Sorbathane under granite slabs for speaker bases?

I’m getting two 12"x12" granite slabs to use as bases under my KEF Reference Model 2s via spikes. They will be sitting on a 5" high hollow tile shelf. Would using thin (.25") 70 duro sorbathane under the slabs help in isolating the speakers or will it possibly negatively impact the sound?

Thanks for any input.
The same reason Sorbothane is used for shoe insoles - shock absorption - makes it unsuitable for use in isolation devices since Sorbothane stores energy, preventing energy from rapidly exiting the system. Compared to what, you ask? Compared to say, Super Balls. Super Balls release energy very rapidly. Or very hard cones, which also release energy rapidly. It’s a subtle thing, the Sorbothane, but quite noticeable compared to real isolation. Tone incorrect, loss of dynamics, closed in sound. Ah, I remember it well.

I guess the question is whether to drain or isolate.  Personally, I've avoided visco-elastic stuff under speakers.   Expect others have opposite experience to share.

I'm using hardwood (3"?) plinths directly under speakers.  Hardwood resting on large 18x18" tile.  Tile on carpet.  The tile gives the plinth stability on the carpet.  The hardwood "drains" vibrational energy from the speakers (or so I think). 
Thanks ghost,

Are you using spikes as well? I think I'm going to roll with just the granite slabs directly on the tile shelf w/spikes under the KEFs.
Always good to experiment, ahahitoro.  Plain granite now doesn't eliminate the possibility of later trying some wood in between.  

To answer your question...yes, I use the spikes as well.  With the Silverline Preludes, I use the spikes they supply though have installed those little dimpled discs to keep the spike from digging into the wood.  With the Forests, they have a "ball & claw" arrangement for coupling.  The balls rest directly on the wood.

Well, I have a thoery that works for me. How you implement it is up to you.

1. Minimize surface area contact with floor, furniture, etc.
2. Minimize opportunity for speaker to move, often by adding mass.

The reactive force of the woofer motor can cause enough motion to distort the sound, or vibrate against the floor, Minimize that by any means necessary.
At one time, I had a pair of floor standing speakers on a 1 inch thick slab of black granite.  It not only tightened up the bass, but removed a slight smear in the midrange.  I placed them directly on the carpet with the speakers with spikes installed on top.  I used the cups for the spikes to fit into. 
Send a message to Robert @ Herbie's with your specific question, he will get back to you quickly.
My floors are raised wood. I  had a hell of a time getting the speakers to sound right.

 I tried just spiking them through the carpet and into the wood floors. Undefined  bass. 

Then I tried them spiked to granite bases.  Improved mids and highs. No bass. 

Finally, I bought a pair of Maple Shade unfinished maple platforms. I spiked the platforms to the floor through the carpet, then spiked the speakers to the maple platforms. Walla! Done. 

Double click on my icon, then double click again to see the Maple platforms under the speakers. 

The very expensive TMC isolation platform uses a thick granite top plate. I have used thick granite and bluestone with springs, sonically exceptional in every way. High stiffness and high mass on springs, cannot beat with stick. Granite cannot ring when it's isolated. Hel-loo!

If I read your proposed installation correctly, the unusual variable I doubt any of us has worked with is the "hollow five inch high tile shelf" that your speakers will be placed on. Your speakers are fairly heavy (75 lbs. or so) and it has been my experience that heavier speakers can do fine on granite, lighter weight speakers perform better coupled to wood platforms. That's just my experience, there are always outliers and ears that hear things differently. I would try both the spikes and the glider feet that your speakers came with, the spikes might not necessarily sound better. You might find that using Herbies products under both the granite plinths and the speakers would prove optimal with that hollow tile shelf. I've never tried sorbothane products for isolation, mainly because I've never known anyone to have anything positive to say about the material for this type of application. 
how much is the TMC ?

My guess is $5K new from factory. On their web site TMC makes the following statements. I know, it sounds like there's an echo in here, right?

"Granite Tops
Granite surfaces are standard with 64 Series tabletop platforms. They are available on special order with other isolation systems. The advantages of a granite top are its relatively high mass and stiffness and the potential for being lapped to a precise surface flatness. Granite’s non-magnetic nature is useful in some applications.

For small tops, granite is an inexpensive, moderate performance material. In larger sizes, however, granite is more expensive than standard TMC top plates, sacrifices damping, and does not have other desirable features."

Thank so again for the replies everyone,

Does anyone know what Herbie’s soft fat and thin dots are made of? It seems there is a lot of advice here to avoid sorbathane but use his products. Wouldn’t they have a similar effect? I don’t mind supporting him at all I just want to make sure I take the best path. My KEFs did come with the spikes and the brass gold feet. I’ll try both the spikes and just the gold feet on granite to see what works best. I’m still wondering what/if anything I put between the granite and tile. I wish I didn’t have to hollow tile shelf but at this time I have to work with it.
If you go over to "Audiocircle" that website has a group discussion devoted to Herbie's products best uses/applications. As far as similarities between Herbie's products and sorbothane, I suppose they are similar in that they are both viscoelastic materials. However, Herbie's products are mixtures of different silicones and fillers and have physical properties that differ from sorbothane. 
In my all-Naim system the best and the cheapest upgrade was Mana Acoustics stands for SBLs. Speakers sit on a light platform which is "floating" on the set of spikes going from Mana frame to the platform, and four more spikes face the floor. So, I cannot figure out if SBLs are coupled or decoupled from the floor, but the end result is truly magical!!!  Heavy granite slabs just lower the resonant frequencies, something I am trying to avoid in my professional business when doing microsurgery under x200 magnification.
My say: four spikes from your slab toward the speakers, four more toward the shelf. Then substitute granite slab for Mapleshade piece of maple. 
Herbie LP mat worked marvels on my Sondek, also keep in mind that I am seriously biased towards Naim/FlatEarth sound... ;-)
Try Townshend Audio Seismic Podium......these are customized to speaker weight and I believe are right up there in terms of speaker isolation solutions....I haven't tried them myself but those who have swear by it. I have a pair on order though.......


if you want to isolate your speakers down to 3hz ,then i second Townsend audio seismic podiums , since Emporium hifi in the uk installed  a pair under my soundlabs my system has improved to levels i didn't know was possible ,
by stopping the seismic vibrations from your speakers travelling threw the floor and up into your equipment , i believe without this vibration your loudspeakers are free to breath and your electronics sound much better as well , it has a very positive knock on effect on the rest of your system
i have never experienced an upgrade in sound quality like it ,
go and audition a pair , they are sold in the uk with up to 40% discount on all sizes to order you need the weight of each speaker and the foot print size,
i tried various cones, squidgy stuff and bearings nothing comes close , some of the bearing ideas where more than twice the price
check Max Townsend you tube video showing the effects of the positive effects of seismic podiums compared to the damage spikes cause , he has proved using spikes under loudspeakers is the worse thing you can do for your loudspeakers and hifi system ,
check out the video you will never use spikes again and will end up buying podiums like so many other audiophiles around the world 
they are a huge break threw in high end audio they are just as important as the speakers them selves

for a cheaper option you can use your granite , but use the seismic cells underneath , you will just need to work out the weight of the loudspeaker adding on the weight of the granite , then you have basically made your own version of the podiums at a bargain price 
the seismic load cells (pods) can be made to isolate any weight , i would recommend a set of 4 under each granite platform , do not use your spikes ,just place your speakers straight on top of the granite or you can use squidgy pads to dampen any ringing between the granite and the base of your speakers good luck 
When granite is used with springs you get the benefit of high mass and low resonant frequency - below 3 Hz if you play your cards right. As a bonus there are no resonance issues with granite since it's isolated along with the component, thus no reason to apply damping, always a plus in these delicate matters. The inexpensive way to play with the big boys. Certainly no reason to spend a fortune. The only issue for springs is center of gravity, I.e., tall heavy speakers might be too top-heavy to place springs directly under them. But there is more than one way to skin a cat. Subwoofers are ideal since they have low COG.

geoff kait
machina dynamica
isolation & resonance control
The Townshend Seismic isloators are also available separately, as individual "Pods". Using three or four of them under a speaker (or any other component) provides isolation to a very low frequency, and is cheaper than the Seismic Shelves themselves, which are not really required---the Pods are doing all the isolating, not the shelf.

I should have mentioned that the Townshend Seismic Isolators are also offered on a number of different "platforms". In addition to the individual Pod which can be used in sets of three or four for use directly under a component, Townshend makes the Seismic Platform, which is a thin shelf with a Pod bolted onto each corner, onto which a component may be placed. There is the Seismic Podium, which is similar but for a speaker enclosure to be placed upon. Then there is the Seismic Bar, a pair of outriggers for a single speaker with a Pod bolted onto each end. That is good for the narrow/deep proportioned speaker enclosures, the outriggers giving the enclosure a wider, more stable footprint. Also available is the Seismic Corner, which has a pair of Seismic Pods bolted onto a metal bar that is placed under the corner of an equipment rack, four Seismic Corners obviously required (with a total of eight Pods). And then the Seismic Rack, which has a pair of Pods under each corner of a four-shelf rack, each shelf being a Seismic Platform.

Each individual pod comes in seven weight-appropriate versions, from 2lbs. to 140 lbs.

For the best sound look at Symposium Super Plus with spikes for cement floors or without for all wood floors, Granite rings and is tipped up for thin highs,Good luck though.

For the best sound look at Symposium Super Plus with spikes for cement floors or without for all wood floors, Granite rings and is tipped up for thin highs,Good luck though.

If you’re afraid that granite rings when you strike it, don’t strike it. When granite is placed on springs it’s isolated so don’t worry, everything will be OK.
asahitoro - sorbothane is a tricky material to use. One might think more is better, but my own experience leads me to believe less provides greater benefit.

I use it throughout my system between the feet and the components.

As an example -  My turntable was sounding great with 1/10" sorbothane on the feet, so I thought I'd try two pieces of 1/8". The result was terrible - the dynamics dropped off and the bass became bloated.

I'd opt for 1/10" sorbothane in your case and even then - I'd put a small 2x2 inch piece at the corners and one piece in the middle

I also spoke to an HVAC installer that uses it to curb vibrations and he said using strategically placed smaller pieces is often more effective.

According to sorbothane’s own site this material dampens vibrations by transforming them to heat. This is basically the "conservation of energy principle." Earlier above someone stated that it just stores energy, but that is not what it tries to do. Its damping comes about because of the transformation to heat.

I have used sorbothane footers for many years but have got far more effective results simply by attaching small pieces of it using the self-stick tape which it can be bought with, or other adhesives. I recommend Lord 7650 a fairly expensive industrial adhesive if you can’t get self-stick I have applied this on turntables amps, transformers and the like with excellent results.

However sorb comes in several grades and sizes. The best results for audio come with the more dense product, 70 duro is about the densest you can get. Also use the thickest you can get. I am using 1/2 inch where I can. It is certainly very effective attached to the front panel of my speakers. It is better to have some form of backing or clamping to the sorb but it is still surprisingly effective (after the adhesive or self-stick dries) just stuck in place, I generally apply two layers of electrical tape to the back to make what I believe is referred to as "constrained damping."

I got into this area when I realized that headphones had major damping issues. They all buzz around because the vibrations in the earcups are neither effectively damped nor able to drain away. So I and others have been sticking sorb inside earcups, on headband and the like.

I was surprised to discover the Sennheiser had already been doing this by installing what it variously terms"space-age material" or "polymer" to the headband of its previous TOL HD800. I would imagine they also do this with their current ultra expensive electrostatic but I haven’t seen anything from them saying this. It could just be that they are using sorb which is also a polymer, but there are other materials now with such damping properties. Grado is using a "proprietary polycarbonate" in its new e-series phones to obtain better damping.

The other dirty secret about vibrational problems in headphones is that there is quite a lot of mechanical cross-talk going on across the headband. That is why the Sennheiser HD 800 works with the damping material in the headband. I have found this to be true in various Stax phones as well. However, I prefer to start the damping right in the earcups where possible, but I am adding it to the headbands as well.

I have been running a couple of threads, mostly dealing with headphone damping, eg.

Well, transforming vibration to heat is what ANY constrained layer viscoelastic type damper does, but Sorbothane is not as good at this as many other materials for whatever set of reasons. Any major dude will tell you. Certainly Sorbothane doesn’t isolate down to 5 Hz. That’s hooey. In the overall scale of things I’m inclined to say Sorbothane is one of those materials a lot like lead that appears to be a good idea but in practice actually hurts the sound. Great for running shoes, though.

Sorbothane, or any elastic substance will allow the speaker to move - esp. when a bass note at high volume is sounded.  This is a no-no in any box speaker, as that will phase-modulate all of the sound.

If you have box speakers, you want spikes.
I use spikes on my main speakers.  However I have to say that the sorbothane applied to the front of the speakers, especially the 1/2" 70 duro, does far more for the sound than the spikes. As regard putting sorb footers under speakers, people have been doing it for a long time and many report good results.  But I tend to agree with the above comment about allowing the speaker to move. Of course many things that would seem to be a problem turn out not to be so.  Given the positive reports, I wouldn't be dogmatic about not trying sorb footers.