The seller has an informative picture in another auction:
http://cgi.ebay.de/Altec-Lansing-287...1%7C240%3A1318
but it's impossible to form an opinion without elaborate technical specifications, and the seller hasn't published any.
And one would pay 5000 euros for these because?
To put them on display...they look so cool, surely no one would ever intend to use them! LOLOriginally Posted by Allanvh5150
And one would pay 5000 euros for these because?
This fellow has displayed good craftsmanship in converting some older JBL drivers to field coil. Unfortunately he has made the same mistake that several others have made by using an oversized center pole and undersized field coil. The old field coil compression drivers generally used a center pole the same diameter as the inner pole piece, which allowed plenty of room in the pot for a nice large cross section field coil. The common mistake of guys who have never seen the early drivers apart is that they look at the widened short skirt on the center pole of the permanent magnet drivers (done to accomodate the ring magnet) and think that this is the proper diameter for the center pole. This results in a skinny, pipe-looking field coil which lacks adequate cross section to properly energize the voice coil gap without excessive heating to the field coil.
I've attached an illustration of the work necessary to convert an Altec 288 to field coil (over a sectional drawing of an Altec Lansing 287 field coil driver). The new center pole section is machined to complete the circuit and the widened skirt of the 288 center pole section is machined off. The 288 magnet and die cast throat section are discarded. The process would be similar for the large format JBL driver.
I wonder if GPA (Great Plains Audio) would consider remanufacturing the 287 field coil, for those who may be interested, with a 12vdc coil...like the Fertin.
JoMoCo, you'd have to call Bill Hanuschak and ask him if he would consider such a project. I believe he is familiar with the early Lansing field coil drivers. Twelve volts is a good choice for the field voltage in my opinion. My past experiments have shown that the ratio of gap flux density to field dissipation is increased as the coil is designed for lower supply voltages. The allowable current of the larger wire sizes increases faster than the number of turns decreases with a given coil cross section, permitting more ampere turns. Actually 14 VDC may be an ideal design target as there are 13.8 VDC switching supplies available (such as Radio Shack) that perform very well at minimal cost.
In my opinion the special sound of the Lansing drivers is partly due to their field coil operation, and partly because of the differences in the diaphragm. The Lansing drivers used a diaphragm with a half roll outer compliance, not the tangential compliance used by Altec beginning with the 288. The simpler half roll compliance does not provide as extended a high frequency response, but does not misbehave as much either and sounds very smooth.
Somehow interesting how speculative forum discussions are some times...
The choosen diameter of my pole pieces are calculated to take cross section of every iron part in the magnetic way into account. They are not too big and not too small. And material matters! Space for coils in my drivers is big enough to handle more flux than needed as the coils calculated from a well known transformer company and not only guessed. About the comments for price: I know that DIYs always looking for getting Gold for less than nothing but my drivers are not built for those people. I do want an equivalent value for the used materials and investments. So please don't argue on price. I wish people could hear what I'm talking about first. (I tried several filed coil drivers from different manufacturers - and mine are excellent, believe me). There are some field coil drivers out there for far more. After several reports confirmed their quality there is not even a word about prices. So be patient please - or go for a pair and hear! Kind regards, Wolf von Langa
Hi Wolf,
I'd love to hear more about your history, why you decided to go this route, how long you have been at it, etc. I have zero experience with field coil drivers, but from a purely technical standpoint their potential is quite interesting to me.
Welcome to our site... good luck with your venture.
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Hi Wolf,
Welcome to Lansing Heritage! I am happy to see you posting here, and I am sorry if my initial post seemed critical of your efforts. Long timers here know that I am enthusiastic about field coils, and try to encourage others to venture "back to the future." I have however consulted with several fellows whose efforts closely resembled yours with the large diameter center pole and thin field coil compared to the vintage units. They had based their choice of center pole diameter on the diameter of the widened skirt adopted when the field coil driver ancestors were converted to an interior ring alnico magnet. One fellow had reported excessive heating in the field coil and was rather down on the technology as a result.
It sounds as though you have good reasons for your dimensions, and seem to be aware that you have apportioned the space inside the pot rather differently than the original designs. Actually I have only seen pictures of your Altec 288 conversion, so I do not know what you have done with your JBL conversion. The production Western Electric 594A upon which the JBL large format drivers were based used a center pole the of same diameter as the inner pole piece, just under 4". Edward Wente's U.S. Patent drawings of the prototype driver that became the 594 actually indicate a center pole shaft of smaller diameter than the inner pole piece. These early drivers all used a solid iron center pole with the conical throat exit bored through the center; the cast throat inserts began with the permanent magnet drivers.
I share an interest in the recent expanding availible choices in field coil offerings. It would be interesting to hear from those who may own them and would be willing to share their considered listening observations.
I just noticed Classic Audio finally updated their web site and are showing field coil components including a 15" woofer, 3 different mid drivers & SHF driver... all 12vdc motor coils!...
Anybody going to CES this year?
In 1949 my dad bought a Hi-Fi it had a 15" field coil speaker. It worked sounded good for the time period.
My gut tells me that the voice coil cannot tell the difference between the flux created by a PM speaker vs a field coil speaker.
Do they list the power required for the field coil in watts?
I think in Volts...
A magnetic filed is created when current flows through the wire.
The larger the current the larger the magnetic field.
WE 594's tend to start heating @24+v ! -- whether they're designed w/ this in mind or not, I'm not sure. I for one would not be comfortable w/ that. ~22 v seems much better for temp stab (just marginal warming)
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