I'm sorry man.

Frank
Old 5th November 2008
  #34
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Quote:
Originally Posted by Weasel9992 View Post
Hahaha...I'm sorry man.

Frank
So, the thinner the non-porous membrane, the better?

So.. cling-wrap?
Old 5th November 2008
  #35
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Quote:
Originally Posted by DarkEcho View Post
So, the thinner the non-porous membrane, the better?

So.. cling-wrap?
Yes...to a point, of course. Ethan could more intelligently speak to the details about what it usable and what isn't, but I think cling-wrap would be fine.

Frank
Old 6th November 2008
  #36
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Last edited by memphisindie; 6th November 2008 at 04:23 PM.. Reason: clarity.
Old 6th November 2008
  #37
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Quote:
Originally Posted by memphisindie View Post
Whatever.

Begin the emoticon war!

limp mass membrane - Google Search
Especially this one:
DIY Panel Bass Traps: what to use for the limp-mass membrane??

Tiny is smarter than both of you and way more generous with the knowledge.
OK so I googled "limp mass" and it wasn't nearly as graphic as I thought it might be. heh

But seriously, why are you just throwing simple insults around without any wisdom to back it up. Totally childish. This whole gravy train idea is completely obsurd. Frank and Glenn and all the rest are never anything but helpful, regardless of their pocket books.

Totally lame.

So what would work better oh all knowing one?

Old 6th November 2008
  #38
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Quote:
Originally Posted by memphisindie View Post
"Plastic wrap" should be ashamed, tisk tisk. Laffing my butt off on that one.
Dood, do you have any hard evidence that thin plastic wrap is not an effective membrane? Have you ever tested different membrane materials yourself? Or are you just going by uneducated intuition? This is the defining difference between a troll, and an expert who happens to disagree.

I'll wait for your reasoned reply before passing judgment. heh

--Ethan
Old 6th November 2008
  #39
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Quote:
Originally Posted by memphisindie View Post
Using the search function.
There are so many posts on this forum concerning this subject with every answer to every question about including the OP's .
UTSF
It still works, it ain't broke. Why not use it?
My insults are like my mind, empty, but even I can use the search function and I'm just a simple flame target.
"Plastic wrap" should be ashamed, tisk tisk.
Laffing my butt off on that one.
Now, for the graphically challenged, I'm going to wrap myself in "cling film" and see if it shuts me up, I'm definitely "low end".
Listen, I've read your other posts and you definitely know what you're talking about when it comes to audio, particularly the technical end of things. No doubt about it. That being the case, I know you have a solid grasp on the importance of test data with respect to the formation of conclusions about whether something is actually effective or not. Ethan actually has tested whether this works or not...and it does. It's not entirely subjective or empirical; there is an objective, real world, physical effect that is measurable. In short, it works. *Why* is works, the physics of it, is what we were discussing, and you have yet to contribute anything but senseless rhetoric and shallow search contributions to the discussion.

No one is here to make any enemies, so why don't you contribute something positive in terms of correction if you think we're wrong? The items from your search are great, but they don't directly refute anything that's been said here. I completely respect your experience and skill, so I'm looking forward to some more positive stuff from you.

Frank
Old 6th November 2008
  #40
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Quote:
Originally Posted by memphisindie View Post
Using the search function.
There are so many posts on this forum concerning this subject with every answer to every question about including the OP's .
UTSF
It still works, it ain't broke. Why not use it?
My insults are like my mind, empty, but even I can use the search function and I'm just a simple flame target.
"Plastic wrap" should be ashamed, tisk tisk.
Laffing my butt off on that one.
Now, for the graphically challenged, I'm going to wrap myself in "cling film" and see if it shuts me up, I'm definitely "low end".
Ok so I did some searching, and I find alot of reference to plywood membranes, but those seem to be in reference to sealed resonator style bass traps, and all other threads refer to the frk faced broadband absorbers. Some suggest a vinyl face. None of them deny or refute the ability of plastic wrap.

I lived up to my end of the bargain...
Old 6th November 2008
  #41
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Ethan, I'm more of a Dued, than a Dude or a Dood, ,
Weasel9992, I know that both of you guys are very well versed at your craft also.

Dykstraster, The reason you can't find info on it is: no one uses plastic wrap.

Depending on how many erg/sec/cm2 you have going into cling film coupled with a porous 703 panel or the like it will reduce waves in a predictable manner. Assuming your damped room needs to decay to silent in a two second period after transient emission, you have problems with modern building techniques for a passable room not built for this kind of work, hence the retrofit of panels. If its a full bandwidth burst you'll get differing decay times at different freqs and lobing, modes, ringing, and need to select a material with a suitable absorption coefficient for the "problem frequencies". In a room not designed to be used as a studio the observation point is the place that becomes important to treat for. The combination of materials plastic cling film which has a low coefficient for all frequencies and the fiberglass panel combine only to stop high frequencies fairly well, better at lower freq's as you move out from the wall but never enough.
Limp Mass materials are heavy so that audio does not turn them into a diaphragm easily and it would take considerable intensity to do so, probably more than you can afford to generate. The Limp factor is also so that it won't become a diaphragm easily.
Cling film does not have that characteristic. You can prove this to yourself by wrapping your monitors in cling film and listening to them, slight reduction in output, mostly at very high frequencies. put a piece of 703 or the like a few feet in front of them between you and the monitor, wrapped in cling film, and you hear what they will reduce, take the cling film off and listen again. You won't use them in this manner but you get where they will be most effective.
Put some limp mass on the panels, (real limp mass like mineral impregnated rubber(vinyl) roll roofing) and you will hear a drastic difference of much more attenuated low end.
Many people talk about using bags of stuff, but, I like a panel that looks nice. The frame edges will become a problem so they should be addressed. The limp mass material is impermeable so it will reflect higher wavelengths of sound. If you just need the impermeability factor, cling film or a plastic bag may serve, but, not as well. For this reason I would put it between two panels. Many people like 2" of 7lb fiberglas panels, I'd put it under both, and have a layer of homesote on the back.
You can make these panels out of 7lb ceiling fiberglass panels and cut them to sizes and shapes that you need. All the other materials including the limp mass can be cut easily.
These aren't as pretty as Ethan's panels or the GIK stuff, but, depending on how you build them, place them, mount them, they can be every bit as effective.
You can shock mount them. You can change the geometry of them by having internal angles under the panels and different backing materials like plywood to change the sound in many different ways.
Burlap is a breathable cloth, terry is, t-shirt is, you can use any of those, heavy canvas is not very breathable BUT it is a pretty good limp mass when you don't need impermeability, not great, just pretty good, but, that might be all your measurements tell you that you will need. You have to find out what your problems are at your sweet spot.
The last room I built, I changed the walls and ceiling to movable panels on a frame to change the geometry of the room to smooth it out first an then treatment was more diffusion with a little absorption and a lot of treatment to reduce through transmission and sealed Limp mass did that well.

Last edited by memphisindie; 6th November 2008 at 06:50 PM.. Reason: apology
Old 6th November 2008
  #42
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Quote:
Originally Posted by memphisindie View Post
Burlap is a breathable cloth, terry is, t-shirt is, you can use any of those, heavy canvas is not very breathable BUT it is a pretty good limp mass when you don't need impermeability, not great, just pretty good, but, that might be all your measurements tell you that you will need. You have to find out what your problems are at your sweet spot.
The last room I built, I changed the walls and ceiling to movable panels on a frame to change the geometry of the room to smooth it out first an then treatment was more diffusion with a little absorption and a lot of treatment to reduce through transmission and sealed Limp mass did that well.
That's alot to take in. I'm digesting it to the best of my admittedly uninformed ability. The portion I quoted, I'm interested in for obvious reasons. What I'm taking from your text, is that my canvas covering will perform as limp mass in regards to improved low frequency absorbtion, (understood not optimally), but not react as a high frequency reflector. Correct?

I also find the portion regarding the "amoeba" room design intersting. Did you build a room where the exact dimensions weren't solidified, and changed the internal volume until the room's performance was to your liking? Sorry, but thats how I understood it. Sounds like quite the undertaking.

Thanks for the info.
Old 6th November 2008
  #43
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See, now that was very positive. Thank you!

My observation is simply that the more massive the limp layer, the more high end is reflected, or more properly, the point of reflection in terms of bandwidth location is lowered. When you say that cling-wrap (for example) doesn't work as well, what you're saying from a physics standpoint is that the bandwidth reflection point shifts in an upward direction, which is exactly what we're looking for. We're not talking about reflecting everything from 500Hz on up...we're talking about balancing decay times from, say 4Khz up. I'd say that something as impermeable as canvas and impregnated vinyl or rubber would be much more reflective than we need it to be.

In terms of MLV or canvas improving the performance of bass traps, do you have any measurement data to support that? I'm not calling you out, I'm just asking the question. My experience is that that is not the case, but you certainly seem to know a thing or two so I'm interested in your experience.

Frank
Old 6th November 2008
  #44
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Quote:
Originally Posted by memphisindie View Post
Cling film does not have that characteristic. You can prove this to yourself by wrapping your monitors in cling film and listening to them
Have you ever tried cling film yourself and measured how the absorption of rigid fiberglass changes? (Hint - it works, whether it seems like it should to you or not.)

--Ethan
Old 7th November 2008
  #45
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Quote:
Originally Posted by [email protected] View Post
That's alot to take in. I'm digesting it to the best of my admittedly uninformed ability. The portion I quoted, I'm interested in for obvious reasons. What I'm taking from your text, is that my canvas covering will perform as limp mass in regards to improved low frequency absorbtion, (understood not optimally), but not react as a high frequency reflector. Correct?
No, it will react as a reflector, you will need something less stiff in front of it. The face of porous fiberglass panels work, but, you don't want that kind of exposure. Burlap, or, what I use, pimpy looking furry cloth, it's very porous and it's what is used on mic windscreens. Hancock Fabrics online will ship it to you.
Quote:
I also find the portion regarding the "amoeba" room design intersting. Did you build a room where the exact dimensions weren't solidified, and changed the internal volume until the room's performance was to your liking? Sorry, but thats how I understood it. Sounds like quite the undertaking.
Thanks for the info.
It was quite an undertaking. The room was already built , so, it was a retrofit. It reduced the ceiling and side wall area where you couldn't use the space anyway. The area that ended up behind the structure was great for storage and once it was finished it was easy to open one panel and get behind them where all the wiring/cabling was hidden. I hid a shelf and light fixture back there.
The new pockets were treated with an old armstrong product that was a rigid wall panel broadband absorber. It reduced bass if installed this way.
I built a rough frame to the shape I desired, isolated the floor and wall connections, put screws through the top and bottom to mount the in the center of the panels so that they could swivel, both sides, 3 panels per side not including front panels which were a window frame for the video monitor. The ceiling panels were mounted to swivel too, four panels running from one side to the other.
The side panels also had a mount for audio monitors on them, then the whole shmear was covered with framed, breathable, cloth/foam roof liner velcro'd onto the main frame. You couldn't see the movable panels, just a nice black smooth surface. The monitors were behind the scrims too, so, you couldn't see them either. You could only focus on your work. But yeah, you could change the characteristic of the room within seconds without changing the look once the scrims were in. Monitors were easy to adjust.

Quote:
Originally Posted by Weasel9992 View Post
See, now that was very positive. Thank you!

My observation is simply that the more massive the limp layer, the more high end is reflected, or more properly, the point of reflection in terms of bandwidth location is lowered. When you say that cling-wrap (for example) doesn't work as well, what you're saying from a physics standpoint is that the bandwidth reflection point shifts in an upward direction, which is exactly what we're looking for. We're not talking about reflecting everything from 500Hz on up...we're talking about balancing decay times from, say 4Khz up. I'd say that something as impermeable as canvas and impregnated vinyl or rubber would be much more reflective than we need it to be.
Right.
Quote:
In terms of MLV or canvas improving the performance of bass traps, do you have any measurement data to support that? I'm not calling you out, I'm just asking the question. My experience is that that is not the case, but you certainly seem to know a thing or two so I'm interested in your experience.
Frank
The trick with using a reflective limp mass material in a panel that must attenuate high end also is that you have to mount it behind the fiberglass or high end attenuation materials. Since it's only 1/8" thick, it's not much problem, but, remember to let it sag, it has to remain limp or it doesn't work properly. There won't be as much high end reflection from behind the panel, so, a thinner layer of high end attenuation would work fine there, but, you will need some.
It's just my opinion that if you modify the geometry of the panels you can also attenuate bass.
I didn't get that the OP was only attenuating from 4k up, my mistake.
My experience with the panels I've made is #1, they were made on site at a large commercial restaurant during a major renovation, I made 4, 4' x 8' panels framed in 2" x 4" frames. frames were covered in foam after assembly then the whole panel was covered in looser canvas. Inside the panels was 2" thick fiberglass panels, 1/2" thick of celotex homesote, it was suspended 4" off the wall. This was to quiet a brick and glass live music stage which killed the audience when loud GTR amps were used and made the room difficult to engineer in. There was an artists employed to tie the look together (painted on the canvas with water colors and metal hallide dies) The canvas was also made more porous by poking bigger holes in the panels which reduced the high end reflection a lot. So, it ended up looking great, sounding weird when you walked around the stage, until a band started playing. The bands all said they loved what it did and that everything was much clearer even when offensively loud amps were used. It helped the monitors too, 4 mixes or more could feed back easily.
Some smaller panels were also employed around the room to tame hotspots. Really changed the vibe in the room and they all survived a second renovation.
I also got the sound booth renovated and a kickass P.A. installed and got a bonus video system that distributed the live band throughout the large bldg's many rooms.
Man was I feeling lucky on that one.

Quote:
Originally Posted by Ethan Winer View Post
Have you ever tried cling film yourself and measured how the absorption of rigid fiberglass changes? (Hint - it works, whether it seems like it should to you or not.)

--Ethan
No I haven't tried it, you're right. It sounds ridiculous, but, it probably does have ability coupled with a panel. It can attenuate high end a little on it's own. I'd still mount it behind the fiberglass panel so that any reflection would be attenuated further. I have to make some panels soon, for myself, maybe I'll give it a shot on some of them.

Maybe having the plastic wrap in between the first two layers of fiberglass before the heavier MLV limp mass layer before the homesote, mounted in a rounded corner frame would make an attractive broadband attenuater panel with some kind of support structure fo monitors and movable focusable panels? hmmm....

Last edited by memphisindie; 7th November 2008 at 05:10 PM.. Reason: spelling.
Old 7th November 2008
  #46
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Thanks for the explanation man. Memphis is a great city!

Frank
Old 7th November 2008
  #47
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Sadly, the reason WHY I did the "Amoeba" design, (oh yeah, I'm keeping that handle) was actually two fold.
One was the regular reason of having a nice room to mix in with desirable acoustics and no visual cue to focus on and the second was to make a room that would give any monitor a leg up in creating a three dimensional image to work in. Left and right, front and back. I like positioning things in space in a mix. Not many rooms take this into consideration, some headphones do and some high end monitors do overcome acoustics to achieve it, but, I'd like the room to do it and the monitors to just sound right.
It worked, even if you were sitting in the back of the room you got a depth image in the stereo field.
Old 7th November 2008
  #48
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Maybe it would be easier to figure things out theoretically if I understood why adding a barrier that reflects high frequencies will help absorb low frequencies....
Old 8th November 2008
  #49
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Quote:
Originally Posted by DarkEcho View Post
Ok- I can't find an answer via searching (though, there are a lot of limp-mass membrane threads that end in: "get FSK").

A. First of all, when adding a limp mass membrane to a broadband absorber, should one glue it at all or just sandwich it between the glass and the outer-cloth? I cant see a limp mass membrane being very limp after adding glue to its entire surface area.
Is this why RealTraps doesnt use FSK?

B. What would be the best limp-mass membrane material? Are we talking like some super thin plastic (like cling wrap)?

C. Why only put the limp mass membrane on one side and not all the faces of the trap?
Put the limp mass on the side that faces the wall, not the fiberglass side that faces the room. The low end wave needs to pass through an impermeable membrane that has so much mass in it that it doesn't want to move easily from sound and will not resonate. The wave has to pass through it, bounce off the wall behind it, pass back through it again, being attenuated on each pass. The stuff in front of the membrane attenuates the waves that would be reflected by such a membrane.
Quote:
Originally Posted by DarkEcho View Post
Maybe it would be easier to figure things out theoretically if I understood why adding a barrier that reflects high frequencies will help absorb low frequencies....
So they don't help absorb lows, they just make the low absorption method tolerable by reducing the absorption material's side effects.
Howz zat?

Last edited by memphisindie; 8th November 2008 at 12:07 AM.. Reason: clarity.
Old 8th November 2008
  #50
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Quote:
Originally Posted by memphisindie View Post
Put the limp mass on the side that faces the wall, not the fiberglass side that faces the room. The low end wave needs to pass through an impermeable membrane that has so much mass in it that it doesn't want to move easily from sound and will not resonate. The wave has to pass through it, bounce off the wall behind it, pass back through it again, being attenuated on each pass. The stuff in front of the membrane attenuates the waves that would be reflected by such a membrane.
Though, to be fair testing has shown that the "cling-wrap" version of the limp mass membrane works fine when fixed to the front of the trap.

Frank
Old 8th November 2008
  #51
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Quote:
Originally Posted by memphisindie View Post
So they don't help absorb lows, they just make the low absorption method tolerable by reducing the absorption material's side effects.
Howz zat?
Do you mean that Fiberglass has a flaw and that by adding a sheet of plastic, it helps to diminish that flaw (thus allowing the panel to do what we want it to do, absorb more bass)?

Also- You've been mentioning Mineral impregnated vinyl... This differs pretty wildly with the idea of using a THIN limp mass membrane of plastic or foil.

Maybe an analogy would help us understand the physics behind why adding a thin membrane will help the panel absorb more low end?
Old 8th November 2008
  #52
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Quote:
Originally Posted by DarkEcho View Post
Do you mean that Fiberglass has a flaw and that by adding a sheet of plastic, it helps to diminish that flaw (thus allowing the panel to do what we want it to do, absorb more bass)?
There is no flaw in that fiberglass is not designed to treat bass, it is adept at attenuating and absorbing high end only.
Quote:
Also- You've been mentioning Mineral impregnated vinyl... This differs pretty wildly with the idea of using a THIN limp mass membrane of plastic or foil.
Again, foil and plastic wrap works for high end and isn't designed for bass. MLV is better for bass.
Quote:
Maybe an analogy would help us understand the physics behind why adding a thin membrane will help the panel absorb more low end?
It doesn't.
But I'll give you this:
Throw a baseball at a wall, then some plastic wrap, then throw it at plastic wrap over 703.
Then throw it at some MLV, see which one stops the ball without breaking or bouncing off.
The baseball represents bass, you could use a wet quilt, paper, foil, the lighter the object you throw, the more it represents highs.
foil and plastic wrap will stop a ping pong ball.
That's not an accurate analogy but it's fairly representative.
Old 8th November 2008
  #53
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but do we want to STOP the frequencies or absorb them?

If we are "stopping" them- isnt that exactly what the walls are doing, in which case the bass get's reflected Back into the room, recombining with the direct sound and causing cancellation?

you seem to be contradicting everything that all the known experts have been saying, which is fine if you can prove it- I love muck-raking!
Old 8th November 2008
  #54
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Quote:
Originally Posted by memphisindie View Post
There is no flaw in that fiberglass is not designed to treat bass, it is adept at attenuating and absorbing high end only.
See, this is where I completely disagree with you. Yes, it absorbs high end, but at 48kg/m3, 6" thickness it absorbs three times as much at 80Hz as it does at 4Khz. I would assert that it is perfectly suited for low end absorption, *and* it does it without throwing the low end/high end decay times all out of whack. If there's an existing imbalance there, that's when we go to adding a *very light* limp mass membrane like cling-wrap...specifically because it's not reflective like MLV is.

Quote:
Originally Posted by memphisindie View Post
Again, foil and plastic wrap works for high end and isn't designed for bass. MLV is better for bass.
Okay, I think I see what's happening. What you're talking about is a totally different concept than what we're doing with a much lighter limp mass layer. First, MLV is *designed* to reflect bass. People use hang it in strips at truck stops or meat packing houses or whatever to cut down on noise transfer. It would only attenuate bass at the lowest frequencies...same with plywood an other materials. That being the case, they can be helpful with respect to low low end control in the sense that you'd probably require fewer square feet to do it, but it would have to be a very carefully designed trap. Back to absorption for a second, as a matter of fact, the thicker the bass trap is (at the right density), the more effectively it will absorb sub-60Hz low end. That's because there's simply more mass at the right density. There are bass traps that are 12" or 18" thick that absorb very effectively down to 50Hz...you're much more likely to get that right if you're building it yourself than your are to get a trap made with MLV right. Plus...

I still am not fully bought into the idea of an MLV layer between layers of absorption; I'd want to see test data on that. I also wouldn't recommend a hard layer of anything on the back of a trap. Leaving it open yeilds much better results than closing it off. There's been test data on that for years. Bear in mind that Ethan, Glenn and I are not making claims that we can't back up with test data.

Frank
Old 8th November 2008
  #55
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Quote:
Originally Posted by DarkEcho View Post
but do we want to STOP the frequencies or absorb them?

If we are "stopping" them- isnt that exactly what the walls are doing, in which case the bass get's reflected Back into the room, recombining with the direct sound and causing cancellation?

you seem to be contradicting everything that all the known experts have been saying, which is fine if you can prove it- I love muck-raking!
Walls do not stop bass.
You can only absorb them and not retransmit. That's why the mass is limp, so it won't retransmit.
Old 8th November 2008
  #56
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Quote:
Originally Posted by Weasel9992 View Post
See, this is where I completely disagree with you. Yes, it absorbs high end, but at 48kg/m3, 6" thickness it absorbs three times as much at 80Hz as it does at 4Khz. I would assert that it is perfectly suited for low end absorption, *and* it does it without throwing the low end/high end decay times all out of whack. If there's an existing imbalance there, that's when we go to adding a *very light* limp mass membrane like cling-wrap...specifically because it's not reflective like MLV is.
Right, but we're not talking about losing that much real estate in the room. 1/8" on the rear of a 2" deep trap and not a hard material, a limp material that would cause the audio to have to pas through the high end absorptive material twice for what will be reflected which isn't much.
Quote:


Okay, I think I see what's happening. What you're talking about is a totally different concept than what we're doing with a much lighter limp mass layer. First, MLV is *designed* to reflect bass. People use hang it in strips at truck stops or meat packing houses or whatever to cut down on noise transfer. It would only attenuate bass at the lowest frequencies...same with plywood an other materials. That being the case, they can be helpful with respect to low low end control in the sense that you'd probably require fewer square feet to do it, but it would have to be a very carefully designed trap.
Exactly.
Quote:
Back to absorption for a second, as a matter of fact, the thicker the bass trap is (at the right density), the more effectively it will absorb sub-60Hz low end. That's because there's simply more mass at the right density. There are bass traps that are 12" or 18" thick that absorb very effectively down to 50Hz...you're much more likely to get that right if you're building it yourself than your are to get a trap made with MLV right. Plus...
and lose a lot of realestate.

Quote:
Bear in mind that Ethan, Glenn and I are not making claims that we can't back up with test data.
Frank[/QUOTE]
I'm not refuting what you and Ethan are claiming, we seem to be discussing to different aspects of one thing. The OP started asking about high end and then you asserted he was asking about low end, so we're all over the map now which is fine to flesh it out.
Quote:

I still am not fully bought into the idea of an MLV layer between layers of absorption; I'd want to see test data on that. I also wouldn't recommend a hard layer of anything on the back of a trap. Leaving it open yeilds much better results than closing it off. There's been test data on that for years.
Right, agreed.
Homesote is not a hard layer, it is a semi loose celotex board that is easily messed up, so, don't bump the corners. It absorbs a little high end and upper mids, what would be bouncing around behind a panel with an MLV layer. The more the room is treated, you would be able to pinpoint it by hearing sound come from behind the panel. A real WTF moment. You could even put a 1" 4x8 7lb fiberglas board on the rear if you like. You can mount the mlv in the frame so that it is literally hanging limp from the top and not squeezed in, but hanging with 1/8" on either side to give it room to work properly.
There won't be any test data on that till I build the next set. Till then you just have to use the AMA coefficient table and add or STC ratings.
Old 8th November 2008
  #57
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Thread Starter
just in case there is any confusion about what I originally wanted to know- I have basstraps of fiberglass and breathable fabric, but I want those absorber bass traps to perform better at LOW frequencies and I hear a limp mass membrane helps the bass trap absorb more bass- which is the goal.
Old 28th February 2009
  #58
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Quote:
Originally Posted by memphisindie View Post
Burlap, or, what I use, pimpy looking furry cloth, it's very porous and it's what is used on mic windscreens. Hancock Fabrics online will ship it to you.
Is this what you were using?
Nylon Nettings - Nylon Black Net Fabric, 72"

Thanks,
Seamus
Old 28th February 2009
  #59
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Old 28th February 2009
  #60
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DanDan's Avatar
More Bass Absorption?

Dark Echo, the answer is yes and no obviously :-)
I would try a light sheet of plastic, one of the heavier clingfilms perhaps. I recommend glueing it around the perimeter only. Personally I prefer to use larger amounts and depths. I have found Studiotips Superchunks to be extremely good performers.
DD
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