What *exactly* do shorting rings do?

[digital desire]

I know they somehow reduce distortion. But thats it. What are they shorting?

[joecarrow]

Here's a wikipedia article on the phenomenon this takes advantage of:

http://en.wikipedia.org/wiki/Lenz%27s_Law

The magnetic field generated by the current in the voicecoil modulates the permanent magnetic field of the speaker. The changing field sets up a current in the shorting ring that produces a magnetic field that opposes the changing field. The net effect is that the magnetic flux stays more constant.

As you may know, one of the common sources of distortion is a non-constant magnetic field. As the voicecoil travels through the field, the force exerted for a given current changes. This distorts the output.

[ThomasW]

This seems pretty "exact".....

http://www.patentstorm.us/patents/5815587-description.html

[digital desire]

Thanks!
(Very exact!)

[Feyz]

http://www.geocities.com/pirimoglu/Articles/FaradayRingsVoiceCoilImpedance.pdf

[TacoD]

This seems pretty "exact".....

http://www.patentstorm.us/patents/58...scription.html

Interesting read, Lars knows his stuff (he is the applicant of this patent)

[digital desire]

Feyz, that link would take me a week to wrap my head around! But it did give me an idea of what exactly a shorting ring looked like.

[Feyz]

I had written that when I was looking at how shorting rings effect voice coil inductance and impedance, as the title implies. So it is not exactly what you are looking for to quickly read on, though it contains what shorting rings do, but in a scattered way. And I have to admit, it was not a good writing for easy reading, besides has grammar errors. Well, you gets what you pay for

In summary, current flowing from the voice coil generates its own magnetic field. This goes through the pole piece and air gap. There is already a magnetic field in the air gap provided by the magnet. Net magnetic field inside the air gap then becomes the sum of the fields from magnet and voice coil current. But linear operation of the speaker requires the magnetic field inside air gap to be constant. (B of BL product, which when current flows on the voice coil, causes the voice coil to move by Lorents force) This causes distortion. Another thing related to this is that, the permeability of the pole piece and other parts of magnetic circuit of the speaker motor gets modulated by the field generated by the voice coil current, which means the inductance of the voice coil gets modulated by voice coil current. Voice coil inductance also is supposed to be constant (for a frequency) for linear operation of the driver. When it gets modulated by current, distortion occurs. The cause of both these distortions is the magnetic field generated by the voice coil current. A shorting ring, which is a single short circuit turn, can be considered as the secondary winding of a transformer that is short circuited. The primary winding is the voice coil. The voice coil current induces a current on the shorting ring, which always has a polarity that generates a magnetic field that opposes the field that induced it. This causes the net magnetic field generated by the voice coil current to reduce, and so BL modulation by current and inductance modulation by current gets reduced, and the distortions caused by these gets reduced.