Kuzma Air Line tonearm Manufacturer's Comment

Sidebar 3: Manufacturer's Comment

Editor: I was pleased to read in the August issue that MF believes that the Air Line tonearm could be "the finest tonearm ever built." MF raised, however, a few points that I would like to address:

"Theoretical problems" with porous-wall bearings... Air bearings are used worldwide by leading manufacturers of the most precise industrial machinery in conditions far more demanding than their uses in audio. In the last decade, porous bearings (acting as an infinite number of small holes), as opposed to the much smaller number of larger holes in standard air bearings, have been generally accepted in industry as the stiffest air bearings available. Also, rotational captured-air bearings must not be confused with air bearings used for moving heavy loads, where a mere lifting effect is required.

"The Kuzma bearing is four times stiffer than the Rockport's..." The stiffness of a captured-air bearing depends on its construction and air pressure. The same air bearing will have a stiffness of around 2N/µm with 1-bar pressure, but 6N/µm with 4-bar pressure. This means three times greater force is needed for the bearing collar to touch the shaft and cause friction. At hi-fi shows, we routinely ask people to pull or twist the Air Line tonearm on a Stabi Reference turntable. The whole suspended mass of 24kg (52.8 lbs) moves back and forth for 1/4!9 while the air bearing maintains zero friction! Most people are shocked, particularly if they have had experience of other arms using air.

"A question of damping..." A system will resonate only when disturbing forces appear at the resonance frequency. If there are no disturbing forces, then there are no problems. However, if a system is overdamped, then instead of one resonance, two smaller resonances occur, one below and one above the previous resonance, which can create further problems. There is, in fact, a level of effective damping on the Air Line tonearm. The cantilever suspension itself and the air supply tube add damping. Our choice was for either too little or adequate damping; we chose the latter.

"Eccentric LPs and any deviation from absolute horizontality will create...problems..." Horizontal disturbances of an eccentrically spinning record occur only at 0.55Hz or 0.75Hz (33rpm or 45rpm). This is well out of the Air Line tonearm's resonance in the horizontal plane, which is between 2 and 5Hz and does not cause problems tracking virtually all LPs. Plus, if one has a defective disc so poorly pressed or off-center that it might cause such problems, it is perhaps most prudent to simply not play it.

Mr. Fremer raises several other technical questions, none of which, however, seems to compromise his conclusion that "the Air Line's presentation was staggeringly better than that of any other arm I've auditioned with the exception of the one included with the $70,000 Rockport System III Sirius." We at Kuzma agree.

Thank you and Mr. Fremer for a thoughtful and comprehensive review.—Franc Kuzma, Kuzma Ltd.

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