bbb63
New Member
Posts: 2
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Post by bbb63 on Jun 15, 2023 17:41:16 GMT
Hi, everyone. Building our 2nd Home Theater and are in need of help to reduce (not totally block) sound that will exit a room which won't have a back wall. (Basement was finished when we bought the house, and existing HVAC in the area that will become the Theater is not adequate to make the room comfortable if we built a physical rear wall). If I set our AVR to 65 DB, sound is barely audible at our property line. Can hear a bit more clearly out at the property line at 70 DB. No need to go beyond 70 as the room is small (14W x 15D in front of stage). My goal is to make it so that 70 is not audible or is barely audible at the property line. Complicating things is that there is a wall of windows (9' wide doorwall and multiple 4' or so wide windows) that is just outside the theater, on the wall that would be perpendicular to the back wall - if we were to have one.
We've been looking at using heavy (22 oz) Velour curtains at 100% fullness and box pleats from RoseBrand as a replacement for the back wall (so, 14'W and would go where the back wall otherwise would be). The fabric was lab tested and has decent Absorption Coefficients, as shown below from the acoustic report. We like the flexibility of being able to open the curtains slightly if the room were to get stuffy when in use. I realize that would create a momentary hole in any otherwise closed off sound barrier, but hopefully we could open them slightly but "enough" to keep the room comfortable while still resulting in "some" sound reduction from the part of the "wall" still closed off by the curtain. I saw an old post from Ethan that said curtains pretty much do "nothing" for keeping sound contained. But I'm also unclear / confused by the Absorption Coefficient data given for the curtains (below), which would seem to imply that the curtain fabric absorbs (and therefore doesn't pass through at the same volume) a good amount of sound energy - at least at frequencies above 160 HZ or so. I also realize Absorption <> STC, but would "think" Absorption does at least impact STC to some extent - so am unclear on the "curtains do nothing" for sound control that I thought I remembered seeing..although I do realize that to be the case for *most* curtains. But these are lab tested, reasonably heavy velour with apparently decent Absorption Coefficients, so not sure on what results we may get if we purchased and installed them.
![]()   Would any of you have an opinion if, given the Absorption Coefficients shown below, this curtain fabric would *reduce* (vs totally block) sound to any extent? And if so, by roughly how much? As mentioned above, my overall goal is to get the sound levels outside the home to be reduced to a point we're not bothering any neighbors when running the Theater at 70 DB or so. And since we're in decent shape on not bothering anyone at 65 DB, I don't think I need "much" reduction go get to our overall goal of being able to comfortably run things at 70 DB.
Appreciate any and all help!
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Post by rock on Jun 16, 2023 1:07:44 GMT
Hi bb,
Welcome to the form.
In general, acoustic treatment of the inside of a room and sound transmission attenuation ("sound proofing") between rooms or the inside to the outside are two completely different subjects.
Sound transmission attenuation techniques should be done in the planning and construction phase and not as an afterthought.
Even though "sound proof" and "sound proofing" are misnomers, it is a term you will find often used. I suggest you search threads here with "sound proof" etc. to see what others here have asked and tried.
One thing to understand is there is progressively more energy in low frequencies than high frequencies with the same apparent or perceived volume (your chart is an example of this) so standard home construction will work fine for blocking conversation from room to room but when you play music with bass content or a movie with explosive sound effects, the low end will go right through the walls not to mention poorly fitted doors, gaps in drywall near the floor which is hidden behind baseboard and a multitude of other things.
You can knock the sound level down a bit with room sound absorption treatment but Ethan is right, it's not "soundproofing".
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Post by Hexspa on Jun 16, 2023 15:34:20 GMT
All I know about sound isolation is that even small gaps reduce a barrier's acoustic performance significantly. For example, small gaps around a door can reduce its effect on blocking sound by, say, 25%. I don't know the exact ratios of gap-to-performance decrease but it's surprising how little will ruin the effect.
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Post by rock on Jun 17, 2023 18:40:53 GMT
That's right Hex, Yes, there is a significant loss in even a really thick, heavy wall with a small hole in it. I can't remember exactly how much but it's almost like if you didn't have the wall there! I just did a quick google search for "sound isolation mistakes" and found this stuff: www.soundproofcow.com/common-soundproofing-mistakes/ and I found this on youtube: www.youtube.com/watch?v=Et7xva8KZN0In Rod Gervais' book, he talks about caulking all drywall seams between multi-layer walls warning if this is not done, the room performance will be compromised. Additionally, he suggests if the work is being done by a contractor that he leave each layer open for inspection before the next layer is installed. He point's out general contractors don't necessarily understand acoustic isolation and may skip vital steps thinking it won't make any difference! |
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Post by Hexspa on Jun 18, 2023 13:55:27 GMT
thinking it won't make any difference! Little do they know  |
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bbb63
New Member
Posts: 2
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Post by bbb63 on Jun 18, 2023 15:52:00 GMT
Hey, everyone. Appreciate the replies. I'm definitely familiar with common soundproofing techniques having built a RSIC-clip, Double Drywall/Green Glue, quiet putty, etc Theater at our old house. I intentionally didn't go down that road for this second Theater for several reasons including having very limited space to work with here at the new house - hence, no room for RSIC clips, DD, GG, etc. But we're also in a much different situation on a 1.5 acre piece of property and nearest neighbor being a lot further away than at the old house.
So, that said..I'm indeed familiar with the difference between what I did at the old Theater and what we're limited to doing on this one.
What I'm still unclear on, though, is the net effect on sound transmission from a material that has a decent, lab-tested Sound Absorption (not STC) rating. It would "seem" that a material of this type would indeed reduce sound "some" - albeit, particularly not as much at 100 Hz and below. But even at 160 Hz, the material appears to absorb (not block..so what's the real difference in those two different terms?) 50+% of the sound energy that hits the material. And it gets a lot better above 160 HZ. So, logically, it would seem to me that would indeed achieve what I'm trying to do - reduce sound "some", so I can run the system at 70 DB or so and not bother my neighbors. (As I mentioned above, I can BARELY hear the system at 65 DB at our property line..it's kind of like a transistor radio in the background and only if I listen hard. 70 DB is a little more audible. So, if I reduce sound "some", I suspect that I won't hear 70 DB at all at the property line).
Ultimately, my question comes down to..what effect on sound transmission (say, to an adjacent room) does sound ABSORPTION of a material have? Not being an acoustics expert, I'm not entirely clear, but it would seem absorption would indeed have "some" effect on transmission..
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Post by Hexspa on Jun 19, 2023 18:18:10 GMT
This is not my area of expertise but sound will go around things at low frequencies and bounce until it finds a way "around" your barrier. Plus any resonance the walls have will transfer through the structure to the other side and cause sound. I guess the absorbers will only transduce the sound that hits it whereas construction will prevent the energy from being transferred outside. Anything your absorption doesn't catch will be reflected or transferred into the structure and ultimately passed on to the outside. You're reducing total acoustic energy in the room but the minute it hits a boundary, that's where construction matters. That's my guess.
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Post by rock on Jun 20, 2023 22:28:09 GMT
I'm no expert either but yes, I agree with Hexspa.
Here's another way to think about it: When you add absorption in the room, how much is actually absorbed and how much is still there? This is easy to measure with REW. Most of us have done this but we're usually looking at details like peaks, nulls and modal ringing and not the overall/average SPL ,which doesn't seem to change very much. Maybe you'll loose 6dB in the low end maybe 12???
So yeah bbb63, I think you're right that you'll get some transmission attenuation... but how much? That's the question! You could measure "before" and "after" to determine how much... but that would mean buying all those curtains and installing them etc. I wish I could tell you how much but if you ask around, I'll bet nobody can tell you because it's not enough to make enough difference and maybe nobody bothered to measure it. Sorry, my best guess.
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Post by Hexspa on Jun 21, 2023 17:47:45 GMT
Energy Decay Curve (Schroeder's Integral) shows how much total energy is in the room at a given time. This is distinct from the Energy Time Curve which is the Impulse Response Envelope showing the discrete levels of individual reflections.
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