DIY faraday ring.

[speekergeek]

I have read a thread in here that adressed this idea but i didn't fully understand it. so i am off to restart a new one. a faraday ring..... couldn't you just take off your dust cap and place a ring made of copper (glue it) on the top of your pole piece and replace your dust cap? Or am i missing the big picture of how a faraday ring acts. i have read that a shorting ring acts to cancel out any magnetic field produced by the voice coil, directly or indirectly. any thoughts ideas or suggestions.

mike

[mrfeedback]

I have seen an old midrange in the past with a copper disc glued to the top of the pole-piece under the dustcap.

Eric.

[speekergeek]

maybe i will use my newly built impedence jig (yay!) and take some response graphs and impedence graphs. i don't know how to take distortion.

[Variac]

Apparently you have to about double the magnetic field to compensate for the shorting and other stuff. Someone had a link to a site that discussd this- maybe a search would work..

[kelticwizard]

I think you have a Faraday ring mixed up with an extended pole piece.

That would be easy to do, because both yield a symmetrical magnetic field.

I don't think you can DIY a Faraday ring, but I think it might be possible to DIY an extended pole piece. In fact, I was thinking of trying it myself.

What I was thinking of doing was to take a real cheap junk speaker, and putting it into a makeshift vented box. Then running a tone generator or test record down the scale until it gets near the Fb, or frequency of the ported box. At that point, the speaker shuold exhibit "suck-in" where it leaves the center of the voice coild and goes all the way in or out. It is very visible, and the sound of the tone changes noticeably.

Then I would remove the dust cap, and glue steel slugs or washers over the pole piece. Of course, their diameter would be slightly smaller than the pole piece's. Since a normal size woofer extends the pole piece about 5 or 6 mm, I would try to get washers that were about 0.5 mm, or 1/32 or 1/64 inch thick. I would then gradually build it up until the speaker no longer exhibits "suck-in" at resonance. Then maybe go one extra for good measure, since I am sure there is a range of lengths of the pole piece can be to prevent "suck-in".

If the experiment worked, I would try it on a slightly better speaker, etc., until I got some confidence in the process. Then I would try it on a good speaker.

I guarantee nothing, but that is how I would go about it.

If anybody has some suggestions to improve this, please post.

Maybe copper or aluminum slugs or washers?

[jazzy]

speeker1qeek,

check the Audiotechnology sitehttp://www.c-quenze.com and give attn, to driver picture!!!!
Why should we invent hot water ????
jazzy

[jazzy]

In Audiotechnology Dk. copper ring called "Symmetric drive".
-Symmetric drive uses a copper ring placed around the enter pole piece.
-The driver obtains a wider useable freq. range with clearer, more detailed sound.
- Greather thermal power handling.
-With S.D. the rise time is constant no matter where the cone is placed - lowers intermodulation distortion.
-S.D. lowers the inductance of the voicecoil and creates a more consistent impedan ce response.
-S.D. typically increases the rise time in the higher frequ. by factor of 10!!!
-S.D. makes possible both full bodied bass performance and fast clear midrange reproduction

jazzy

[speekergeek]

welly welly well! an extended pole piece is what it is then! could someone give me a laymans explanation of a faraday ring then? the extended pole piece thing is a great idea if it would work. so adding washers would extend the reach of the magnets control over the voice coil then? could you do it on the other end also? i am sure it would take quite an effort to cut out the pole piece, glue it onto a circle of metal and glue that onto a plate. whew! i just confused myself! anyways, this sounds like a very do-able idea! i have many many cheap drivers laying around from old speaker i could try this on.

[Circlotron]

Originally posted by speekergeek
could someone give me a laymans explanation of a faraday ring then?

This is how I think of it. Imagine yourself sitting in a small boat and holding onto a pier, pushing yourself away from, and pulling yourself toward the pier. If the pier is made of 1000 tonnes of concrete then it is going to remain almost perfectly still, but if it is made of sticks of wood poking out of the water then it is going to move back and forth a little; the opposite direction to you as you play physics experiments in your boat.

When the voice coil flux pushes (or pulls)against the magnet's flux, seeing the magnet is not infinitely strong, it's flux is reduced somewhat (or increased, depending on the polarity of the voicecoil flux). Now if we put a copper shorting ring in the airgap, the varying flux from our wobbly old magnet induces a current in this shorted turn copper ring (only while the flux is varying!). This secondary flux has it's own magnetic field which opposes any change in the main field. It doesn't make the main field any stronger, it just makes it resist sudden changes better.

Sort of like putting a really big capacitor across the output of a dc power supply. It won't supply any greater continuous amps, but sudden changes in load won't shake the voltage around very much. Or like a big flywheel on an engine. It lowers the dynamic "impedance" of the magnet.

[jazzy]

speekergeek,
I,ve attached Jpeg of S.drive - only for better understanding!