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Tracking Booth - acoustic insulation - How Much
Old 6th September 2019
  #1
Gear Head
Tracking Booth - acoustic insulation - How Much

Hi all -

I'm going to build a booth at my house to track vocals and acoustic instruments.

I work for a company that uses acoustic insulation in some of our products.

One of our suppliers sells acoustic fiberglass insulation in many sizes - some very large - blanket size. I could probably get them to cut 10'x10' - - looking into it.

This specific insulation is rated to decrease 125 Hz by .95% ranging up to 1.10 % at 4000 Hz. It's a pretty potent absorber.

My room is going to be roughly 4'x6' finished interior dimensions, double drywall. I am not that worried about stopping sound from in or out. I am far more concerned with controlling tone and resonance. I want clean usable tracks.

My question: given the specs on this insulation, should I be thinking about covering all interior surfaces with it or should I be thinking about breaking the walls and ceilings up with panels and allowing some resonance to exist?

And of course.....what is obviously in front of my face that I don't see yet?

Thanks,

Tim
Old 10th September 2019
  #2
Lives for gear
Quote:
Originally Posted by zydeceltico View Post
4'x6' finished interior dimensions,
4' x 6' is really too small.

A couple issues, it seems that your rating for this absorber is incorrect, or at least .95% is basically no absorption at all (that's 95 hundredths of a percent). But also percentage is a bad indicator for absorption as well because it's a linear scale and dB is logarithmic. 40dB translates to a whopping 10,000%.

There is nothing magic about porous absorbers, really just a few variables. Gas flow resistivity, depth, and air gap. You can play with them here-

http://www.acousticmodelling.com/porous.php

You can see that even 48" of low GFR material (which is the best choice at that depth) isn't going to reach an absorption coefficient of .95 at 125hz.

And this is the first reason why small booths aren't good for clean usable tracks- the boundaries are so close that this is little to no ability for the sound to dissipate in the room and the amount (depth) of absorption required to minimize very short early reflections becomes very impractical. IE if you were going to have 4' of absorption on all surfaces, you could, at this point, just have a room that was 12' x 14' and have corner traps and some panels with slats and have a better tracking room.

The other issue is that the only real choice for this sort of size is to make the room completely dead. The problem with that is that small movements of the performer relative to the mic will create significant changes in treble response, and any reflective object in the room (music stand, window, door, guitar case etc) becomes a single specular reflection source with no other natural reflection sources to mitigate that specular reflection.

Rather then going that small, it would make more sense to have a single room to mix and record in.
Old 10th September 2019
  #3
Gear Head
Quote:
Originally Posted by RyanC View Post
4' x 6' is really too small.
Rather then going that small, it would make more sense to have a single room to mix and record in.
I've rapidly come to the same conclusion. I did a test mockup of the space with some large blanket we have at work. And yeah - it was claustrophobic both physically and aurally.

So instead I'm going with the "whole room" approach with treatments.

My office is a strange shaped room so I'll need to get creative with the jigsaw and traps but I do know you're very likely right.

Thanks!

Tim
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