Posted by Duke [ 63.87.108.184 ] on July 01, 2006 at 18:25:10:
Assuming that anyone who comes here is somewhat interested in loudspeaker design, I'll relate a problem that I ran into a few days ago and then describe what I'm hoping will be the solution.
One of the designs I'm working on is aimed at a very specific niche: Owners of entry-level output transformerless (OTL) tube amps. Such amplifiers like to see a high impedance load, but there aren't many high impedance loudspeakers to choose among. Hopefully in a few months there will be one more.
But this means that either I have to use two 8 ohm woofers in series, or find a 16 ohm woofer that meets my requirements. The dual woofer format was pushing driver and cabinet costs up higher than I wanted to go, but I couldn't find a 16 ohm woofer that I liked (and there aren't many to choose from). So I decided to take the plunge and have a custom woofer made to my specs.
A couple of days ago I received the prototype 12", 16-ohm woofer. The measurements look very good, but the woofer didn't sound that way. Clarity was disappointing.
Now it just so happened that a week or so ago I exchanged e-mails with Earl Geddes about the lack of clarity I'd heard in some fullrange drivers, and he named flux modulation as the likely culprit. So perhaps that was what plagued my custom woofer.
I described the symptoms to the engineer who designed my woofer, and he said that it sounded to him like flux modulation. So he is now changing the design to a different (and much more expensive - arrgh!) motor that will use demodulation rings ("shorting rings" or "Faraday rings"), which hopefully will improve the clarity. This woofer still won't be as good as the alnico one in the Jazz Modules, but even with the more expensive motor the cost will be much less.
I should get the new prototype woofer with the demodulation rings in two or three weeks, and I'll post my findings here.
Duke
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