Building Sound Absorption Panels

[iggrok]

This is an interesting topic. I am in the process of a move and I am looking to turn a barn into a studio. I am particularly interested in soundproofing for a drum room as I’d like to play at any hour without worrying about neighbors.

[Larrea]

I am particularly interested in soundproofing for a drum room as I’d like to play at any hour without worrying about neighbors.

Perfect example of how acoustic treatment can be so confounding: tuning a room with absorption, diffusion, etc., has almost nothing at all to do with stopping transmission of sound in to or out of the room. That’s isolation.

I designed that in to my studio too, within very tight limits. True isolation was not possible; floating floors were not possible, although since the room is a room within a house, sharing no exterior walls, there is a fair degree of ‘accidental’ isolation; but it is not mechanical isolation–vibrations can still be transmitted directly through hard material.

The interior room was built with two layers of 5/8" drywall, solid core doors (HEAVY!, and a pain to install when dealing with custom installations). Crucial is the total elimination of air gaps. Nothing. Not even a 1/4" hole. You will want to caulk every corner, every angle, every seam. All door and window jams must be sealed. There are neoprene-ish, sort of soft, squishy seals you can get, with adhesive backs, that will work.

Windows should be sandwiched between such material; no glass in direct contact with wood, metal, etc. Seal the bottoms of doors, where they contact door frames, etc.

Doors will be tight. Everything will be tight. The room will be pressurized and sealed. If you don’t have HVAC, it’s no problem. Introducing HVAC makes everything exponentially more complicated.

All of the above will go a long way to greatly reducing transmission. It’s not perfect, but it’s good. When I first finished my build, I had a drummer sit and whale away, and I went outside, on the sidewalk, a linear distance of only about 10 feet from where he was playing, and amongst ambient day time noise, he was hard to hear. Across the street, for someone in their house, he was inaudible. Neighbors never said they heard anything.

Sorry for the ramble. I hope it helps a little.

EDIT: I forgot about insulation. I used a non-standard R-value fiberglass insulation; can’t remember the details, and doubled it up. There are other insulations that are not fiberglass that work well for this, but they are very expensive. Thin lead sheeting made for this purpose is also sometimes used.

Oh, I also forgot that behind both layers of drywall is a 1/2" layer of fiberboard. This makes a big difference. It also means your drywall installation will be miserable and a pain, but you’ve got to deal with it. It’s a crap job. The whole thing is miserable and crappy, but when you’re done, you will smile.

[praffensperger]

(If you have a sealed room without HVAC then do you get too hot or cold?)

[Larrea]

In general, I suppose that would depend on how much gear/lights are running in the room, size of the room, number of people, and climate.

In my case, I do have cooling via a mini-split system which does not use ducting, only thin copper piping, which is easily sealed in the wall. One caveat is not running it when silence is critical, but it’s quiet enough that for all times except live takes or critical low level mixing, it’s not a problem.

[tehn]

minor connect to this thread:

Studio treatment

Continuing the discussion from Speaker Preferences: following up on great post from @Tyelr http://llllllll.co/t/speaker-preferences/2712/8 i stumbled across this DIY diffusor article on tapeop. http://tapeop.com/tutorials/83/diy-diffusors/ [image] would be curious to hear more tactics regarding studio setup.

[abalone]

Studio treatment

I have some acoustic foam in a few places.
But the thing I noticed the most impact from were packing blankets!

yes, packing blankets

[carvingcode]

When I converted a room to my studio I did quite a bit of research on creating a space designed primarily for listening to the mix. Reducing bounce and bass boom was a priority as I recall.

I looked at building absorption panels, but decided on a collection of Auralex foam panels and designed them into specific groupings along the four walls and in the four corners. Works well.

[damianschwartz]

“Home studio, build it like the pros” by Rod Gervais, despite its kind of self help title, covers all you want to know about this matter and more, including room ratios, sound treatment… It is very well written and explained too, and demistifies with facts many wrongly assumed issues about acoustics, can’t recommend it enough…

[ermina]

well, i did some panels for my own space last year.
In the interest of documenting that, I wrote a hopefully useful blog post about it (well, currently the only finished post, your question being actually the motivation to put the whole thing online).

That was my second time doing diy “things” to correct a room acoustics, so i guess i got it better that time. The first time i used a mix of various elements, amongst which the most efficient was a half-decently dressed up pile of fiber 60cm deep in a corner, from floor to ceilling.
I also did some rockwool+fabric+wooden frame panels, but i hated manipulating rockwool, and my carpenter’s skills are not great, and i lacked space on the walls to hang them.

[christopher_wilson]

Wow! The interest and experience in this topic is encouraging

Yes, a sound proofing project, recording space sound treatment, and listening room sound treatment are three different undertakings.

The project of balancing the room sound of a professional mixing or mastering room, and its associated maths, will be a delightful project when someday I can afford a better room to work with. Hopefully we’ll all will get there someday. Until then, we must enhance the quality of what we do have to work with.

The project I have in mind is fairly simple: Make the space in my apartment better for listening and composing. The room isn’t large enough to warrant diffusors. Removing buildup of bass frequencies and flutter echo are the goals I’m starting with. The tasks, in order of importance are 1) Bass traps for areas (corners or back wall) where low frequencies build up 2) Install absorption at first reflection points 3) Absorption on the rear wall.

Building things from wood (frames in this case) is not something I have experience with so I thought I’d share the learning process, hoping it helps a few other people learn in less time than it takes me.

[bradfromraleigh]

I’m so glad this came up as I am getting started with this project for my room as well. I struggle with to strike the balance of being good enough while not underinvesting in materials that may be worthless later and opening a money-pit of a project by overinvesting a little too much in the end result (if that makes sense).

My room is not overly small at 11’ x 19’ and these dimensions lend themselves to audio fairly well. My real issue is that the room has 4 doors and a window that create the impossibility of keeping access to all of these while simultaneously effecting sound. It looks like I’m going to have to block at least 1 door and possibly 2 if I want to center the listening position between the side walls.

I’m interested in hearing what other people have done with difficult rooms. Moving blankets would be the easiest thing for me but I’m not crazy about the esthetic this creates and I’m concerned this wouldn’t help my particular situation as much.

I’m currently considering DIY bass traps in the corners, moving blankets against the front wall, acoustic panels at the reflection points, and possibly a minidsp 2x4 to counteract the off-center listening position.

[dude]

every time i stumble onto a thread about acoustics/absorption it produces a sense of anxiety knowing my best effort thus far has been a twin mattress somewhere behind me in the studio. i never have taken the time towards a better absorptive setup. my only answer is to do my best attempt at a meticulous mixing stage at very low volumes. my thinking being that if i can get a mix working at very low volumes and on nice cans and on laptop speakers and in my car then the need for a great room might be superseded. i hope at some point i buy a house and take the time to set up a great room on the smallest yet most functional scale i can muster.

[jasonw22]

How do people deal with windows and doors? All of my rooms have too many windows and doors. I have actually considered building an entirely new building on our property. This seems excessive.

[iggrok]

I have the most ghetto studio at the moment. Crazy hard surfaces all around with some basic foam panels peppered throughout. In dire need of something better. Working on it…

@jasonw22 that’s always tricky. A lot of people resort to very thick drapes which are cost effective. If you’re willing to spend some money on replacing windows, you can also go this route.

[christopher_wilson]

Careless deployment of absorption can do harm; you need to account for the full frequency range. Merely throwing up tons of Auralex will leave you with a room that has an acoustic tilt, for example.

This statement, especially as it relates to standing waves, is reenforced by the book Acoustic Absorbers And Diffusers.

“Poorus absorbers are ineffective at these modal frequencies , because the particle velocity near walls and in corners is essentially zero for these long wavelengths; and also the treatment would have to be made so deep that significant space within the room would be lost. This problem can be solved by using a resonant absorber, such as a membrane design. A membrane absorber converts the high sound pressure fluctuations typically found at wall surfaces and in corners into selective absorption in the modal frequency range. As the use of sub-woofers has become more popular in small sound reproduction rooms in recent years, there is a growing need for modal frequency management.”

The author adds the cautionary note:

“If the absorber has a sharp resonant peak with a high Q factor, there is a risk of creating a notch at the wrong frequency, thus aggravating rather than ameliorating the modal problems.”

Tuned absorption is (for myself) a couple steps down the road, but we’ll get there! A quick google search for acoustic membrane surfaces (upon which to attach porous absorption as explained in the book) suggests commercially available micro-perforated surfaces are costly. If the size and spacing of holes can be determined, one can contract a water-jet company to cut a panel with your supplied measurements (usually in a DXF file) fairly affordably.

Having never fabricated any absorber, I’m starting at the very beginning and building a prototype wood frame. Hopefully the community here will have a look and respond with some suggestions.

[Larrea]

“This problem can be solved by using a resonant absorber, such as a membrane design.”

Exactly what I did.

There are plans available (I think) for how to build these with commonly available grades of plywood, pine 1x4s, 1x3s, 2x2s, compressed fiberglass panels, silicone sealant, hardware, and a few other odds and ends. Not sure where anymore, but surely such plans can be found.

[ermina]

It may be obvious, but before anything, measuring the room response seems mandatory to me.
Calculation is one thing (that should be also done), but depending on the walls material/structure, some absorption might already occur (or the contrary…).

As for tuned absorbers, in my first attempt to tame a room, i settled on the BBC designs, because they made sense to me:

• they were backed by research and measures
• they were designed to be easy to build in situ with materials available at the local store
• the second B means Broadcasting, and the room was a radio studio, so…

Membrane absorber : http://www.bbc.co.uk/rd/publications/rdreport_1992_10
Wideband absorber: http://www.bbc.co.uk/rd/publications/rdreport_1992_11

[christopher_wilson]

Flutter Echo Attenuation Prototype Absorber #1

With a borrowed drill, mitering hand saw, and a few other borrowed tools, I was able to build my first attempt at a frame.

Wood Selection
Without access to a table saw, my material choices are currently limited to precut measurements such as 1X4 (3/4” X 3-1/2”) or 5/4X6 (1” X 5-1/2”)

In these sizes, the two main varieties of wood planks available were framing lumber and decking boards. Decking is well finished, structural wood that is a bit heavy for this purpose. Framing lumber is not pretty but was the better option. It’s surprisingly cheap too.

Note: If using 1X4 framing lumber, look through the stack to find sufficiently straight boards as some planks were better suited for boomerangs than absorber frames. Clamping everything into place first does help with drilling the holes straight and preventing your project from becoming a parallelogram absorber.

Even then, the only way I could think to keep the boards straight was to screw a short and a long side together, making an L shape for the absorption material to sit in.

Screws
The wood screws were selected to be used on a variety of materials and sizes. #8 X 2-1/2” is probably larger than necessary for 1X4 planks. This is my guess at logical screw placement. It’s the fewest number of screws that accounted for everything. And of course we are countersinking all screws!

This screw placement attaches all sides of the wood planks with the fewest number of fasteners possible. The backing board is also screwed to the side beam at the center point to help prevent warpage.

Summary
So far so good. Because the purpose of these absorbers is to attenuate flutter echo, this frame should work well enough.

Perhaps we’ll try hole sawing the planks in some places to increase the absorption area. I’m not sure the wood is strong enough.

Both the cover fabric I have on order and the insulation itself are fireproof. These 1X4’s are the only flammable part of this prototype. If I can acquire (or get access to) a table saw, I will make the next prototype frame from a sheet of MDF instead of lumber as MDF is a lot less flammable. The center plank is intended to help hold soundproofing insulation in place as well as help straighten the frame. If you have ideas of how to improve this design, please share them.

Thank you for playing along, your feedback is appreciated.

[eesn]

To second, acoustic treatment and soundproofing are distinctly separate. With treatment, you want a choice of absorption over the audible spectrum, as well as zones within a space (LEDE etc). Soundproofing is a more expensive (and expansive) scope, ideally you suspend the room within a room. Without referencing a specific manufacturer, I can say there are some very effective and pretty affordable non-foam treatment panels on the market.

[strettara]

About ten years ago I was working on a documentary about life in the Bombay slum of Dharavi (https://www.nfb.ca/film/dharavi_slum_for_sale/). One of our subjects was a brilliant young jazz/fusion drummer who was making a soundproof practice room for his fusion band in the tannery area of the slum. He fitted the entire interior with mattresses… it worked quite well, but the heat and humidity in that room had to be experienced to be believed. We used to shoot for ten/fifteen minutes, then everyone would leave the room to relax and smoke a cigarette outside and drink gallons of water. Unfortunately he didn’t make the cut, but he was a great guy.