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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
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.
pittsflyer
8 posts
 
While we have some expertise on the line, I'm trying to go the opposite direction. I have a Grado Reference Sonata on a Graham Robin with a resonant frequency of 8.5Hz. Two questions come up: Will reducing the tonearm mass help reduce the substantial infrasonic signal, and if so, does anyone manufacture a very lightweight headshell?
nsgarch's avatar
nsgarch
2,517 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.
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