$5 per sheet of OC-703 ?!?!? Only 1in. Backing needed?

[israelhands]

I've got a 24ftx19ft garage I just converted into a practice room/studio. I've done all my "behind the wall" treatments. And my 2x drywall. With concrete floors. You can imagine the echo. Now I'm ready to "tune" my room (so to speak. I was originally leaning towards 24x48x2 OC-703 from an Internet company for $70 for 6 (shipping NOT included). But I recently befriended a local studio owner who had extra (100+) sheets of 24x48x1 OC-703 left from his build. He graciously offered it to me at $5 per sheet. Will 1 inch of thickness as opposed to 2 inches provide the absorbion I would need to "deaden" my room? Also he insists on me backing the panel with a quarter inch "peg board". Is that needed? Or could I get away with just the standard outside wood frame with burlap covering?

[Soundman2020]

Here's the spec sheet from Owens Corning for their 700 series products:

703-specs.jpg

Take a look a the section for "703 Plain" with "A" mounting. Notice the absorption coefficients for 125 Hz, 250 Hz and 500 Hz, comparing between 1" and 4" (which is what you really need).

It's clear that the answer to the question "will 1 inch of 703 do the job?", is a massive, whopping "NO WAY!"

4" thickness is more than eight times more absorbent at 125H, more than 4 times more absorbent at 150 Hz, and twice as absorbent at 500 Hz. Only above 1kH do things start getting similar, but high frequencies are not much of a problem anyway, so that part isn't important. What matters most is the low frequency numbers.

So plain and simple, 1" of 703 WILL NOT do the same job as 4" of 703, and that is according to the company who makes it. They pretty much know what their products are capable of, better than someone who just bought some if it...

The answer to other question, about adding pegboard in front of the 703, is also "no", although in this case it is not such a resounding "no". The issue is that, in reality, pegboard is what is known as "perforated panel", in acoustic terms. It is used to create tuned absorbers, that absorb a specific range of frequencies, and reflect all others back into the room. Basically, peg board ("perf panel") is an array of small Helmholtz resonators: each hole is a resonator, and is tuned to a specific frequency. A board that has a bunch of holes roughly the same size in a regular array, is tuned to a narrow range of frequencies that it absorbs very well. The size of the holes and the distance between them and the % coverage of holes vs. wood and the depth of the cavity behind the panel and the absorption in the cavity are all factors that affect the tuning. Yes, perf panel is a useful tool for the acoustician when designing a studio, since it can be used to target certain problematic frequency ranges by tuning different piece of perf panel, suitably, and locating them correctly in the room. But covering the entire room with one single type of perf panel, all tuned to the same frequency, is a recipe for disaster! It will massively absorb one particular frequency range while not touching any others. So rather than treating the room smoothly, it will destroy what little acoustic balance it happened to have!

Treating a room is not just a matter of throwing up some insulation here and there, and hoping it works. Acoustic treatment must be designed for each individual room, based on the existing acoustic response and the desired acoustic response. In other words, first you run an acoustic analysis of the room as it is right now, then based on that you design specific treatment devices that go in specific places in the room, to produce whatever final outcome is desired. That's the only correct, logical way to treat a room, when you think about it.

In your case, it is a rehearsal room, which is treated more or less the same way as a tracking room or live room, and does not need to be done to the same stringent standards as a control room, but the treatment plan still needs to be designed. And it needs to be designed for that room. You cannot use what was done in any other room, since all rooms are different. The only time you could use what was done in another room, is if that "other" room is identical to your in every aspect: same shape, size, volume, layout, construction techniques, positions of doors, windows, and everything else. So unless your room is identical to another that has been treated successfully, you CANNOT use the same plan as that "other" room.

Having said that, there are certain "generic" layouts for treatment that will roughly treat certain commonly shaped/size rooms, and get them sounding reasonable, but it is still nowhere near as simple as just throwing up some 1" 703 all over the walls and putting some pegboard of unknown acoustic properties on top of it.

OK, to answer your actual question: You can still use 1" 703 for your treatment. You just need to "double up" or "quadruple up", to get the thickness you need for each treatment panel. So in places where you need 4" thick panels, you would put 4 layers on top of each other, and in places where you need 2" thick panels you'd put two layers on top of each other.

So what that guy is offering you seems to be a reasonable price, and is usable in your place. Just not in the way he is suggesting.


- Stuart -

[israelhands]

Thanks for the reply. But just to clarify the pegboard would go on the backside of the panel. In between the frame and wall. NOT ON THE FRONT. but I do still he how it would reflect only one frequency that those holes are "tuned" for back into the room. Maybe that's what his room required when the panels were designed. Idk for sure.

But I think we can all agree that the price he has offered me is a great deal and I probably will take him up on that. But let me run my other option by you. I found a local contractor that can get me Roxul Rockwool R-60 @$3.08 per sheet (1inch) and $6.16 per sheet (2inch). Just skimming through some past post I see a lot of use of Roxul inside the walls but not as much use in panel (as compared to oc-703). Should I consider making my sound panels and bass traps out of the Rockwool or just stick with the oc-703?

[israelhands]

Also the "other" studio in question is a George Augspurger (personally) designed studio. My "friend" was charged $50 per sq foot just to have him design his studio (and panels) I would hope George Augspurger wouldn't "doop" him into getting 1in 703 as opposed to the 4in.

I don't wanna get into a pissing match of who says which is better. All I know is I've been in the tracking room (which is covered in 1in 703 with a peg board backing), I've heard the room and I've heard the tracks coming out of this studio (rough and mastered) and it sounds pretty Amazing. But like you pointed out EVERY ROOM IS DIFFERENT AND EVERY ROOM HAS TO BE TREATED ACCORDINGLY. I get that. I just need to know if 703 is the way to go? Is R-60 the way to go? How many and how thick? I saw on a different thread something about a 2D room calculator program. How accurate is that?

[Soundman2020]

But just to clarify the pegboard would go on the backside of the panel. In between the frame and wall.

Why? What purpose would it serve there? Are you sure you are describing it correctly? Pegboard tight up against a solid surface is not going to do anything useful. In order to work, a Helmholtz resonator has to have a sealed cavity behind it, and if it is flat against a hard surface, there is no cavity. So maybe I'm just not understanding what you are describing. Can you get photos of that? That would make it clearer. I suspect that "peg board" is actually the front panel of something else that you can't see easily... It also might look like peg board, but probably isn't your typical off-the-shelf Home Dept style pegboard: It was probably carefully designed with the correct hole sizes, spacing, and % perforation to absorb the right range of frequencies.

I found a local contractor that can get me Roxul Rockwool R-60 @$3.08 per sheet (1inch) and $6.16 per sheet (2inch). Just skimming through some past post I see a lot of use of Roxul inside the walls but not as much use in panel (as compared to oc-703). Should I consider making my sound panels and bass traps out of the Rockwool or just stick with the oc-703?

Roxul is usually good stuff, but since I don't live in the USA I'm not familiar with the relationship between the "R" numbers and the actual density of the product. If you want to go with any type of mineral wool, then you should be looking for a density of roughly 50 kg/m3 or even a bit less, for bass traps. Perhaps they publish the density some place, or you might be able to call them and ask them. (In reality, it isn't the density per se that matters, but rather a property know as "gas flow resistivity". Unfortunately, most manufacturers don't even bother measuring that, as it means nothing for thermal isolation [only acoustics], but fortunately density is a reasonably good indicator of the gas flow resistivity for each different type of insulation. Not fantastic, and not linear, but close enough to be useful.) For bass traps, you could go down to a bit lower density to improve the low frequency performance, so maybe 30 to 40 kg/m3 would also be fine. But that's just for bass traps. For wall damping (in the MSM cavity) you'd still need it around 50.

My "friend" was charged $50 per sq foot just to have him design his studio (and panels)

A bit on the high side, but well worth it for a good designer.

I would hope George Augspurger wouldn't "doop" him into getting 1in 703 as opposed to the 4in.

Like I said before: every room is different, and every room needs it's own design. If that's what the designer figured was needed FOR YOUR FRIEND'S ROOM, then that's what it needed. Especially if he designed the entire room from scratch: that might have been all that was needed as the final touch. But YOUR room is different, and needs ITS OWN acoustic design, tailored for the room itself. In acoustics, one size does not fit all, unfortunately: it would be great if it did, but sound doesn't always behave the way you'd like it to, and even small changes to room geometry can have large consequences. And of course, Murphy always get's ya when ya ain't lookin!

I suspect that the 1" 703 you can see on the walls is actually just the final high-frequency absorption, the "icing on the cake", and the real acoustic magic is happening behind the "pegboard", in places you can't see.

I get that. I just need to know if 703 is the way to go? Is R-60 the way to go?

Either will do, if use correctly. That's kind of like saying "Is a skateboard the way to go? Or should I use a bicycle?". Both will do the job, if used correctly in skilled hands, on the right type of road.... I know that's not very helpful, but the point I'm trying to make is that you can't just slap insulation on the walls to fix a problem, unless you first fully understand what the problem is. Perhaps neither of these is the way to go: maybe you really need an F-16, or row boat, or a submarine (to stretch the analogy way beyond being useful! ). You haven-t really provided enough information for anyone here to be able to judge what you need. It would be helpful to know the interior dimensions of the room (inner-leaf surface to inner-leaf surface in all 3 dimensions), as well as the location of doors and windows, and the details of the construction method used so far. Photos would be useful too. But most useful of all would be some proper acoustic data from the room itself, so we can analyze that, see what the real issues are, and suggest how you can fix them. It's easy to get that data: just download "REW" (its free), and run that on the room, then post the data file here. Based on that, along with all the other info, we'll have enough to go on to be able to help.

I saw on a different thread something about a 2D room calculator program. How accurate is that?

There are several calculators mentioned here on the forum: Chris Whealy's might be the one you mean: it deals with porous absorbers, perforated panels, slotted panels, micro-perforated panels, and suchlike. Is that the one? Or are you talking about Barefoot's 2D wall bounce calculator? That's probably not what you need, unless you are designing a control room. Another really useful tool is Bob Golds' room ratio calculator, which does what it says and much more too, but that's a 3D tool, and you were talking about a 2D tool, so that might not be it.

There are lots of tools, calculators, and in general mountains of solid acoustic data here on the forum!

- Stuart -

[israelhands]

Went over the design of the panels again with my guy. He said the frames are made of 2x6's cut long ways with a table saw to make a 2x1.25 piece of wood. then make a 2x4 rectangle frame. Then the 1in oc-703 panel AND the quarter inch pegboard set INSIDE the frame. covered in "burlap" and hung directly on the wall with no space between the pegboard and wall. I quizzed him as for the need for the pegboard. His was reply was just to trust him and George Ausberger. I politely "argued" with him for a little bit about it before he kinda got upset saying (you'll be wasting your time and money, and MY materials if you dont use the pegboard). In fear of losing the sale I agreed to use his pegboard method
http://johnlsayers.com/phpBB2/posting.p ... =3&t=18406#
Im supposed to go to his storage unit later to purchase 36 panels at $5 each and 8 sheets of the "magical" pegboard at $12 each (which i will try to back out of upon arrival unless anyone can concur that it will be benificial to me.

Anyway here are some rough stats on my build as requested.

West Wall - 230.5 in
North Wall - 266.5 in
South Wall - 265 in
East Wall - 122.25 then a 40 in door then 67.5 in

Ceiling to floor - 7.5 ft.

No windows.

24x15in Silencer box on the wall by the door.

walls and ceiling were filled with 1/2 pound spray foam insulation

2 layers of 1/2in sheetrock on walls with a green glue substitute in between each layer.

even though i didnt do a "room within a room" design I am still going to do 2 doors. currently have just a regular Steel exterior door opening out. Plan on sandwiching it with some MDF for mass. Made my own frame on the inside out of 2x4 and 2x6's. planning on a solid wood core door for the inside

also i know this probably isnt the thread for this but i am using a portable air conditioning unit for cooling the room. runing through the silencer box i built. works great. very list sound can be heard outside. kinda proud of myself. im trying to upload the pics now. did have to open it back up and run a dryer ventilation hose through the "maze" as i burned up the motor in two other units before realizing the box was giving too much resistance. had this one running almost 24 hours a day with no problems. stays at a cool 70-75 all day.

[israelhands]

room pics

[Soundman2020]

no space between the pegboard and wall. His was reply was just to trust him

That figures.... In my experience a non-answer like that either means he doesn't have a clue if it even works or not, or it means that there is a major trade secret involved. And since there's no science at all to back up that arrangement, I'm betting there are no trade secrets involved here...

Unless he has some actual technical data that backs up his rather curious claim, I'd forget it. Perf panel does not work like that. Helemholtz resonators do not work like that. Diffusers do not work like that. Absorbers do not work like that. I think he needs to read this book:

http://www.amazon.com/Master-Handbook-A ... +acoustics

Here's a basic summary of the way acoustic treatment devices work:

http://www.soundonsound.com/sos/aug98/a ... ustic.html
Note the section on Helmholtz resonators...

Here's some commercial products that work: note which way they face, with respect to the wall...

http://www.stylepark.com/en/architectur ... ets/325480

Here's some more in-depth stuff on how real perf-panel works:

http://www.iperf.org/IPRF_ACUSES.pdf

(which i will try to back out of upon arrival unless anyone can concur that it will be benificial to me.

It MIGHT be beneficial to you, but NOT in the way he describes. Only if used correctly: see the above PDF for info on that. The hole size and spacing, and the percent open area, would have to be in a usable range for the available depth. So if he won't sell you the 703 without the panels, then you have two options: 1) Check the hole size, spacing and percent open area to see if it is any use, 2) Go to Home Depot, spend the same amount of total money, and get ONLY what you need, instead of patly what you need, and partly useless.

I'm wondering if he's just trying to dump that panel on you, since he has no other hope of off-loading it any place else... ?

walls and ceiling were filled with 1/2 pound spray foam insulation

That wasn't a lot of use, acoustically: most spray foams are closed-cell, which means air cannot penetrate, and therefore it is useless acoustically. Only open-cell insulation has usable acoustic properties. Closed cell works fine for thermal, but not for acoustic. Most spray foams also set rigid, which creates flanking paths through the wall. So that wall isn't isolating very well at all.

2 layers of 1/2in sheetrock on walls with a green glue substitute in between each layer.

1/2" is a bit thin for good isolation. It is too flexible, low mass, too thin, etc. The resonant characteristics are not ideal for isolation. The normal recommendation is for 5/8" drywall.

with a green glue substitute in between each layer

"Green Glue Substitute" What's that? There are no substitutes that I'm aware of. Or rather, none that have been tested and proven in independent acoustic labs, with published results. There's a few manufacturers that make interesting "claims" about their products, but for some reason they don't seem to want to show the results of independent testing.... Makes you wonder, doesn't it?

Do you know what the "substitute" was, in this case?

runing through the silencer box

There's a few issues with that box:

First, the lining should only ever be proper duct liner. Ordinary foam, fiberglass and mineral wool will work, acoustically, but they don't last over time, as the airflow ablates the surface, shedding fibers or particles into the room, into your gear, into your instruments, and into your lungs.... Duct liner has a coating on the surface that keeps the insulation together.

Next, the airflow path must be kept to a constant cross section that is at least twice the area of the inlet. Since the foam bulges in several places here, that greatly accelerates the flow, causing turbulence and air noise. It also increases the static pressure greatly, which makes the fan work harder, outside of its optimal range, which means it will fail sooner, and is also not operating efficiently: operating costs go up, duty cycles are longer, etc.

And finally, the inner surface should be as smooth as possible, for the same reason as above: any discontinuities create turbulence, increasing noise, static pressure, etc.

So although that worked for you to a certain extent, now you can do it much better, improving on performance, costs, quality, etc.

as i burned up the motor in two other units before realizing the box was giving too much resistance.

Yup! Not surprising, really. There are a number of calculations that you need to do when designing a silencer box. Actually, for designing the entire HVAC system. There's a large number of variables that need to be considered, and not taking them into account can lead to issues like that: burning out fan motors is just one of many expensive things that can go wrong....

But like I said, that can all be fixed now! That's what this forum is all about: helping folks get their studios done right, and fixing all the problems that they already have.

- Stuart -

[israelhands]

the conclusion of this Madness is resolved here
http://johnlsayers.com/phpBB2/viewtopic ... 03#p130003