(yet another) green glue question

I've been trying to make my way through the info available on GG and I am super confused... I've been in a bunch of studios that are built as double drywall, 2X4 stud and rigid insulation, and double drywall construction, and they seem to have no sound transmission at all...but yet I've read postsby Rod Gervais that say you can lower the STC by 10dB. How can you lower near silence by 10dB, what am I missing?

Ptownkid wrote:

How can you lower near silence by 10dB, what am I missing?

.. an updated profile for one.

Sorry, fixed...

one persons' loudness is another persons' silence... given most wall constructs in a typical home studio, with best construction details, give you around 60db or so of reasonable isolation, you're still looking at 50db (assuming 110db in the live room) levels in the other room... depending on how you view that, your ability to hear the low frequencies coming through, etc. will determine if you think that is silence... or not. so with GG, you're getting another 10db potentially so now you're hitting 40db coming through (which will seem decently quiet if your control room monitors are hitting 77-85db). so if you can afford it, GG is a good choice.

gullfo wrote:

one persons' loudness is another persons' silence... given most wall constructs in a typical home studio, with best construction details, give you around 60db or so of reasonable isolation,

This is very true - but it's in the mids and high frequency ranges - no one is reaching that with a couple of layers of drywall and isolated frames in the LF frange (Below 200Hz.). The 60 would be more of the weighted average STC rating - not total isolation across the sprectrum in dB. Looking at double 2x6 walls with double 5/8" each face and fiberglass insulation (taken from IR716) TestID TL-93-283 STC 69 50 Hz.......... 26.7 63 Hz.......... 31.8 80 Hz.......... 36.6 100 Hz........ 39.5 125 Hz........ 44.6 160 Hz........ 51.3 200 Hz........ 55.9 250 Hz........ 61.8 315 Hz........ 64.9 400 Hz........ 67.3 500 Hz........ 70.1 630 Hz........ 72.9 800 Hz........ 78.0 1000 Hz...... 81.5 1250 Hz...... 85.6 1600 Hz...... 83.9 2000 Hz...... 75.3 2500 Hz...... 75.9 3150 Hz...... 81.7 4000 Hz...... 87.4 5000 Hz...... 91.5 6300 Hz...... 90.7 OK - this wall is 2x6 construction - 24" oc - fiberglass insulation - double 5/8" GDW each face - weighted average brings it to an STC 69. But look at the fall off from 200Hz down - it drops below 60dB for the first time - and then plummets down to 26.7dB at 50 Hz. 50 Hz.......... 26.7 63 Hz.......... 31.8 80 Hz.......... 36.6 100 Hz........ 39.5 125 Hz........ 44.6 160 Hz........ 51.3 200 Hz........ 55.9 Above that you're in great shape. So what you might deem as "quiet" isn't anywhere near that in the LF range - and when you have a Marshall double stack pushing 110 dB of bass guitar at you - the 70.5 dB you hear on the other side of that wall is significant indeed. Seeing as a 10 dB cut cuts the volume in 1/2 according to the human ear - that's pretty significant IMHO. Sincerely, Rod

When you say fiberglass insulation for that test, are we talking about the type you would actually use in a sound proofing wall?

Ptownkid wrote:

When you say fiberglass insulation for that test, are we talking about the type you would actually use in a sound proofing wall?

Without knowing what you mean by "the type you would actually use in a sound proofing wall" it means standard heat insulation used in walls. Andre

Sorry, what i meant was that it seems like a lot of people either use mineral wool batt or rigid insulation yes/no?

I thought I answered your question. So what is your question now? What was used in the tests Rod referenced was standard wall insulation. There is no advantage to using semi-rigid insulation in walls. Andre

Sounds good, no pun intended