Sunday, March 21st, 2010 | by matthew mcglynn
Last summer I conducted an informal test of the idea of putting a voiceover microphone into a foam box to dry out the sound of the room. This seems to be an increasingly common technique for VO artists who don’t have easy access to a proper recording space.
The first comment on that article was written by James Lindenschmidt of RealTraps, to suggest that their “Portable Vocal Booth” might yield results superior to my precariously-stacked box of discarded off-brand studio foam. James subsequently contacted me to offer a PVB for evaluation.
I took the opportunity to compare the PVB to a couple other acoustic treatment products. Read on for the full review.
The RealTraps “Portable Vocal Booth” is a 2×4 foot acoustic panel with a hinge down the middle. According to Lindenschmidt, it is very similar to the company’s MicroTrap; both employ a limp-mass membrane and other sound absorption materials, suspended within a rigid metal frame. The PVB is designed to be folded into a “V” shape, with a microphone in the middle.
The PVB includes a metal track that allows the unit to be mounted on a boom microphone stand, with the microphone. I like this approach, because it means the height of the PVB can be adjusted simply by raising or lowering the mic stand. All my DIY foam enclosures suffered from an inability to be conveniently raised to working height, so I appreciated the convenience of the PVB’s design.
For storage, the PVB can be folded in half. At two feet square, it’s not exactly unobtrusive, but it is not especially bulky either. The RealTraps website suggests that the folded PVB can be stored and carried in a pizza delivery bag. It could also be leaned against a wall, or in a corner, where it would provide additional absorption.
The construction quality is excellent. The acoustic fabric was tight and even, without ripples or waves. After a half-dozen setups, the painted metal parts still looked new. My impression is that this device is solidly built and will provide many years of service.
Setup is quick and easy; see RealTraps’ illustrated instructions here. Be sure the mic stand’s clutch is tight; at 11 pounds, the PVB weighs a good deal more than a microphone.
The PVB can also be used without the V-rack — it is basically a small gobo, useful for surrounding a guitar or bass cabinet, or as a baffle between an acoustic instrument and a second sound source in the room. I suspect it would be useful at reducing the amount of bleed from a hi-hat into the room mics, too.
I tested the PVB against a couple other acoustic-treatment solutions.
My pal Harry from Route 44 Studio loaned me a “Sound Absorption Sheet” from AudiMute. He keeps them around as portable, lightweight gobos. They’re inexpensive: $40 per sheet individually, or as little as $20 per sheet in quantity.
I also have a cache of Auralex Studiofoam, which I figured I’d rig into another DIY foam box of some sort. Studiofoam panels are not sold individually, I believe; a box of six 2×4' pieces (48 square feet) costs about $360 without adhesive or any sort of mounting solution.
(I’d hoped to also test the sE Reflexion Filter, which may have been the first portable wraparound isolation device, but I was unable to get one in time for this review. See below for additional discussion of the Reflexion Filter.)
I set up an MXL Revelation microphone in the middle of my live room. The Revelation is a multipattern tube mic, set to Cardioid for this test. (See my MXL Revelation review for more about this microphone.)
The following samples were recorded from a distance of about 9 inches. As you’ll hear, I am not a voice actor, but hopefully the samples will serve as a useful demonstration anyway.
Working distance and reflected sound
An earlier round of tests at about 24 inches produced less-favorable results — none of the products performed adequately.
This is due, in part, to the Inverse Square Law, which describes how the intensity of a sound wave will diminish over distance. By reducing my distance from the microphone, I gained over 6dB of signal level as compared to the volume of ambient and reflected sounds. In other words, at equal output gain, working closer to the mic makes the volume of reflected sounds a lot less audible.
Also, by standing closer to the mic and whatever acoustic absorption product was deployed behind it, I reduced the amount of sound escaping from my virtual iso booth into the room. The closer a sound source is, the more effective absorption these products will provide.
Untreated room #
The first sample was recorded with no acoustic damping or absorptive products. The sound of the room is easily heard. It is big and ringy, and clearly unsuitable for voiceover work.
Audimute sheet #
The second sample was recorded with the AudiMute sheet behind the microphone, draped over a tall boom stand. The vocal sound with this setup is definitely cleaner than before. I can hear the sound of the room, but it is more controlled. The echo is less sharp.
If I’d had a second AudiMute sheet placed at a right angle to the first, forming a “V” around the microphone, the results would no doubt have been better. The large size of the sheets works in their favor.
RealTraps PVB #
The third sample was recorded with the PVB. I set it up with the mic deep in the crotch of the “V.” I was standing within the “V” as well, to reduce the amount of sound leaking into the room.
I think this sample sounds great. My voice is significantly drier than in the earlier samples. I could use this sound for a vocal track. In fact, I’ve already done so.
Did the PVB turn my 420 square foot, cathedral-ceilinged live room into a real vocal booth? I welcome your comments on that question. I can still hear a bit of presence from the room, but the improvement is remarkable.
Auralex Studiofoam #
The fourth and final sample was recorded with a pair of Auralex Studiofoam panels, again in a “V” shape — I actually just stood the foam on the PVB’s mounting rack.
The quality of the resulting audio is excellent. In a blind test, I couldn’t distinguish it from the audio sample recorded with the PVB.
That said, without the PVB rack, it would have been hard to get the foam into position. My earlier DIY solutions suffered from the same problem — there’s just no easy way to suspend a foam box six feet in the air, although you can certainly kill your session’s momentum by trying to.
Just as with my earlier foam-box test, this process proved that it is not necessary to record vocals in a dedicated vocal booth. For most applications, bad room sound can be sufficiently mitigated with portable absorption products.
To my ear, the PVB delivers on its promise of allowing the user to capture a dry vocal sound even in a challenging acoustic space. I love the product’s design and its versatility, and I can imagine numerous uses for it — so much so that I bought the evaluation unit.
I’ve since recorded vocals and harmonica for two local artists in this space, with excellent results.
The PVB looks good. It sets up quickly. It is undemanding when in session. And it works as advertised. I wish I could say that about the rest of my gear.
PVB vs. sE Reflexion Filter
I couldn’t help but notice that RealTraps and sE Electronics have published some critical comments about each other’s products. I did not compare the two products, but I find the opposing claims fascinating.
sE goes on to state that putting a “simple V shape behind the mic… creates one of the worst coloration problems you can manage to achieve.” To which RealTraps would probably reply that a V shape built of highly absorptive material doesn’t cause coloration at all, because coloration is caused by reflected sound.
Ultimately, the only way to determine which one might work better for your application is to try them both side-by-side. Note that both products have been well-reviewed in the past, and both products cost the same ($299).
I have no affiliation with MXL, Audimute, Auralex, or RealTraps, and received no compensation for this review. As mentioned previously, the Audimute sheet was loaned to me by a local studio owner. The MXL Revelation and RealTraps PVB were loaned to me on a fixed schedule by their respective manufacturers. I purchased the Auralex Studiofoam through a large catalog retail business about 10 years ago.
A hearty hat-tip to JWL and Ethan at RealTraps, Mary Ann at MXL, and Harry at Route 44 Studio for their assistance!