improving studio doors on the cheap

[Brian Ravnaas]

This is copy of text entered here: http://forum.studiotips.com/viewtopic.php?t=2780

I think that the suggestion below represents a really cheap, very effective way to get more from your doors.

Recently, more or less for the heck of it, while running some tests at Orfields lab this experiment was conducted:

A frame of 25 gauge steel studs was in the opening, with 2 sheets of 5/8" drywall (damped) installed on one side only - a simple panel that should approximately follow mass law.

Then we had R13 insulation installed in first 1/3, then 2/3, then all of the spaces between the studs. the results were very interesting and are presented below in the first diagram. What was observed was a marked improvement in middle and high frequency TL when the absorption covered the entire specimen.

The results appear to follow the absorption of the insulation itself (R13), and i would guess that if you took an impedance tube measurement of absorption of R13 fiberglass, you would find a strong correlation between this improvement in TL and the results of the impedance tube absorption test.

I then dug through the NRC's published tests to find a historical precedent, and located one. The TL of a floor/ceiling with and without carpet is shown. The same phenomenon is observable - marked improvement in TL at those frequencies where the carpet is a good absorber.


So it is established that absorption can improve TL at mid and high frequencies (or possibly lower freq's if the absorption in question was very effective at those freqs). But while it isn't cost-effective (especially at low-frequencies), or probably practical from a sound-quality standpoitn to cover your entire wall in absorbing material... it isn't that expensive or that impractical to cover your entire door.

And with a door you have this:

-generally a solid core single-door is quite heavy and
-generally doors found on studios or home theaters are quite small

and both of those will work to have the low-frequency performance of the door be generally pretty good. But a strong coincidence dip is generally found in doors such as solid wood and other heavy doors, and the lack of an air cavity/absorption/decoupling, etc. in doors will generally keep their mid and high frequency TL well below that of the walls they serve.

Therefore i hypothesize (and hope to test oneday) the following:

-when planning acoustic treatment for your studio you should plan to cover the entire door and frame with absorption. This will accomplish the following for you:

1. improve the TL of the door at the frequencies where it needs help the most
2. help (especially if absorption is present on both the frame and the door, making a small "tunnel" for sound passing through the seals of the door to pass through) mitigate less than perfect seal conditions.


Hope that's helpful, it really should be.

[Sound byte]

Thanks for that post.

[DanDan]

Reverberation time affects TL