Rerurn to Romy the Cat's Site
In the Forum: Horn-Loaded Speakers
In the Thread: Vitavox’s S2 Survival Guide.
Post Subject: Re: It's not about field strength...Posted by guy sergeant on: 4/15/2005
I don't know the full story of how loudspeakers went from field coils to permanent magnets. I believe that ultimately it was dictated by the price and availability of Alnico. Eventually Alnico became cheap enough to make similar or higher strength magnetic fields viable and the additional complications in implementing a field coil(DC Supplies, heat build up etc) made field coils unnattractive.
I think that something was lost when this technology was abandoned and I admire the Cogent people for their efforts in trying to resurrect the RCA driver. I've never heard one so I can't comment on whether it's a good design but I can imagine it could be. Having said that I've never heard a properly working WE555 or 594 either and given the problems of getting the S2 to work well I can't imagine there are many installations using those drivers with the right sort of horns to get a really good result anyway.
A friend, whose ears I trust, listened (I urged him to go there) to the Cogent System at the MAF last year and said it was poor which disappointed me. I'd have to say maybe their room acoustics were bad but he said they were reasonably happy with the result they were getting. Time will tell.
I did have alot of experience with the Japanese made Audio Note cartridges. (I know Romy isn't a fan) I even spent some time at their factory learning how to build them so I learnt something of why the designs ended up being how they are. What was interesting was that while the diamond, cantilever, coils, former, and body stayed the same between the Io and the Io Ltd the only thing that changed was the magnetic circuit. The Io used 2 alnico magnets and (as I recall Iron pole pieces) whereas the Io Ltd used a 2 piece horseshoe of Permendur, each piece wound with a coil that were joined in Series to form an electromagnet. 2 additional wires down the arm supplied 1.2v at half an amp to this.
What was interesting was the field strength (and output signal) from the electromagnetic cartridge were significantly lower than that from the permanent magnet design. However the performance of the two was incomparable. (bear in mind the body and all the moving parts were exactly the same on each model. The Io Ltd had it seemed a fraction of the distortion of the standard Io (and any other cartridge imho) but this was NOT because of the field strength, rather the linearity of the field and how it replenished itself when bent out of shape. It's rare to have the opportunity to do a truly like for like comparison between a field coil and a permanent magnet, I can't think of any pair of speaker drivers that would allow you to do it. But what could be heard was the potential improvements that could be made everywhere there is a permanent magnet in your system.
I'd love to have a pair of S2's spare that I could put field coils into. Having seen Mike Harvey's cut-away S2 I'm sure it could be done. I'd also like to change to Permendur pole pieces but that would be expensive. It's why the Ale drivers cost so much. I've got some redundant JBL2361's, maybe I should attack those!
Chris, Do you have & use some of the RCA drivers? I'd love to hear them. Where abouts are you?
enough for now,
GuyRerurn to Romy the Cat's Site