Re: Lets plan a theater space
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Joined: Mar 2014
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OP
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The ceiling backer boxes are in. They were a pain to get into the front of the room just in front of the LVL beam. Some brainiac thought it would be a good idea to spray foam that entire area.... I got to spend some quality time scraping away with a putty knife. Fred Style. The other issue that made it difficult was the floor joist are 7 5/8" and the boxes are 6" deep. Not a big deal until fiberglass batts are crammed behind them. Pretty tight fit, but doable. I used utility banding as a temp support until the channel is up. Only lost one knuckle on the screws poking from above. The result x 4
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Re: Lets plan a theater space
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Joined: Dec 2007
Posts: 7,786
axiomite
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axiomite
Joined: Dec 2007
Posts: 7,786 |
.... I got to spend some quality time scraping away with a putty knife. Fred Style. ... Hey that's not funny. Well, OK, maybe a little bit.
Fred
------- Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!
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Re: Lets plan a theater space
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Joined: Sep 2004
Posts: 5,422
axiomite
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axiomite
Joined: Sep 2004
Posts: 5,422 |
So you crammed insulation between the boxes and the bottom of the subfloor?
Good for stopping airflow from seeping in through any gaps, not so good for sound proofing where you want a gap. Just trying to help now before you fire up speakers that might as well be directly mounted to the subflooring above.
Farewell - June 4, 2020
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Re: Lets plan a theater space
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Joined: Mar 2014
Posts: 1,593 Likes: 1
connoisseur
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OP
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Yes, I put insulation up first and pressed the backer boxes up into the cavity. They are pretty much spring loaded in there and I had to put the screws in on an angle to suck them up higher.
I was thinking as I was doing it the pros and cons of keeping them that way. Looks like even though the speaker will never be in physical contact with the box the sound will cause vibration through the box--->insulation--->floor. I will have to revisit these and remove the insulation.
So I should put nothing behind/beside the boxes in the gap? I wish I made the boxes shallower, but that really limits speaker choices.
When it comes to soundproofing Seems like: More is not more. Less is not more. Just right is more.
Thanks Nick! That would've sucked big time.
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Re: Lets plan a theater space
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Joined: Sep 2004
Posts: 5,422
axiomite
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axiomite
Joined: Sep 2004
Posts: 5,422 |
Yeah, that is the benefit of pictures and frequent updates. Fluffy insulation compressed into a little more than 1.5" space basically becomes solid.
Soundproofing is some strange stuff. I spent so much time reading and asking questions about what to do, what not to do, what I cant do (because of space limitations, financial limitations, etc). I am not an expert, but I've got a few things hammered into my head from my own design mistakes and I was happy later on to have had someone jump in and stop me before drywall got hung.
Farewell - June 4, 2020
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Re: Lets plan a theater space
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Joined: Mar 2014
Posts: 1,593 Likes: 1
connoisseur
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OP
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Ok, updates and wierd results to share. Contrary to our thoughts. I set up a RTA reading in the kitchen directly above one of the ATMOS locations. First I measured before removing the insulation. I didn't take a screen cap but am kicking myself now. To test I wrapped a knucle against the top of the box as it hung in the ceiling. I went ahead and removed the backing insulation and thought all was well... Until I repeated the measurement. Here is what it read. The RTA ran as I went downstairs and wrapped on the box and came back. A worst case scenario test. The peak values were stored as the blue lines in each octave. It peaked at about 55db at 200hz. Ignore the reading in the right top corner. It is the RTA ambient room db in the kitchen after the peak reading. Insulation Removed I swore the values were worse with the insulation removed so for the heck of it I put it back and resecured the box for another measurement. I wrapped harder than before just to be sure.... Insulation Replaced The peak was reduced to 45db at 200hz. A 10db drop in the world of sound isolation is pretty significant. Anyway, it seems the reason this wild result occured was how poorly 1/2" MDF acts as a speaker cabinet. The insulation was actually acting as a damping agent for the rear panel. With it removed it rang like a bell. What I can't decide is if the lower frequency readings reduced with insulation removed vs replaced can be trusted. It was a pretty makeshift test and for all I know a truck could have driven by while I was downstairs to skew the result. I'm glad Nick pointed this out so I could discover this completely by accident.
Last edited by Serenity_Now; 01/20/15 12:19 AM.
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Re: Lets plan a theater space
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Joined: Mar 2014
Posts: 1,593 Likes: 1
connoisseur
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OP
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Just repeated the "with insulation" measurement with a lovely but reluctant assistant (my wife) and confirmed that insulation reduces higher frequency box resonances at the expense of coulping lower frequencies to the floor.
What to do....
Given that these are impact tests, and far more energy is being exerted than a speaker would create in the back panel, I'm inclined to leave the insulation as is.
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Re: Lets plan a theater space
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Joined: Sep 2004
Posts: 5,422
axiomite
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axiomite
Joined: Sep 2004
Posts: 5,422 |
Yeah, too bad all frequencies weren't easily contained using the same methods. Also keep in mind that knocking on a speaker cabinet box isn't exactly real world either, it would take systematic frequencies played through the installed speaker and measured upstairs to get the actual best effect, thus the reason that I trust the experts and people from multiple trusted companies that say that fluffy insulation is good, packed insulation is bad (for in wall/ceiling absorption) and you want to disconnect as much as possible from inside the room to outside.
That is where the gap comes in. My guess is that you are compressing the insulation just the right amount to impact certain frequencies only instead of having it fluffy and being able to grab a wider frequency range.
Farewell - June 4, 2020
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Re: Lets plan a theater space
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Joined: Mar 2014
Posts: 1,593 Likes: 1
connoisseur
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OP
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Well, given that I respect your opinion and research so much FINE we'll do it your way! ::stomps away like a toddler:: I think what I'll do is remove the boxes and add a layer of MDF to the back with GE Silicone II sandwiched between. This should make me happy with the ringing problem and increase mass. Then I'll get some thinner insulation to line the joist space directly above the speaker. I can get 1" thick stuff I think. I'll add whatever is left over to the inside of the cabinets on the down facing side opposite the rear panel. I agree the knuckle tests arent telling full the story too.
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Re: Lets plan a theater space
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Joined: Sep 2004
Posts: 5,422
axiomite
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axiomite
Joined: Sep 2004
Posts: 5,422 |
You don't happen to have green glue to put between the box and the extra layer? It would help a little better than the silicone , but for the back of a set of speaker boxes, I don't know if there is THAT much benefit to worry about it if you don't have GreenGlue.
Great call on the GE Silicone II in general by the way. The clear is a really good product to use for sealing up any gaps in a theater.
Farewell - June 4, 2020
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