Killing reflections from a studio wall

[Iamthesky]

We're setting up the new rehearsal studio in a fairly large finished basement, and a simple test with the drum kit (the first thing we set up) shows we need to ameliorate reflections drastically from the wall behind the band. It's laid out like a full stage, everything's miced, and we have four monitor wedges -- which are therefore pointed at the back wall behind us. To avoid this turning into a booming/ringing nightmare with everything bouncing off everything else, my (not-well-informed) intuition says we need to deaden that back wall completely. The floor is industrial carpet (glued down) over concrete; the ceiling is wood with a couple of wood-enclosed HVAC cross-ducts.

 

Would gluing something like the Auralex Studiofoam panels over the wall work, or is there something better? Or am I totally on the wrong track? Budget for the back wall and drum corner ideally would come in under $1200 (i.e. we can afford materials, but can't afford specialist installation). We are not concerned at all with being able to convert it back to a "regular" room.

 

(Yes, I know we'll need treatment elsewhere in the studio too. That'll be the next stage, separate budget.)

 

This is a six-piece rock band (drums, multi-synth rig, two guitars, bass, lead vocals). We are putting a premium on keeping stage volume down (with amp stands pointed at guitarists' heads .png.197c47f720636f02390cc2b0a33804da.png' alt='smiley-veryhappy'> ) as a selling point of what might be otherwise be pre-judged as "too damn loud for my venue", which is why I think this full stage setup is practical. If anyone wants to turn up "for tone", they'll either need a load box or to find another band.

[Lee Knight]

On the cheap...

 

Use either attic insulation if you have exposed studs, then cover with chicken wire and burlap. Or Owens Corning 703 board, etc. Behind the band. Then... opposite wall use polycylindrical diffusors you make yourself.

 

http://studiovictor.ca/wp-content/up...sers-copie.pdf

 

 

But you don't have to be all precise like above. Get the thin 4' x 8' plywood, like "door skins". Mount them under 1" x 2" strips running vertically, the panels pinched so they bulge out. Now what you have...

 

...are your very close reflections killed, and your longest refections elongated. That sounds great. You've just increased the size of the room psychoacoustically by extending the longest reflections, scattering them into longer, less direct return paths back to your ears. And created a decent bass trap wall as well with the polys.

[Phil O'Keefe]

What are the dimensions (l/w/h) of the room?

 

Like the floor, are all of the walls also concrete?

 

Any opposition to doing some light construction along the lines of what Lee was describing?

[WRGKMC]

Those wedges are pretty expensive. I'd use them in a checkerboard method.

 

Two items very inexpensive and easy to apply.

Pressed ceiling tiles are a very good choice because you don't loose all the reflectivity, especially around the drums where you want some reflectivity to liven them up. The tiles come in 4X2 sheets and are fairly inexpensive.

If this is a concrete room and you have allot of boom you might want to use what I did. I went down and bought that foam rig under matting. It real cheap like a buck or two per square yard. It will definitely suck up the sound like a sponge. I did all 4 walls and ceiling and turned my studio into a dam coffin. My main concern was soundproofing first and used it as a last layer of many.

 

I had to add back reflective paneling to get rid of some of the deadness afterwards to make the room better for recording but its my first inexpensive recommendation if you want to kill reflection. The ceiling tiles leave a more living room sound with soft reflections so if that's what you want its a good second choice without having to pay outrageous prices for acoustic tiles.

 

If you want to go that route see if you can find an acoustic materials outlet builders used. You can find what you want there for 1/4 the price but you may need a contractor to buy it for you because most sell wholesale to builders.

[Iamthesky]

Very roughly (by pacing it out) 18 x 30, with the band along the short wall. There's a 10 x 6 extra section to stage left. The outside double door is at the opposite end from the band, on what would be stage left along the far short wall from the "stage".

 

Walls are finished sheetrock.

 

Outside noise insulation is not an issue. Aside from the outside door wall, the rest is mostly below ground level, with brick walls, and there aren't any houses close enough to care anyway. With no acoustic treatment at all and the drummer beating as hard as he could, it's pretty much inaudible well before the property line. My main concern is how it sounds in the studio.

 

The ceiling is wood strips in kind of an overlapping layout, and that's a surface that I'm expecting to provide some depth and life to the room.

 

I'd rather not do too much in the way of construction, but what Lee suggests is certainly feasible. It doesn't have to be totally on the cheap -- I figure money spend now setting things up is money saved later, and it lets us get the band rolling without disrupting the layout too much. We're already 3 months behind schedule with the band -- just about to hold auditions for the remaining slots, and I don't want to book shows until I have the lineup set -- but I'd rather start late and ready than go in half-finished and have to break the momentum halfway.

[Phil O'Keefe]

The hardest part is isolation, so you're really lucky there.

 

Are the double doors on the 18 foot wall opposite the band roll-up style garage doors, or something else? Approximately how wide are the doors?

 

Is there any padding beneath the industrial carpeting?

 

You mentioned that the room has sheetrock on the walls, but also that it's brick - do you know if the sheetrock is laid directly over the brick, or is there wood furring strips between the brick and the sheetrock as spacers, and if so, do you know if there was any insulation placed in the space between the sheetrock and brick? Also, was the sheetrock attached with z channel? Depending on the presence of insulation and the way it is mounted, the sheetrock itself can contribute some absorption at the low end of the frequency spectrum.

 

Do you have any pictures of the room? I'd love to have a look at the ceilings...

 

[Lee Knight]

I think a key point here is to not necessarily be wooed by commercially fabricated panels or foam, etc. There's nothing wrong with the products per se. But the fact is, they way underperform for way too much money.

 

The perfect absorber is an open, glassless window. A simple hole in the wall. That's the holy grail of absorption. Everything that hits the imaginary plane of this window will not return into the room. All frequencies. That is an Absorption Coefficient of 1.0 Sabine. But a room full of windows is no room. Look at carpet:

 

125 - 250 - 500 - 1k - 2k - 4k [TABLE=align: center]

[TR]

[TD] Floor materials

[/TD]

[TD] 11525 Hz

[/TD]

[TD] 250 Hz

[/TD]

[TD] 500 Hz

[/TD]

[TD] 1 kHz

[/TD]

[TD] 2 kHz

[/TD]

[TD] 4 kHz

[/TD]

[/TR]

[TR]

[TD=bgcolor: #CCCCCC] carpet

[/TD]

[TD=bgcolor: #CCCCCC] 0.01

[/TD]

[TD=bgcolor: #CCCCCC] 0.02

[/TD]

[TD=bgcolor: #CCCCCC] 0.06

[/TD]

[TD=bgcolor: #CCCCCC] 0.15

[/TD]

[TD=bgcolor: #CCCCCC] 0.25

[/TD]

[TD=bgcolor: #CCCCCC] 0.45

[/TD]

[/TR]

[/TABLE]

Note how different the amount of absorption is per frequency. Almost half a Sabine at 4k, meaning more than half of our 4k that hits our carpet will not be absorbed and will return into the room. Now look at 125Hz. Virtually no absorption. What does that sound like? Muffled. Dead and limp. All lows and lo mids and bleh and no highs.

 

Now look at Owens Corning 703 fiberglass board. [TABLE=align: center]

[TR]

[TD=bgcolor: #CCCCCC] Fiberglass board (100mm(4") thick)

[/TD]

[TD=bgcolor: #CCCCCC] 0.99

[/TD]

[TD=bgcolor: #CCCCCC] 0.99

[/TD]

[TD=bgcolor: #CCCCCC] 0.99

[/TD]

[TD=bgcolor: #CCCCCC] 0.99

[/TD]

[TD=bgcolor: #CCCCCC] 0.99

[/TD]

[TD=bgcolor: #CCCCCC] 0.97

[/TD]

[/TR]

[/TABLE]

Almost total absorption and virtually flat across the spectrum What does that sound like? Deader And EVEN.

 

Commercial foam won't do that. It's easy to handle, won't get you itchy, looks fairly pretty... but pretty much sucks for even, efficient absorption. Go DIY. It's cheaper and way, way better at achieving what you want to achieve. Check here...

 

http://www.readyacoustics.com/produc...f-acoustic-bag

 

note that I suggested regular pink attic insulation if you had open walls and studs. that's because that stuff does perfectly well for your issue. It's cheap. And itches like an SOB. So take care, chicken wire it in and cover with burlap. That is effective beyond your wildest desires. No open walls? go 703 board and some bags. Or make your own frames. Just don't waste money on foams for an ineffective solution.

[Lee Knight]

Sorry, the frequencies didn't' come through in the graphics above. From left to right as follows:

 

125Hz - 250Hz - 500Hz - 1kHz - 2kHz - 4kHz

 

 

[WRGKMC]

^^^ That's basically the stuff I used on my walls except it had a plastic barrier on one side. I put the foam under matting over it because I didn't want the glass fibers in my lungs.

[Lee Knight]

^^^ That's basically the stuff I used on my walls except it had a plastic barrier on one side. I put the foam under matting over it because I didn't want the glass fibers in my lungs.

 

I'm not going to question what you did there. Covering the fiberglass board with something else. However... I'd like to make a point to anyone reading and learning. Fiberglass is a very good absorber. If you're going to cover it, and you'd better, you need to cover it with something that is invisible acoustically. If you don't, you're putting up fiberglass but it isn't doing anything for you. If you cover it with something that has any reflective qualities, you're canceling out the absorption. How can it do it's thing if you' defecting sound away from it.

 

So once again, I'm not suggesting you did anything to negate the absorption qualities of the fiberglass, but for anyone else who might be unsure as to how they proceed? Use an open weave fabric. Burlap or an "acoustic fabric". You want to let sound in without any reflective proprieties. And the fiberglass won't let it reflect back out. Believe it not, lots of fabrics even have high end reflective properties. Open weave fabric like burlap or "acoustic fabric". Look at studio pictures to see what I mean. those panels are 703 board covered in acoustically transparent fabric. Simple and effective.

 

[Iamthesky]

Excellent information, thanks!

 

Looks like it's hard to resist just picking up a bunch of DIY panel kits from that ReadyAcoustics link you provided. Is there any reason not to do that?

[WRGKMC]

 

I'm not going to question what you did there. Covering the fiberglass board with something else. However... I'd like to make a point to anyone reading and learning. Fiberglass is a very good absorber. If you're going to cover it, and you'd better, you need to cover it with something that is invisible acoustically.

 

It was a sound proofing decision not a sound treatment concern.

It did work out well with all the other multiple layers of materials I used including Brick face, blown in insulation, multi layered walls separated by air barriers between them. The results worked out much better then I could have hoped for because anyone whose tried it knows how difficult it is to block bass frequencies from passing through a wall. I have a neighbor that's only about 25' from my house and they tell me they cant hear a full band going in there. You have to get right up to the outside wall to know something's going on inside.

[Lee Knight]

There is no reason not to go buy a bunch of those from them. There isn't anything better than Owens Corning compressed fiberglass board. Get unfaced so you can stack 2, 2" pieces to get to 4". You want 4" for flat absorption down to 125Hz. Faced is fine if you're not stacking but once you stack... you're wasting the next piece with a faced side as that's reflective. Unfaced is the way.

 

Look for insulation supply places in your town. For contractors. Then call and see if they have it in stock. Sure, you can order online but that's a lot of space. Much easier to locate locally, bring a truck and fill it boxes of the stuff.

[Iamthesky]

Excellent. Thanks!

[eflatminor]

A REALLY cheap way...as in free...for dealing with room reflections is to glue egg cartons on the wall. Go to a place that serves lots of eggs, like a breakfast joint, and they will but their eggs by the case. Each layer of eggs is separated by square soft cardboard pieces, probably 12" x 12". Just glue or blu tack them on the walls for excellent dispersion of sound.

[Phil O'Keefe]

I'm afraid I must respectfully disagree.

 

Egg cartons are available very inexpensively in roughly 1x1' squares from dairy supply companies, but even the non-foam / cardboard variety is less than optimal as an absorber or as a diffuser. They're definitely not broad-band absorption, which is generally what you want / need in a home recording studio or rehearsal studio, as Lee pointed out.

 

As Lee also noted, high frequencies are easily absorbed compared to low frequency sounds... and we've already got a room with a notable amount of high frequency absorption (from the carpeting) so unless you want to build a bunch of other traps and absorbers to deal with all the other frequency ranges that egg cartons simply won't affect, it's probably best to stick with broadband absorbers and purpose-built DIY bass traps based around semi-rigid compressed fiberglass or mineral wool in the 3-6 lb/ft³ density range. Don't get hung up on it having to be Owens-Corning Type 703 / 705 - that's great stuff, but other companies such as Knauf and Roxul make pretty much identical materials. The key is the density. Fiberglass or mineral wool - they're both roughly equal in performance, so get whatever's available locally (check with insulation supply companies) and is cheaper. If you can't find anything local, Auralex (yes, the "foam company" - although to be fair, they make a lot more than just foam) sells mineral wool, and you can buy it online.

 

2" of 3lb/ft³ semi-rigid compressed fiberglass or mineral wool placed flat against the wall (and covered with some acoustically transparent fabric such as burlap) is pretty effective at absorbing mids and highs... for better absorption at lower frequencies, space it away from the existing wall 2-3" or so... and for even better performance at low frequencies, use thicker panels of 4 - 6" of material spaced 4-6" away from the walls.

 

Corner traps are also an excellent idea. They're basically the same materials, angled across the room's corners. Wall meets wall corners are a popular place to put them, but they are also effective when placed at the wall / ceiling junctures too. I'd start in the wall / wall corners, and add them to the wall / ceiling corners if you find you still need to tame the low frequencies a bit more. In a fairly large room like that, you may need to take it in stages, depending on the budget, but you can DIY and save a lot of money, and it's amazing how much you can get done with some relatively inexpensive fiberglass, fabric and lumber.

[Lee Knight]

what he ^^^ said