Tonearm microphonics

Regards.

Correct me if I'm wrong, I really don't mind.

A cartridge doesn't care where it's signal comes from and if any constituent part of a turntable can resonate, it will. 

Resonance can be either constructive or destructive, airborne or mechanical. Constructive resonances are typically considered to primarily fall in either the fifth harmonic or at the first octave, The enhancement of these resonances are usually considered pleasant, sometimes even desirable (think piano or strings). Destructive resonances may be generated by extraneous mechanical vibration or reflected airborne energy such as sound reflected from walls, a nearby speaker or other objects close by. This may also be described as  proximity resonance.  

Sources of these resonances can be autonomous, sometimes described in terms of Eigen value. Imagine a large, heavy plinth coupled to a light tonearm. If the plinth is energized it will act on the tonearm to some commensurate degree. The tonearm resonates to it's own value. When these resonances couple to resonate in phase and not disproportionate to the recorded signal these resonances may be said by some listeners to be considered as desirable.

Resonances not in phase are said to be destructive. In this sense and depending on degree, damping can generate either constructive or destructive resonances.

Just when one thinks they've a handle on the phenomena and your turntable is performing in a wonderfully synergistic manner, a change of cartridge or headshell shifts mass, nodes are redistributed, phase goes out of kilter and unanticipated boundary resonances return unwanted signals.

The cartridge doesn't care where the signal comes from.


Peace,


  

Regards, rotarius:

Thanks for the considerate manner of your post. Please consider: "Constructive" and "Desirable" are not necessarily synonyms.

First, neither are resonance or interference technically the same. However, when considering transducers sometimes resonance can generate interference.

Here're a couple of relatively easy to grasp descriptions from:  

Frank Heile, P.h.D. Physics, Stanford University (quote):  
"Resonance is when a driving force is at a frequency that is close to the natural oscillation frequency of a system. This makes the amplitude of the oscillation of the system greatly increase.

Interference is when two waves at similar frequencies are superimposed which results in either constructive interference when the waves are in phase and add together, or destructive interference when the waves are out of phase and interfere with each other."

And:

Bruce Thompson, former Computer programmer at University of California, Berkeley:
"In some systems it makes sense to use either "interference" or "resonance" to describe what is happening. For example in a trumpet, the waves created by the vibration of the player's lips interfere constructively, creating a resonance effect."

 In a paper presented to the AES, Shure technician C. A. Anderson states:
"Resonance exists because the arm and pickup assembly behaves like an effective mass that is coupled to the record groove by means of a stylus assembly with its own mass, compliance, and mechanical resistance".

If a 1kHz signal recorded to vinyl represents a displacement of 80 microns (according to a study by St. Andrews College), it would be difficult to argue that unwanted vibrations of the tonearm have no influence on the signal. The cantilever doesn't discriminate from which end movement originates, sometimes the tail DOES wag the dog.  ;-)  

When a recorded signal matches the natural resonance of our tonearm/cartridge, Mr. Anderson states the recorded signal can be enhanced by 6 to 20 dBl. He doesn't state such but with out of phase  resonances then distortion, diminution or even cancellation of signal at specific frequencies might be anticipated. Resonances can then be considered as constructive or destructive.


Poem.
by Henry Gibson

Her name was Grace, she was one of the best,
Late last night I put her to the test.
She looked so sweet, pretty and slim.
The night was quiet and the lights were dim.
I set everything up as nicely as I could.
I handled her gently for I knew she was good.
She was just one big thrill and the best in the land.
Then she hummed but it was not for joy.
More effective damping was obviously in demand.

Peace,