loudspeaker voice coil using steel wire

[Circlotron]

An idea I had many years ago - what if a loudspeaker voice coil was wound with steel wire or some other ferrous material so that the magnetic flux passing through the air gap would be drawn to pass entirely through the voice coil instead of some flux bypassing it because the voice coil is momentarily not in the ideal position as it moves back and forth.

Obviously one downside would be this voice coil would have a greater resistance than if it were made of copper, but putting that aside, would it help things if this coil managed to reduce the magnetic reluctance of the air gap?

[andy3055]

The bigger problem with using a ferrous material will be that it will become magnetized. It leads to residual magnetism that will contribute to the coil not staying at the neutral position when there is no signal. That cannot produce "true" sound.
Other factors will be poor frequency response, high resistance, etc.

[Zoli]

Look up magnetic liquid/ferrofluid; it was used first in the 80's.

[Gyro]

A couple of thoughts...

A steel voice coil would tend to be attracted to the side of magnetic gap, potentially requiring a much stiffer spider and cone surround and probably, wider gap. Manufacture  would be ok because it is magnetized after assembly, it would be a real alignment problem the surrounds needed replacing though. Also (as andy3055 mentions) the voice coil would become magnetized and non linear. The factory magnet energizing process would magnetize the coil to saturation level - it might actually propel it (and the cone) out of the assembly.

Ferrofluid is an excellent solution for increased flux, particularly in tweeters where it also provides mechanical damping. Unfortunately the carrier fluid eventually evaporates, leaving a nasty sticky ferrous mess that is almost impossible to remove. Not a problem if you accept that the driver is going to have a limited life and its characteristics are going to slowly degrade.

[Seekonk]

A friend was in management at a speaker company so you can discount anything he said.  He told me they used ferrofluids as a cost savings measure to auto center the voice coils of tweeters.  Of course that is not wat the advertising department said.

[langwadt]

A friend was in management at a speaker company so you can discount anything he said.  He told me they used ferrofluids as a cost savings measure to auto center the voice coils of tweeters.  Of course that is not wat the advertising department said.

afaik ferrofluid is primarily for cooling

[amyk]

The bigger problem with using a ferrous material will be that it will become magnetized. It leads to residual magnetism that will contribute to the coil not staying at the neutral position when there is no signal. That cannot produce "true" sound.
Other factors will be poor frequency response, high resistance, etc.

The hysteresis alone would probably produce very high distortion.

[Kokoriantz]

To my opinion, the permeability of the steel wire will retain the magnetic field inside the wire and will not interact with that of the gap. If you make an air coil with magnetic wire, it doesn't radiate.
I don't know what happens after saturation.

[ME]

Why reinvent the wheel ! ?.