Cogent horns

Well, Paul, you never know what is out of your reach until you ask....

There is a big thing (tempest in a tea cup) right now with people from LA to Germany and Japan taking Altec and JBL large and medium format vintage compression drivers and hot rodding them as field coils.

Several things are cogent (pun intended) to this driver transformation- the actual structure of the permanent magnet driver and whether it can properly be converted to a field coil motor given its pole piece and the room within the casework for an adequate FC motor. The other issue is the diaphragm design and compliance, phase plug, and how that sounds unto itself. In other words, if you never liked an Altec 288, no matter what diaphragm it had, do you really think you will like the field coil version?

These are issues I do not usually see addressed.

Jonathan

Many revered audio products were the result of DIY endeavors. Simple reasoning tells us this much. So I assessed my DIY potential vis a vis the sort of performance levels and product refinement I require and proceeded to shop for finished product. Each of us must make that determination for ourselves, however.

As for field coil drivers, I have no personal experience, but will speculate that they may well offer slightly better performance than the best of conventional drivers. In my case that didn't matter because I couldn't spend $15,000 for a pair of Cogents.

Given the vast price differential between field coils and the best conventional compression drivers, I had no choice but to choose conventional. They've worked out very well and only cost me $1000.

Paulfolbrecht, the Classic Audio Loudspeakers model T-1 with the field coil drivers is about $52,000 for the pair. The T-3 set up the same way is about $36,000 for the pair.

The reason field coils sound better is that they are like ESLs in the way that the field reacts to the energy in the voice coil. That is to say, it does not react (or sag) whereas permanent magnets of all types do (Alnico sags the least and so has the reputation for the best sound). The difference is quite audible.

Thanks for that insight, Ralph. I hadn't made the connection between the static field of an ESL and the electromagnet in a field coil, but it makes sense. And in my experience both types excel at low-level detail and nuance and liveliness, though of course the high-efficiency field coil drivers do macrodynamics better.

In permanant magnets, as you said alnico sags the least (has the least flux modulation under dynamic conditions), followed by neodymium and then ferrite - but shorting rings (Faraday rings) can help ferrite and neo motors more closely approach alnico.

Duke

Why do field coil drivers cost so much? Are they particularly hard to make? Or is the answer just the inverse effect of the economy of scale?

Regards,