Quote Originally Posted by Todd W. White View Post
I talked with Bill Hayes today, who'll be 90 this July incidentally, and he says that there was never any diaphragm change in the production model of the 604C.

Any differences, he said, would be due to the fatigue of the diaphragms, plus weakening of the magnets. It could also be the crossover(s).
Hi Todd, sorry I don't know who Bill Hayes is? Was he an Altec employee or an Altec engineer? What I was told is not so much a change in the design but rather a change in supplier of the materials used to manufactur.. a better metallurgic mix if even by accident. Now I'm not sure if this is Urban legend or what.. just digging for confirmation/information. As to crossovers they are new GPA manufactured xovers designed by them for use with the 16ohm 604's. The listening tests were conducted with my face planted squarely infront of the speaker about a foot away.. moving back and forth between speakers and replaying certain passages over an over again for comparisons sake.. all other factors are the same. Speaker leads were swapped back and forth between mono block amps etc..

also in regards to magnetic loss.. this is copied from audio asylum forum and I have read and heard much the same elsewhere.
Actually, if not abused, they should last almost forever. After a magnet stablizes, the loss of magnetic strength is on the order of 1% per thousand years. Its rare for loudspeakers used in a home environment to be run at the levels that would cause demagnetization of the magnets. This is usually only seen in commercial venues that run systems at full rated input levels for long periods of time. And even then, its not as common as you would think, going by all of the repeated mis-information you always find on the internet. Take your loudspeakers outside, away from sources of reflections, and feed them the same input level with a signal generator, and measure the sound level of both, from the same fixed distance. If they measure reasonably close to each other, I would not worry any more about it.

another copy paste on the same subject..

Google up Alnico or Cobalt You will soon read that Alnico is projected for a 2,000 year Life before mag field Fluz degradation is significant.
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