The arm resonant frequency depends on its mass and its support springiness, which is the cartridge compliance. Output drops rapidly below resonance, so it should be pitched high enough to reduce lower frequency rumble, disc warps and ripples which can otherwise produce large amplitude subsonic signals that could overload the amplifier and even damage the speakers. Rumble and flutter can produce intermodulation sidebands at audio frequencies. Their amplitude depends on the resonant frequency, decreasing as it rises. So a high resonant frequency is desirable, yet it must also be below the lowest recorded audio frequency of 20 Hz. A frequency only just below is therefore the optimum; 10 Hz was once recommended, but 16 Hz is now the preferred figure. A quick check is that the product of the mass and compliance should equal 100 for a resonant frequency of 16 Hz. For a frequency of 10 Hz the product is 250 which is the upper limit. High compliance is clearly undesirable unless mated with an arm of low mass. In addition to the mass/compliance resonance, there is a self resonance that falls usually within 10-250 Hz. The main effect of this is a considerable increase in crosstalk between channels. It can be minimized by viscous fluid arm-damping and flexible decoupling of counterweights.
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