The first rule of acoustic treatment

If your studio doesn't have acoustic treatment, then you're not making great recordings. But what is the first thing you need to know?

By David Mellor

I recently came across an ad from an acoustic treatment company. Prominently featured was a list of "What you need to know..."

I can see that it is a problem for a company to sell products to a market that doesn't correctly understand the need for them. All the points on their list were important, although not all of them well-explained.

But their Number 2 point, which I would have put at Number 1, or the 'First Rule of Acoustic Treatment' was this...

"Acoustic treatment is NOT sound proofing."

The reason I put this point at the top of my own list is that I have had to explain this very many times to very many people. And when I have explained it in full and precise detail, they go away not believing me and still cling to the idea that somehow acoustic treatment and soundproofing are the same.

(By the way, some people like to refer to soundproofing as sound isolation or insulation. That's fine, I'm happy with any of these terms. I'm not so happy with 'acoustic insulation' as it sounds far too much like acoustic treatment for comfort.)

To try and make things crystal clear I'll put two important facts in bold...

Soundproofing reduces the amount of sound coming into or going out of your studio.

Acoustic treatment makes your studio sound better.

But why are they separate things? Couldn't you kill two birds with the proverbial one stone? (As I once won two coconuts with a single throw at my local fair!)

The problem is that it is impossible to provide any reasonable degree of insulation against sound using absorbing materials. Even the best sound absorbing materials, thickly applied, can only absorb a relatively small amount of sound energy at mid and low frequencies.

It is much more practical to block sound by reflecting it. Build a heavy wall from plasterboard (gypsum board), bricks or concrete and a decent degree of soundproofing will quite easily be achieved. (But note the word 'heavy' in that sentence. For truly effective soundproofing, you need a lot of mass.)

A soundproof studio will therefore require heavy walls, floor and ceiling, windows made from thick, multiple panes of glass, and a thick, heavy door with good seals around the edges.

At this point however, since most of the sound energy produced in the room will be reflected back and forth many times, the room will be VERY echoey.

So you need acoustic treatment to reduce the amount of reverberation, and in particular control it carefully across the full range of frequencies. For this you will use absorbent materials and structures (and some irregular hard surfaces for diffusion).

Absorbent materials and structures can soak up sound, but only over multiple passes, which is what happens in a soundproofed and acoustically treated room.

You can buy materials for soundproofing and acoustic treatment at a builders' merchant. But for acoustic treatment it's quicker and easier to go to a specialist such as www.universal-acoustics.com whose ad inspired this article.

Publication date: Wednesday November 23, 2011
Author: David Mellor