Acoustic Foam: yea or nay?

For sure, they’re attractive—there, we said it! They usually come in huge packs of 4 panels, or 8, or more, and have delightful—or classy—color schemes; don’t even mention the cool protruding shapes they come in. Looks are an important part of a studio environment, we agree, but how do acoustic foam panels actually perform when it comes to sound?

Poof, there goes the bubble..

..they don’t, well, not very well, at least. Not very well at all, we should say. The acoustic foam that is commonly found in the ‘pro audio & recording’ section in music stores (both mom n’ pop stores, but also that big one) is usually the first thing people think of when ‘soundproofing’ a room. Whether this room is going to be used as a critical listening environment (think mixing suite or control room) or a recording room, or perhaps simply a rehearsal space—most DIY’ers will use these acoustic foam panels as their starting point (and endpoint, sadly).

This immediately shows one of the upsides of these acoustic panels, made popular by brands such as Auralex and Ultimate Acoustics. They’re readily available, light-weight, can look very flashy, and are generally easy to install. This said, when it comes to the dollar-to-performance ratio, they don’t perform so well. For what you’re getting, they’re generally on the pricey side (twelve 2″ thick 2’x2′ panels will set you back almost $300).

2" thick acoustic foam panels, © Auralex.
2″ thick acoustic foam panels, © Auralex.

Performance, as measured in absorption coefficients

The big downside of acoustic foam panels is the actual performance part. And let’s be honest, this is the only part that everyone should be concerned with. When we mention performance, we’re referring to its ability to effectively absorb sound, and additionally, the more linear they do so, the better (although this is not the main concern). We use absorption panels to gain control of the reverb of a room, not to block inside sound from going out or outside sound from coming in. Read more about the difference between absorbing and stopping sound.

Now, every item that can be advertised as some type of acoustic absorber usually comes with a specification or performance sheet (spec sheet). This spec sheet outlines the product’s absorptive performance across the speech range (125Hz-4kHz). An absorption coefficient is a number between 0 and 1, where 0 is a perfect reflector and 1 is a perfect absorber.

To give an example of the absorption coefficients of the panels mentioned above (Auralex 2″ thick ‘StudioFoam’ panels):

125Hz 250Hz 500Hz 1000Hz 2000Hz 4000Hz
Auralex 2″ StudioFoam
0.11 0.30 0.91 1.05 0.99 1.00

To give some contrast to this, let’s look at the absorption coefficients of a mineral wool Roxul panel, 2″ thick:

125Hz 250Hz 500Hz 1000Hz 2000Hz 4000Hz
Roxul RXL 80 (2″) 0.43 0.78 0.91 0.90 0.97 1.00

Note that when an absorption coefficient is shown to be more than 1, it’s simply 1. There’s no such thing as a material absorbing more sound than is available—absorption coefficients that are ABOVE 1 should simply be interpreted as 1.

Put the Y in DIY

You’ll see that the Roxul mineral wool board performs a lot better in the lower end (125Hz and 250Hz). Also, a pack of 6 panels (2’x4′) of Roxul RXL 60 will run for about 75$. That’s 75$ for 48ft²; as opposed to almost 300$ for 48ft² with worse performance. The only downside with purchasing bare mineral/glass wool boards is that you’ll have to create a ‘friendly’ panel yourself by wrapping it in breathable cloth:

Simple panel construction for mineral/glass wool panels.
Simple panel construction for mineral/glass wool panels.

To put it into perspective. For the prices listed above, you could very easily create at least 18 panels (144ft²!) of superior mineral/glass wool absorption panels (including the wood and cloth needed) for less money than the Auralex package. This with the added benefit that you can personally choose the cloth/print you want (let’s be real, shopping for fabric at Jo-Ann is Hobby Lobby is great) to give your space a more unique look.

Now, for some making your own panels is a deal-breaker. Let’s look at another situation, where we would specifically target the low-end of the spectrum. Your option with Auralex would be a 4″ thick StudioFoam wedge:

125Hz 250Hz 500Hz 1000Hz 2000Hz 4000Hz
Auralex 4″ StudioFoam 0.31 0.85 1.25 1.14 1.06 1.09

A 4″ thick Roxul panel would have the following absorption coefficients:

125Hz 250Hz 500Hz 1000Hz 2000Hz 4000Hz
Roxul RXL 40 (4″) 1.03 1.07 1.12 1.04 1.07 1.08

The numbers speak for themselves, really, and so do the dollars.

To sum it all up

Again, it’s a toss-up of pros and cons. Do you have the time and are you willing to create your own panels? Great! Get a pack of mineral/glass wool and start creating those panels (WITH that cool fabric you found)! If not, the acoustic foam panels will always be there, and they will always be convenient, but unfortunately will also be a bit (or a lot) more expensive and won’t perform as well.

Lastly, when acoustically tuning a room, linear absorption—in terms of frequency-related performance—might not actually be beneficial, as targetting the low-end with this type of absorption could very easily turn into killing off the high-end, resulting in a dull and boxy response. Get in touch with us if you could use some guidance in finding the perfect absorptive balance for your music room.