Tuesday VO Tech Tip: Thwack That Echo!

I often mention the idea that a mic never will never sound better than the space it is in. Yet we can be very poor judges of acoustics and environmental sounds. Our brains do a great job of focusing our attention. As humans became more dependent upon spoken language, it was critical to understand verbal information being shared. So, our brains evolved with a strong bias to discern speech emanating from others of our species.

Simplifying a bit, that means that our brains focus upon what it thinks is important – the speech-y bits – and tends not to focus on imperfections and distractions – issues like echo and background noise. Those problems continue to exist, but our grey matter has filtered them from our awareness.

Recording Spaces Are Seldom Perfect

That’s why most new voice actors and narrators are surprised when they first put a microphone in a “quiet” room and become aware of how much “other” stuff gets captured. Traffic, tree trimmers, and tintinnabulations suddenly leap out of those recordings. Eliminating those can be exceedingly difficult, the main cause of VO isolation booth lust.

Once we lock ourselves away in a closet or cubicle, the second challenge appears: reflection, or  the “R” step I referred to recently. Dealing with reflections is a bit of an acoustic whack-a-mole. As soon as we address one core reflection issue, we’ll notice another. Those “new” issues were likely being masked by the more major challenges. As I always stress when teaching home recording classes – developing a usable space will be an “iterative” process.

Foam Frequently Fails Us

Many online resources push foam for recording space treatment. There’s certainly a lot of voice actor cultural reinforcement for utilizing acoustic foam products. A backdrop of foam looks very “recording studio-esque” in those studio photos we all study. However, there are some noticeable drawbacks. In the first place, not all foam is created equal. There are many inexpensive foam products which look cool but do nothing acoustically. True acoustic foam is different in ways you’ll notice if you are able to do a little A/B testing.

Secondly, the commonly used 2″ thick egg-crate or wedge-shaped foam doesn’t actually do that much to reduce reflections in the vocal range. If you look at the testing results between a sample of 2″ and 4″ wedge foam, you see that both of them work best for higher frequencies. The higher the Sound Absorption Coefficient the more it absorbs, which means that numbers closer to 1 are better for our needs. Looking at these graphs, you’ll see that both 2″ and 4″ Wedge Foam have better results as the frequencies in the room go above 2.5 kHz (2,500 Hz). But the damping effectiveness is much less in the range where most voices exist. A typical male voice will have a fundamental frequency in the 90 to 155 Hz range, where typical female voices land from 165 to 255 Hz. The fundamental vocal range is outlined in yellow below. 

As the frequencies come down into the range of spoken word – under 1 khz – things start to look very bad for the thinner foam. The sound absorption continues to fall. By the time we get down into the common frequency range of a human voice, very little absorption is taking place using 2″ thick foam. The 4″ thick wedge foam hangs in there a little longer, but then drops off as well.

In most small spaces, the foam is typically mounted directly upon a hard surface. Envision those unattenuated lower frequencies penetrating the foam and hitting the drywall behind it. Those frequencies then get immediately bounced back out into the room with little reduction. A room with only 2″ foam on the walls is going to reflect a lot of lower frequencies back into the space – right where our vocal range lives.

Another Option – Acoustic Blankets

Heavy acoustic blankets, such as Filmcraft or VocalBoothToGo dot com’s “Producer’s Choice”, often sound quite good when used to treat a small space. Hanging those blankets with an air gap between them and the wall can also help quite a bit. The acoustic blankets end up doing double duty – sound waves go through the mass of the blanket one time on the way out, then a second time on the way back in after bouncing off any surfaces. Even with an air gap, blankets are less likely to take up as much as 4″ wedge foam panels. This allows blankets to provide a bit more useful space in which to set up gear and physicalize your performance.

Of course, the downside is that those blankets can look a bit “unfinished” in studio photos. Perhaps there’s an app for that…

If you would like a free review of your vocal recordings, please use the upload tool on my Audio Review page.

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