Subwoofer Isolation

What do you guys recommend using to isolate my sub. Its a big ol' bird so bear that in mind. I took a punt at some rubber (or Sorbothane to be precise) feet from eBay which helped isolate it a far bit, only for the bottom end to sound far more ponderous and slow. I'm still using them as they are the lesser of 2 evils but I'm sure there is a better solution......thats where u guys come in. Sub is an M&K MX150, if that bears any relevance??? Thanks, Ryan.

 

Do you really want to isolate it? It might be more fun when it has good connection to shake the floor!

Anyway I would suggest a large lump of granite or marble then some spikes or cones onto that. Rubber feet will make it sound less accurate, punchy, etc, because when the woofer makes a large moment it is pushing against the sub, if the sub is not fixed down well (like being on soft rubber feet) then the sub will move rather than the woofer!

 

I too would be inclined to go high-mass for the sub.

 

I second the suggestion of granite, but lose the spikes/cones - completely worthless and negate many of the positive effects granite brings.

 

The cheaper option is to stick the sub on a paving slab; won't be as effective as granite (being less dense) but a step the right way. Actually, I realise in saying that I'm assuming your sub is on a suspended wooden floor, which it may not be?

 

Necessary to isolate the sub if it's sitting on carpeted floor?

 

Don't you think soft rubber feet on top of a granite slab kind of un-does the whole point?

I suppose you don't need cones, but still get rid of the rubber feet.. maybe replace them with blue-tak which will hold the sub still.

 

Mine sits on a paving slab which is painted black with Plastikote. I'm still using the spikes. The slab gives it a lot more impact than it had when it was on the carpeted wooden floor.

 

Mine sits on a painted paving slab (grey is soooooo 1980's) with 4 whopping lumps blu tack between slab and sub

 

If you can afford it a set of three Stillpoints, you will be amazed at the difference in control and speed of the bass. They are the best we have ever tried on a subwoofer and we have a beast of a sub that will eat anything by REL and M&J for starters, leaving anything else as main course and desert!
It has never sounded better than when it was on Stillpoints with the Risers (it's purely on it's OEM spikes at the moment).
Check out some of the Studio Spares type outlets as well that sell isolation products for the studio application.

 

Sounds like a plan! Next question - Where do I get the granite from?? Are we talking a few of the Argos jobbies? Also what stops the sound just transfering straight down through the granite and to the floor, hence ending up at square 1? Does sound not travel through granite? So let me get this straight: Granite/Paving slab, straight on wooden floor (nothing underneath?), with sub sat on top of it using 4 dollops of bluetack. I think even I could get this one right. Issac what did you mean by "High Mass"?

 

Yes. Just sit the sub directly on the granite...

 

I'm presuming, f'ckin' heavy and f'ckin' dense. Also granite has a fairly random molecular structure, which minimises the transferral of vibration.

 

I think most people here have their slab on top of carpet, if you put it on wood it could damage it so I would suggest more blu-tak under the slab if you are putting it directly onto a wooden floor. Because the granite has a large footprint compared to spikes or feet it will spread the weight and the carpet should actually help isolate it from the floor.

High mass as in the huge piece of granite. It's so heavy the sub can't move it much.

 

Not dismissing the subjective experience but how does using a granite slab underneath a sub isolate it from the floor? Where is the energy lost (or converted)?

Also I'm not sure adding mass would reduce movement (if we consider movement as enclosure vibration) since it's impossible to make anything infinitely stiff in respect of reaction to the opposing motion of the sub driver. Shift the resonant frequency of the 'structure' higher by all means which may have some useful effect.

I'd suggest the type of foam used to build drum risers in recording studios ('Platfoam' available for about a tenner a metre) for isolation PB.

I don't use a sub tho' so it's probably best not to listen to me!

 

My take...

Sound transfer from one medium to another depends on acoustic impedence, with less being transmitted across large mismatches (like electrical signals and electrical impedence mismatches). For plane waves the acoustic impedence of a material is the product of its density and the speed of sound propagation within it. Having a piece of granite on a carpet, or a suspended wooden floor, offers a significant impedence mismatch and so reduces directly coupled sound entering the floor. Note for this argument the total mass doesn't matter, it's more to do with density.

The large mass argument is I assume more to do with it's inertia giving a stable base for the sub?

On suspended wooden floors I think the granite/paving slab idea is worth it (I've used it), but for those with solid floors I'd be inclined to just use spikes to couple directly to the floor. I've never lived anywhere I could try the second route though.

 

Good explanation!

Having the sub coupled to a high mass as far as I can see is to make the sub itself harder for the woofer to displace and thus more of the magnate/coil assembly's energy is transferred into the woofer directly moving the air. With the sub not being on any 'sprung' support such as rubber feet, and being harder to move due to its effective weight, the woofer should have a sharper transient attack.

 

Sound transfer based on acoustic impedance mismatch relative to respective density and speed of propagation?

The largest mismatch I can think of in this respect would be air and water. Yet if I immerse myself in the middle of a lake I can still hear clearly (sufficient to determine the nature of the sound) sound waves that have penetrated the water from the air above and are propagating through it.

I'd recommend trying this by all means if tomorrow is as hot as today as been!

The mismatch in terms of density and speed of propagation between two solids (the sub feet and granite platform) are less so than the mismatch between a gas and a liquid - as with the example given above.

This doesn't sound particularly effective to me in terms of isolation or preventing the passage of energy from one medium to another. Sounds like hi-fi blurb (but of course could be subjectively effective for some other possibly unrelated reason).

Irrespective of mass every action has an equal and opposite reaction. Thus all that can be done by adding mass is to shift the resonant frequency of this counter-action energy upwards. Perhaps smaller more frequent movements of the sub enclosure (higher resonant freq) are more preferable to larger less frequent movements resulting in less physical displacement of the cone away from it's stationary central axis.

 

I'd suggest one of these:



They were doing them for £55 over at www.avtalk.co.uk on a powerbuy - not sure if the deal is still on.

Matt.

 

Well granite/air would be bigger...

Good example. Surely you'd admit the sound level is reduced though, which is all I was suggesting above.

The significant mismatch is between the granite and carpet under it, or the wooden floor. Yes you'd get a bigger mismatch going granite/air, so an air platform as I use specifically for this reason under my speakers takes things a step further.

FWIW the basic physics I posted earlier is not something I've ever come across mentioned in any "HiFi blurb", although I'll grant you how effective this approach is in terms of improving/changing sound quality is up for debate.

I think you may be onto something here.