arm mass/ cartridge compliance mismatch

The suspension of a cartridge can be modeled as a spring. The stiffness of the spring being the analog of the compliance of the cartridge suspension. The entire moving system has a primary resonance, or actually two primary resonances in the case of an arm using a decoupled counterweight. Think of the effective mass of the arm as being a weight on top of the spring, causing it to compress. The heavier the effective mass of the arm, the lower this resonance will be, the higher the compliance of the cartridge, the lower this resonance will be. When the arm resonance is excited, the arm rings like a bell, uncontrolled motion if you will, so the desire is to have a primary resonance away from things that excite it. Sonically, the implication is anything from muddy sound all the way to motorboating of the arm, with the cartridge losing groove contact, in the most extreme cases. On the low end, there is warp wow, in the six to ten cycle range. On the high end there is the actual bass recorded onto the record, twenty cycles. So we shoot for a primary resonance somewhere in the middle and even this is open to some debate. Since there is a range of acceptable resonant frequencies, there is usually quite a bit of leeway involved and most commonly used combinations fall well within the range that will not have audible consequences.

http://www.theanalogdept.com/cartridge___arm_matching.htm

Many thanks for your informative help. And I shall look into the Allsop Orbitrac- it sounds very interesting.

Can you hazard a guess whether a van den Hul FROG (recommended arm mass 6-10g- compliance 35u) would work in an Audio Kuzma STOGI arm (modified by removing the finger lift)? The STOGI is specified as having an effective mass of 13.5g, but that is with the finger lift- so call it 13G.

Eguth

That figure of 35 x10-6/dyne is too high. It may be STATIC compliance (at 0Hz) rather than dynamic (measured usually at 100Hz). Dynamic compliance is usually b/ween 10-40% of static.

Whatever the case may be, VdHul's recommend'n for a 6-10gr arms seems to indicate average compliance AND that yr proposed set-up consisting of Stogi+Frog is MOST likely to resonate outside the acceptable range.

ANYWAY, the formula to calculate resonant frequency (RF)is,
RF= 1000/2pi x sqrt (total mass x cu).
Cheers

Won't Van Den Hul tune the suspension of any of his cartridges to match the effective mass of a given arm? I think that this is one of the selling points of a bespoke product like this.