Tuning a Tracking Booth (video/audio files included)

[Guitar Guy]

Hey Friends,

I was hoping that I might get some personal advice for the tracking booth I am working on. Here is my dilemma.
This is my second booth. I am very inexperienced, but willing to try anything. The first booth I made was a very small closet. I pretty much drenched the room in foam and killed everything. The results were decent, but singers always complained that it killed their voices to sing in there, even after I added reverb to their headphones.
Then I moved into a new house. All I have is a guest room with a little larger closet than before. Rather than kill everything, I went the perforated board bass trap rout. Everything was covered in rock wool/burlap with metal framing between. I then installed the perforated bass traps (rock wool inside) to the metal studs in hopes to create a more lively sound. BINGO! I had a singer in there this week and she loves how open it sounds now.
But here is the thing. It's more alive, but now certain mid-range frequencies are swirling around that sound awful (harsh and honky).
Below is youtube video of my tracking booth, and an audio file of some guitar I tracked last night (I have tried various typed of mic positions, and this one has pretty average results).
Can you help me keep some of the life while balancing out the mids? Is there anything else it needs that I'm not hearing? Thanks for any help.

YouTube Video
Audio File of Guitar

[Emcha_audio]

The main question is what's the dimension and how are you breaking the box effect. Are your pannels/bass trap that you installed in angles to each others? That would help. If you can't change things much, try to find a material that actually absorbs the frequency range where you are having problems.

[Guitar Guy]

Thanks for replying! The room is a closet...5x5x8. I am going to try removing panels that are parallel with each other and leave just the rock wool exposed to see if that helps. I may experiment a bit with the auralex as well.

[dave911]

Tuning a room by ear can be an endless process.
It's an art and a science, but the art part comes after the science.
If you use a spectrum analyzer you can at least find the problem freqs.
Just killing everything leaves the singer screaming into the void, they hear reverb but the space doesn't respond to their voice.

[Emcha_audio]

Originally Posted by Guitar Guy

Thanks for replying! The room is a closet...5x5x8. I am going to try removing panels that are parallel with each other and leave just the rock wool exposed to see if that helps. I may experiment a bit with the auralex as well.

If they are parallel, try to re-frame them so that they become at an angle to each others. But for a booth that size, you're better off with absorbing products for the frequency range that you need to deal with, while keeping what you already have. Get the frequency graph, maybe also a recording of the problem and send it to auralex, they might have what you need for that specific frequency problem.

[O.G. Killa]

Not that this helps, but I've never heard a singer say a dead booth kills their voice. Most professional singers I've worked with prefer the vocal space to be as dead as possible in order to help their pitch.

Anyway... that auralex you put in the corners isn't doing anything. The pegboard isn't far enough out from the wall to really effect the bass frequencies anyway, so it's not really helping you, you might as well have the bare walls at this point.

Something to keep in mind. Frictional absorbers (like auralex or rock wool) absorb the velocity of sound moving through air. As sound approaches a surface, that velocity transitions into pressure. Think of a basketball being bounced. the ball, when it hits the ground stops moving and instead compresses down on itself (which is pressure, not movement) it then springs back off the floor and starts moving in the other direction.

A frictional absorber can only effect sound that is still moving when it hits the surface and hasn't switched to pressure yet. in a sound wave, the point of "most movement" and "least pressure" is at the 90º and 270º points of the wave, also know as the 1/4 wavelength. Sound waves at 0º and 180º have no movement and are all pressure.

So, if you have 1" foam/rockwool attached directly to the wall... what is the lowest frequency that foam can absorb?

Frequency = Speed of Sound / wavelength

Now 1" isn't the wavelength, it's the 1/4 wavelength. To find the wavelength of the sound that this 1" panel will stop, we have to multiply by 4. So,

Panel depth is 1/4 Wavelength
Panel Depth is 1"
Wavelength is 4"

Frequency = 13,560 in per second (speed of sound in inches) / 4" (wavelength)

Frequency = 3,390 Hz

So your one inch foam panels when attached DIRECTLY flush with the walls, will at best absorb ONLY down to around 3.3KHz and then stop absorbing.

Notice you said you are having problems from 600Hz to around 2KHz??? That's because the foam is absorbing from about 3KHz and up.

How low would a 2" thick piece of auralex or rockwool absorb?

Panel Depth is 2"
Wavelength is 8"

Frequency = 13,560 inches per second / 8"

Frequency = 1695 Hz or 1.7KHz

How low would a 4" thick piece of auralex or rockwool absorb?

Panel Depth is 4"
Wavelength is 16"

Frequency = 13,560 inches per second / 16"

Frequency = 847.5 Hz

How low would one 4" panel together with one 2" panel absorb (so a total of 6" thick)?

Panel Depth is 6"
Wavelength is 24"

Frequency = 13,560 inches per second / 24"

Frequency = 565 Hz

So as you can see... in order to STOP 600Hz~2000Hz from reflecting and ringing in the booth, you will need to make your foam/rockwool panels 6" thick (not 1" or 2"). This makes the size of the room go from 5' x 5' x 8' to 4'6" x 4'6" x 7'6". But then, putting up the pegboard is now going to reflect sound off of it, so you are limiting the effectiveness of the foam. Pegboard can only work as a bass trap when it is the face of a completely sealed (air tight) box. And even then, since the holes are so small it's not extremely effective (the smaller the holes the higher the lowest frequency it will absorb). If it's not sealed air tight, then it's just reflecting sound and not doing anything else. Look up "Helmholtz" resonant absorbers to learn more about how to use pegboard to absorb bass and low mids WHILE reflecting mids and highs.

Anyway...

there is no "perfect" solution since the space is so small. There are always going to be acoustic problems with the space that you can't overcome because of it's size.

Personally, if I were you... I would go back to just absorbing everything and buy some $99 shure SE215 in-ear monitors for the singers to wear when in the booth. Then just focus on getting a good headphone mix for them. And I would leave their voice dry when tracking, but that's just me. Most likely they are blowing their voices out because the track is too loud compared to their voice in the headphones. It usually has nothing to do with how dry the room is.

Also, in a 5' x 5' x 8' room you are going to want to try and use some "membrane" type absorbers to tame the standing waves at 113Hz, 226Hz and 339Hz. Something like Realtraps mondo traps (http://www.realtraps.com/p_mondotrap.htm) might help. But remember, mondo traps (as with most membrane absorbers) reflect mids and highs while absorbing lows. Also INSTEAD of mondo traps you could try stacking megatraps in one corner (http://www.realtraps.com/p_megatraps.htm)

so the best thing to do is maybe to try and put these mondo traps on the wall that the singer faces (so the back of the mic is facing the mondo traps) OR put mega traps in one of the two corners in front of the singer. have all the other walls covered with 8" of foam/rockwool. This way the reflections off the mondo/mega traps will hit the backside of the mic instead of the front. You could also try getting two 2' x 4' mondo trap for the ceiling if the ones on the wall/corner in front of the singer aren't enough to bring the fullness of the voice back when listening in the mic. Or you could do one mondo trap and one rockwool panel on the ceiling, or you could do one 2' x 2' mondo trap and the rest foam/rockwool on the ceiling, etc... If you do put mondo traps on the ceiling, remember to try and angle them so they aren't parallel surfaces to the floor. You need at least a 6º angle OUT of parallel to stop flutter echo.

[getz76]

Great post Derek. Thanks for sharing.

[Guitar Guy]

Wow, thank you SO much for this information! I've learned more about sound wave absorption since reading your post than I ever have before! I took the pegboard off, (bringing the deadness back) and it did help the mid honkiness, but not completely. Here's what was behind the pegboard:

The entire booth is lined with 3 inches of Roxul Safe in Sound (covered with burlap). I have Auralex and Rockboard, but currently none of that is in the booth (I took out what was in the video).
According to your formula:
3" of panel
12" wavelength
13,560 ips
I should be absorbing down to 1130 hz.

Yet, I'm still getting some trouble around 1.5kH and lower.


It might be helpful for me to explain the quantity of materials I have left to work with.

1. Enough 2" Auralex to cover the whole room if necessary
2. Several feet of Rockboard 60 panels (2 inches thick)

I KNOW it is possible to get a better sounding room than this, because I've done it before in a slightly smaller booth. I just want a flat curve to work with vocals and acoustic guitar so I can eq in what's missing.

Should I go ahead and cover the 3" of Roxul with the Auralex? That would be 5" of absorption (down to 678 Hz). Better yet, should I take the panels of Rockboard, place it into corners and then cover THAT with the Auralex to kill any reflections? Thanks so much for the insight!

[Emcha_audio]

Originally Posted by Guitar Guy

Should I go ahead and cover the 3" of Roxul with the Auralex? That would be 5" of absorption (down to 678 Hz). Better yet, should I take the panels of Rockboard, place it into corners and then cover THAT with the Auralex to kill any reflections? Thanks so much for the insight!

That might not work as the density of the product might not be the same between the 2" auralex and the 3" rockboard, which is also something that needs to be taken into account when calculating the frequency absorption. I''m not talking of thickness but how dense the fibers of the product are packed together. A thing that wasn't said is that the sound wave compression doesn't happen on the product it self, but the sound wave will in fact go through the product, compress at the wall and bounce back through the product again. It's better if you can leave a small air space between the product and the wall, but if you can't it's not really a problem either. The more dense the product is, the more the sound wave has to force it's way through, too dense and it will simply act as a wall and the sound wave will bounce on it instead of on the wall. At the same times, it's not all the frequencies that will be bounced back through.

[Guitar Guy]

I see what you're saying. I don't know about how close the two products are in density, but I do know that neither product will reflect very much. I was just hoping that the concept of having 5" of absorbitive material before compression takes place would be better than the 3". I guess it couldn't hurt to try.