Limp Mass Vinyl in Broad-Band Absorber?

[RKrizman]

So I thought I'd give it a go. I decided to mount the limp vinyl in the corner behind my traps, hanging loose. I got a roll of 1 lb per sq ft vinyl and cut a 19" x 48" piece with a box cutter. I had some 2 x 2s left over from my diffuser build so I cut the first one 22" long then mitred it so it would sit in the corner. Then mitred another one to continue the angle. I then sandwiched the end of the vinyl between the two and nailed them together. Finally, i added a thin, horizontal piece of wood at the bottom to keep the vinyl straight, as it wants to curve in on itself.

Tomorrow I'll put some studs on my walls at the studio so I can hang these, then mount the bass traps (probably Real Traps) on the wall in front of them. They should hang loose about an inch behind.

[Millo 3.1]

RKrizman:

Excellent--do you have a way of measuring the effect these have? Could you possibly test w/o them, then with them?

[RKrizman]

No idea how to measure their effectiveness. Any suggestions?

-R

[1ManGarageBand]

Hi RKrizman--

I'm so glad to know that someone else thinks this is worth experimenting with! Your trap looks well executed and quite pretty.

My initial plan is to try the stuff as backing behind my first reflexion point broad-band diffusers (2'x4' rockwool panels left and right of mix position and 4'x4' rockwool cloud above).

I agree with Millo 3.1 that it's important to measure the effect before and after and I hope we can use the same method. I've had big problems with measurements up to now.

Long, painful story: When I started acoustic treatment in my small bedroom studio I took a full set of measurements under three conditions: [1] original carpet-on-walls attempt; [2] stripped bare; [3] finished treatment. I used an analog Radio Shack sound level meter to measure the RealTraps bass test tones (every frequency from 10-300 Hz) and the Mix Magazine Reference CD for 1/3 octaves from 315Hz to 20kHz. Thats a total of 930 data points. As a trained scientist (Ph.D.) I now consider the entire data set to be worthless for two reasons: [A] I discovered that my body position could change measurements by several dB and, [B] the transitions when I changed ranges on the meter were not smooth/accurate (often off by several dB). Very disappointing.

I hope forum members will advise us on how to take accurate measurements.

Best regards and good luck, R!

[memphisindie]

You guys do understand that this stuff has to lay very literally "limp" to be effective and wideband low end absorption?
You can stretch it to tune it to counter a specific Freq.
It's going to reflect mids too so you'll need to have something to absorb that too.
Just saying.
You can use it in walls to seal one room from another if you seal the edges.

[Millo 3.1]

Originally Posted by 1ManGarageBand

My initial plan is to try the stuff as backing behind my first reflexion point broad-band diffusers (2'x4' rockwool panels left and right of mix position and 4'x4' rockwool cloud above).

These would be absorbers, right?

Krizman,

Well, I think maybe you can measure the room w/ the typical program everyone uses, using a SD condenser at the listening position. You can measure with or without. You wouldn't be accurately testing for absorption, but I WOULD IMAGINE that if it does alter your corner absorbers' effectiveness (hopefully for the better), your reading will reflect that.

I think most people use RoomEQ Wizard.

[johndykstra]

In the Primacoustic version, it is mounted behind the trap vertically on both sides, there's got to be some degree of tension in order for this to work I thinks. RKrizman, when we talked of their model at an earlier time, you had suggested that perhaps they mount it that way to keep it intact during shipping, however, those traps are shipped unassembled, so I think there's more to it than durability. Your wood block at the bottom may be a good start, but I'm thinking perhaps something with some degree of mass should be pulling it downward.

It'd be interesting to suspend some sort of vessel from the bottom of the MLV, where you could add or subtract mass to tune the tension of the trap. Perhaps a length of PVC that you could add or remove rebar from. Just thinking out loud here. After all, the absorber in front of the MLV is already broadband. If we are going to take the time to add to the broadband design, it may as well be calculated.

Sorry, but I just don't see a flappy sheet of rubber having any effect. This hasn't gone with out some considerable thought, though it's not rare that my thinking is flawed . Imagine hanging a guitar string. Or a drum head without tension. These transducers are very light compared to mlv. They produce no audible or visible vibration in the presence of sound without tension... what chances does heavy vinyl have? Slim and none I'd imagine.

[johndykstra]

Originally Posted by Millo 3.1

These would be absorbers, right?

Krizman,

Well, I think maybe you can measure the room w/ the typical program everyone uses, using a SD condenser at the listening position. You can measure with or without. You wouldn't be accurately testing for absorption, but I WOULD IMAGINE that if it does alter your corner absorbers' effectiveness (hopefully for the better), your reading will reflect that.

I think most people use RoomEQ Wizard.

If you haven't had experience with REW (room eq wizard) be prepared for some headaches. I downloaded it last night and spent 2 hours with it, no usable data. It should be noted, that I didn't read the manual until this morning, where I learned a great deal about what I did wrong. Typical male. You will need an SPL meter, or a lot of time for guesstimating and re-doing. Also, testing the effectiveness of room modes based on the performance of a singular trap my be discouraging. I would recommend placing your mic very near that particular corner, and move it incremmentaly until you find a measurement with the most pronounced modal activity with your "unvinyled" trap already in place. Mark that exact location, or leave the mic there if possible; alter your trap and re-execute the test.

[Ethan Winer]

Originally Posted by 1ManGarageBand

I hope forum members will advise us on how to take accurate measurements.

Room EQ Wizard, Windows and Linux and Mac OSX 10.4+, Freeware
ETF, Windows, $150
FuzzMeasure, Mac, $150
Using ETF explains how I use ETF, but the principles apply to all such programs.
Comparison of Ten Measuring Microphones

--Ethan

[RKrizman]

My room is too large to be much affected by a single trap. My thought was to put a mic up near the trap and run some tones and measure with my SPL meter, just to get a rough idea if it's doing anything at all.

As far as tension goes, I remember looking at the back of one of those Primacoustic traps and noting that the vinyl was not tensioned. Having now fooled with the stuff I can't imagine what you'd have to do to make it resonant. It just seems designed to not be that.

here's a question. When you use this stuff to stop transmission of waves through a wall, how does that work? I assume by turning the wave energy into heat. Certainly it doesn't reflect the low frequencies back into the room, does it? It seems reasonable that the same properties that make it work in a wall will also lead it to stop retransmission of bass waves in other applications.

But what do I know? We'll see. Hey, it took me all of 15 minutes to build these things.

-R

[tINY]

The only time I've really played with it was when it was bonded to acoustical foam.

With a 1/4 inch foam sheet bonded to one side and 2" bonded to the other it definately reduced the sound transmission into/out of a phone test cabinet.

Can't say exactly what it was doing in the bass region as the phones we were testing only went down to about 300Hz....



-tINY

[RKrizman]

Originally Posted by RKrizman

My room is too large to be much affected by a single trap. My thought was to put a mic up near the trap and run some tones and measure with my SPL meter, just to get a rough idea if it's doing anything at all.

Actually, I'm suggesting two different things. One would be to put a mic near the trap, play some pink noise and measure the freq response in something like PAZ in Protools. The other is to put the SPL meter near the trap, generate tones in Protools and measure them.

-R

[LX3]

I'm a bit lost. I'm not an acoustics expert, and maybe I'm not understanding where most of you are coming from, but this is how I understand things.

If a sheet of limp-mass material is hung freely in a room (near a boundary or anywhere), in such a way that air can flow around it (i.e. not as a membrane fronting a sealed box), surely the pressure of the soundwave behind it is the same as the pressure in front of it?

So it won't move. So it won't dissipate any energy.

All that it'll do (surely?) is reflect high frequencies to some degree, just like any other surface.

Porous absorbers work by slowing down moving air molecules... but this isn't a porous absorber.

And the hangers you sometimes find in large bass traps or ceiling traps work by trying to lengthen the path of the soundwave so that it reflects off multiple boundaries and/or passes through multiple thicknesses of porous absorber.

Meanwhile, sealed-box membrane absorbers work by responding to the pressure compenent of the soundwave. Limp mass material as a membrane to a sealed air-space should work great - well-damped so fairly broad Q, and high mass per unit area, so would have a resonant frequency down in a useful range. I've been intending to experiment with designs like this for a while now (but never had the right circumstances to do it - until now).

But just hanging a sheet of limp mass behind/in front of another absorber... I don't see how that works.

Mind you, I bought a load of Ethan's traps thumbsup

[RKrizman]

Well I'm now inclined to agree with you. I spent the afternoon testing these different traps. I put up a mic about 3 feet from the trap, sent tones out out my monitors at half steps from 27 hz to 804 hz, and measured the amplitudes with a PAZ meter in Protools.

In one corner of my room I stacked up two 2' x 4' x 2" Primacoustic Broadway panels, essential fabric covered 705. Behind those I installed my hanging limp mass devices, floating freely about an inch behind the fiberglass. I made measurements with and without the limp mass.

Conclusion? The results were so similar I didn't even bother to graph them for comparison. The differences were often identical to a tenth of a db, and generally within one db or so. There were only three notable differences:

At 99 hz the glass alone measured 2.2 db less than the glass/vinyl.

At 444 hz the glass/vinyl measured 5.2 db less than the glass alone.

At 718 hz the glass/vinyl measured 3.2 db less than the glass alone.

I also measured the corner without any treatment. Notably, in the three instances in which there was a significant difference, the glass/vinyl measured very close to the bare corner with no treatment. Go figure.

So unless someone else has a brilliant idea I'm going to write off this whole exploration as a fail.

-R

[Jeffrey Hedback]

Well...interesting.

I've used LMB (MLV) many ways for both Transmission Loss and internal room acoustics.

Your system is essentially the Primacoustics Maxtrap with one large variant...their's is a sealed system (although there is no acoustical sealant on seams).

It may be worth capping top and bottom of each segment and see what you get.

The Primacoustics testing was done at Riverbank and they're a straight up company. No reason why your assembly won't work.

[RKrizman]

Originally Posted by Jeffrey Hedback

Well...interesting.

I've used LMB (MLV) many ways for both Transmission Loss and internal room acoustics.

Your system is essentially the Primacoustics Maxtrap with one large variant...their's is a sealed system (although there is no acoustical sealant on seams).

It may be worth capping top and bottom of each segment and see what you get.

The Primacoustics testing was done at Riverbank and they're a straight up company. No reason why your assembly won't work.

First I want to say that in no way am I making any veiled conclusion regarding the Primacoustic trap. I heard a stack of them working in a small room and was really impressed. I saw what they did inside but don't perfectly recall.

My own experiment was not sealed on the sides--the photo may be misleading. So someone's suggestion that the sound energy could just go around the vinyl now seems very sensible. Do you think it would make sense to just build a wooden frame straddling the corner and just staple the vinyl to it, keeping it as lose as possible?

How have you implemented this yourself, if it's not proprietary?

Thanks,
-R

[DanDan]

R- A sealed box with a flexible panel front is pretty much the old BBC design. Or for that matter the original RealTraps panel design.
They of course did work! They did not allow the panel to touch the damping fibre fill.
I suspect the Modex, Primacoustic, and many others are exactly the same thing.
The problem, as ever with such devices, is that one would need a lot of them to achieve anything significant. So if you go ahead, I am afraid you should probably do all the corners in order to see the effect. As I said way back, not many people go there, but if you do, good luck.
DD

[Glenn Kuras]

Originally Posted by DanDan

R- A sealed box with a flexible panel front is pretty much the old BBC design. Or for that matter the original RealTraps panel design.
They of course did work! They did not allow the panel to touch the damping fibre fill.
I suspect the Modex, Primacoustic, and many others are exactly the same thing.
The problem, as ever with such devices, is that one would need a lot of them to achieve anything significant. So if you go ahead, I am afraid you should probably do all the corners in order to see the effect. As I said way back, not many people go there, but if you do, good luck.
DD

Panel traps are great, but see them as icing on the cake.

[Nexus.6]

Originally Posted by Jeffrey Hedback

Well...interesting.

I've used LMB (MLV) many ways for both Transmission Loss and internal room acoustics.

Your system is essentially the Primacoustics Maxtrap with one large variant...their's is a sealed system (although there is no acoustical sealant on seams).

Hello,

I am evaluating this solution, it doesn't seem that Primacoustic is a sealed trap.

See pictures... Primacoustic Acoustic Solutions

One Hometheater maniac experimented that in France with great success :
Traitement "Control Room" et choix d'un diffuseur DIY - Acoustique

(use Google translator!)

Any feedback since 2010?

regards

Laurent

[memphisindie]

Thank you!

[matt thomas]

I just removed all the walls from my iso booth as I am moving to a new property, so I had to return the rental to the state it was when I moved in. I had mass added vinyl in there and about a million other things. I threw out well over a ton of material from my 6 x 8 feet booth..

(and that was only the interior leaf walls, the outer walls were part of the original building)

matt

[Syncamorea]

Originally Posted by Millo 3.1

I wonder if it can still make a 6" or thicker absorber more efficient... I assume if you put it straddling a corner, the thicker the fiberglass/mineral-wool front the further back you'd have to place the membrane, so the narrower it'll be. I would assume this design becomes less and less effective the narrower the membrane is. However, I do plan on eventually placing two 6" 2x4's on my back wall, with at least 4-6" air gap. I wonder: If I build the typical wooden back-frame and hang a limp mass encased in it, will it make it more effective? These panels would go over a low-profile, 13"-deep, 4-ft wide bookcase I had made precisely w/ plans of installing these bass absorbers on that back wall, over it. It seemed like the only place where I could place this very necessary bookcase in my room w/o really messing things up. I also wonder how heavy such a design would be, LOL!

I made a limp mass absorber that was 9' tall x 13' wide and 8" thick. Mounting it was a pain in the butt. It basically killed the LF problem in the room. The difference in the room was like flicking a light switch on. After repositioning and adding more diffusion, the room went from lousy to revealing.

I've seen larger membrane traps that use wool carpet as a substitute for canvas or burlap but haven't spent much time in the room to make a personal assessment.

I've worked in manufacturing facilities that have alot of steel-on-steel impact noise. It's common to see hanging blanket absorbers. There used to be a family business in the Detroit area that made them with a porous nylon cover over layers of vinyl and rigid glass wraps over rock wool. Pricey but effective. I really need to make up a jig and try to DIY one of those. Basically, two convex rigid rectangles sandwiched the vinyl and the inside of each convex glass "frame" held an inch of a dense rock wool. Each sandwich was around 2.5" thick, maybe a little more. The dimensions looked to be about 2 x 3' for each in most installs but they made smaller and larger units on special order. Those were nasty environemnts to work in.

[4 the Max]

Primacoustic makes these 2 traps using MLV (Mass loaded vinyl). They are in a sealed cavity, just as much as Ethan Winer's original bass traps had a sealed cavity.

Ethan Winer links:
Build a Better Bass Trap

Modification of Ethan Winer's trap showing acoustics and build:
Studio Bass Trap Build and Test - YouTube

Rubber membrane instead of MLV:
Building a Better Bass Trap

Primacoustic Acoustic Solutions
Primacoustic Acoustic Solutions

I have some leftover EDPM rubber from building an outdoor pond.
Any thoughts about about using it instead of MLV?
EPDM rubber - Wikipedia, the free encyclopedia

[NLP]

I have succesfully build it many times from cheap bitumen in rolls.

[Ethan Winer]

Originally Posted by 4 the Max

Modification of Ethan Winer's trap showing acoustics and build:
Studio Bass Trap Build and Test - YouTube

Wow, very nice. I never saw this before. Thanks for posting the link.

--Ethan

The Acoustic Treatment Experts

[Glenn Kuras]

Modification of Ethan Winer's trap showing acoustics and build:
Studio Bass Trap Build and Test - YouTube

Great video but I would make the panels more square and you do have to be careful when using wood. Not all wood is the same quality. Also when testing I would use REW
GIK Acoustics. REW Room EQ Wizard Room Measurement Tutorial video.