The Mapleson Cylinders - Program Notes
|The Mapleson Transfers|
|The Early Stages: 1979-81|
The first order of business was to design a playback apparatus capable of accommodating cylinders of all types, that imposed no mechanical vibration, offered light-weight tracking, accommodated speeds from 40 to 200 rpm, could be servo-driven, had digital mandrel readout in rpm, and could track vertically with no side angling at 100, 150 and 200 lpi (lines per inch). Obviously, this was no small order. Art Shifrin, a restoration engineer, developed a machine which accomplished most of these goals, and with further modifications at Rodgers and Hammerstein, it was able to fill our needs.
I made a search of the existing literature on the analysis and playback technology of acoustical recordings--an area that proved to be under-investigated. (This was before the Audio Engineering Society published their index of publications.) However, an article by Hans Meulengracht-Madsen, "The Transcription of Old Phonograph Wax Records" ( AES Journal, XXIV/1 ) describes an extremely thorough acoustical analysis methodology, and should be required reading for anyone working with this technology. It is based on cylinders recorded from 1919 to 1923, 23 years after Mapleson did his recordings. My associate John Fesler and I knew that in order to do viable acoustical analysis, the cylinders would have to be recorded methodically, under calibrated conditions, on equipment similar to that used by Mapleson. This was not difficult, since many Edison Home Model A's are still to be found in good working condition. We will discuss the recordings and their setup in a moment, but first let me discuss the acoustical concerns.
One of the most important articles to date concerning acoustical analysis is that of Maxfield and Harrison (in the Journal of the American Institute of Electrical Engineering, XLV [February 1926], 334-48), in which they relate acoustical energy to electrical energy, and describe what was later known as the "theory of matched impedance." In fact, they were describing the pre- and post- (record and playback) equalization, or pre-emphasis/de-emphasis that is still the manner in which records are cut and played today.
To ascertain some of the general characteristics of cylinders, I collected samples of every type of cylinder I could find from our archives, from collectors, and from other sources: a representative batch of brown waxes, Amberols, Blue Amberols, Concerts, Columbias and others. These were sent to the late Ed Catalano, chief chemist for the Gamma Omega Association. He reported that the surface deterioration of the cylinders was caused more by internal stress then by mold and mildew. Photomicrography was done on cylinder surfaces, and several samples were broken to enable photography of the various layers. A test washing of a moldy cylinder surface produced the results shown in Figure 1. Despite the frequent statements in the literature about Maplesons that the extreme surface noise is due to fungus attack, they do not in fact suffer from excessive fungus attack. The fact is that by 1937 Lionel Mapleson and his colleagues had played some of the cylinders to a physical point of no return.
I then sent our sample cylinders to George Alexandrovich of Stanton Magnetics, and asked him to evaluate the various cuts with the scanning electron microscope. He took wax impressions of the grooves and measured the different cutting parameters such as depth, width, and sidewall deformation characteristics. This was extremely important for determining tracking parameters, stylus size and shape, vertical/lateral phasing problems, and the like. In general, we found that the processed molded cylinders tracked at approximately 2-7 grams, but Blue Amberols were sturdier and could be tracked more heavily, if necessary. The brown waxes (the type used by Mapleson), on a cleanly shaved, freshly cut surface that had been warmed and prepared, were cut at an 8 mil diameter to a very shallow depth at 100 lpi. The commercially produced cylinders we evaluated fell within the same depth parameters for the most part, but were played back with a stylus in the 7.4 mil tip radius for the two-minute (100 lpi) type, and 4.2 mil for the four-minute (200 lpi) type (see Figure 2). The surface content varied
according to the material composition. On some of the unmodulated-groove brown wax cylinders that John Fesler cut for me, surface content was measured (with a BaDap and HP spectrum analyzer) at levels as low as 3 to 8 dB. Black waxes measure at least double that; unmodulated grooves cut on a shellac disc are triple.
As far as the level in recording originals, the horn and diaphragm like to see an spl (sound pressure level) of between 90 and 105 dB. When you consider that Mapleson was 40 feet away from his sound sources, it's amazing that he was able to get any modulation at all, even with his large horn. It would seem clear that the singers and orchestras of his day must have performed with a great deal of gusto.
With an spl of over 105 dB, the radius of curvature of the wound track modulation becomes equal to, or smaller than, the radius of replay stylus, and a curvature overload occurs as tracing distortion where high levels are coupled with signal frequencies. In the case of the Maplesons, the track configuration was seriously degraded by constant and improper playing, thereby nullifying any standardization applicable to the lot. We decided (mainly because of comparative performance considerations) to transfer all the cylinders at one speed: 184 rpm. A few more were transferred at 120 and 160, but most ran from 184 and up (the old machines had variable speed for pitching, but all tracked at 100 lpi via a feed screw mechanism). Tracing distortion, surface cracks, internal stress cracks, out-of-roundness, groove deformities, different signal-to-noise ratios, and different speeds rendered each cylinder a project in itself.