Adding STC together

[roughly]

Hi gang,
After reading several books several times on recording studio design and construction, I keep being troubled by the methodology used to "add" various STC barriers together. EG: Take Everest's book on sound studio construction: on page 186 he charts out several wall units and their STC rating. What troubles me here is that adding two 36 STC walls next to each other (with an appropriate air gap between) only yields some 60ish STC not the 70+ that one would expect by simply adding it together! What gives?

Any help on the this brain teaser would help me sleep.
thanx
jeffrey

[Eric_Desart]

Hi gang,
Any help on the this brain teaser would help me sleep.
thanx
jeffrey

I think you better forget it, rather than making your sleep dependent on this.

You can't just add STC.
Everytime you make another wall, the insulation will be defined by the exact buildup of that wall.
All elements in such a wall interact with one another.

Adding a STC 20 gypsumboard to a brick wall will hardly increase the STC of that brick wall with anything.

If you read the technical pages from this site you get a better impression already.
http://greengluecompany.com/index.php

[roughly]

What about in the case of indepentant structures , for a theoretical example - room with in a room. Room 'A' STC 40, Room 'b' STC of 45 . with no sharing walls/structures and a significant air gap between. Would yeild what as a STC all in.


THX again
jeffrey

[Eric_Desart]

What about in the case of indepentant structures , for a theoretical example - room with in a room. Room 'A' STC 40, Room 'b' STC of 45 . with no sharing walls/structures and a significant air gap between. Would yeild what as a STC all in.


THX again
jeffrey

Jeffrey,

You really can not define an STC by adding both or whatever calculation.
A room in a room system can visibly be decoupled, but is in reality coupled by the airlayer.
Only at very large distances versus wavelength (and in as far flanking does not limit this) you can add Transmission Loss values (and roughly, but not correct STC).
But what you're looking for is not possible.
One does not add additional insulation to an existing insulating separation, but one creates a new system.

Higher numbers, and larger cavities will likely result in higher total values (unless you make it multi-leaf systems which are discussed in the link I gave you). But that still doesn't mean that you can simply add such numbers.

Here's a document how STC is defined:
http://filexoom.com/files/5434/Acoustic ... ITC_RW.doc