Ringing granite

[Clarifixer]

This is about damping vibrations.

I just had some 1" thick granite plates made to sit atop my Snell C/IV speakers to see if they make a difference.

Initially, I spaced two 4" x 11" pieces of 1/8" thick very dense industrial felt on the bottom of one plate to prevent scratching the speakers and also to isolate any possible buzzes. Thick double sided tape was used to bond the felt to the granite, and the felt covered about 60% of the granite surface.

On the other plate, I decided as a comparative trial to use some 3/4" diameter Sorbothane buttons with peel-off adhesive and stuck them to felt disks of the same diameter cut out of special 3/16" thick material used for sonic dampening. This felt was thicker but much less dense than the first felt I used. I utilized one button/felt (felt side down on the speaker) on each corner and one in the middle of the speaker top and installed the granite. I was quite pleased with myself--high tech, baby!

Ahem.

Just by chance, I rapped my knuckle on the Sorbothaned granite. *BING!* Rang like a bell.

Hmmm, thought I.

I rapped the other felt-only granite plate. -thunk- Dead.

Say what? Apparently the more surface area that is deadened, the more effective the damping is. True?

I have yet to do definitive listening comparos, but wonder if anyone else has had any experience with this sort of thing. Does it mean anything sonically? Are all these tippy-toe spikes on fancy stands allowing things to ring more freely rather than truly isolating/deadening them?

I dunno. Anyone?

[AKA_Hyfi]

I place my Dynaudio 82s and previously older Mirage M790s on 1-1/4 thick granite slabs using the spikes. But the slabs sit on top of the carpet, I never placed weight on top of the speakers. I get better bass response in this setup with the Danes.

[GaryProtein]

Originally Posted by Clarifixer

I just had some 1" thick granite plates made to sit atop my Snell C/IV speakers to see if they make a difference.

Initially, I spaced two 4" x 11" pieces of 1/8" thick very dense industrial felt on the bottom of one plate to prevent scratching the speakers and also to isolate any possible buzzes. Thick double sided tape was used to bond the felt to the granite, and the felt covered about 60% of the granite surface.

On the other plate, I decided as a comparative trial to use some 3/4" diameter Sorbothane buttons with peel-off adhesive and stuck them to felt disks of the same diameter cut out of special 3/16" thick material used for sonic dampening. This felt was thicker but much less dense than the first felt I used. I utilized one button/felt (felt side down on the speaker) on each corner and one in the middle of the speaker top and installed the granite. I was quite pleased with myself--high tech, baby!

Ahem.

Just by chance, I rapped my knuckle on the Sorbothaned granite. *BING!* Rang like a bell.

Hmmm, thought I.

I rapped the other felt-only granite plate. -thunk- Dead.

Say what? Apparently the more surface area that is deadened, the more effective the damping is. True?

I have yet to do definitive listening comparos, but wonder if anyone else has had any experience with this sort of thing. Does it mean anything sonically? Are all these tippy-toe spikes on fancy stands allowing things to ring more freely rather than truly isolating/deadening them?

I dunno. Anyone?

I am not surprised that total area coverage with felt damping material resists ringing better than (relatively) point coverage with sorbothane.

As far as sonic tests are concerned, that is for someone else to test. If someone thinks a 500 pound or even 100 pound speaker needs anything to hold it to the ground, for reasons other than preventing the speaker from noticeably rocking on a floor that isn't quite flat underneath the speaker, they are going to have a hard time convincing me.

[Clarifixer]

It isn't the weight I am talking about--it's the damping of the broad felt pieces vs Sorbothane buttons.

If the ring of the granite is deadened much more by sitting it on a large surface area of damping material, wouldn't the same be true of, say, a CD transport?

If the whole bottom of the chassis was resting on a thick felt blanket or pad as opposed to little feet of whatever high tech material was utilized, wouldn't the sheet metal and attached components and circuitry be much less prone to resonate with either mechanical or sonic vibrations because so much surface is dampened? Is this a bad idea as long as there is plenty of ventilation if needed?

There are all kinds of weights and pads to put on top of a component (HRS damping plates comes to mind) to reduce vibration with a large surface area being the key, but I haven't seen the same attention given to that concept for the bottom of the chassis. There is a plethora of high tech chic buttons, spikes and pucks offered by various manufacturers.

Does anyone know any more about this? Heck, three yards of 1/4" F15 felt can be had for about $70. You could make many bottom pads and get as complex as you wanted by sandwiching layers of felt, Sorbothane, cork, or who knows what. It ain't sexy, but if it works really well......

[GaryProtein]

I realize it isn't the weight you were talking about, I was just adding my two cents there.

The felt sounds like a great idea to me.

[Clarifixer]

Originally Posted by GaryProtein

I realize it isn't the weight you were talking about, I was just adding my two cents there.

The felt sounds like a great idea to me.

Ha! GaryProtein, it took me so long to edit and re-write my last entry that you got in there before I finished it and I didn't know your post was already there. Thanks for the two cents, by the way.

[chessman]

I am no expert at vibration control, but I think the difference has to due with the relation of granite's harmonic resonance and the ability to off-load vertical vibration. The narrow feet will allow more drain of vertical vibration, but may exacerbate harmonic resonance because of the increased surface area resulting from being raised. My view is that substances that ring should be avoided, rather than attempted to be controlled. NB: I am not real sure about this; it is just what I think is going on.

[audiot servant]

Great post thanks Randy... Trying to get my head around mechanical isolation myself ATM and that helped a lot.

Sent from my iPhone using A.Aficionado

[Clarifixer]

I will leave the felt sandwiched between the granite plate and speaker top since it works well as protection for the wood and doesn't seem to degrade anything.

Originally Posted by chessman

I am no expert at vibration control, but I think the difference has to due with the relation of granite's harmonic resonance and the ability to off-load vertical vibration. The narrow feet will allow more drain of vertical vibration, but may exacerbate harmonic resonance because of the increased surface area resulting from being raised. My view is that substances that ring should be avoided, rather than attempted to be controlled. NB: I am not real sure about this; it is just what I think is going on.

That does make sense--especially pertinent for elements with rotating/moving parts like transports or turntables that can be affected by mechanical vibrations?

Now that I have three yards of 1/4" F15 acoustic felt, I'm considering other uses......

I'm thinking about doing something with my ARC CD3. Leaving the factory feet on the unit and making a pad or blanket of the F15 acoustic felt that covers the entire area under the unit between the four feet is what I have in mind. Making it thick enough so that it is quite snug without raising the component off the feet will perhaps deaden some vibrations of the chassis without affecting the vertical solidity.

Has anyone tried a similar approach with the bottom of a component? If so, can you tell any difference? Tweak, tweak.