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In Reply to: RE: is compliancy like weight? what MCs suit low mass arms? posted by digda_beat on November 08, 2008 at 00:30:41
At a simple level, the cartridge and tonearm system behaves like a mass and spring.The spring is the suspension of the cartridge stylus and cantilever. You may notice when you lower the tonearm onto the table that the cantilever/stylus gives a little bit, and may even bounce before it settles down. The frequency at which it bounces is the natural resonance frequency of the system. Below this frequency the cartridge does not put out a signal (this is a crude approximation) because at very low frequencies, as the stylus moves the entire cartridge and tonearm moves along with it. Above this frequency the cartridge does put out a signal because the stylus/cantilever moves independently of the cartridge body and tonearm. Generally speaking the output of the cartridge is flat above the resonance frequency.
At the resonance frequency the cartridge output peaks up. Therefore it is desirable for the resonance frequency to be below the audible lower limit which is around 20 Hz so the low bass frequency response is flat. On the other hand. warp frequencies tend to peak at around 3-4 Hz, so it is also desirable for the resonance frequency to be above the warp region so that those signals are not reproduced. Thus the optimum low frequency resonance is around 8-12 Hz.
The compliance of the cartridge suspension describes the stiffness of the "spring." A high compliance is a soft or "floppy" spring whereas a low compliance is a stiff spring. As a general rule, MM cartridges tend to be moderate to high compliance while MC cartridges tend to be low to moderate compliance, however there are exceptions.
The mass comes from two sources, the actual mass of the cartridge, and the effective mass of the tonearm. The effective mass of the tonearm is not the same as the actual weight (mass) of the tonearm because it is pivoted. The effective mass represents the "resistance" of the tonearm to being moved up and down (or side to side) on its pivot. Usually, this effective mass is on the order of 5-6 grams for a "low mass" tonearm and can be up to 20 or more grams for a "high mass" tonearm. In a few case, e.g. linear tracking tonearms, the effective mass in the vertical direction may be 5-6 grams whereas the effective mass in the horizontal direction may be 50-100 grams because the linear arm is pivoted moving up and down, but not moving sideways! In your case, with a carbon fiber ADC arm it is on the order of 5-6 grams.
Cartridges can weight anywhere from 3 grams (some of the B&O models) to over 30 grams (early Ortofon SPU). The cartridge mass is then added to the tonearm effective mass to get the total effective mass of the system.
This total effective mass, in combination with the "spring" compliance of the cartridge suspension, then determines the resonance frequency of the system. The higher the total effective mass, the lower the resonance frequency. The higher the compliance, the lower the resonance frequency. In fact, mathematically, the resonance frequency is proportional to the inverse of the square root of the compliance times the effective mass. For most people, it is easier to look up the resonance frequency on a graph rather than trying to calculate it. :-)
A low compliance cartridge tends to put more vibration into the tonearm and so generally is thought to benefit more from a stiffer, and hence higher mass, tonearm. A low compliance cartridge can be used in a low mass arm by adding weight to the headshell, but this does not stiffen the arm and so may be a sonically inferior option.
So to get back to your original question, your ADC arm was designed when MM cartridges were the norm, and moderate to high compliance was the norm. So your arm was designed for moderate to high compliance cartridges of light to moderate weight, such as the ADC cartridges (duh!). A heavy cartridge may work in your arm if it is of moderately low compliance, but may not work as well as it would in a higher mass, stiffer arm.
Bottom line, when choosing a cartridge you have to consider cartridge weight, tonearm effective mass and cartridge compliance in combination, as it affects the tonearm/cartridge resonance, as ONE of the the factors in your choice. Hope this helps.
Edits: 11/08/08Follow Ups:
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