Tonearm Damping
Article By Bob Graham
The BAS Speaker Volume 3 No. 4, January 1995

  After reading Leigh Phoenix's article on damping, I was sufficiently impressed with his findings to re-evaluate my own tonearm's performance. I remembered my earlier days in hi-fi, when the Weathers turntable "mounted on a seismic platform" (as the ads used to say) together with its (then) revolutionary 1-gram cartridge mounted in the Weathers damped tonearm generated "oohs" and "ahs" whenever a salesman would toss the arm onto the spinning disc. Nothing bad ever happened, of course, because of the viscous damped arm; it just settled very gently into whatever groove happened to be beneath it at touchdown. Very few of us thought of this as anything more than an impressive demonstration; I certainly didn't realize the importance of damping then, and it has been only recently that I've even encountered damping again.

A couple of years ago, I owned the absolutely beautiful/ugly (take your pick) Transcriptors Hydraulic Reference turntable. It was impressive, with the records sitting on those 24k gold pads; too bad the Transcriptors' idea of anti-shock-suspension was to mount the whole thing on hockey pucks. But the Fluid Arm — that was different! It was a single jeweled unipivot, surrounded by a thick, gooey damping material. The arm was very low mass, and, together with the damping, which I now realize is very important, probably made it one of the best tonearms around. I sold the Transcriptors, hockey pucks and all, and resurrected my AR turntable, eventually improving it by adding the SME 3009 Series II arm. Now we come to the real reason I'm a believer in damping. When I added some of the newer cartridges to the old SME a couple of years ago, I began to notice some trouble. An ADC 10E Mk IV, for example, wobbled all over the record — I just couldn't keep the stylus from moving around, independent of the tonearm. Likewise, the XLM was less than spectacular, and warped records were now a real annoyance. Happily, SME came out with their new series arms, and I purchased one. NOW I would have perfection — I thought!

Almost, but not quite. True, the arm did perform a lot better, but there were still some warped records, particularly organ discs, where the arm bounced several times after each sharp warp, and I could hear the organ tones being modulated by this. Still, it was better than before, and the XLM was now my favorite, so I couldn't bring myself to give up the combination. Well, all the problems are now in the past. After reading the article on damping, I tried an experiment. I mounted a piece of thin brass rod on the back of my tonearm, and fastened two"paddles" on the end of this rod. These paddles are submerged in STP oil additive, which is held in a small metal trough. The paddles are mounted perpendicular to each other, so there is force applied whenever the arm assembly is in either a vertical or horizontal motion (see sketch). The principle, of course, is viscous damping. You can demonstrate this principle by placing your hand, fingers together like a paddle, in a bucket of water and moving the flat of your hand slowly through the water. You will feel almost no resistance. If, however, you try to move your hand quickly, you will feel considerable resistance; the quicker you try to move, the more resistance you will feel.

This is the principle on which a damped tonearm works. It will follow the relatively gradual motions of a warped record, but the damping action will "put the brakes" on any bounce following a particular warp. This is superior to merely taking an undamped arm and tightening up the bearings so that you increase the Coulomb friction, which is constant with velocity; that would only cause the arm to stick and do other unpleasant things. By starting out with a low-mass, lowfriction  arm and then adding controlled resistance with fluid, you will have a really first-rate damped tone arm.

 As for my own arm and cartridge, the XLM has never sounded so good. The previously annoying records are now playable with absolutely no "bounce," no warbling tones. The stylus stays virtually motionless (to the eye) relative to the tonearm, so I'm not generating low-frequency tones to modulate all my music.

Although my system is somewhat clumsy-looking, the improvement in performance is so profound, particularly with a high-compliance cartridge, that I would not consider being without  it. I'm sure that adding fluid damping to the old SME arm would have made the XLM very usable. How many cartridges like the XLM are considered "too fussy" for most tonearms, when the addition of damping might have made them compatible?

The only maintenance that might be required would be an occasional oil change — perhaps every 1000 miles of stylus travel or so, to get rid of accumulated things that might end up in the bucket of oil (like dust or a housefly). This device could be added to any tonearm, even those that could not otherwise have viscous damping. You could use a heavy paper clip for the rod, and glue some small paddles on with 5-minute epoxy. The container for the STP could be just about anything. It should be wide enough to allow the full horizontal motion of your tonearm, and deep enough to completely cover both paddles with fluid. The amount of damping force exerted can be varied by changing the size of the paddles. I've found that the vertical motion paddle works well if it is between 1/4 and 1/2 inch in diameter. The horizontal paddle size is somewhat less critical.

Try it — you'll like it! !

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