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Tonearm / Catridge matching?

I have a potentially stupid question about tonearm in general, and linear tracking arm in particular. I am using the Rockport 6000 tonearm, and in his reviews, Michael Fremer had repeatedly stated that the 6000 sounded excellent, but a little weak in the bass. He stated that “ The 6000’s relatively low vertical effective mass put its resonance frequency above the ideal 8-12 Hz region with moving coil cartridges of average weight and typically low compliance, causing the bass to begin rolling off prematurely”. He also stated that Rockport had solved this problem in the 7000, and the arm on the Sirius III, by using heavier armtubes.
Now, if the objective is to make the armtube heavier (so it has a higher effective mass), and assuming the armtube is already rigid enough on the 6000, can I simply add a little lead spacer between the cartridge and the headshell to increase the effective mass and achieve similar result. If this method is workable here, does it also apply to fix pivot arms. Am I missing something here?

Thanks in advance

Michael
thekong

Showing 2 responses by dougdeacon

dougdeacon
3,338 posts
 
Increasing effective mass will in theory cause greater problems when tracking warped records. The higher inertia of the arm in the vertical plane will cause a greater swing in effective VTF at the top and bottom of warps. How much this will effect you in reality depends on the warp tracking capabilities of your rig, and of course on your records! If your Rockport has vacuum hold-down then it's probably a non-issue.

Adding the weight on top of the headshell may be better, as Raul suggested. Not only will your cartridge/headshell interface be unaffected, but your VTA/SRA will too. If you put a shim between headshell and cartridge, you'll have to raise your arm by a similar thickness to compensate.

Read Twl's HIFI Mod thread for a very thorough discussion of the positive effects of increased eff. mass on bass and dynamics. His mod was designed for certain pivoted arms, but the principles are the same in many respects.
dougdeacon
3,338 posts
 
Pittsflyer,

What made you decide your woofer pumping is related to your arm/cartridge resonance frequency? For that to be true, there would have to be some source of energy at or near 8.5Hz to excite your arm/cartridge into resonance. What energy source do you suspect?

I can't think of any myself. Except for the rare 8.5Hz warp, few if any LP's contain modulations below 16 Hz or so. Footfalls and other floorborne vibrations are typically said to fall well below 6 Hz.

I'm not conviced your tonearm has anything to do with the woofer pumping. I suspect a variation of the infamous Grado dance. The solution, like it or not, may be to choose a cartridge with a properly damped suspension.
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