Help with basement studio acoustic treatment

Greetings! I’m a recent member to the list and have been trying to educate myself as much as possible before submitting a request for help. I’ve read Everest’s studio and acoustics books and have a reasonable grasp of the terms and concepts. I’m looking for advice on how to best treat the control room and adjacent studio space of my basement project Studio in Ohio. Music recorded will include drums and electric guitars, but also acoustic music including guitars, mandolin and upright bass, Jazz trios, etc. I’m hoping to achieve a bright / balanced acoustic space without over-doing the absorption. I have a well equipped wood shop in the other half of the basement, so building bass traps, broad band slot resonators, DIY 2x2 QRD type diffusors, DIY tube traps etc. is within my skill level. I have a local supplier for industrial fiberglass products like mineral wool and OCF 705. I have attached a Sketchup drawing of the space and a lengthly Word Doc with a detailed description. Since I am new to forum world, please advise me if this is not the way you would like the info submitted. Thanks in advance for any advice you can offer!

I don't have Sketchup so I have no way to view your drawing. Can you upload a GIF or JPG render? Then everyone can see your drawing. --Ethan

I've created a few views of the 3D model. I can also take photos if there are any areas that need more clarification. Please delete any you find redundant. There are a number of Quad duplex plates at about 32" AFF that are not shown. I will find a way to revise them if needed. Thanks Ethan. Don

buelltwin wrote:

I've created a few views of the 3D model.

Much better. A rectangle room is standard, so all the usual advice applies. All rooms need: * Broadband (not tuned) bass traps straddling as many corners as you can manage, including the wall-ceiling corners. More bass traps on the rear wall behind helps even further. You simply cannot have too much bass trapping. Real bass trapping, that is - thin foam and thin fiberglass don't work to a low enough frequency. * Mid/high frequency absorption at the first reflection points on the side walls and ceiling. * Some additional amount of mid/high absorption and/or diffusion on any large areas of bare parallel surfaces, such as opposing walls or the ceiling if the floor is reflective. Diffusion on the rear wall behind you is also useful in larger rooms. Also, avoid having windows or other objects at the side-wall reflection points. I assume you can't move the water meter, so you may need to hang a panel from the ceiling or use a stand if that ends up being at a reflection point. This short article How to Set Up a Room may help also: http://www.realtraps.com/art_room-setup.htm For the live room you'll want absorption over where you'll record drums. --Ethan

Thanks for the reply. I was hoping for a bit more specific advice – particularly with the studio side of the project. I’ve consolidated my text to some specific questions. Please offer any suggestions you might have on how to approach treating the room without deadening it too much. Studio: Dimensions: 16’-6” x 13’-8” x 7’-8” Wood laminate floor over concrete Soffits around ducts are 10” deep and dimensioned accurately on the drawing. 24”x65”x6” box adjacent to duct is a sealed ¾” plywood box concealing more furnace ducting. ½” drywall on ceiling, walls with window and rear wall 6” bat insulation in all ceiling joists – ½” carpet pad glued to every joist on ceiling beneath drywall. 3 ½” bat insulation in framed side and rear walls Two Poured concrete walls, formed to look like brick. Basement window framed in with ¾” plywood 33” x 8” high x 12” deep w/hinged bottom to allow opening window if necessary – all joints caulked and filled with 6” bat insulation All door and wall joints and electrical outlets thoroughly caulked The gray box in the corner of the east wall is the electrical panel. Ceiling: I thought about a grid ceiling 6” deep on the west half of the studio. This could be a cloud over the drummer and would conceal the ugly plywood box on the ceiling. I’d like to keep a little more ceiling height on the east half to make it less Closter phobic. -Is 2” of fabric covered mineral wool in the ceiling grid adequate? -Is there any real benefit to increasing the thickness to 4” if I am spacing it 6” down from the ceiling? -Is a mixture of 2’ x 4’ absorbers, diffusion panels, panel bass traps a better approach on the ceiling? The roughly 2’x 12’x 10” deep hollow area on the ceiling between the duct soffit and the wood beam is going to serve as a wire chase (the pipe that runs from the AC unit in the furnace to the heat exchanger outside is installed there also) -Would bass trap modules built to fit up in there be beneficial? Walls: I’ve considered everything: wall slot absorbers, polys, Super Chunks DYI QRDs, Bass traps etc. Most of John’s designs show a wall of slots, an angled wall that appears to be a broad band panel bass trap, and a wall of absorption. -Any suggestions of what and where? I have access to a friend with a TEF20 who can take accurate RT60 measurements for me. If you can recommend the logical starting point for treatment, I could complete that, take measurements and build the remaining treatments based on real data. Its kind of a lousy space to work with, I’m hoping you suggestions might save me a lot of trial and error. Thanks in advance of any advice you can offer!! Don

buelltwin wrote:

½” carpet pad glued to every joist on ceiling beneath drywall.

Carpet pad is not useful for acoustic treatment if that's what you intend. I suggest rigid fiberglass at least two inches thick.

I thought about a grid ceiling 6” deep on the west half of the studio. This could be a cloud over the drummer and would conceal the ugly plywood box on the ceiling.

Okay, there you go.

-Is 2” of fabric covered mineral wool in the ceiling grid adequate? -Is there any real benefit to increasing the thickness to 4” if I am spacing it 6” down from the ceiling?

If it's six inches down, two inches thick should be pretty good.

Is a mixture of 2’ x 4’ absorbers, diffusion panels, panel bass traps a better approach on the ceiling?

I wouldn't put diffusion on a low ceiling.

Would bass trap modules built to fit up in there be beneficial?

Bass traps are good wherever you can fit them!

Most of John’s designs show a wall of slots

I have no experience with slat absorbers so you'll do better getting an answer from John, or someone else here who has used that. --Ethan

Thanks for the prompt response Ethan. It gives me confidence to get started. Regarding the broadband slot absorbers that John recommends, should I post my drawing and desription on the the studio construction forum, or is there a way of asking John to just look at what you and I have already discussed? Thanks for your time - it is appreciated. Don

Sorry Trouble with server I'm working for 3/4 hour just to get 1 post right.

Was double post (difficult very slow access to forum server or whatever). See further If wanted please remove these obselate posts.

Ethan Winer wrote:

-Is 2” of fabric covered mineral wool in the ceiling grid adequate? -Is there any real benefit to increasing the thickness to 4” if I am spacing it 6” down from the ceiling?

If it's six inches down, two inches thick should be pretty good.--Ethan

How does this fit the optimum 1:1 ratio (50% material & 50% cavity) as noted for years on your site (the "optimizing the airgap" topic)? As per that FAQ the panels should 6" thick for a 6" cavity. Here you advice a 1:3 ratio (25% material & 75% cavity), thereby even diminishing the asked 2:3 ratio (40% material & 60% cavity). Or was I right all along questioning that 1:1 rule?

Eric_Desart wrote:

Sorry Trouble with server. I'm working for 3/4 hour just to get 1 post right. Was double post (difficult very slow access to forum server or whatever).

Eric, I think god is trying to tell you something. :) --Ethan

It should be nicer and much more useful to get an answer to the content of my question.

Ethan Winer wrote:

Eric, I think god is trying to tell you something.

Maybe God was telling me it had no sense to pose a question you should divert anyhow.

lol :)

Ro wrote:

lol :)

I don't see the LOL whatsoever. And I want an answer, or maybe what you call LOL Ro implies the answer to my question. The diversion in itself is the answer. There is no LOL for me in fighting for 7 years to get rid of the non-substanciated 1:1 material/cavity slogan read by many thousands and taken over and spread by hundreds as an axiom on the net.

May I leave the room? Perhaps my questions are better suited for the Studio Design forum. With respect to all, I would like to repost over there - please no hard feelings. Don

Don Sorry, the thread is yours.

Hi Eric, maybe it would be helpful to both Don and the rest of us, to understand what the best ratios are for porous absorption type absorbers - for example, do we just go with the tested (and documented) results for products based on standard mounting methods? or is there some additional information regarding how we could compute an expected response for a trap using the absorption properties, depth, layers, etc... assuming we're talking low frequency here, do we speculate on 1/4 wavelength as a function of insulation and cavity? what is the effect of varying the cavity vs insulation? should we put insulation on the boundary surface - i.e. is there value in that since the velocity at the boundary is effectively zero.

Glenn, The best an easiest accessible theoretical approach in which you can simulate this is the Chris Whealy spreadsheet which is based on the algorithms to be found in the d' Antonio/Trevor Cox absorbers book. http://www.whealy.com/acoustics/Porous.html There aren't simple exact approaches because a lot of factors are involved. In this spreadsheet plane waves at pure discrete frequencies are calculated and no integration for multiple angle of incidences are integrated (nor random incidence). Still it's the best available easy to access and use for anyone. This file is very educational and also shows the importance of gasflow resistance versus thickness. I still have some question marks about this fime since a real soundfield is more complex. Therefore and on my request Chris entered this additional sentence in that spreadsheet:

This plot is a simplification of reality because it is only calculated for sound incident at exactly the specified angle. In reality, sound will hit from all angles at once (random incidence)

In fact this should be extended with the notion it relates to plane waves & discrete frequencies, because even the harmonics of a fundamental will shift and alter the velocity area/range of a complex (superposed) wave. Yet this calculation file is the best I know of and allows to include cavities. Also note that the calculation in octaves and fractional octaves can wrongly suggest that this is an integration over the noted bandwidth, but it isn't. It remain discrete frequencies, hence the smooting over broader bandwidths doesn't work. This can give some false impressions. Increasing the bandwidth here just means that less discrete frequencies are shown. (this file could use some upgrading. Better should be that is always calculated in discrete frequencies (e.g. 1/24) and then integrated in the respective bandwidths) Very long ago (Mon Aug 11, 2003) I entered a post here, giving the empirical relationship between thickness of material, wavelength and absorption. http://www.johnlsayers.com/phpBB2/viewt ... ength#3993 See this thread from the start. You will also note that tradional picture there of maximum absorption at 1/4 wavelength. (That was there before the current picture in the "Optimizing the Airgap" thing was there). On that picture is CLEARLY noted: Theoretical simulation for a PLANE wave at STRAIGHT incidence for a DISCRETE frequency. And that picture is ca a 1:11 relationship (can't remember exactly, must be between 1:10 and 1:12) within the above described boundary conditions (the scale/thickness of that board is sketched in MS Word, not meant to represent an accurate CAD drawing). Basically that is a basic approach to explain where the velocity and pressure areas are located in a very STYLIZED situation. A real soundfield is much complexer. That notion PLANE in PLANE wave must be the most ignored notion in audio/studio groups. Such a picture is a base to start from to understand acoustics. When you absorp sound, then this velocity area will be flattened and spread out and shift somewhat to the walls (that superposed wave will start traveling towards the wall as an old limp guy with bad legs). When you have harmonics (and which musical instrument tone hasn't?) this velocity area will be shifted somewhat. I'm working on Excel files making this clearer by simulating this in a graph. Now practical: at Galaxy my bass traps have (1st time I mention this on the net) a 1:2 (33% material) ratio to 1:3 (25% material) ratio (and as per my measurements back then beat the hanger approach). And for less critical applications you can go easily to 20% material. At a more recent job last year I used +/- 1:2 to 1:2.2 defined by practical and pragmatic reasons, but if I use a ceiling with enough height I should go further. I specially made Gobos without backing in order to use them as movable bass traps when and where needed allowing me a 1:3 to 1:5 ratio. Just check the ratios used in suspended ceilings and how these so called absorption dips (which is the base for this 1:1 ratio slogan), behave in real live with real soundfields. I've numerous measurements with different thicknesses and cavities. There is lots to say about all this (but I don't give all info free). But important is that this 1:1 ratio is based on some basics from pictures of the first chapter (matter of speech) of any acoustics books. This approach is correct as a theoretical approach within the boundaries it is calculated and meant for. More wool is always better but that's a gradual thing (and related to gasflow resistance), at a certain moment it's just not worth it anymore, unless you come in situations as often rightfully described and referred to by Andre (Avare) that it becomes almost cheaper just to fill the complete cavity with lower density wool, rather than making more expensive support structures to create the cavity. Hence for me the cavity is also a technical matter, how, where and cost efficiency.

Just a couple of graphs to show how pressure and velocity areas adjust. On this graph you find 1 100 Hz wave. The base wave itself is dark blue but hidden by the red total line (since there is only one wave total = wave). This represents 1 single cycle. The wave is 70 dB = RMS 0.063 Pa The y-axis represents pressure. Hence where the wave crosses the 0 Pa line (minimum potential energy) you have the highest velocity (maximum kinetic energy). For absorption in open cell material (the traditional mineral fiber or foam or whatever) you convert this kinetic energy (the 0 Pa line and around) into heat by friction losses. This does not work (unlike our ears or electro equipment) as some fourier analysis, but this kinetic energy is defining. Forget the upper blue line which is in fact a cumulative RMS, while the horizontal green line is the the RMS of the Total superposed wave (equaling the 100 Hz wave since there is no other present) Now I add the second 200 Hz harmonic, for simplicty now as strong (70 dB) as the 100 Hz fundamental. The total RMS becomes 0.089 Pa = 73 dB You see the total now does not cover/hides the dark blue fundamental anymore (unlike in the above graph). Both 100 Hz and 200 Hz are visible as individual waves. The total of both (red) is the resulting superposed wave. Look how these areas of highest kinetic energy has shifted to the left and gets a different shape. You get resistance (absorption) on these moving air particles closer to the wall. It's the velocity within the total superposed wave which acts in function of absorption. Just compare where the total superposed waves of both graphs cross the 0 Pa line (both graphs have identical x and y-axis scales). I have to remake my files simulating reflection and standing waves (damaged by past crash). Hence I can't show everything I should like now. This is not the same as triggering the resonance of a panel absorber, which by itself defines (mass-spring system) at which frequency it gets excited. This are just a few things to wonder about. We measure and hear discrete frequencies (fourier or filters), porous absorption works in function of transforming kinetic energy (velocity) where it is located (around the 0 Pa line but gradually of course). Please use a bit phantasy: these files don't give reflections, hence there are no walls in this. I know the highest pressure should be against the wall. But it doesn't alter the idea of the influence of combining waves.