Portable voiceover studio — the foam box test

Tuesday, July 14th, 2009 | by

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.)

Foam box, front viewIt 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.

Foam box, side viewThe 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:

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.

The small room testWhat 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.

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:

  1. 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.
  2. 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?

Posted in Technique | 10 Comments »

10 Responses to “Portable voiceover studio — the foam box test”

  1. JWL

    July 14th, 2009 at 9:24 pm

    thanks for the test. Nice job.

    Most likely, the lack of results have to do with the size of the foam panels used, as well as the thickness of the panel. Or more accurately, the low frequency limits of its absorption effectiveness.

    We ran similar tests for our Portable Vocal Booth, which you can hear for yourself in the videos on the page. This PVB unit is large enough (2 – 2’x2′ panels hinged together) to really make a clearly audible difference. Each panel is 1″ thick and is effective down to about 200Hz.

    More importantly, when used for VO or vocal tracking, the unit is large enough to absorb much of the voice sound on its way out into the room, preventing the room from resonating as much in the first place. Then, when you place the mic inside the PVB hinge, it also absorbs room reflections on their way back into the mic. The size of the unit is why it performs so well.

    I have 2 PVBs and use them literally on every session. The difference is not subtle.

  2. Joe Gilder

    July 15th, 2009 at 10:01 am

    Nice! I posted something similar to this, I made a make-shift reflection filter of sorts. You can check it out here:

    You went a step further, and I think you got better results. Thanks for sharing!

  3. mrpewett

    August 9th, 2009 at 1:55 am

    I don’t really think that’s all that subtle. You can really hear the box deaden the reflections and take off a bunch of the top end. Way less bright and a lot more focused sounding.

  4. Rewind

    August 16th, 2009 at 2:01 am

    The room echo without the box in the first clip is not so much now, but will probably be amplified by effects like chorus and reverb plugins. The deader the better. I think I will build that box. I have heard you should have a meter to the foam from the sound source, i.e. the mouth, but this seem to work just fine.

  5. Bob Johnson

    October 12th, 2009 at 7:12 pm

    I also don’t think the difference is subtle. I’ve done similar things, you’ve discovered part of what I learned quite a while ago. A cardioid mike cares only a little what acoustic treatment you use off axis. Try the same test, with the same cardioid mic, but position some absorption BEHIND the speaker (as in on-axis). You’ll hear the difference.

  6. bob

    October 18th, 2009 at 2:07 pm

    I have used a cheap foam mattress (20cm x 155cm x 200 cm) and a blanket as an improvised vocal booth. Bent into u-shape, with a blanket laid on top and over the open side. The resulting space is a bit small though. Nevertheless you can easily fit a normal mic stand in it, and the vocalist can be placed sitting halfway inside the U. The mattress damps sound with a quarter wavelength shorter than the thickness of the material, in my case above maybe 500 Hz.

    As a result I got a very dry recording. The mattress also damped what little sound my macbook pro made, with a distance of only 1 meter between laptop and mic.

  7. Debbie

    December 12th, 2009 at 12:07 pm

    I am an at-home VO talent, looking to improve the quality of my recordings. I am a technical num-num and would like some advice. I have read the posts, and am still a little confused as to what would work best to create that studio sound. I currently record inside of my walk in closet. It ix 5′ x 6 ‘, carpet, 9’ ceilings. There are clothes on one wall, and no other insulation on the other three. I would like to also deaden the sound of my laptop fan.. I use a large diaphram condenser mic.

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  10. Will

    June 21st, 2012 at 8:43 pm

    Great idea I’m just starting v o work thanks for sharing I’m going to make my own and and post photos when I’m finished.

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