The Korf Blog

The inside story: our research, development and opinions

11 July 2017
Vibrometry on a budget, part II
As I am preparing a tonearm prototype for measurements, I think it is only fair to speak about what exactly we will be measuring and how. If you're a dedicated DIYer, you might actually be interested in doing some of these measurements yourself!

Today, we'll take the measurements of 2 tonearms. One is well-known classic from the 1970s: a SAEC WE-308L. It is a reasonably rigid 11" arm with ingenious double knife edge bearings that supposedly eliminate "bearing chatter."

The second is a no-name modern Chinese tonearm, obviously "inspired" by Rega. The suspension is with usual ball bearings, probably of the cheapest kind.

After data conversion and FFT, here's what we get.

The first chart is a SAEC WE-308L with a cheap aftermarket headshell. You can see the pronounced, but low Q, main bending mode and the counterweight wiggling about a bit. The clever preloaded knife bearings really do work, barely contributing to the picture. And the headshell, well, is quite bad.
And here is unnamed Chinese Rega copy, substituting a 10mm aluminium tube for Rega's tapered magnesium one.

It sounds quite horrible, and it is easy to see why. There is a sharp high Q third harmonic bending mode, and then the further main tube and counterweight resonances make a complete hash of things. Cheap ball bearings ring stronger than the main tube. And the headshell is even worse than a $10 piece of bent aluminium I used on a SAEC.
Area under the curve is a good rough indicator of the arm's sonic potential, as the total energy of the system is a function of this area. In our case, SAEC's area is less than half of noname's.

This data was gathered using an Endevco Picomin 22 accelerometer, Audio Technica AT-7V cartridge and a Clearaudio CA-TRS-1007 test record's vertical modulation track.
Next week, hopefully, the measurements of our first prototype arm!
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