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Randy,
I think Tom is right: the airborne vibrations are probably small compared to the earth vibrations.

Maybe we can subject out turntables (or tonearms really) to some loud speaker wave front and try to look for that signal at the output of the preamp? We can do the same thing for earth connections by knocking on the plinth and seeing what signal pops out of the preamp into our oscilloscopes.

Chances are that we'll see a signal on an oscilloscope on the output of the preamp when knocking the plinth or jumping on the floor, but most likely we won't see anything when we blast the tonearm (and room, house, spouse) with incredibly-loud tone through a speaker.

Hmm, put the turntable on the speaker, sweep the audio band, and look for resonances at the preamp output. Has anyone tried this or something else to find resonances?

I was thinking of trying this kind of setup to look for the resonant frequency of my plinth, but like everything else I haven't tried it yet.

_________________
- Guy

I posted based upon the use of cones as vibration control devices used on my VPI table. It was my understanding that cones are used to drain vibrations from the device(s), and pucks are used to isolate vibrations to the device. If I tap my rack or even the maple block on my stand, I hear nothing. If I tap the top of my turntable plinth, I can easily hear the tap. The reasoning behind using cones on speakers is to sink the cabinet vibrations to the floor, where the energy is dissipated in the larger sink that the floor provides. So that would seem to negate the concept of floor vibrations traveling into the speakers. Also, the directional aspects of cones work to drain away, and not conduct into, the device that the cones are attached to.

of course, the best way would be to try both and see which works better, I only offer my own experiences and the reasoning behind what each of the devices is used for.

I had an AR "The Turntable" once. The platter was comprised of two rings, inner, driven by the belt, and outer, which covered the workings and provided support for the record. Tap either one, individually, and it rang like a bell, but at different frequencies. Assemble them (just one atop the other), and all a tap creates is a dull thud.

Same concept should work when a table is coupled to the mounting surface, as opposed to being isolated from it. Change the effective mass of two different resonant materials and damp the ringing.

Most turntables work better with their suspensions defeated; partially because the suspension resonance leads to worse problems than footfalls would otherwise cause. I think that such tables coupled to a solid surface which most likely resonates at a very different frequency also sound better because of the damped resonances.

The Basis has an exceptional suspension, properly designed, with differing frequencies of resonance in different planes. So it works better suspended.

Let's face it, airborne or solidly transmitted vibrations will excite any resonance, and resonances are inevitable. Damping the differing resonances with firm coupling should work better to minimize negative effects.

Same idea with vacuum hold-down systems to clamp the record to the platter. A lot harder to vibrate a record that is solidly coupled to a platter.

Of course I'm probably just full of crap, so YMMV!

Stuart

When using cones on a turntable, my guess is that they will drain vibrations out of the turntable but also fed them back into it. Again, they are bidirectional devices. I know of nothing in a cone that will make it unidirectional. David Berning has had a lot of experience with different physical mounts in and under his amplifiers. Maybe he can shed some light on this.

Tom

I was always under the impression that cones were one way filters. Since the decreasing demension acts as increasing apparent mass to the point that mass is so high that vibrations are at minimum. I think I said what I mean it's clear in my muddy mind

I have not heard that so I cannot comment. However, if it were true the increased apparent mass would not absorb the energy, only lower the frequency of resonance. And that would be true in both directions as any vibrations would to pass through the same path. BTW, if you consider the mass of the floor and rack that may be in motion, the total mass of the cones is of no consequence. I'm also assuming that the cones are made of some material such as metal where the change in length is minimal with an increase in force.

Generally, when working with any material, as the area gets smaller such as with a pointed cone, the total force transmitted by the material does not change, only the force per unit area or pressure. That is the basis of hydraulics. The energy does not change except for any potential losses in the system. You can lift a heavier weight because hydraulics let you use a small piston to apply a smaller force over a larger distance to achieve at the other end with a large piston a larger force over a smaller distance. Work is the product of force times distance so the total work is the same.

Tom

Makes perfect sense, Tom
Thanks