Opinion is only as valid as its verifiable supporting evidence.
Wow, diyAudio is a nice place to visit but I wouldn't want to live there! Makes me appreciate this Altec User's Board! Pano's job moderating there is like herding cats!
I'll copy a comment about the DIY thread I made yesterday on the High Efficiency Speaker Asylum:
Thank you for the interesting thread link, Deon.
I won't get into the merits of field coil conversion except to say that IMO the results are worthwhile and not subtle. One thing I'll mention is that a mistake is often made when converting Altec or JBL compression drivers to field coil, and I see it happening again in this thread. The original Lansing 1930s field coil compression drivers used a constant diameter on the center pole from the voice coil gap to the back (actually front) plate. A sectional view can be seen at the bottom of this page:
http://www.lansingheritage.org/image...943/page07.jpg
When the conversion to Alnico V magnet was made in 1944, the center pole was shortened so that it could sit atop the interior ring magnet. Also, a skirt was added below the voice coil gap to widen the center pole to the diameter of the top of the magnet. This occurred with both small and large format drivers, as can be seen in the drawing of a small format driver here:
http://www.lansingheritage.org/image...804a/page1.jpg
Most folks who convert these drivers to field coil have never seen an original Lansing apart, so they machine a new lower center pole section to replace the magnet using the incorrect wide diameter of the skirt. Then a rather anemic field coil is wound to fit over this wide diameter, which will have inadequate cross section resulting in low gap flux density and/or possible coil overheating. When making the conversion, the skirt should be machined off the existing phasing plug/center pole and a new section of the same diameter machined to replace the magnet. Then a field coil of correct dimensions can be wound and the motor will work as well as the priceless 1930s Lansings.
I don't understand why field coils would sound any better than an Ainco or ceramic magnet, Isn't Magnetism just that? Or is the field coil a stronger magnet? or less stronger magnet?
I am sure there are more than one reason.
One I can think of is the ability to change the field strength to suit taste.
I'd like to hear this stuff, but probably never will.
Enjoying Altec Speakers since 1972
i have limited experience, but the WE 555s I have call for 7 volts input, no idea on the current. I also had an old Jensen which would scream with a 10 watt amplifier, and sadly let out the magic smoke after a while. But I had no idea of the voltage or current I supplied it with. Made lots of smoke and did it stink.
some magnet materials and configurations, maintain their flux better than others.Originally Posted by cradeldorf
guns kill people,
like spoons made rush limbaugh,
fat ....
Learn some of the terms associated with magnetism such as hysteresis, coercivity, and saturation, and you will automatically gain an understanding of why different magnetic sources can behave differently, especially in regard to the effects inductive pulses(an audio signal) have on them.
Not all vegetables make good leaders.
Whew, tough crowd over there in that Multi Way forum! Never got hate mail PMs before that thread.
It is very hard to have a conversation with all the topic cops and Parts Express catalog hit men lurking in the shadows. Pano deserves battle pay.
To think I went over there because I was interested in Altec field coil conversions...wound up fighting off idiots who think they are scientists but they are more like the Taliban.
Best way to look like a moron is to argue with morons, so I am guilty myself.
Definitely makes me appreciate the civil and friendly attitude on this board all the more!!!
Steve, appreciate your comment on the mechanical aspects. Where I am trying to get to is Lansing territory. That is a good place to be. Back in the day, I did compare Lansing 415s and 287s with the original Altec PM versions and it was a night and day difference.
Lansing was my main system for a few years. Now my parts are in the Silbatone museum. I'm trying to push to set this stuff up and reevaluate it, maybe take it out to a few shows so people can hear the glorious Lansing sound. That was some really great sounding theater gear.
Granted there are other differences in the drivers besides the motor, including those beautiful roll surround Lansing diaphragms, but they do share strong family resemblances.
So, maybe it wasn't a tightly controlled lab experiment but it was enough to teach me to think for myself and trust my listening experiences. At least I did the experiment. Thankfully, I was lucky enough to have that opportunity in the pre-ebay good scavenging days. It would be difficult and crazy expensive to assemble all that ancient stuff now.
The most compelling technical argument I saw for field coils discussed overload conditions and recovery characteristics of various magnetic materials. Most well-behaved were electromagnets, followed by AlNiCo, ferrite, and neodym in that order.
Now if only I could find that study again....does this sound familiar to anybody?
I tend to speculate that the presence of an external power source for the magnet forces the system back into line, but this is just a mental picture that I like.
Thanks for the info and pictures, Steve.
Jan
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