In earlier installments of this series, we’ve focused upon the various types of phono cartridges—pickup cartridges, if you prefer. Though wildly different in their internal construction, all these cartridges have one thing in common: a stylus (needle) that traces the record groove.
But: in terms of minimal record wear and plain old blue-sky theoretical elegance, wouldn’t the best needle be no needle?
Through the decades a number of designers have thought so, but actual working devices didn’t appear until lasers were readily available, and a commercial product—well, sort of commercial—only appeared after mass-acceptance of CD players.
The Laser Disc first appeared in 1978, and was the first consumer product to utilize a laser to scan a disc. Admittedly, Laser Disc players would only play, well, Laser Discs—which may have been the size of an LP, but were shiny aluminum/polycarbonate discs that presaged CDs. The Laser Disc player and disc were designed hand and hand as an optical scanning system.
The same year that Laser Discs first appeared—1978—saw the appearance of an article in the June issue of Audio that fascinated me then, and which still has serious tweak appeal. In “A New Standard in Turntable Speed Consistency”, [scroll to page 78, et seq—Ed.] three physicists at the University of Virginia describe how an extremely stable and consistently-rotating turntable could be used to examine three distinct fields of interest:
” 1)We wish to do a laboratory experiment in which we can unambiguously test the theories which predict that the force of gravity gets weaker as time goes on; 2) another experiment(currently underway) is one in which a study of the motion of rotating cylinders would tell us whether or not matter is being created in the universe and, 3) it appears that we can test the earth’s rotational speed fluctuation and wobble, measure latitude fluctuations, and study other geophysical phenomena by observing the forces acting on small masses placed on an almost totally constant -speed turntable.”
Who knew you could do all that with a turntable?
The snag in all this? A really, really consistent rotational speed was needed. As in “between 10,000 and 10,000,000 times better than the finest commercially available turntables.”
Obviously, getting an old BSR at a yard sale wasn’t going to work. The UVA physics crew must have still had a decent experimental budget back then,judging by the rig they built for their experiments:
“The turntable we are currently using for these experiments is shown in Fig. 1. It is a 95 -lb. brass disc that has been mounted on an air bearing with no mechanical contact between the bearing surfaces. Instead, the rotor of the bearing floats on a cushion of air approximately 0.0001 -inch thick. The turntable (moment of inertia 500 Ib.-in.2′) is mounted on a 500 -lb. granite block which rests on damped pneumatic springs which sit on an 8000 -lb.granite block. This, in turn, sits on four damping isolators, each consisting of eight steel plates separated by ribbed neoprene pads.”
The Big Rig. Note the LP.
Given that the device described weighed in at nearly 8600 pounds even without the steel isolators, their experimental set up wasn’t housed in an old Army barracks.
So given this remarkable construction, what did those physicists do? They figured out how to play records on it. Clearly no SME tonearm with a Shure V-15 would do for such an exotic set-up.(Ironically, the same issue of Audio is chock-full of ads for cartridges and turntables, as well as an article on the current state of phono cartridges, written by six engineers at Shure. There’s also an article on disco—but we’re getting way off-topic.)
From the article: “Finally, such a turntable needs a suitable cartridge and tonearm. In a future article we hope to report on the laser -optical pickup system we have conceived. Finely -focused laser light is guided to and servoed onto the record grove; then position -sensing detectors produce the two components of the stereophonic signals. A microprocessor sorts out the signal from record imperfections (the noise) by spectral analysis and provides appropriate control for the light beam as well as processing the signal. Such a system will be most useful if it can function with current records, and it seems likely that it can. The overwhelming advantage of such an arm is the delicacy with which it treats your records. The “stylus force” is only 0.000000000000000000000001 gram.”
I don’t think Shure ever approached that sort of tracking weight!
The disappointing aspect of this project? I’m not sure the laser playback system was ever built—the article says “we have conceived” the system, not “we have built”.
As I mentioned, the article fascinated me, and buried itself in the back of my brain. Back in 2001 I finally took the time to check up on the three authors of the article, and discovered that Prof. George Gillies—seen in the pic—was still at UVA. I emailed Professor Gillies, asking if the apparatus still existed.
I was disappointed by his response: “Although we gave up the precision rotations experiments years ago, we still do keep a finger in the gravitational physics pie with some experimental searches for anomalous effects in gravity. A couple of relevant publications are:
Ritter, R. C., Winkler, L. I., and Gillies, G. T., “Search for
Anomalous Spin-Dependent Forces with a Polarized-Mass Torsion
Pendulum,” Physical Review Letters, Vol. 70 (1993), pp. 701-704.
Ritter, R. C., Goldblum, C. E., Ni, W.-T., Gillies, G. T., and
Speake, C. C., “Experimental Test of Equivalence Principle with
Polarized Masses,” Physical Review D, Vol. 42 (1990), pp.
977-991.
“These are not exactly recent, but they are representative of the type of work that goes on here in that area.
“Most of my effort these days is in medical physics and biomedical engineering. ”
I asked what was to me an obvious question: what do you do with a 4-ton block of granite?”
Gillies responded, “One of the nuclear physics groups here took over that lab and use the block as a stable base-plate for some precision work of their own.”
And doggone it, I never asked about the laser playback system. I have to email Gillies, who is still at UVA. He may well think he has the world’s most patient stalker.
[I did hear from Dr. Gillies on December 3rd, and he confirmed that the laser playback system was never built.—Ed.]
As Yogi Berra supposedly opined, “In theory, theory and practice are the same. In practice, they ain’t.”
Next time in Copper, we’ll take a look at what happens when laser record playback goes from theory into practice.
0 comments