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Discussion Starter #1
The way my family-room theater is situated, it's on the adjacent wall to the neighboring townhouse. I'd really like to be able to use my sub here, but I'm sure it would go straight through the floor to the adjoining house.


What's the cheapest way to isolate the sub from the structure of the house? That should be enough, right? It shouldn't travel well through the air, or am i still in for a world of hurt?


Thanks!

--Mike
 

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Isolating the sub from the floor may help somewhat, but I suspect the LF sound isolation is not that impressive. Depending on the wall type and thickness, you will probably just have some 20-30 dB sound reduction for the low frequencies where your sub operates.


If you still want to vibration isolate your sub from the floor (it's very cheap, so why not?), try to find some very flexible rubber or foam material to put under your sub. If it compresses more than 1/4" when you load it with the sub, the vibration isolation will be more than enough. You can vary the area to fit the requirement above. Note that the material still has to be elastic, i.e. not "collapsing" under the load.


Furthermore, if the sub is located close to a corner in the room, the vibration isolation will be more efficient. This will probably not be necessary if you are able to adhere to the advice above. A corner well away from the house separating wall would be advisable in this case.
 

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Discussion Starter #3
iceman, thanks for the reply.


a few things to clarify:


- how much compression is too much? how do you define "collapsing"? Do you mean that the sub goes all the way back to basically sitting on the floor?


- if it doesn't compress at least 1/4", are you saying it probably won't help to reduce the vibration (such as firm styrofoam which won't compress at all)?


- where's a good place to find stuff like this?


Just trying to get a more concrete picture in my mind of what you're talking about.

--Mike
 

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You are in a world of hurt.


The only way to keep the sub from vibrating thru the wall is to tear down the wall, stagger the studs, decoupling the walls - like the isolation sytem from Owens-Corning.


No matter wear the sub is, it will excite certain frequencies in the floor and vibrate them projecting the sound.


Remember, when you hear a sub from another, closed off room nearby, it is not actually the sub you are hearing but the vibrations of the wall elements dividing you and the sub.


I am dealing with this issue in my own house in that my home theater is to share a wall with the living room. The wall has been designed as decoulped so as to eliminate any sound transfer.


To keep the sound isolated from your neighbor, get rid of the sub (higher frequencies not as obnoxious) or play at lower levels.


Sorry.


Jeff
 

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Consider using tactile transducers in place of or in addition to your Sub.
 

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OK guys, you asked for it :):


1. If you want to be able to use the sub without disturbing your neighbors overly much, you have to improve your airborne sound isolation. In your case, this requires you to create a so called double wall. Building a new wall well on the inside of the older wall will be quite efficient - if you do it right. The longer the distance between the new and original wall and the higher the mass of the new wall, the higher the sound reduction will be. You may be able to get an additional 10-15 dB of LF reduction this way. Just staggering the studs in the original wall will not do much to improve LF sound isolation but will make MF and HF isolation significantly better.


2. Reducing structure-borne sound may also be a good idea after taking care of the airborne isolation. The ONLY way of doing this efficiently is mount the sub elastically according to my previous post. Spikes will not lead to any useful level of LF vibration isolation. The reason for recommending corner placement is that the mechanical impedance of the structure Zstruct is higher in the corners. This makes the ratio of Zstruct/Zlayer higher and thus the isolation more efficient. Increasing the sub's mass will further improve isolation.


3. A way of testing if the material under load is still linearly elastic is to first load it with say half the sub mass and noting the deflection. If the material deflects twice (or close to twice as much) as much when loaded with the sub, you are home free.


4. What you need to achieve with your elastic mounting of the sub is a resonance frequency at least an octave below the lowest frequency you are going to reproduce. Depending somewhat on the dynamic stiffness of the material you are using and the mechanical impedance of the floor, the recommended 1/4" will probably be enough to make this happen. A deflection significantly lower than 1/4" will make the resonance frequency too high and may in fact increase the floor vibration levels if you are unlucky!

Note that a stiffer material may be used if you just make it thick enough and/or with an area that is small enough.


Another positive side effect from the vibration isolation is that the sound of the sub will be improved, sometimes dramatically so as you will not be listening to the SQ of your floor boards :) anymore.


5. Since I am not based in the U.S., I am unfortunately not able to recommend a source for this stuff. Perhaps some of the other forum members are able to help you here. Remember, you will not need any fancy high-loss space-age material to do this, plain old foam or rubber will do nicely.
 
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