Voice coil wound with steel wire.

[Circlotron]

About 2 years ago I was thinking about all things magnetic and it occured to me that if you had a loudspeaker voice coil wound with steel wire (most resistors and small caps have steel leads BTW) then the magnetic flux passing across the airgap would see the ferrous voice coil as a lower reluctance path than the surrounding air, therefore the flux would almost all go through the voicecoil instead of much of it also going past either end of the coil as now. The steel coil would tend to "focus" the majority of the flux upon itself. Of course the steel coil would have a greater DC resistance than copper, but even so, it might work better. I haven't got the facilities to try it out so has anyone ever done anything like this?

[onebadziggy]

A few other things to consider are steels ability to resist heat without failure, and its weight. I dont know what those parameters are for steel, but I'm pretty sure it would weigh more than copper and definately more than aluminum.

I am curious also to if anyone has ever seen a steel vioce coil.

[Bill F.]

Yes, I've considered steel VC windings for the same reason. However, there seem to be some pretty big downsides. Steel is a ferromagnetic material with a relatevely high remanence. Therefore it has a wide hysteresis loop when subjected to AC or an alternating magnetic field. This will show up as efficiency loss and nonlinearities.

One way to minimize hysteresis would be to use a magnetically soft alloy like MuMetal or Permalloy. These have much narrower hysteresis loops. However, IIRC, they have even higher resistance than steel. (This is a benefit when the application is an inductive core, as it reduces eddy currents.)

Hysteresis becomes less of a problem if you're thinking of a low-frequency application.

[woody]

http://Lowtherloudspeakers.co.uk/ has mention of doing
something along these lines. I seem to recall that they may
have used iron wire in some of there speakers.

[Sch3mat1c]

Steel is very resistive...I can't imagine much power coming of it.

Nonetheless, if the magetic field thus induced is worth something, whatever.. Maybe you can cut off some narrow strips of a band-wound core to try it yourself.

BTW, somehow I doubt mu-metal would react too well to the strong field inside a speaker magnet. It has a very high mu, but IIRC it saturates very easily, which is why it isn't used (besides expense).

Tim

[jackinnj]

you're just begging for distortion.

[navin]

while i agree with Bill F. there are a dozen reasons why steel is not used (weight, resistance, BR curve, etc...). in short dont do it.

i have designed magnets (large electromagnets) for a living see http://www.emagindia.com so i have done considerable ammount of work in this space.

pound for pound edge wound flat aluminum coil is best (maybe hexa core but I have not worked with that).