How do I effectively isolate induced vibration from a sub on wooden flooring ?

marcstang

Well-known Member
As you can all tell by my many topics with stupid questions, this is the first time I owned a more powerful sub, and thus never had to set one up properly. :suicide:

I currently use the supplied plastic feet on my xls200 as the spikes would damage the wood flooring. I however noticed that this induces vibration into the floor at certain frequencies. Not wanting to upset the neighbours to much (I live in a flat unfortunately) I was looking for another effective way to isolate the sub.

I was looking at the superspikes which can be obtained from the BK Electronics website. Has anyone got any experience with these, or is there another way I could solve this problem ?

It also needs to be an aesthetically pleasing solution to keep the wife quiet :D .

Any help or suggestions would be greatly appreciated.

Marc
 

hufartd

Active Member
A small blob of blu tac under each foot should do it.
or use the spikes sat on a 5p to protect the floor.
 

Badger0-0

Member
One of the lads on here managed to isolate his SVS cylinder with a paving slab or similar.

Either that, or get some form of EQ to kill the booms that are probably causing the problem
 
K

kstrain

Guest
I currently use the supplied plastic feet on my xls200 as the spikes would damage the wood flooring. I however noticed that this induces vibration into the floor at certain frequencies. Not wanting to upset the neighbours to much (I live in a flat unfortunately) I was looking for another effective way to isolate the sub.

Marc
first some "theory"

I'm often a bit bemused by seeing the words "isolate" and "spikes" in the same sentence. Spikes make a firm connection between the sub and the floor (right?) and therefore they couple and cannot isolate. With that moan out of the way :)

Isolation of mechanical vibration requires compliance. The most difficult direction in which to isolate is vertical, as the feet have to be solid enough to hold the sub (and solid is not compliant).

The compliance (bounciness) of the feet will create a resonance, and you want that to be around 10 Hz, not higher, to avoid it making the situation worse, and to make the isolation effective in the 20-100 Hz range where I guess you have your problem.

To reach 10 Hz the feet have to be so soft that they compress by nearly 3mm, which means rubber feet of considerable thickness and not too much area. Rubber is not a perfect spring and needs to be at least 15mm thick to work well when compressed by 3mm (hard rubber like butyl will work with relatively tall thin feet, soft rubber like sorbothane with wider feet).

More towards application:-

Spikes don't compress much, and what they do is ensure there is no resonance in the sub band (although I really doubt that there is with the plastic feet fitted to my monolith on a hard floor anyway). Unless, of course they are sitting on a carpet or other soft floor covering, in which case there could well be a resonance just in the middle of the band, and that could be your problem (or not, see below).
Use of a platform will spread the load over a bigger area and move the resonace to higher frequency, spikes will move it to much higher frequency, and blutac can be used to damp resonances in some cases (at least a bit). None of these are isolation but could (possibly, if you are lucky) help.

Unfortunately life is not so simple, and if your problem is at one of the main resonances of the suspended floor (very likely) the sound itself could easily be the main route by which it is excited (that depends on very many factors). Suspended floors can have resonances anywhere in the sub band depending on size and construction. At those resonances the sound waves, especially if there is a coincidence with a room mode, can very easily drive the floor. "Isolating" the sub would make no difference in that case.

So what do I recommend?

If you can figure out what is happening (by playing a test tone that hits the main resonance) you might be able to figure out what is vibrating (this might require some negotiation with your neighbour). You could, for example, sit the sub on a thin cushion or some other temporary solution, and see how much of a difference it makes, and if the vibration is large enough to feel, you can walk around the room to try to guage whether the coupling is through the floor or the air (not easy, sometimes possible).

Cures? While there is a chance that spikes or isolation might work, I'd not bet on it. One option (probably not acceptable) would be to move the sub to where it excites the worst modes minimally (chances are it won't be good for sound or convenience).

So that leaves EQ, as already suggested - it is the only certain cure. Just bung a notch in where the worst resonance is, chances are it can be quite narrow and it is as likely to do more good than harm to the sound quality.
There are usually BFDs on Ebay (like today) and the prices can be OK.
For what you want to achieve setting up is very easy (you need a couple of cables though for the 1/4" jacks). Play test tones or sweeps to find the problem frequency, estimate the bandwidth (probably not terribly broad - probably a few/20 octaves at most) and dial down the gain step by step till you are happy.

Then of course you can later do the whole EQ thing.

Good luck either way.

Ken
 

binbag

Active Member
I've used homemade (squash balls and marble slabs), the Killvibe (used to be available as a forum powerbuy) and a Gramma for isolation duties on my suspended wooden floor.

I found the best sounding one in conjunction with an XLS200DF was the Killvibe (Its like a 6lb baking sheet!) However I suspect that the gramma had better isolation properties but it was too flat a sound in the room for me.
 

AngelEyes

Distinguished Member
I'm often a bit bemused by seeing the words "isolate" and "spikes" in the same sentence. Spikes make a firm connection between the sub and the floor (right?) and therefore they couple and cannot isolate. With that moan out of the way :)
So glad you saved me the trouble :D

Unfortunately life is not so simple, and if your problem is at one of the main resonances of the suspended floor (very likely) the sound itself could easily be the main route by which it is excited (that depends on very many factors). Suspended floors can have resonances anywhere in the sub band depending on size and construction. At those resonances the sound waves, especially if there is a coincidence with a room mode, can very easily drive the floor. "Isolating" the sub would make no difference in that case.
My thoughts exactly. I also concur with the suggestions on EQing the room to alleviate the problem.

To make isolating the frequency in question easier you could use REW (Room EQ Wizard) which allows you to play a frequency test tone and then use the mouse to drag it up and down the frequency range. This should very quickly and accurately demonstrate where the problem lies.

BFD is short for Behringer Feedback Destroyer a piece of equipment aimed at the Pro market which just happens to have a good Paremetric Equaliser, 'ideal' for domestic subwoofer EQ tasks. :smashin:

Unfortunately Behringer have stopped making this so eBay or the forum classifieds seem to be the only places to find them.

Adam
 

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