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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
nsgarch's avatar
nsgarch
2,524 posts
 
Pittsflyer: according to the interactive table at cartridgedb.com, your Robin tonearm (effective mass 11gm.) combined with your Grado cartridge and mounting hardware (6.5 gm + ~1.0 gm. = 7.5 gm.) with a compliance of 20 x 10-6 cm/dyne, gives you a system resonance of 8 hertz. Quite acceptable without any alterations to arm or cartridge.
kel34
64 posts
 
What about a Grado Reference on a RB300 is it a good match and can any of the above tweaks improve things?
pittsflyer
8 posts
 
Thanks for the replies. I'd prefer not to replace either the arm or the cartridge, but the inescapable fact is, the combination produces a ridiculous amount of woofer pumping. The resulting IM distortion is so unpleasant that I inserted a couple of capacitors after the turntable to roll off the lowest frequencies. The problem, however, is a mechanical one, and I hope to solve it as such.
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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