Tonearm Types: What's In a Name?
onearms come in more different types, shapes and sizes than you might imagine: gimbal-bearing, unipivot, passive linear-tracking, servo-corrected linear-tracking, thread-bearing, split-bearing and pivoting-cartridge designs -- a list that covers just a few, with each type having subcategories, each available in a host of different lengths and critical dimensions. Thankfully, for the most part, we can concern ourselves with two basic types, while anything more exotic will be deserving of specialist dealer support (or an owner who is prepared to take the time to learn all about his new toy). Most budget record players these days include (and more ambitious designs that don’t will generally find themselves fitted with) a basic pivoted design that uses a gimbal or unipivot bearing -- generally of "standard" 9” length. The two different types are easy to tell apart; a gimbal design uses separate closed-cage bearings to allow lateral and vertical movement (designs of this type include the various Rega 'arms and their derivatives, the VPI Traveler 'arm and the Pro-Ject 'arms) while unipivots sit the tonearm on the point of a needle, allowing free movement in all directions (the VPI JMW and Graham designs are perhaps the most common unipivots). Neither type is inherently superior, and you can achieve good results using either approach. Once again, it not is a case of what you use but how you use it that matters. However, although all bearings need to be treated with care, precision gimbal bearings can easily be damaged if they are subjected to inappropriate shock or torque, so these need to be treated with special consideration.
The main difference in the setup protocol between the two different tonearm types is the requirement to set azimuth -- the lateral attitude of the stylus to the groove -- on any unipivot. While this should be a standard consideration in aligning any cartridge, many gimbal 'arms (the Regas and SMEs, for example) dispense with the facility in the name of greater rigidity and structural simplicity, instead relying on the fixed plane of the tonearm bearings and accurate cartridge manufacturing to ensure the accurate attitude of the stylus. The free-bearing arrangement of a unipivot enjoys no such luxury, so the rotational attitude of the tonearm (and hence the cartridge) needs to be set. This is generally achieved by the use of outrigger weights or by simply twisting the eccentric main counterweight or even the headshell. It is not a difficult task, but in the case of an 'arm that uses the main counterweight to set azimuth, adjusting the offset of the weight while retaining precise downforce adjustment can be tricky, requiring double checking of both parameters.
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Longer 'arms also exist, generally around 10.5" or 12" in length,
with many of the more expensive designs being available in a range of lengths. The longer
the 'arm, the lower the inherent tracing distortion as the 'arm moves in an arc across the
record, but that advantage comes at the cost of increased effective mass and inertia, and
can easily be eroded by less-than-perfect cartridge alignment or choice. That demands
either a dedicated or a truly universal protractor. Again, 12" arms can offer some
advantages over shorter designs, but it is far from a given, while they also demand
lower-compliance cartridges to deliver their best results -- not a problem per se, but
another thing that it’s possible to get wrong, especially if moving up from an
existing deck/'arm combination.