VPI TNT Bladder replacement

I think the "stock" apparatus was removed when the air bladders were installed by VPI, thus no threads. Same boat here.

I recall speaking directly to Harry many years ago about my air bladders and he remarked that they needed to be adjusted to <3psi in order to take the resonance frequency below the audible range. You may want to try drilling holes in the tennis balls to try to do the same.

Look forward to reading what you discover, poonbean.

Dave

I guess I forgot the use of a simple tap to cut new threads.  Seems the tennis balls are way to big to fit into the cavity.  You want the towers to sit ON the tennis balls?

wntrmute- just read your post on vpi forum - that clears up the construction questions for me - thx for the additional info.

I tried the tennis balls and yes, the towers sat perfectly right on top of the tennis balls, just as I planned, and compared with what I'd been listening to (tower basically resting solidly on top of the vpi feet), the sound was far worse - unfocused, honky, lacking bass.  Odd, I thought, since it's pressurized air supporting the table - pressurized air as originally designed.  

Moving on - from dlcockrun above, if vpi wants 3 psi or less to deal with resonance, tennis balls and racquetballs are built with about 12psi - or so says google.  So, I'm thinking neither of those ball solutions come close to the vpi goal, and the solid connection - tower to foot - sounded better than my silly easy tennis ball idea.

For those following this thread, Brf from the vpi forum also provided this:
The first thing to do is to contact VPI and enquire if they have any TNT Ball Suspension conversion kits still available. If so, it's any easy conversion, otherwise you will need to fabricate a few parts to help accommodate the racquet ball.  Please see this thread for some ideas. http://vpiforum.com/viewtopic.php?f=9&t=6049&p=13322&hilit=Weather#p13322
If you have leaky air bladder, you can insert some Stans NoTubes sealer which is readily available at most bike stores. (yet, another simple solution!!)

However, while the link provided by Brf provides a nice description of how to construct a solid wood insert for the tower, it does not accommodate a ball.   But, wntrmute's elegant solution does include a ball.    

So, I took my setup into the direction of a better solid connection and took the vpi feet off.  Then, simply supported the table plinth on top of three BDR cones that sit on top of a pair of 1-5/8" x 4" hardrock maple sticks running left to right, at the front and back.  That gets the cones up high enough to clear the towers, and gives the tonearm cable plenty of room to gently bend as before.  Best of all, it provided a very nice improvement from the prior tower to foot support.  Then, I substituted the BDRs for some stillpoint knockoff - don't know what these actually are - and that sounds even better.  

I'll guess that my preference for the solid connection over the air bladder/ball support might have something to do with the room and the rack.  In my case, the "rack" is custom built into the exterior wall so that each shelf consists of a pair of hardrock maple (same size as above) arms secured to triple thick wall studs so as to extend horizontally into the room.  Basically, all gear (except for the amps at the speakers) sit on maple shelves that sit on maple arms that are mounted to an exterior wall.  This rack construct came from Rives audio, who provided some designs for the room - cheap, solid, sounds good, looks cool, and forget about moving it.    

At this point, I'm moving away from the ball in tower support idea and towards a solid connection to the plinth.  Might try a ceraball or small stillpoint under the table next ...

Thx to all for the help.  

Good feedback poon. I suspected as much re: the tennis balls. I have found that vibration/resonance control has to do with two principles: 1) Dissipating the vibration coming to the component and 2) Drawing and dissipating the internal vibration/resonance away from the component.

Soft, squishy things can do 1) well but fail miserably at 2), actually trapping the internal vibrations inside the component with unpredictable results. Direct coupling the plinth to the sub-base as you have done will accomplish 2), but can amplify 1). Direct coupling the plinth to an effective constrained-layer base that draws the vibrations from the table while also isolating the table from the vibrations coming up through the stand addresses both. I like the Symposium platforms for this, but there may be other equally effective (cheaper) solutions.

Hopefully you have already isolated (separated) the motor from whatever platform you are using under the plinth.

Best to you poonbean,
Dave

Very helpful.  Hmm, based on that, I suspect my rack does a good job at isolating the gear from external vibrations.  So, I'll focus on dissipating internal vibrations.  Obviously a turntable will have those.  How much internal vibration can be generated by a power supply, preamp, or dac?  

Re isolating the motor from the plinth - good point - not clear how to do that beyond what I've got set up now, which btw, generates less rumble than original setup.  Currently, the plinth is resting on three stillpoint-esq feet which sit on 1-5/8" thick maple, which rests on the same maple shelf as the motor.  Thoughts?