Dawbox

[vince.cimo]

Hi guys, I'm considering buying drum booth plans from dawbox.com (http://dawbox.com/V-Drum-Booth-8x8.htm), but I'm having trouble finding any good "I built this, and it has STC X, and it sounds like this" reviews. Does anyone here have any experience with these things? A few concerns come up about the plans:

1. It's all built with MDF, which is significantly less massive than drywall.
2. The dimensions of the booth are essentially a cube = terrible room modes.
3. After talking on the phone to the guy, he claimed STC 60, but has nothing to back that up.
4. The plan for acoustic treatment inside the booth is just a pack of crappy foam, no mention of any real broadband absorption.

What do you guys think? I like the fact that I can build this thing without violating my building codes....

[Soundman2020]

I'm considering buying drum booth plans from . . .

Hmmmm.... I think I'd skip on that! The forum is free, and US$ 74.95 will buy you a pretty nice steak dinner at a good restaurant, with a fairly-decent bottle of wine (Chilean wine, of course... ).

That would be a much more useful purchase!

1. It's all built with MDF, which is significantly less massive than drywall.

Actually, MDF is more dense than drywall, usually. The average density of drywall is commonly around 685 kg/m3, and the average density of MDF is commonly around 750 kg/m3. Of course, the MDF is going to be much more expensive, and there's only a little bit extra mass in there... probably not worthwhile.

2. The dimensions of the booth are essentially a cube = terrible room modes.

Yup, not good at all. And with an 8foot cube, guess where your first five huge problems will be? 70 Hz, 100 Hz, 141 Hz, 157 Hz, 173Hz . But gee, aren't those all frequencies that you'd expect to find on things like kicks, toms and snares? Yup... you betcha.... Not a happy situation...

3. After talking on the phone to the guy, he claimed STC 60, but has nothing to back that up

The fact that he's talking STC is already a huge red flag, because it is no use at all for telling you how well your booth will be isolated! STC was never meant to measure such things. Here's an excerpt from the actual ASTM test procedure (E413) that explains the use of STC.

“These single-number ratings correlate in a general way with subjective impressions of sound transmission for speech, radio, television and similar sources of noise in offices and buildings. This classification method is not appropriate for sound sources with spectra significantly different from those sources listed above. Such sources include machinery, industrial processes, bowling alleys, power transformers, musical instruments, many music systems and transportation noises such as motor vehicles, aircraft and trains. For these sources, accurate assessment of sound transmission requires a detailed analysis in frequency bands.”

It's a common misconception that you can use STC ratings to decide if a particular wall, window, door, or building material will be of any use in a studio. As you can see above, in the statement from the people who designed the STC rating system and the method for calculating it, STC is simply not applicable.

Here's how it works:

To determine the STC rating for a wall, door, window, or whatever, you start by measuring the actual transmission loss at 16 specific frequencies between 125 Hz and 4kHz. You do not measure anything above or below that range, and you do not measure anything in between those 16 points. Just those 16, and nothing else. Then you plot those 16 points on a graph, and do some fudging and nudging with the numbers and the curve, until it fits in below one of the standard STC curves. Then you read off the number of that specific curve, and that number is your STC rating. There is no relationship to real-world decibels: it is just the index number of the reference curve that is closest to your curve.

When you measure the isolation of a studio wall, you want to be sure that it is isolating ALL frequencies, across the entire spectrum from 20 Hz up to 20,000 Hz, not just 16 specific points that somebody chose 50 years ago, because he thought they were a good representation of human speech. STC does not take into account the bottom two and a half octaves of the musical spectrum (nothing below 125Hz!), nor does it take into account the top two and a quarter octaves (nothing above 4k). Of the ten octaves that our hearing range covers, STC ignores five of them (or nearly five). So STC tells you nothing useful about how well a wall, door or window will work in a studio. The ONLY way to determine that, is by look at the Transmission Loss curve for it, or by estimating with a sound level meter set to "C" weighting (or even "Z"), and slow response, then measuring the levels on each side. That will give you a true indication of the number of decibels that the wall/door/window is blocking, across the full audible range.

Consider this: It is quite possible to have a door rated at STC-30 that does not provide even 20 decibels of actual isolation, and I can build you a wall rated at STC-20 that provides much better than 30 dB of isolation. There simply is no relationship between STC rating and the ability of a barrier to stop full-spectrum sound, such as music. STC was never designed for that, and cannot be used for that.

So forget STC as a useful indicator, and just use the actual TL graphs to judge if a wall, door, window, floor, roof, or whatever will meet your needs.

That said, I VERY much doubt that you'd get anything like STC 60 from a couple of bits of MDF with insulation in between! Even assuming the MDF is 3/4", and the foam is 4" 703, I can't see you getting much better than STC-40 out of that... Even worse, the resonant frequency would be around 51 Hz, so there's no isolation at all until around 72 Hz, and you'd only get good isolation above 102 Hz.... Kick, toms, snare....

4. The plan for acoustic treatment inside the booth is just a pack of crappy foam, no mention of any real broadband absorption.

So let's see now: The design is a cube that is going to have very major issues at low frequencies, which are extremely hard to treat anyway, even with deep and well designed treatment, and all that you get is some flimsy foam?

What do you guys think?

See above!

I like the fact that I can build this thing without violating my building codes....

You could glue bits of cardboard boxes to some old broomsticks as well, then throw a blanket over the top, also without violating your building code... and probably get about the same total result.... (OK, so I exaggerate a little, but you get my point....)

If you wanted a booth that you can dissemble and truck around, and that offers some level of sound isolation, then you could talk to these guys: http://www.whisperroom.com/sound-booth-models For only around US$ 16,000 or so you could get one of their enhanced 8x8 booths, that will give you close to STC-50. It only weighs about 2,600 lbs, and takes just five hours to assemble. But that is also a cube, so you'd probably need to go bigger, to their 8 x 14 model, which you can get for just US$ 25,000, in the enhanced version... It only weighs 4,000 pounds...

Or you could build something yourself, for quite a bit less money, that would get you the same or better isolation. And since you'd be saving a large chunk of that 25k, you could even afford to hire John Sayers to design it for you, buy a great drum kit, and a small car, and still have plenty left over, for many more steak dinners with fine Chilean wine!



So, in summary, I think I'd be rather skeptical about those plans, and I think I'd pass on spending a great steak dinner for a dozen pages of drawings and a couple of CD's...



- Stuart -