While recording audiobooks for family use, I discovered that I could reduce the amount of room reverb and even some of the ambient noise in the track by building a foam box around the microphone. My reasoning was that even though I didn’t have an isolation booth, at least the mic could have one.

I was surprised to see later that this idea is a legitimate voiceover product, targeted at people who do VO work on the road and need a portable studio setup. (Search the web for “Porta-Booth” to find this — current retail price is $129.)

It forced the question that comes up around here a lot — what does it sound like, really? Does it make any difference?



It didn’t seem necessary to spring for the fancy collapsible box and precut foam just to test the concept. I had a piece of 4'' Auralex Studiofoam for the back, and 3'' convoluted acoustic foam for the top, bottom, and sides. The inside measured about 20'' deep by 16'' tall by 10'' wide.

With a boom stand on the side, I lowered a large-diaphragm condenser microphone into the box, and covered the top with more foam.

The mic was about 8'' back from the front of the box, and I sat about 10'' from the front edge. I didn’t use a pop filter.

I was in a big room with high ceilings, which I think affected the results. Listen for yourself:

http://recordinghacks.com/wp-content/uploads/2009/07/large_room.mp3

The difference seems pretty subtle. In fact if you’re not listening through headphones you might not hear it at all. Which either means my box just wasn’t working, or that particular room wasn’t causing a lot of bad reflections. I think it’s the latter. In any case, both samples sound pretty good.

What is the effect of the room size, you ask? I have an answer for you. I repeated the test in the smallest room in the house. A true isolation chamber, in a manner of speaking.

http://recordinghacks.com/wp-content/uploads/2009/07/small_room.mp3

Both of these sound terrible, but the difference between the two is certainly more audible.

The size of the box might make a difference — a smaller box, or at least a box with a smaller front opening, would probably sound deader. I would have had to start cutting up foam to try this, so I didn’t. If all the edges of the box would be tight, that would probably reduce reflections somewhat too. And it might have helped to push the mic farther back into the box.

Nonetheless, I think these tests yield two useful conclusions:

The bigger the room, the better the sound. (Is anyone really surprised by this?) Note: big spaces with huge echoes, like gymnasiums, are obviously an exception. The foam box really does help. Be sure to experiment with mic placement though.

See also my Neophyte’s Guide to Home Voiceover Recording.

Any real VO engineers out there with opinions to share?

Tags: voiceover

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