# Damping vibrations through ceiling



## Zeitgeist (Apr 4, 2009)

My home theater room is in the basement, it's a 10x20 room with a drop ceiling.

The other day I was doing some testing w/Avatar (yes, the loud scene where the mother tree falls) - and I had the volume up. I have subs that are calibrated (and EQd with BFDs).

The floor above was vibrating - the low frequencies were hitting the ceiling and passing through to the floor. Has anyone found a solution that they like for trying to deaden the ceiling itself? 

I've thought about stuffing with pink fiberglass - and using rockwool/OC705(or some other accoustic treatment - but that gets expensive).

My understanding is that most insulation grade fiberglass - is really only effective at absorbing higher frequencies. I'm trying to see if there is something that I can do - since rebuilding the room (ala room within a room type construction) isn't a possibility.


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## bpape (Sep 14, 2006)

What is it you're trying to accomplish? If you're trying to stop sound from transferring up through the floor insulation won't help (though it is recommended to stop cavity resonances.

How fiberglass absorbs with direct waves vs how it acts between a hard sub-floor and ceiling is completely different as there would be zero high frequency absorption as those waves will be reflected by the ceiling. It will, however, damp the cavity and allow it to act like an absorber as opposed to a resonating drum.

Bryan


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## Zeitgeist (Apr 4, 2009)

bpape said:


> What is it you're trying to accomplish? If you're trying to stop sound from transferring up through the floor insulation won't help (though it is recommended to stop cavity resonances.
> 
> How fiberglass absorbs with direct waves vs how it acts between a hard sub-floor and ceiling is completely different as there would be zero high frequency absorption as those waves will be reflected by the ceiling. It will, however, damp the cavity and allow it to act like an absorber as opposed to a resonating drum.
> 
> Bryan


Sorry - I wasn't very articulate about what I wanted to accomplish.

I really would like to to cut down on the vibrations on the floor above (and prevent the "resonating drum" effect). I'm not concerned about the actual noise transmission to the room above.

So, from the sounds of it, stuffing the floor joists above the dropped ceiling - would mitigate the drum effect a little bit?

Thanks for your advice.


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## Ted White (May 4, 2009)

The insulation will do little in combination with the dropped ceiling as Bryan said. The dropped ceiling lacks mass. A drywall ceiling has a lot of great mass.

The dropped ceiling is also poorly sealed.


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## bpape (Sep 14, 2006)

Ah. Drop ceiling is a different story altogether. The bass will go right through that like it's not even there. Insulation between drop and the subfloor will help with overall broadband bass control but there's no cavity to resonate. The best thing to do would be adding a layer of 3/4" MDF to the underside of the floor above with Green Glue between layers. 

If that's not feasible, cut drywall pieces to sit on top of each ceiling tile to add some mass. You'll need to beef up the hangars on the ceiling grid though.

Bryan


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## Zeitgeist (Apr 4, 2009)

Sorry - I thought I mentioned that it was a dropped ceiling in the first post.

I guess I thought that the space between the drop ceiling and the floor above would act like a cavity - but that makes sense. Little mass and leaky.

So, if I could totally rebuild the ceiling (without isolating the ceiling from the floor joists.. I don't have enough height) ... what would be the best practice?

Glue MDF to the sub floor - and install drywall?

Last time I talked about installing drywall - I was talked out of it by people that kept talking about the acoustical benefits of a drop ceiling.


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## Ted White (May 4, 2009)

You can recess the clips as an option to preserve height


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## bpape (Sep 14, 2006)

I suspect that you'd actually lose LESS height with channel and drywall rather than the space it takes to drop a ceiling grid down.

Bryan


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## Zeitgeist (Apr 4, 2009)

Ted White said:


> You can recess the clips as an option to preserve height


Cool. Thanks for that suggestion - I totally forgot about using clips.. I'm familiar with RSIC clips - it looks like whisper clips are similar.

I had not seen people use clips for ceilings before - but that makes sense.


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## Zeitgeist (Apr 4, 2009)

bpape said:


> I suspect that you'd actually lose LESS height with channel and drywall rather than the space it takes to drop a ceiling grid down.
> 
> Bryan


It would. Whomever installed the drop ceiling only installed with about 2 in of clearance - which makes it a pain to change/move panels.

How would MDF on the subfloor and drywall screwed to the joists (like a traditional ceiling) compare to just using the clips w/drywall?

My only concern is it seems like when I look at calculators for acoustical clips - it seems like it ends up being a few hundred dollars - even for just a 10x20 room.


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## bpape (Sep 14, 2006)

Doing those things instead of clips will likely not cost a lot less but will still perform pretty well. I'm assuming that the insulation is a null cost as it should be done in either case. 

By the time you figure 2 layers of drywall and the Green Glue to go between layers, it's probably a wash for 1 layer of drywall, 1 layer of MDF, and Green Glue between MDF and subfloor. 

Bryan


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## Zeitgeist (Apr 4, 2009)

Thanks for all the comments.

You've given me a lot of food for thought if the time/money becomes available to dramatically change the ceiling. 

With a newborn due in a couple months - sounds like I'll just need to turn it down for the time being.


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## dmm (Jul 13, 2006)

I used green glue with great success for my basement hometheater with a drop ceiling. I used the green glue on the FIRST FLOOR floor above the hometheater's drop ceiling. 

I still get sound that flanks thru the AC duct work. But the sound leaking out of the basement to the floor above is much improved.

description and measurements here:

http://www.avsforum.com/avs-vb/showthread.php?t=1136101


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## Ted White (May 4, 2009)

If you have a lot of mass, single leaf damping can be quite effective.


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## patchesj (Jun 17, 2009)

You could always use staggered joists to hang the new drywall ceiling. Probably cheaper than clips. As long as you don't have HVAC ducts, plumbing, etc taking up space between the existing joists.


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## Ted White (May 4, 2009)

Sure. This Floating Joist system can be seen 1/3 of the way into this article:http://www.soundproofingcompany.com/library/articles/room_within_a_room/

The risk is using standard SPF lumber, which can warp badly. You can also use the much more stable I-Joists, but that's getting expensive. Clips and channel is less.


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