Shure V15VxMR to be discontinued

The resonant frequency of the V15 in a medium mass arm is, indeed, lower than is customarily considered optimal. However, the brush damps this resonance to the point that warps and footfalls are not the problem (sonically or structurally) that an undamped resonant frequency of ~6Hz might suggest.

Keith

No doubt resonance of the arm/pickup is an issue. Conventional wisdom is to arrange for the resonant frequency to be in some particular range that is thought to be best.

In thinking about WHY my servo controlled "Biotracer" arm in the Sony turntrable works so well, I realize that it has solved this problem in a different way. Instead of moving the resonant frequency to the "best" point, resonance itself is eliminated. There is no resonant frequency for this arm.

Everything has a resonance, especially an electro-mechanical device such as a tonearm. There's no way around it although the Q of the resonance can be played with. Sean
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Sean would have had my agreement up until the last 10 or 15 years, during which my work involved electromechanical systems including many digital servos. (It was a missile guidance system, and had about a dozen servos of one kind or another, but all digital). Given sensors that are accurate, motors that are strong, and a powerful microprocessor, the dynamic characteristics of the controlled member are entirely (well as close as you could want) a function of the algorithms you design and run. It is as if the actual physical mechanical item, in our case a phono pickup arm, no longer exists, and what does exist is a "phantom" item, which "inhabits" the physical device, but which completely defines its properties. This phantom is defined by the lines of code in the control algorithm, and can be just about anything that the designer wants. Lack of resonance would be one of these desirable properties.

And, for those who don't believe in science but would rather go with what actually works, let me tell you straight out that the servo-controlled arm in the Sony PS-X800 turntable exhibits no resonant behavior at all. I attribute this to the servo design. Do you have another suggestion?

El: One would have to have an equal yet opposite controlled reaction that responded on a phenomenally time sensitive basis in order to cancel the type of resonances that we are discussing here. Given that a tonearm has freedom of movement in both the vertical and horizontal planes that responds on a dynamic basis to the modulated grooves being tracked, and i've never seen an arm that had servo controlled motors responding to and driving an arm in both of those planes simultaneously, i'm pretty sure that the arm on the Sony ( along with all other tonearm / cartridge combo's ) has some type of resonance to it.

The only other approach that i know of to address such a resonance is "fluid damping", which several different advanced design tonearms make use of. Even using such an approach, the resonance is not removed, it is just altered in bandwidth and amplitude ( "Q" ). Sean
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