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In Reply to: RE: Suggestions For Cap Size With Monsoon Tweeter w/ Fulton FMI80 posted by tubav on March 07, 2017 at 03:25:39
I don't know anything about your ribbon tweeters but I have had a pair of FMI-80s since the 1970s so I do know something about them. The "crossover" is as you described---just a 6uf cap in series with the Peerless tweeters. The 8" woofer runs full range. The woofer's natural rolloff in the highs allows it to blend nicely with the tweeters. This may seem like a haphazard or economy crossover, but it is actually one of the keys to the 80's high quality sound especially its natural dynamics. At one point I disconnected the Peerless tweeters and just used my RTR ESR-6 electrostatic tweeters with a 1.5k crossover. I figured since the RTRs were rated down to the same frequency used in the 80's crossover, this should give me the benefit of the electrostats down to a lower frequency and be an overall improvement. Wrong! The sound had an obvious hole or suckout in the crossover region and what was left was an incoherent mess. That taught me that the Peerless tweeters were important for a smooth transition from the paper cone woofer to the super-fast electrostats. I suspect you will find something similar with your ribbons. However no harm in trying provided your crossover cap provides enough protection for the delicate ribbons. The proper value of the cap will depend on the impedance characteristics of the ribbon in the crossover region. You will probably also find that the ribbons are not the same sensitivity as the woofer so the ribbons may be too loud or not not loud enough. If I were you I would just keep an eye out for some Peerless cone tweeters. I suspect they come up on EBay pretty regularly although I have never checked.
Edits: 03/07/17Follow Ups:
...by simply reversing the polarity of the tweeters.
When you can't make them see the light, make them feel the heat.- Ronald Reagan
I tried reversing the polarity. As I recall there wasn't much difference. The 6 electrostatic panels were angled for better dispersion and they were also open on the back. Perhaps those made the phasing less critical.
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