The Korf Blog

The inside story: our research, development and opinions

12 September 2017
Prototype 4, Rigidity vs Damping
Prototype number 4 has a 10 mm diameter thin-wall stainless steel armtube. Wall thickness is 0.25mm. No surface treatment of any sort was applied.

Below is the vibrometry chart. I think we've seen enough of SAEC WE-308L tonearm data, so I removed it. Prototype 2 with "clean" counterweight is in light green, Prototype 3 is purple and the current one is red.
The steel tube with thin 0.25 mm walls flexes less than aluminium tube with 2 mm walls. While the 1st mode resonance @ 260 Hz is only about 0.05 g lower, the second and third harmonics are completely gone.

But the high rigidity of steel brings a different problem. While the damping capacity η of stainless steel is more or less the same as the aluminium alloy that we use (about 4-6), there is a lot less steel to do the damping! As a result, counterweight resonance shoots right up, and is now the dominant resonance of our arm. The counterweight stub is a solid aluminium rod, ringing with a very high Q peak.

Subjective evaluation
It is an interesting test. What is more important, the increase in rigidity in Prototype 4, or better damping of Prototype 3?

And the answer is clear. Prototype 4 beats Prototype 3 by a significant margin. All the good qualities of Prototype 3 are still there, but on top of that there's resolution and timbral accuracy. Vocals don't sound the least bit nasal despite that 0.25 g resonance peak right at 800 Hz.

Sonically, our Prototype 4 feels comparable to typical mid-priced (around $1000 retail) commercial offerings.

Result: ★★★★
Next week, next arm tube! Although I am very tempted to stay with this thin-wall configuration, apply additional damping and see how it changes the sound.
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