Ultra Low Frequency and how to stop it? Modifying floors

do you really need all that ULF ..to enjoy ur HT? its seems like overkill to me!!!!!!!!!!!!!!

Sure he does, that's not the point. It takes some serious capability to experience low distortion, full LFE bandwith (3-120hz) listening at reference level.

I've got 4x18's, and 4x15's myself, in addition to some highly capable mains.

Can you enjoy it with less, sure.

check out the last build bigmouthinva did http://www.avsforum.com/t/1437336/fall-frenzy-bigmouthindc-hits-the-road-again-destination-columbus-indiana

there is huge sub in that one and from if i remember correctly it is a room in room design with four layers drywall and GG to contain the sound.

Hi Fatshaft,

Unfortunately you've discovered first hand how difficult it is to contain low frequencies.

It is my understanding that the best way to stop sound transmission that low is to create a decoupled system and load it with damped mass. You've already got the decoupling, so adding a third (or even fourth) layer of drywall with Green Glue to the system would help to lessen the escaping energy. One thing to pay attention to if you decide to do this is your clip spacing and whether it can accommodate more mass.

I know that there are some products that go down on the subfloor, or you could add another layer of plywood with Green Glue to the subfloor, but I believe these methods are designed more to stop impact noises from getting into the theater than preventing low frequencies from escaping. You'd get better results from loading your decoupled system with more mass.

You might want to give Ted a call and see if he has any other ideas for you.

The room looks great by the way! You've got a wonderful space.

The bad news is, because your HT in your house, you will have to rip down everything and redo.

It isn't decoupled enough, nor has enough mass to stop the quad 21's with 8400watts behind it.
Is it a room-in-room design? Probably not I'm assuming...

What you need to do is make the walls out of ciderblock (not touching anything but the foundation) for all 4 walls, and then either make the ceiling out of cement too or at least out of solid GG'ed 2x4's with a layer of cement stepping stones on top.
You'd have to check with an architect to ensure the wood could support such weight.
The top 2 materials for adding mass is: cement or multiple sheets of aluminium; because it's 170-200lbs per cubic foot!
Sand, glass or roofing-shingles may also work, if your in a pinch.
Or in a real pinch, solid GG'ed 2x8's might also work.

You want it a solid 8 inches of pure-mass, with a 1 or 2 inch air gap for decoupling.

Ensuring that none of this is coupled to the 2nd floor, at all.

Long story short, you'll have to sacrifice about 10 inches of ceiling height to get enough mass in there.

You need a wall Fs of ~3hz or lower to damp out the ULF, whatever that works out to be mass-wise...

That's about all you CAN do, short of going with an external structure.
Edited by BassThatHz - 12/22/12 at 8:51pm

If you're really dealing with ULF - which you probably are - the amount of mass required to damp those waves is entirely impractical. This came up back in November when a thread starter said basically, "No holds barred, what does it take?" He got good technical and realistic responses from folks who know. Check out the conversation here.

Because they are cancelling out some of the bass in the vertical direction.
In theory, you could buy a DCX and 4 low-profile subs, mounting them directly to the ceiling in the 4 corners above your regular subs, and then use the DCX to add the 4 discrete vertical time-delays and invert the signal 180 degrees out of phase, and that should cancel out a tonne of the bass from the above floor.

Say 4 of these:
http://www.parts-express.com/pe/showdetl.cfm?partnumber=297-292
with 4 of these:
http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-802

You could jam them in four 12x12x4 inch boxes.

All total it would be probably around $1000.
I've heard of people doing something similar in other scenarios, but never tried it myself...