Tonearm mount on the plinth or on Pillar ?

Atmasphere wrote,

"Unless, that is, if you are claiming you have a damping system so profoundly effective that ***zero*** vibration is the result- if that is the case, then you will have been successful where no-one has been before and the world will beat a path to your door."

i don’t think anyone is suggesting that damping techniques are 100% effective. Nor is anyone claiming that vibration isolation techniques are 100% effective. However, there are two points I’d like to make. One is that - generally speaking - vibration damping techniques, e.g., constrained layer damping, are regegated to frequencies, say, above 30 Hz, whereas vibration isolation techniques, e.g., mass-on-spring methods, are primarily regulated to frequencies between 0 Hz and 30 Hz. And for the latter, vibration isolation, one should address as many of the 6 directions of motion as technically feasible for best results, not to mention attempt to produce as low a resonant frequency for the iso system as possible. Since the resonant frequencies of the cartridge and tonearm as I mentioned previously are circa 10-12 Hz then even such heroic iso means as Vibraplane and some other examples, with resonant frequencies around 3Hz, can provide isolation effectiveness of perhaps only 50-70% at 10-12 Hz. Obviously, obtaining a resonant frequency below 2 or even 1 Hz would be great. Nevertheless, one should do the best one can, including isolating the other gear from seismic type vibration, too.

geoff kait
machina dynamics

i don’t think anyone is suggesting that damping techniques are 100% effective.

Actually Geoff, I was being accosted about that very thing when I pointed out that it was impossible for any damping system to be 100% effective (perfect).

Halcro.

Yep, transmission, WRT vibration, means the same thing here in NZ. 

You mentioned transmission at resonance (FR) and at this frequency, it is obviously at is maximum since the excitation frequency and resonance frequencies are the same. At excitation frequencies below FR, transmissibility approaches 1,  so we more or less get out (vibration) what we put in. At excitation frequencies above FR, we get attenuation (partial isolation} as Geoff has explained above. The further we move above FR the greater the isolation. The curve being asymptotic to zero as the excitation frequency is increased.

It all depends upon the FR of the material or structure, So in your apartment wall example, the FR of the wall is well below the audio band and this fits perfectly with what has been said.... Your excitation frequencies are well above FR so no vibration would be detected.

So we have the question of what is the FR of the structure of the TT or pod? If this falls within the audio band then there is a potential problem.

Maybe a test would be to suspend one of your pods from a thread after removing any damping you have applied. Tap it to ascertain its FR.  

Cheers. 

atmasphere
4,796 posts
05-09-2016 5:00pm
Geoffkait: "i don’t think anyone is suggesting that damping techniques are 100% effective."

to which Atmasphere replied,

"Actually Geoff, I was being accosted about that very thing when I pointed out that it was impossible for any damping system to be 100% effective (perfect)."

Oospy daisy! In that case consider my post to be in defense of your position. As for your point about damping, I actually didn’t address damping effectiveness, only vibration isolation, in my previous post.

Cheers

We do agree on this point. We both recognize that air borne vibration can be a problem.

No we don't....
I pointed out that:-

If air-borne sound pressure is a problem in the turntable playback system, then every increase in volume would of necessity degrade the sound.

You said that was correct....
You then contradict yourself by writing:-

The result is it is quite impervious to the volume level in the room; even at 110 db the sound is still very relaxed.

The two statements are logically incompatible.
No amount of plinth dampening will avoid the effects of air-borne sound waves on the vinyl, cartridge, stylus and tonearm.
The fact that you and many others can listen to vinyl played back at excessive volumes demonstrates conclusively that air-borne sound waves have no effects on the turntable system.