by Joe_DS »
Mon Jun 23, 2008 2:21 am
The best sounding Edison Diamond Disc phonographs I've ever heard were those fitted with a replacement diaphragm designed by the late Bob Waltrip. Those who knew Bob may point out that some of his ideas about replacement diaphragms were eccentric. While many far exceeded the performance of the originals, others produced just the opposite results. But in the case of his "Waltrip Wonder-tone" Diamond Disc diaphragm, he seems to have hit the mark. Not only did they have a nice sonic punch, but there was no break-up or distortion. In fact, they seemed to expand the sonic range of Diamond Disc records.
According to what Bob wrote me, years ago, he took a good look at the way the original rice-paper/cork dampened diaphragm was designed, it's overall texture, what it sounded like when rubbed, weight, etc., and concluded that styrofoam --the type used for meat trays--would be the best replacement, PROVIDING it was properly shaped and gasketed. (This conclusion was reached after numerous unsuccessful attempts Bob made to create a diaphragm from scratch, using rice-paper and cork rings.)
Bob experimented with a number of sample styrofoam diaphragms and found that in order to perform correctly, the diaphragm's edge (circumference) had to be as flat as possible, while the center portion of the diaphragm increased in thickness to about 1/3 inch--directly in the center. This, he said, allowed a greater area of the diaphragm to plunge--much like an Orthophonic spider-driven diaphragm is designed to. Bob, in fact, told me that this was the purpose of the ceramic center used in the original Edison diaphragm--low in mass, but totally resistant to compression. (Welch and Read also cover this point in "From Tinfoil to Stereo," in their comprehensive review of the Edison Diamond Disc phonograph, though they go beyond this by saying that the "Theory of Matched Impedance" applies more to the Edison Diamond Disc reproducer than to the Victor Orthophonic sound box!)
To shape the diaphragm, Bob used a simple method of heating a (properly sized) cup (using boiling water) and pressing its bottom onto the styrofoam until it held it's shape. He then mounted the diaphragm in the reproducer shell using a small amount of non-hardening silicone calk in place of gaskets. A tiny drop of calk was also used to seal the center where the silk linkage thread was inserted. Bob insisted that the diaphragm should not be clamped too tightly; nothing, in other words, should be done to restrict it's ability to plunge up and down.
I'm not sure if any of these Waltrip Wonder-tones still exist, but if so, it would be interesting to hear from collectors concerning how well they've stood the test of time.