Grown-ups only please to offer support

I'm looking at the equipment isolation v equipment coupling (through the supports to the floor) question.

I would ask that we stay away from naming specific manufacturers and talk about general principles and practical experience.

My questioning results because of my speaker designing experience, particularly the original System IVs. I placed a fibreglass egg inside an MDF cabinet with sand between the two. I had expected that this would work really well to dampen any vibration in the cabinet due to 'airborne sound'. What I actually discovered was that the vast majority of vibration was caused by mechanical coupling of the drive units to the cabinet.

Fast forward a few years (stay with me here, you know it's worth it) and my parents were living in the downstairs part of our house. As my father was partially deaf he listened to his TV very loud and this kept my kids awake in the room above. So, I put some isolation (superballs - you know me) under the TV. The problem was 90% solved. In other words, mechanical vibration rather than airborne sound was the main cause of the problem.

So ...

It seems to me (theoretically) that - in a hi-fi system - the major part of the vibration is imparted through the floor by the speakers - mechanically. Only a minor part comes through airborne sound.

Therefore, it seems to me (again theoretically) that coupling equipment to the floor would be counter-productive as the equipment would pick up more vibration than it dissipated. Therefore, according to my theory, equipment should be isolated (such as by air, inner tubes, etc.) rather than coupled to the ground.

On the other hand, more intelligent and knowledgeable people than me have argued precisely the converse.

So, what do you think (from your experience or theory)?

... puts on his anti-flack jacket and stands well back ...

 

To my mind, there are two issues to contend with, regarding equipment support (speakers we will come to...).

The first issue is borne out of simple newtonian mechanics. We are imparting a significant energy to the floor, which is then attempting to shake the equipment. In other words, kinetic energy is being imparted to the equipment. Any schoolboy (schoolperson?) knows (or should!) that KE = 1/2 mv^2 . We want v to be as small as possible. Since the kinetic energy imparted is essentially constant, this is achieved by increasing m. Mass. And lots of it.

The second issue is that it's all very well directing energy about the place, but that may not necessarily solve much. What is needed is somewhere for it to go. Ideally, we want to change it from kinetic energy to something else. Inevitably, that is heat, although that is not desperately important. Simply, we need some sort of conversion medium. This is springy, stodgy stuff, like sorbothane, inner tubes, whatever.

Now, speakers and spikes... This comes about from the desire to keep the cabinet as still as possible. Initially regard the floor as of virtually infinite mass (if you have a concrete floor, this is a reasonable assumption!). By firmly coupling the speaker to this "infinite" mass, the cabinet becomes a part of it, and it is hopefully held very still. Thus the driver is free to move without interference from cabinet-borne vibration.

Similarly, spikes between components and rack shelves aim to achieve the same thing.

From all of this came the ideas behind the rack I built. The frame wants to be coupled to the floor for the same reason as a speaker. However, we know that welded metal will likely resonate. Thus some sort of energy absorbtion WITHIN the frame was required, and hence the sand-filled uprights. This also has the advantage of adding mass. Sand absorbs energy by the vibration passing through it and causing the grains to move. They rub on one another, which produces a small amount of heat by friction, absorbing the energy.

Then each shelf is decoupled with an inner tube, so that any remaining vibrations in the rack would not pass into the shelves. However, this lead to the possibility of each shelf vibrating autonomously, as the inner tube is not completely damped (wobble it and it takes a few wobbles to settle). This calls for mass again, hence the 30mm granite shelving (each shelf coming in between 15 and 20kg). Finally, this mass wants to be coupled to the object upon it, which will be done with spikes in the near future (although it is presently done to some extent). Blu-tak is also good for coupling like this.

So, a quick resume of my ideas, and how they manifest themselves in my rack. I'm sure many out there won't agree, but the rack works pretty well, and cost no more than a 4-tier Atacama or soundstyle or similar would have. All of which ring (I tested).

 

There's a swedish firm that offers squashy feet that work on this principle. It's been debated on hifi forums til the horse is dead whether this is the way to do it, including the red herring as to whether the movement of a cone has enough mass to cause an opposite movement of the cabinet. I can't remember the company name I'm afraid, but another that seems to think the same way is vibrapod. Some creative googling could pull up a lot.

 

This much I understand. However, in the process of the speaker being coupled firmly to the floor, energy is imparted into the floor. Concrete vibrates, as does wood and I wonder whether the floor still acts as an earth point or infinite mass, from the perspective of the equipment support.

If I understand correctly, Isaac, you couple the support to the floor, damp it with mass and decouple (isolate) the equipment from the support. Is this right or is this over-simplifying?

Would it be possible to have a support that is partly the other way around? The support would be isolated from the floor rather than spiked. The function of the spikes is to hold the stand steady but if it was isolated from the floor, what would cause any movement in the first place?

If the mechanical vibrations from cd players, turntables, etc. need to be dissipated, they could be coupled to the support, which is mass damped and would act as as 'infinite mass' to the equipment.

Other non-mechanical equipment, amps, tuners, etc. would be isolated from the support.

Is this feasible, is it done and would there be any point in trying it?

 

someones posted about voodoo airtek speaker platforms HERE

I've also wondered about this. I posted THIS THREAD (complete with the comment "brilliant post" ), to try and get some feedback on the various types of techniques.

There seems so be a few contradicting methods, and I guess it's a case of working out what's MOst important? Isolation from external vibration, or good coupling (working BOTH ways).

I look forward to seeing this thread develop! Hopefully it will do so nicely

Wall shelves seem appealing t me at the MOment!

 

You need Mana.

 

Exactly. At some point, such as my large chipboard floor, the "infinite mass" model breaks down, and the floor has one or more modes of vibration.

This is where things like slabs under the speakers come in. They act more like this "infinite" mass than the floor alone does (but still not perfect). One support company describes their granite platform as a "pseudo earth platform" which is essentially the idea.

That's correct. The damping (sand) is a little more than just mass (although that is helpful as described previously) in that it also provides a means for energy conversion.

I believe that is the idea behind the townshend seismic sink stand

As long as you have some provision to dissipate this energy, then yes.

It is feasible. You're effectively talking about coupling components to a wobbly stand like the seismic sink stand. However, this is effectively similar to what I've done, but you put the isolation at a different point in the process. There's always point in trying things...

 

I've been playing with various supports for quite some time. I have had great success with very high mass rigid (granite - HNE) equipment stands, medium mass flexible (TNT FLEXY using 25mm MDF shelves) and very low mass flexible (Quadraspire Reference). I have also used Sorbothane to great effect.

I think that there are two separate but interlinked issues here: vibration and resonance.

My current theory (and liable to change by the second) is that there are a number of different problems, not necessarily the same for speakers as for equipment:

For speakers, we have the desire to hold the enclosure perfectly still to allow the cones to work. Clearly, the movement of the cone exerts a Newtonian force upon the cabinet. This causes two things to happen: firstly it induces resonance that may cause an uneven frequency responce, secondly it causes the front of the enclosure (holding the driver) to move creating smear in the time domain.

In order to reduce these effects we can try to increase the mass of the cabinet by coupling it with a high mass. This works to an extent (hence high mass spiked speaker stands) but introduces new issues. The stands themselves will resonate (sand/lead shot filling helps to further increase mass/coupling with the floor and to damp these vibrations) and some of the vibrations will be reflected back up the stands at the stand/wall interface, causing the speaker cabinets more vibrational problems. In addition, if you have suspended wooden floors rather than concrete, the vibrations caused by the speaker get transmitted to eveyting else in the house including the hifi kit, with possible resonance effects caused by the flexible floor.

An alternative approach is to try to dampen the vibrations in the cabinet by using a some vibration absorbing technique. This would be the Sorbothane or Voodoo approach and has the added benefit of decoupling the speaker from the floor thus greatly reducing the vibrations reflected back to the cabinet and the vibrations transmitted to the floor. It does mean that the cabinet is more free to move but as the mass of the cone inducing the movement is orders of magnitude smaller than the mass of the cabinet, this movement will be at a mich lower frequency than the generating one and thus may not affect the time domain of the signal so much.

This leads to the question - why not suspend the speakers totally freely so that the only effects are those caused by the movement of the cone? I haven't had time to try this yet but it might work!

 

Theory part 2 - for equipment:

Here we have two sources for vibration: the environment (floor, air) and the equipment itself (transformers, CD mechanisms etc.). We clearly wish to isolate the equipment from external vibration while giving the internally generate vibration an efficient method of damping.

Here, coupling closely with the floor might not be too desirable as it would allow vibrations to travel more efficiently into the stand/equipment. Thus it may appear that a high mass stand is undesirable. This is not necessarily true. A high mass stand will have a low resonant frequency and will reduce the amplitude of the vibrations and would provide much needed stability on the suspended wooden floor. On a concrete floor, we can take advantage of the high mass of the floor (low vibrational frequecy and amplitude) and use a low mass stand.

If using a high mass support we can always decouple using air suspension (Voodoo, Townshend or an inner tube) under the component. This will also stop vibrations generated by that component from entering the stand/other equipment. But this method does not offer very good damping hence the introduction of Sorbothane or similar feet may be beneficial if we do not wish to apply damping directly to the casework of the component.

In summary, the reason that there are so many stands/feet/tweaks on the market is that there is no simple solution for every situation and what works well for one person may not be effective for another.

 

Alex



Do all grown-ups use such long words and stuff?

 

Indupitably my diabolical comrade. A practice much aproved by my fellow disestablishmentarians.

 

That is exactly I wanted to write. We very often think that what is good for us is also good for the others. This ist mostly not true.

Unfortunately, IMO, the only way to find out which is the best for your system is to experiment and listen yourself. As starting point you can certainly use the experiences and suggestions of other people. My experience told me also that "the best" solution found for one unit doesn't imply to be a good solution for another unit paced in the very same spot. In other words if you change unit (upgrades) you might need another "solution".

Another point slightly OT (which was already raised in other threads) is the fact to consider if the time and money spent in optimizing the system in this way would be better spent in simply upgrading the hardware (loudspeakers, pre-amplifiers,...). Sometimes the result is much better..

 

Not going to enter this one or than than I personaly find sorbethene feet, tend to kill the music, IE flow/groove and dynamics, they do offer more air and openiness and maybe a slightly cleaner detail retrevial in the upper freqs'.Wm

 

How about surrounding the spike with sorbothene, thereby dissipating some of the energy as it travels through. Seems to work very well with my Z feet

 

In my experience this depends upon where you use them - agreed for CD players and TT's but they seem to work well with power amps and <i>some</i> speakers - particularly small bookshelf models sitting on furniture rather than proper stands.

 

Speakers are the only system components that are active in a physical sense - i.e: the driver units move back and forth.

So, in order for transients to be reproduced accurately without smearing or overhang, the drivers should move and the cabinets stay completely still with absolutely no wobble whatsoever.

Moreover, if the cabinets are allowed to wriggle atop something squidgy like Sorbathane, the tweeters will also move slightly, so bye bye focused image.

It may be ok to stick something compliant and squidgy under amps, less so under CD players, but surely never under speakers.

Spikes are the only way under speakers - they provide rigidity for the speakers, and a single point - or four single points provide the lowest surface area possible of contact with the ground through which energy transfered back up into the speakers is minimised.

 

Sounds fair enough, assuming the surface is a non (low) resonating solid floor. But many aren't. Therefore spiking straight onto this floor, be a good ground for vibrations produced by the speaker, but it's also a good was for them to get back into the speaker. Along with the footfall, and those produced by the music, to be passed on through the floor and up into the cabinet.

I was sceptical about having my speakers anything but as rigid as possible. But from what I can tell, the speakers aren't MOving any MOre than before. The "platforms" (in my cowboy aproach that being 3 heavy paving slabs with a blob of silicone gel in each corner), should be heavy enough and a little air/flud/etc... so ensure there's only a little MOvement in them at all anyway.

As far as I can tell, my speakers are as rigid as before when playing music. If they're pushed, yes they'll MOve a little.

It would be interesting to see actual measured results to see speaker vibrations with, and without, various sorts of *platforms*.

MO

 

Sounds ok to me. The little blobs of silicone aren't going to be compliant at all, what with all the mass of those concrete slabs.

It seems to me as though you are recreating a concrete floor in on what is a suspended one.

My own system sits on wooden floorboards, and one day I may experiment with those Welsh slates that Marco kindly gave me to place under my speakers.

Meanwhile I'm sticking with my M*** Sound Bases. My speakers are not 100% rigid, but they are as good as you can get with only the floorboards beneath giving any flex - still better than squidgy feet!

*** Please don't confuse me with those who constantly peddle the M*** brand as the fix-all to your hi-fi issues/worthy upgrading.

F*** measurements, use your ears!

 

Just wondering

I said how I find it physicaly to be pretty much the same as far as I can tell, but I seem to have missed off my views on how it effects the sound.

Tricky one, certainly nothing drastic. The main reason for wanting something under the speakers was MOre to do with wanting to raise them a little. I found my stands to be too low. Things seem better. But this could be just as much to do with having raised them approx 4 inches as it is to do with what's underneath them.

With sand filled stands, and the three heavy slabs, it's quite heavy and to tell the truth i'm too lazy to swap it about (bearing in mind the need to make sure the speakers are still same position relative to walls and such), to really test for differences.

 

Quite a few manufacturers are now going to three spikes/feet to remove any chance of rocking.

I have also used the Clearlight RDC cones instead of spikes, there might have been a small improvement in sound (or it may have been wishful thinking) but they have the advantage of not marking the floor.