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Yet another way to measure arm/cartridge resonance...

Simply drop the tonearm onto a blank portion (run-out area) of a stationary LP while digitally recording the cartridge output. You get a waveform that looks like this.



The beauty of this waveform is that not only can you measure resonance frequency, but you can also measure the damping ratio of the cantilever suspension.



The resonance frequency in hertz is the reciprocal of the waveform period.

The damping ratio, zeta, can be calculated by measuring the amplitude of two successive peaks and calculating the logarithmic decrement, delta, by applying the following equations.



Now, we can apply some slightly more elaborate resonance frequency equations that incorporate cantilever suspension damping into the mix.



The following waveform was produced from my Technics SL-1200 Mk2 with Denon DL-S1 cartridge mounted in the standard Technics headshell. I disabled the KAB tonearm fluid damper for this test so that only cantilever damping is being measured. Cartridge mass is 7-grams and mounting hardware is 0.7 grams. The Technics tonearm supposedly has 12-grams effective mass thus yielding a total effective mass of about 19.7-grams.



The reciprocal of the waveform period shows a cantilever suspension damped resonance of 8.60-Hz.

The damping ratio computes to 0.1066 and total effective mass is 19.7-grams yielding a cartridge compliance of 17.19-mm/N.

Best regards,
John Elison


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Topic - Yet another way to measure arm/cartridge resonance... - John Elison 22:07:47 03/6/10 (32)

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