paving slabs under speakers

they look hideous to me - goto a garden centre and get some slate slabs, they're over an inch think and cost me 6.49 each...

you can catch glimpses of them here -
http://www.flickr.com/photos/weardaleone/sets/72157594557490121/

 

Hi, Couldn't agree more, and about F=ma, it is a good place to start though.

Actually B&Q do some 1" thick x 2'x1' slate slabs that weigh plenty for about £5 a go and dont look too bad if you oil them. Cheap is always better in my book
Sand boxes are another good base but if you have a cat can get a bit messy.Speaking of cats....
I'm always of the opinion there's always more than one way to skin a cat and unfortunately there's even more ways to f*** things up.
F

 

A while ago, a calculation of loudspeaker cabinet movement magnitude was done both on the forums and in one of the UK mags I believe. IIRC, an 8" woofer vibrating at 50 Hz with a 0.5 cm cone displacement in a 20 kg cabinet will move the cabinet 6x10^-6 m, (6 millionths of a metre). The cabinet is assumed to be free floating in air, attached to nothing.

The conclusion was that the resulting movement is small enough to be totally inconsequential. You could however suggest that spikes could improve things ever so little but spikes have by their very nature a high q resonance. A high Q resonance will multiply the movements until they become quite noticeable. That won't be a problem with a wobbly air support.

 

Depends on the energy input needed to move this notional driver surely? ie high efficiency less input power, low ie usually higher moving mass, considerably more. Also the free space notion conveniently removes the rotational momentum caused by the driver movement (about the axis ie its fixing point to earth).
Anyway in the interests of the discussion.... this 'movement' is/can be larger than that of a nominal dome tweeter reproducing the subtleties of hf content in music programme, so go figure.

 

How does all this affect a speaker such as the KEF R107 which has two 10" bass drivers joined with a rod firing up dpwn within a coupled cavity slightly decoupled from the main cab, where only the midrange fires forward, this sitting slightly decoupled within its own head assembly which sits on a spigot atop the bass cabinet?

And would this sort of speaker driver arrangement still benefit from a design such as Townsend's Seismic speaker platform, which as far as I can tell only decouples a speaker via up and down dampening?
And in which way is this type of decoupling beneficial?

 

I now have 2 slate slabs under the speakers. It seems to have tightened things up although am wondering whether TOO much is possible? The resulting sound is very clean but almost too clean.
I also ended up with a cut down wine cork under each corner of the slab and this seems to help. Any comments appreciated!

 

By the way I started this thread and have enjoyed reading the comments - some more illuminating than others.

 

I suppose the more slabs you use the closer you come to a solid floor floating on cork or carpet-dunno really.
Frank

 

The tests suggested otherwise. The conclusion came to was that any likely movement was inconsequential. So "in the interests of this discussion"...do you have any evidence that contradicts this?

As for it's rotational movement, would you suggest that this was on a par with it's fore and aft movement and would you agree that this will only become a factor if the drive unit is operated outside of it's linear frequency range?

 

i use a granite `sandwich` with a heavy granite base then a layer of silicon and then a tesco granite base. it is slightly wobbly but still safe and sounds great

 

I usually go for a Tuna and cucumber bap, at Tescos, myself. They're a bit more substantial than the sandwiches, I find.

 

Hi Mike,
Lets asume that this single frequency(50hz?-why not 20 or 30?) assesment of speaker movement in any way relates to real world broadband energies found in ls drivers(it patently doesn't);
I'm sure you can understand the microscopic vibrations associated with hf drivers being in the region of microns, places the tweeter on effectively a moving platform with to accept for the purposes of this discussion, a fore and aft oscillation of =/-1 micron.
Invert this and imagine the same bass unit with the same cone excursion on a baffle moving @+ or- 0,5cm too...this is whats happening to the tweeter(on a proportionate scale obviously).
The issue of rotational movement cannot be reduced to fore and aft(it doesnn't cancel out cos it isn't even-unless you listen to sine waves all day and even then..) The piston motion from drivers manage to flex cabinet panels too so we actually wind up with a bit of a vibrational mess in reality.
I can see that a driver operating out of it's linear range will make matters even worse.
I think in all honesty the experiment you refer to probably produce the tiny movement you say and at a single 50 hz it might not mess things up higher in the frequency range (I dispute this as stated) but the energies involved are much greater due to their broadband nature in the real world.
As you are well aware virtually every LS manufacturer goes to great lengths to lose this mechanical energy from their cabs, DMT (high mass/lossy)in the case of Tannoy, Harbeth go for a stiff but light/lossy route B&w have their own approaches including lossy mounting gaskets in the 801.
So if this energy is venting to ground through the stands into the floor you can give it more work to do ie increase the mass of stands or the base or you can isolate(2 route for simplicity) with say bubble wrap and just let it vibrate and ring away slowly rocking in simpathy with the input signal-but sucessfully preventing the energy getting into the floor-hopefully..
Finally the principal is very easy to illustrate. a small monitor speaker unsecured will move on a meter bridge when driven hard ,it wont if it is 'secured' with blutak.
Either way I have fundamental issues with the relevance of this particular test.
The 'inconsequential' assesment intriques me-how can you measure that? by listening, laser interferometry, what?
At what level does it become otherwise?
What effect does broadband low frequency energy have?
How was the speaker mounted?
What was the mass of the box -'cos obviously if it was very dense and heavy it is much less likely to move.
To be in any way conclusive you have to conduct the relevant kind of test-ie if you want to measure the effect of speakers on stands, that's where you put the speaker in the test...
I know it isn't you who conducted the test so remember to be a decent human being when you respond to my reply.
Frank

 

I had a Thai sandwich once

 

Frank,

to be reasonably conclusive you just need to put some largish speakers on some slabs and something compliant like bubblewrap and have a listen to see if has any negative effect on their soundstage.

Dos, I'd say you have shown its having an effect of some sort ... which you may or may not like. I'd experiment some more. I'm not sure something can be too clean ... but I'm not sure what you mean by clean. Which frequencies does it seem to be affecting and how?

 

A guy called Doug Purl did a lot of work IIRC but I can't find any details on the web for you so I can't answer a lot of your questions. I just remember reading the calculations and thinking it made sense - especially given that the best results I've ever had with any loudspeakers has been on Max Townsend's air bladders with certain caveats.

Without access to data for or against, we cannot conclude whether movement of a loudspeaker cabinet caused by rocking is an issue - I'm sure you would agree.

Obviously manufacturers employ different methods for dissipating energy, from the old thin walled BBC principles of a resonating surface to the use of carbon composite sandwiches and constrained layer damping in more modern designs. The issue is of course where does the energy go. If the cabinet has an effective method of converting the form of the energy and dissipating it in other ways then this has to be the ideal solution. The conversion of vibration to heat through friction appears to be a good solution, indeed likely to become incresingly popular with more and more damping compounds arriving on the scene.

Now if we have a vibrating cabinet, do we really want to connect that to the ground? Firstly, any spike, cone, whatever has a resonant frequency. At that frequency, (which due to the materials used will be within the audible frequency range) the spike will increasingly vibrate uncontrollably, sending that vibration both into the floor (causing a wooden floor to act as a soundboard) and back into the cabinet - it's a myth that spike only sink in one direction of course. So does it not stand to reason that whilst you may have theoretically reduced any measurable fore and aft movement, you can equally introduce measureable energy spikes from the spikes themselves, both through the floor and the cabinet walls - something the manufacturers have gone to great lengths as you say to avoid.

 

Absolutely agree, I'm not a great fan of spikes myself.
It's what happens after first principals are addressed that controversy usually rears its head.
Sure, every 'solution' has a habit of throwing up problems of its own making.
F

 

I think the phrase "Your Mileage May Vary" springs to mind.

 

Most speaker systems I have used have benefited from speaker spikes? It does seem to sharpen up the image and tighten bass.

I had thought the concrete slab was meant to soak up the energy before it reached the floor boards, though not sure where or when I read this. But it did seem that bass was tightened up in the bedroom system while less energy was transmitted to the suspended floor, though there was vibration present in the concrete?

Which brings me back to Townsend speaker platforms, if they are designed for forward firing drivers, why do they utilise up-dpwn motion dampening? And how will this work with up-dpwn firing bass drivers?

Are the vibration affects different with up-down drivers and therefor would they require a different method to combat the transfer of energy into flooring?

Regading thin wall construction, I have found such speakers to benefit from no extra concrete slabs on top or beneath, and also they seem more suited to open top plate stands of medium mass on an open frame.