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Re: Double loaders...

Posted by Steve Schell (M) on February 8, 2007 at 00:05:56

In Reply to: Re: Double loaders... posted by Paul Eizik on February 7, 2007 at 20:54:56:

Hi Paul,

Olson was indeed a genius; just ask RCA-fan (himself a bass horn master) who knew him! In many of Olson's writings I also detect the uncredited insights of Frank Massa, who collaborated with Olson at RCA all through the 1930s and refined the science of voice coil and transducer design to an amazing extent.

The 64 Monitor design was no doubt tailored to Olson's dual voice coil driver. These amazing 8" (6" cone) relics still define what is possible in a single wide range driver. At the last Oswald's Mill gathering, Jonathan Weiss had scored a 64A Monitor cabinet with altered exterior cosmetics for something like $35 on ebay, and had procured the correct RCA dual voice coil driver to install. The assembled audio crazies listened to that system in stunned silence except for the occasional "Wow." Though a bit limited in bandwidth in both extremes, these systems possess incredible resolving power and see-through clarity.

Olson's dual voice coil driver design can be studied in detail in his U.S. Patent #2,007,748. The dual voice coil was incorporated in the driver (can't remember the model #) used in the 64A, which otherwise was the same as the MI-1425A 8" cone driver used in most of the early 1930s RCA horn systems. By the 1940s there were modernized versions of the driver, MI-4410 (permanent magnet) and MI-4411 (field coil) which were fitted to the 64B monitor; either available at equal cost. Then the trail went cold, and to my knowledge Olson's dual voice coil driver has not been heard from since.

The 64B contained at least one acoustical improvement over the A, a sheet metal vaned high frequency diffusor. It is decribed in Olson's patent #2,102,212.

Until carefully reading the patent we discussed earlier, I assumed that the purpose of the two necked-down sections was to limit the output of the bass horn. The output of the horn does seem a bit timid in comparison to the driver's front output. Perhaps Olson did seek to limit the bass output a bit, as these monitors were listened to in the nearfield in small control rooms.

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