Here is an extract from the Shure white papers...
what happens at the resonance frequency? One important characteristic of resonance is that motions are magnified considerably, in this case, typically from 2 to 10 times.
In both situations, the output from resonance frequency signals in the groove will be increased from 6 to 20 dB. These numbers are just the dB equivalent of the magnification numbers previously mentioned. By itself, this may not be all bad, since this resonance peak determines the low-frequency response "limit" of the pickup and system, and a bit of boost here may not be unpleasant. This was certainly true fifteen years ago, when arm resonance frequencies of 30 to 50 Hz were common. However, with modern pickups and arms, these resonance frequencies are usually subsonic (below 20 Hz), so that reproduction by the loudspeakers may cause distortion. Additionally, preamp overload is most likely to occur at boosted low frequencies since the preamp clipping level is lowest here. Consequently, the arm resonance has lost whatever usefulness it once had and must now be regarded as a liability.
The most pernicious effect of the resonance is shown in Figures 1 and 2 by the "scrubbing" notion developed by the stylus in the groove. This causes program material to warble in pitch, just as if the turntable speed were fluctuating. In fact, the groove speed is changing (relative to the tip), because a fraction of the velocity of arm vibration is added to the groove velocity. (See Appendix I.) The effect is that about 1/3 of the arm vibration velocity is alternately added to and subtracted from the groove speed. For example, at arm resonance, total amplitudes of 1/32" are easily observed by eye. If the frequency is 8 Hz (typical for high compliance pickups and average arms), the resonance velocity will be about 2 cm/sec (see Appendix II). This velocity will produce a "scrubbing" velocity of 0.6 cm/sec along the groove axis. The groove speed at a 4.5 inch radius is about 40 cm/sec; so the frequency modulation will be about 0.6/40 = 1.5% and easily audible.
Another less obvious consequence of the arm resonance is that the stylus force is "used up" when the arm is vibrating. In the previous example, if the compliance of the pickup is assumed to be 20 x 10-6 cm/dyne, 2.0 grams of stylus force will be required to accommodate the arm vibration alone. This is larger than the usual stylus force, so mistracking is quite certain at the extremes of the vibration.
AJ Van den Hul
Recently I bought a very good looking rather long tone arm made in Japan around the ’70s. Suddenly the bass response is very different. What happened ?
It sounds like you bought a 12 inch Fidelity Research arm with probably even silver wiring inside. These arms were made for the, in those days, very famous cartridges of the same company, like the FR-1 and later FR-7.
These cartridges had a stiff suspension and worked with a tracking force of around 2.0 gram or even more. The compliance (flexibility) of the suspension was not very high. But with some extra coupled weight around (your heavy arm) the basic resonance frequency of cartridge and arm would be around 10 Hz.Your actual cartridge has a much higher compliance and already tracks well at 1.35 - 1.50 gramf. So the heavy arm combined with the softer spring (the suspension’s steel wire and rubber together) resonates at a much lower frequency and at a higher amplitude - like 5 Hz. The sonic result is that a lot of extra energy of your power amplifier is used to move your woofer at around 5 Hz and the real bass is gone.
Lesson: Never match what is not made for each other. New arm designs are made for today’s cartridges with a dynamic compliance of 10 - 15 μm/mN. The other way around is also a fact of live: For instance your SME Series V will not work so well with the Fidelity Research FR-1 because the compliance of this cartridge is too low here. So the resonance frequency of the cartridge/arm combination (see Appendix 2) is too high and your bass reproduction is too strong. The whole acts asa low frequency resonator at around 25 - 30 Hz, so the output at these frequencies is also higher. But even worse is the fact that the tracking ability of your cartridge is gone. This because any resonating cartridge/arm combination already causes a healthy number of microns in excursion at the stylus. So what’s left is for your music. And in worst case that is not much.
So, sudden tracking problems are partly caused by uncontrolled low frequency resonances. A way to solve this problem is a reduction of the headshell mass. And also some fluid damping can help, but ONLY when you play flat records. Otherwise the cure causes your cartridge to age faster than you age yourself.
Halcro, you have an FR64S as do I. I can easily demonstrate that changing the effective mass by changing the counterweight ( I have multiple counterweights for my FR64S ), there is an audible difference with both low and med/high compliance cartridges. Similarly on the latest Shroeder CB multiple head shell plates are provided to dial in optimum effective mass.
This is not to say mismatched arms/cartridges wont work, and or may not be audible in some systems, but there are some latent benefits from matching effective mass and compliance including shortening the life of the cantilver suspension as suggested by Van Den Hul.
For those with a fetish for vintage cartridges, unless the cartridge has been completely rebuilt, you have no idea what the actual compliance is given that the rubber suspension will have deteriorated. A cynic would suggest that the reason why the much vaunted FR7 series cartridges never wear out is that they were built with a dual layer rubber suspension, that is, when the softer first layer is f**d then the much firmer second layer kicks in and at least keeps the cartridge somewhat functional, albeit now out of spec.