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The headshell is the platform at the end of the arm tube where the phono cartridge is clamped. A mechanically tight coupling is essential to prevent microrattles and to help conduct resonances away from the stylus. The best mechanical connection is provided by an integral head- shell as this eliminates any joint between arm and headshell—both are cast or forged together from a single piece of metal. A less expensive and slightly less desirable integral design is to make a permanent joint between the headshell and arm tube, either welded or pressure fit. Permanent glue joints are the least desirable and least rigid due to their compliant adhesive.
When you use a detachable headshell, the surface contact between the headshell and arm tube is incomplete. Overtightening the headshell screws in an attempt to improve coupling is likely only to deform the parts and make matters worse. A removable headshell should be made of an inert, very rigid material to fix the cartridge in position as rigidly as possible and transmit resonances effectively without adding any of its own. Metal is best as it permits really torquing down the cartridge screws, thus minimizing “leakage” in the mechanical grounding loop. Carbon fiber, while a good vibration absorber, is less rigid and is also soft enough that screws cannot be tightened down securely. As a rule, avoid carbon fiber headshells.
Unfortunately, the choice of good removable headshells is quite limited—Sumiko makes one of the very best. One reason there is so little choice is that the good arms almost always have integral headshells and so their designers have thus had no need to develop a replaceable one. Mass-fi manufacturers produce many but without having considered the refinements of what a headshell really has to do.