Originally Posted by BIGmouthinDC
Interesting. Do you think you are measuring the room or the door STC ? Does the room share a wall with any other space? How about measuring directly above?
Originally Posted by HopefulFred
I hope you can do this. I would say it's important to get your procedure verified first. But especially since the traditional wisdom is that the door is the weakest link, an uninterrupted wall would be a more digestible test.
My tests are absolutely dominated
by the door! In fact, that's one of the reasons I thought to start this experiment -- would fixing that door to properly seal it cause a notable improvement in the STC rating?
Okay, so I don't always have strongly defined goals when I start following my experimental muse. This was triggered because STC is only ever done in highly calibrated laboratories and they are testing specific partitions in complete isolation from any other typical components that would be associated with them. It's a necessarily artificial number because a real world room will never have the idealized conditions of the lab. Most articles I've read have mentioned dropping 5 STC off of the rating to give a more accurate "real world" rating.
But I think even that's a little too pat, because that implies that you don't have any flanking paths and there will always be flanking paths.
What that tells me is that in an assembled room, it's physically impossible to measure the STC value of just one specific partition. What you're always going to be measuring is that partition PLUS all of the flanking paths that are associated with it.
So I have potentially EIGHT different segments in my theater that could have different STC ratings. There's the ceiling, which is right below an attic which currently has no insulation (soon!). The west wall is an unbroken expanse of inner wall + space + concrete block. The south wall is similar, but also has two relatively large windows. The east wall has 10' that's just like the west wall but then it's inside space and so it switches to a segment with two stud walls, one side with double drywall + GG and the other side with just one layer of 1/2" drywall. The north wall can be split into three segments, with part of the wall shared with a bathroom; part shared with the hallway and dominated by the door; and part shared with the closet in the adjacent office.
The only two of those segments that I'd expect to have the same rating would be the west wall and the outside portion of the east wall. All of the other six segments would attenuate sound at different levels.
So what's the overall STC rating of my theater? I'd argue that there isn't just one rating, because it's going to be highly dependent on where your frame of reference is coming from!
Can I then pronounce the STC rating of any of the individual walls or wall segments? Only to a point. My interior wall segments are theoretically somewhere in the STC 60-67 range so the fact that the door is half
of that shows just how much it dominates the overall soundproofing inside. For instance, if I am measuring the noise level on the inside portion of the east wall, then I'm still affected by the door because I can hear the sound coming down and around the hall. If I'm outside than the door doesn't matter, but now the fact that the ceiling is "bare" means that you can hear the sound coming from the eaves.
I guess all of this blathering on is maybe convincing everybody that no, it's not worth doing STC testing at home. Maybe it's not. I don't feel like my muse has been satisfied, though
I'm internally splitting this into two conceptual paths. The first is the test procedure itself. Is there a way for me to modify my procedure to get more accurate results? Is it possible to get accurate results, by which I mean that if I had the same measurement equipment that the labs have, then would I come up with similar enough results? Or are my DIY results so far off that they aren't comparable at all?
The second is the performance of my theater. If I make full measurements of my theater from different frames of reference, then can I get numbers that mean something in context? Perhaps I could compare my results to "expected" results and thus extrapolate what kind of effect flanking could have in the real world that's more accurate than just "5 STC points"? I could have numbers that answered what kind of difference a second door makes; what do window plugs do; how much will adding insulation in the attic matter; and so on. Overall frequency sweeps still matter as do simple dB C measurements, but if STC can come into play, then that's interesting, too.