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Wrapping acoustic panels in thin plastic wrap?

Hello,

I am building some acoustic panels to hang on my wall and ceiling and as I have a dust allergy I want to make sure they are totally contained and can not leak dust through fabric. (I have not decided yet whether to build these from 2 inch 703 or 8lb density 2 inch rockwool panels.)

But whichever one I choose I will be wrapping the acoustic material in a thin .31 mm painters polyethylene sheeting from home depot. My plan was then to layer the front of this with some polyester batting and then wrap the entire panel is a soft polyester 110z velour fabric.

I have read varying opinions on several forums about the reflectivity of a thin plastic layer at higher frequencies with most commentators saying that if the plastic is thin enough and then covered with a soft fabric it will not cause reflection problems.

However, many threads warn against non "breathable" fabric and how it it can negate the absorption effect of the rockwool or fiberglass laying behind it?

Is this general idea for panels of 2ft x 4ft and 4ft x 8ft a bad plan?

Comments

Profile picture for user Brien Holcombe
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6 years 2 months

Brien Holcombe Tue, 12/13/2016 - 17:27

Well...the plastic isn't going to create an issue one way or the other since it, in the real world, will be hidden behind a breathable fire retardant fabric.

Directly to your concern about " warn against non "breathable" fabric and how it it can negate the absorption effect of the rockwool or fiberglass laying behind it"

Ok, on the face of it, it could be true...but in the grand scheme, it isn't. While you haven't mentioned room size, most people are working in environments less than 2500 cubic feet, and these rooms are considered small rooms.

The reason is because the acoustic energy generated by instruments and monitors, both often found in the same room, basically over power the rooms ability to keep this sound distributed evenly. what happens first and foremost is the low frequency that can escape due to the actual structure materials will leave. But everything else pretty much stays in the room battling for a piece of the air space.

Still, even thou low frequency has escaped, maybe from 40 or 50 Hz on down...you still have to deal with everything above that. And a typical acoustic panel has the ability to reduce/remove frequencies at a specific range according to insulation and material density, gas flow and those things.

Knowing your target frequency helps you to better understand what you can and cannot install. Panels mostly are aimed at mid low frequency and high frequency so even thou you have or may put what is considered a non breathable fabric as your finish material, it does not mean the panel will be useless.

Simple thing is this. Low frequency requires mass and density to isolate...but your panels will still be able to trap some mid low frequency so are not rendered useless.

Now high frequency...this is what the naysayers are referring to without explanation to you my friend.

It is true that if the weave is tight enough you can reflect highs. But let me submit this to you. Small rooms have low frequency issues, and that is a fact supported by data for decades and I only have to point you to F Alton Everest the author of Master Handbook of Acoustics for support on this statement.

With this build up of low frequency, your going to lose the highs anyway...that is also a known fact.

I would rather you build a panel that by design will help you as it is intended BUT if you either cannot or will not get a breathable fabric, then do it as you will and chances are you will not notice anything but improvement.

Just stay away from anything that is really tightly woven as your final covering.

Profile picture for user Brother Junk
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Brother Junk Wed, 12/14/2016 - 04:52

Brien Holcombe, post: 445729, member: 48996 wrote: The reason is because the acoustic energy generated by instruments and monitors, both often found in the same room, basically over power the rooms ability to keep this sound distributed evenly. what happens first and foremost is the low frequency that can escape due to the actual structure materials will leave. But everything else pretty much stays in the room battling for a piece of the air space.

That is part of what makes sound quality installations in cars difficult. The cabin space is very small for the desired volume. Older cars had a lot of squared off corners too. Many acoustical battles won and lost in Volvo's lol.

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GlassTubes Wed, 12/14/2016 - 09:15

Brien,

Thanks a lot for this very informative and well thought out response! My room comes in around at just over 6000 Cubic feet, but I occasionally do work in rooms below 2500 cubic feet so that is good information to take into account for those situations.

Unfortunately, I do not know what my "target frequency" is. My problem at the moment is some nasty flutter echo and muddled mid range and highs. This is basically a shell building with thin fiberglass insulation and plastic sheathing covering it - so I think not much mass for bass build up except a concrete floor? I do not detect any serious bass buildup in this room, at least by ear. But as you said, is the lack of bass trapping contributing to the muddle I hear higher up?

The muddle and lack of clarity is pronounced when playing electric guitar or listening to music in this room. The whole room is constructed of mostly hard reflective surfaces save for a rug and a couch and some gear covered with moving blankets. I had read somewhere that you need to cover minimum of 20 percent of a rooms surface area to treat a problem like this and the moveable panels solution appealed to me as I can add and subtract until it sounds good to my ear. (I wish I had a more scientific way of approaching this but my ignorance in these matters is high!)

I am going to go forward with the plan for the panels and will look for a loosely knit front fabric covering since the acoustic material is going to be sealed in the thin plastic anyway there is no possibility for dust leakage.

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GlassTubes Wed, 12/14/2016 - 10:10

24ft x 29ft with a sloped ceiling from 12ft to 9ft. The ceiling is sloped along the 29ft long wall axis so when you open the door it is 12 ft high and at the back wall which is 29 feet away the ceiling is 9ft high.

So excuse me my earlier post listing the room volume as over 6000 cubic feet is incorrect. Calculating an average room height of 10.5ft the volume would be 7308 cubic feet.

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Brien Holcombe Wed, 12/14/2016 - 10:27

Ok 7308 cubic feet. That sloped ceiling is sending reflections back to the room you may already be aware of this sonic phenomena. And all the plastic sheathing you mentioned earlier is adding to high frequency.

You won't even begin to have lf energy build up till around 23Hz...so you are good.

We seldom see someone with the opportunity to actually be in such a large environment...pretty cool.

But that canted ceiling is going to continue to be a problem unless you develop overhead clouds at the areas where musicians are located and specifically if you have a monitoring/ mixing area.

If you do have a mixing area...if it isn't like this already..you want that slanted ceiling sloping up and away from your back to allow early reflections a way out of your area.
Basically you want the mixing monitoring area at the 9 foot wall side with the mixer person facing that shorter wall.

It will improve clarity and help remove the muddiness you are experiencing.

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GlassTubes Wed, 12/14/2016 - 10:51

The way it is set up now the mix position is reverse to what I think you are suggesting - the listening position is in the center of the short 24ft wide wall just a few feet off of that wall. Above my head to my back it is 9feet high,and I'm looking towards the other 24ft wide wall that is 12ft tall at that end. I'm moving stuff around to get a few more feet between me and the rear wall but I can't easily reverse positions the way everything is wired and set up and face the 9ft wall. Is this a big problem?

I had one friend who is by no means an expert suggest setting up a RFZ behind the mix position. His plan was to deaden the entire back wall with 3.5 inch thick safe n sound rockwool that you get at home depot. So the entire wall of 24ft by 9ft would be stuffed. It's a lot of material and I don't know if this is necessary Vs just deadening the area behind the mixer plus 3 or 4 feet on each side - so in total a 10ft wide area stuffed with 3.5 inch thick rockwool.

I like this cloud idea - would a few 2 inch thick 4ft by 8ft panels be a good place to start by hanging these in the playing area - which is the high part of the room? As well as overheard the mix position?

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Brien Holcombe Wed, 12/14/2016 - 11:13

Yes...the clouds will work wonders. It will take the erratic reflections of the ceiling out of the mics and ears of players.

Now rfz...reflection free Zone is a complete system...to deaden the entire wall may not be what you want to do at this point.

But if you can get a cloud over your mix position it may help to get rid of what you are hearing as compared to what you should be hearing.

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4 years 6 months

GlassTubes Thu, 12/15/2016 - 06:34

Thanks Brien great advice.

So I've got 3 different ways of doing ways of approaching this:

1) Build 4x8ft panels and hang them from the ceiling along the angle of the ceiling or 2) hang them parallel to the floor.

3) There are beams running across the width of the room - (so they are 24 feet long beams) - and spaced 4ft apart from each other that create a natural cavity - Instead of making panels I could just fill these cavities with acoustic material and then pull fabric over them.

Plan 3 would be probably be easiest from a construction point of view. BUT would the separate panels be more effective because of the space behind them - the space between the back of the panel and the ceiling?

Also - if I go with the third option - does it make sense to fill the entire length of the cavity - so deaden a 4ft section of the ceiling 24 ft wide or even multiple 4 ft sections 24ft wide? I guess what I am getting at here is whether it makes sense to have the entire width of the high part of this room to be dead - or instead deaden one side and keep the other side reflective to give an option when recording?

The panels are better in the sense that they could be move around and filling these ceiling cavities would be more of a permanently installed and less tunable solution.

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Brien Holcombe Thu, 12/15/2016 - 19:40

Hey...I need to draw up a diagram to explain some of my thinking on this project...for clarity on my part mostly. But I am pressed for time at the moment. I will get back to you in a few days, assuming no one presents the same ideas, with a sketchup diagram and questions and more opinion on my part.

Hope that is fine with you.

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GlassTubes Fri, 12/16/2016 - 09:16

Of course. I'm in no rush do things wrong on my end! Professional insight like yours is invaluable and the real time involved that needs to be factored in is the many many years of study and practice that go into doing things right. Years that you are really saving me by waiting for your help..

Very much appreciate it

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Brien Holcombe Sun, 12/18/2016 - 09:56

So here is my thinking on it. You have a larger enough environment but for matters of the situation being as it is, your mixing area is not in the optimum placement. Still, it should be workable. As you can see in the picture I have assigned a panel to the left and right of the mix position on either side wall boundary. The overhead cloud in my thinking should be more forward of the mix position to aid in removing the reflections that are coming back at the mix position from the ceiling.

As a point of clarification, when I say mix position i am speaking in reference to where the engineers head and ears are. Everything in the mix area as far as treatment is always balanced, symmetrical and based on where the head and ears of the engineer are while working...its a static point that should be defined early on before anything is installed.

Ok, I choose to have the overhead cloud horizontal rather than at the pitch of the existing ceiling for 2 reasons. 1 is that an air gap behind treatments has shown to make the treatment better at absorbing to a lower frequency than the panel may have been designed for the target frequency. 2 is because there is a chance that certain frequencies could be pushed back into the mix position which is what we are trying to eliminate.

A thing about your current setup and why it is failing to respond as hoped for: In any mix room I have been in, monitors have a hard boundary behind them and this hard boundary, while it has to be treated as well, helps contain the sound so you can hear it before it starts to degrade via treatments and activity.

You do not have that wall or hard boundary and may always have an issue with this until you can develop maybe some gobos with a hard back to aid in keeping the sonic energy in your face rather than it expanding directly out into the room having never been heard at its best at the mix position.

3) There are beams running across the width of the room - (so they are 24 feet long beams) - and spaced 4ft apart from each other that create a natural cavity - Instead of making panels I could just fill these cavities with acoustic material and then pull fabric over them.

Plan 3 would be probably be easiest from a construction point of view. BUT would the separate panels be more effective because of the space behind them - the space between the back of the panel and the ceiling?

Also - if I go with the third option - does it make sense to fill the entire length of the cavity - so deaden a 4ft section of the ceiling 24 ft wide or even multiple 4 ft sections 24ft wide? I guess what I am getting at here is whether it makes sense to have the entire width of the high part of this room to be dead - or instead deaden one side and keep the other side reflective to give an option when recording?

Yes, you should do that as well...in addition to what we just discussed about the mix position. What you have is like an un-tuned diffuser that is sending who knows what to god knows where in that room.

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GlassTubes Wed, 12/21/2016 - 09:07

Hey Brien,

Thanks a lot for this drawing and advice!! Great tip to keep the cloud at an angle to the ceiling. I will do that. I look forward to updating you with some photos of how things turned out in the new year. Will also be stuffing the ceiling in the high part of the room as per your recommendation.

This is definitely a doable plan on my budget that I'm sure will greatly increase the performance of this room. Thanks again

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3 months 2 weeks

cetanorak Sat, 03/06/2021 - 09:40

Hey GlassTubes,

I was curious to know if you ended up wrapping your insulation in the .31mm plastic sheeting and, if so, how you found the resulting performance to be affected by it. I'm about to build some gobos with Rockwool Safe'n'sound and was also considering wrapping with something like painters plastic to ensure that the insulation fibers can't escape. Of course, I became conflicted with this idea when considering that tightly weaved or non-porous fabrics can start to reflect high frequencies. Thanks!

GlassTubes, post: 445721, member: 50236 wrote:
Hello,

I will be wrapping the acoustic material in a thin .31 mm painters polyethylene sheeting from home depot.

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3 months 2 weeks

cetanorak Sat, 03/06/2021 - 12:27

ronmac, post: 468110, member: 24337 wrote:
https://www.homedepot.com/p/Vigoro-3-ft-x-50-ft-WeedBlock-Weed-Barrier-Landscape-Fabric-with-Microfunnels-1242RV/302720132

I have used this type of weed block fabric for wrapping DIY rockwool panels, before applying Guildford of Maine acoustic fabric. It is inexpensive and will not impede acoustic energy transfer as much as solid plastic wrap.

Ah! I've read of many folks wrapping the rear side with this weed barrier fabric but I've also heard many say that it may reflect HF. Seems like a very cost-effective method. Have you seen acoustic testing done on this weed fabric that suggested it was acoustically neutral? Another point that some have made, particularly folks who are trying to build non-toxic acoustic panels, is that this weed fabric may contain petroleum distillates and other chemicals. It's probably damn near impossible to build any truly effective acoustic tuning solutions without the inclusion of some kid of born-in-a-lab and potentially toxic (milld or otherwise) components.

...personally am right up there on the proverbial fence deciding whether to invest in that lovely Guilford of Maine. Would take my highly effective economical build quickly out of my economical realm! Decisions. Never thought that I would get hung up with so many of them in taking this DIY project on. There is tome after tome to be discovered on internet-based acoustician forums about the minutiae of building acoustic panels.

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Paul999 Sat, 03/06/2021 - 13:29

I suspect you can wrap them in a layer of craft paper. When I built my control room @Ethan Winer recommended I use insulation with craft paper on it for the layer of wall that would be covered in fabric. It reflects high end and double the low end absorption. As per his advice, I did not do this around the console to minimize early reflections at the console.

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ronmac Sun, 03/07/2021 - 05:57

I highly recommend the GofM fabric for both it's fire rating and aesthetics. There is no getting around the expense....

Frankly, using Rockwool (versus fiberglass) allows you to forgo the intermediate layer, and use the GofM fabric as the aesthetic/containment wrap.

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cetanorak Sun, 03/07/2021 - 12:22

ronmac, post: 468121, member: 24337 wrote:
I highly recommend the GofM fabric for both it's fire rating and aesthetics. There is no getting around the expense....

Frankly, using Rockwool (versus fiberglass) allows you to forgo the intermediate layer, and use the GofM fabric as the aesthetic/containment wrap.

I do believe that this is the route I will take for building some moveable gobo's for voice over work. I may wrap the Safe'n'sound in a thin layer of polyester batting for added security.

Is there any competition out there to the coveted Guilford of Maine fabric?

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ronmac Sun, 03/07/2021 - 12:37

If they are for your own use you could go a cheaper fabric route and spray them with a flame retardant.

I generally buy GofM fabric in rolls of 40 to 60 yard lengths (they are very helpful in letting you know if they have off-cuts, etc.) to make shipping costs/yard a bit less painful.

Both Rockwool and GofM offer a downloadable certificate indicating flame rating that is recognized by insurance agencies throughout North America. If I am quoting an install job, being able to supply an insurance certificate goes a long way to making the facility owner or board members accept the quote.

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