Acoustic Treatments and General Mayhem

Now that I have skin on my hands again and it doesn’t hurt to type this—
Proper acoustic treatment is vital in studio and performance spaces to avoid echoes that will prove destructive to audio quality. Sometimes it’s done right. Sometimes it’s done wrong. To me it’s utter black magic but I know what works for the most part.

The first thing you want to look out for is stray sound entering your studio space. This may be trickier to do unless you’re constructing a studio from scratch. The methods I’ve seen used to great success are either adding insulation batting inside walls as they’re being built, or using cinder block walls to enclose the space instead of hollow. Either way, avoiding the use of walls shared with noisy things like air conditioning units or bathroom plumbing are very good ideas. Don’t use the other side of the wall pictured here if you can avoid it 😉

The second stage in acoustic treatment is to manage reflections within the space. Any hard flat surface within the studio may cause echoes which can become unpleasant and generally make your recordings sound like you’re standing in the shower.

The typical method of dealing with this is to put up some kind of sound absorbing material on the walls. A number of criteria should be considered when selecting your sound absorbing material:

  • Cost
  • Durability
  • Acoustic performance
  • Fire retardant properties

Materials I’ve seen used:

  • Carpet. Can be obtained anywhere, extremely cheap and actually very durable, since it’s made to be walked on. Works pretty well, but double check that all materials you are using will meet fire code standards for use on a wall. (Carpets may only be rated for proper fire retardant action when installed on a floor, as the flame spread dynamics are a hell of a lot different. Consult the manufacturer and/or their documentation before use.)
    You can glue and/or staple it to the wall or even use the self adhesive carpet tiles that peel and stick.

    CAN BE CLEANED. This is a big advantage. Over time, airborne contaminants will settle on the wall material and should ideally be removable. I’ve found that in an old studio with textile walls, allergens will gather and cause some people to get sniffly if not removed. Your mileage may vary, but I’ve found that the ideal maintenance interval to vacuum the walls is about 2-6 months. That’s all it takes, actually – just use a vacuum cleaner with a hose and an upholstery attachment and suck the dust out. More major junk may be dealt with using carpet shampoo and a wet/dry vac.

  • Cloth and Fiberglass. I’ve seen this one in a couple of older studios and it works very well. Small wooden strips were attached to the wall followed by fiberglass batting being installed between them, with a fairly open weave upholstery cloth used to cover it all up. The cloth is finally secured by tacking a small wooden moulding to the wooden strips below it.

    Performance is very good. Flame resistance will be identical to that of the upholstery fabric used. Durability isn’t as good; wheeled chairs, furniture, irresponsibly sharp spiked leather gauntlets (of course I say this from experience), and other things can tear the fabric. Repair is easy though.

    You can also buy prefabricated panels using these materials, or build your own. How to Build Your Own Acoustic Panels

    DIY acoustic panels – from article on acousticsfreq.com

    Cleaning: Can be surface cleaned. I’ve always just used a vacuum – with a HEPA filter just in case glass fibres are released through the surface fabric as you’re sucking the schmutz off. When I’ve done it, I have never noticed glass fibers visible in the vacuum as I cleaned it out – just lots of fine dust and pollen!!

  • Foam. This is a very common acoustic treatment material and I kind of wish it wasn’t. Performance is good, yes, but durability is totally in the dumper. When it’s new, it’s easy to tear up, especially when…. SOMEONE… decides to get creative and try to hang decorations from it. By the way, don’t cover your acoustic treatments with posters, because the essentially airtight paper of the poster will just form a really nice REFLECTOR, completely defeating the treatment. Some materials have fire retardant ratings, check with the manufacturer.
    A really swank looking example of Auralex SonoFlat foam installation from their website, with corner diffusers and wall and ceiling panels.

    When it gets old, some foams will just crumble and disintegrate horribly, especially if touched.

    Cleaning: …. maaaaaaybe. If you’re lucky.

    Shop-Vac 9018000 soft bristle brush. Horsehair vacuum brushes work fine too. BE GENTLE!!

    I’ve had okay luck with vacuuming the surface of Auralex StudioFoam products using a soft bristle brush. Work slowly and gently going along the ridges. In one studio I started doing this and the foam turned from dingy gray to its original burgundy red— I didn’t even know that was the color it was supposed to be! Yeeeechhhhh.

    I wouldn’t even try this at all on the type of sound insulation where it has alternating deep, thin vertical and horizontal ridges.

Now here’s where I talk about strange things.

A while back I was in the studio of The Jeff Adams Show and as soon as I walked in, I saw his wall panels and couldn’t believe my eyes. They’re wood! They did not contribute to any unpleasant echoes, yet had a little bit of a warm reverberation. You can see one in this picture:
I didn’t get a closeup picture of the panels when I was there, but they did not have a smooth planar surface. The different planks are overlapped forming a convoluted surface, which would contribute to diffusion instead of a clean surface reflection. Notice the mic he’s holding here – that’s a Heil PR 40 cardioid dynamic that is just INSANELY sensitive. You’d almost think it’s a condenser (I mean— it kind of even looks like one). The Heil PR 40 is NOT forgiving to bad room acoustics. It proves that these funky wooden wall panels work perfectly as an acoustic treatment!
In contrast, the Electro-Voice RE20 that’s used at close proximity by a lot of radio jocks couldn’t care less what your room acoustics are like as long as you aren’t in an all glass aquarium or something.

The same soft vacuum brush cleaning I mentioned above will work if they ever start to gather dust. Since he’s doing video on the same set, avoiding lighting glare is definitely a plus – they’re not shiny in any way.

Now, you may have a sick curiosity and wonder what the first sentence of this post is all about. Well…. I had to displace some very old carpet on a wall at work to hide a cable behind it, and I don’t know if it was the 20+ years of old crud built up in the carpet, the glue that held it to the wall, or a likely combination of both, but something caused a very bad reaction on the skin on my hands that caused it to blister, crack, and weep as if it had been severely burned.

If you’re really curious, I have a picture of the results here. Content warning: extremely gross. There’s good reason I put /nope/ in the URL. It’s mostly healed now and all that remains is a little redness. That week sucked, man.

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