about the shorted ring (flux stabilizer ring)

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Haggy:

If you have a tone generator, (you can download them off the internet for free), and a ported box with an inexpensive speaker, you can run an experiment to illustrate.

As you run the tone generator down through the bass range, you will finally approach and then hit the box tuning frequency. At that point, unless your speaker has a shorting ring or other special aspect, you will suddenly notice the speaker will actually get sucked into the enclosure, so that instead of the speaker going back and forth from it's centerpoint, it goes to the inward end of it's excursion and moves only in the forward direction from there. In other words, half the waveform becomes clipped off.

You would think such a situation would sound terrible, but in fact that waveform has very high second harmonics, (overtones). Incredibly, it sounds quite musical. The only problem is, of course, is that you are missing your deepest bass notes and are having the notes from the octave above subsitituted for them.

The reason this happens is that in most speakers the magnetic structure is located mostly BEHIND the voice coil. Near ported resonance, this unbalance asserts itself, and pulls the speaker back toward the inside of the box.

There are different ways of handling this. Some manufacturers change the suspension of the speaker to compensate. Some extend the pole piece-the round bar the voice coil surrounds-forward so it juts into the cone area, (a larger dustcap hides it). That method eliminates the unbalance. And some manufacturers, like Peerless and others, put on a shorting ring. Precisely HOW a shorting ring works, I do not know, but it somehow eliminates the unbalance between the amount of magnetic material in the front of the voice coil and the back. This eliminates the waveform clipping that results in such high second harmonic distortion, because the speaker does not travel into the speaker near resonance-it stays right at it's customary centerpoint and moves back and forth from there.

[Edited by kelticwizard on 12-07-2001 at 03:26 AM]
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Haggy:

The shorting ring is also called a Faraday ring. Here is more on it from the highly respected Lambda people. I will be honest, I I will have to spend more time going over it before I understand it, if I ever do. All I know that is with the shorting ring, the speaker stays at it's midpoint during resonance in a ported box, and that just HAS to be a good thing!!

Anyway, here is the link. Scroll down the page slightly until you see "Motor Questions". http://www.lambdacoustics.com/library/whitepapers/PLDriversFAQ.html#Will you offer a 3" VC version with the copper Faraday?

Good luck!!
 
thank you fo the information and Happy new year everybody!

I understand about the Faraday ring like the below...

the currents in the voice coil produce magnetic field
and that magnetic field affects the magnetic field in the yoke.
the change of the magnetic field generate currents at the Faraday ring and the generated currents produce the magnetic field and the produced magnetic field cancel the magnetic field produced by voice coil . so the entire magnetic field is stabilized.

I'm not native, so I'm axcious about that so many wrong is in my writing.

any problem is found , please post reply...

thank..