Cartridge Loading and Compliance Laws

I understand the need to keep the system resonance out of the audible frequency band and footfall band. But why would a low mass arm be useful in doing that. I would have thought that the idea was to keep the arm from moving in sympathy with the stylus, and a higher inertial would accomplish that. In fact, if we could maintain a ridgid mount of the cartridge body, and only allowed the stylus to move in response to the groove modulations, wouldnt that be the perfect set up, no losses due to the arm moving in the same direction as the stylus or gains for that matter when the arm moves opposite to the stylus. So wouldnt a high mass arm accomplish that goal better than a low mass arm, even with a high compliance cartridge.

Lewn,
To use your truck/sports car analogy however, a truck would be less likely to be knocked off its straight path than a sports car hitting the same bump. I dont know that the analogy works because the tonearm is not moving, and therefore has no momentum inertia of its own, only its fixed inertia as an impediment to motion. But since I dont want the tonearm to move relative to the stylus, why wouldnt that be better. Dont we want to keep the headshell/cartridge/stylus relationship fixed except for those movement in the stylus that correspond to the vinyl groove. Why would we want the tonearm to move? And if it did at the same rate as the stylus, which of course it can't, wouldnt that result in no sound at all. Isnt it the movement of the stylus and coil assembly relative to a fixed magnet what produces the sound. And if that fixed magnet moved the same as the stylus/coil, no sound would be reproduced.

Tony,
I accept your analogy with respect to record warps. I was more referring to the stylus/arm relationship in the normal condition of tracing a flat record groove.

Lewn,
What I meant is that the tonearm is not moving in relation to itself, while a car or truck is moving, thereby creating what I referred to as momentum inertia. You know, an object in motion tends to stay in motion. Knocking a moving vehicle off its line requires a force that increases with the speed of the vehicle. You dont have that issue with a tonearm, which is relatively fixed as compared to theh speed of the record groove. Sure, it has to travel across the record, and up and down over warps, but not at anything close to the speed of the wiggles in the groove, which at the outer groove is traveling around 1.74 ft per second. A 20 minute record requires the arm to move horizontally about .001375 ft/sec assuming a 4" playing surface. Hardly a meaningful comparison. That makes me believe that holding the cartridge steady and just allowing the stylus to move is the more accurate method. Again, I am not addressing warps. I do see, however, that once the arm does move, a heavier arm will tend to overshoot and be slower to react and return to the neutral position.

Doesnt the Townshend fluid damper trough at the headshell end essentially create a condition that the stylus would see as a more massive tonearm. I can tell you from experience that the Townshend system works very well, and cleans up the bass tremendously as compared to the same cartridge/tonearm without the damping trough.

I wasnt making a general statement that a heavy arm is better. I was just trying to think through the variables and it seemed that a heavier arm would do the things an arm is supposed to do better than a lighter arm. I dont know if that is true, however, since I havent been able to hear and compare the universe of arms out there. My thoughts were just that I seem to hear a mantra of heavy arm = low compliance cartridge, light arm = high compliance cartridge and was questioning whether that is true. Again, I dont know and only seek to understand and learn.

And those ideas are...?