How to DIY / add a Faraday ring to a loudspeaker

[Freedom666]

Here a description how to add DIY a Faraday / copper ring to a loudspeaker in order to reduce distortion and minimize inductivity of the voice coil.

First some information on how to remove a dust cap of a loudspeaker driver (detailed description follow the link) :

https://www.diyaudio.com/community/threads/how-to-remove-a-dustcap.397165/

 

[Freedom666]

After you have access to the pole piece you can add a copper ring or a 20 euro cent or 50 euro cent piece to the pole plate.

Copper ring added of appropriate size:

https://www.diyaudio.com/community/...-firing-speakers.121385/page-175#post-6707993

Read carefully how to use the glue for fixing ring or coin. Do not put too much glue as no glue is allowed to drop into the voice coil gap.

The small Euro coins of 10, 20, 50 cent contain copper so they can be used for this purpose

12cm driver with added 50 cent coin to the pole plate, I call it "50 cent trick":

https://www.diyaudio.com/community/...fication-to-current-drive.389985/post-7197710

https://www.diyaudio.com/community/threads/visaton-bg20-impressive-mod.408081/post-7576162


For who wonders about the alu foil on the paper cones -
My fullrange drivers get an aluminium sandwich cone DIY:

https://www.diyaudio.com/community/threads/how-to-make-a-loudspeaker-sandwich-cone.402917/

 

[Freedom666]

If you do this modification you can compare the effect by removing the dust cap of two identical drivers and listen to Mono music and use the balance knob of your pre amp to switch between the two drivers fastly. You just drop a copper ring without fixing it into one of both drivers on the pole plate.

25cm driver with "50 cent trick" :

https://www.diyaudio.com/community/...loudspeaker-sandwich-cone.402917/post-7495721

 

[Freedom666]

If you want to transform your driver to a fullrange driver you can DIY add a full metal aluminum whizzer / double cone:

https://www.diyaudio.com/community/threads/how-to-make-a-whizzer-cone.398063/

You can also put back the original dust cap glued back into position if you only do a clean and wide cut out like in image 1 of this thread.

But here I prefered to add a double cone.

 

[Freedom666]

If you want to dive deep into this topic just read this

The Effect of Faraday Ring (Shorting Ring)
Usage on Voice Coil Impedance and Its
Benefits

http://www.diy-audio.narod.ru/litr/FaradayRingsVoiceCoilImpedance.pdf

 

[Boden]

Could you show your own impedance measurements with and without the penny-in-a-polepiece?

 

[Arthur Jackson]

Great idea! Unfortunately, I don’t think any US or Canadian coins will work, they are mostly non-magnetic nickel. Unless non-magnetic nickel works as a faraday ring? I guess I could use copper pipe, end caps, or washers. Also, it’s easy to machine aluminum to the right size.

 

[Freedom666]

@Boden

I did once measurements and have them on some harddisk archived.

But now I have no working equipment for doing this.

If someone wants to try this mod feel free to post it here with measurements. Like impedance, THD and IMD for a given loudness with and without copper ring.

Maybe valuable to mention:

You can add several copper rings or coins for covering / shorting the full travel of the voice coil in one direction.

I found no possibility of adding a "full sleeve" shorting ring which would cover the voice coil travel into the other direction towards the magnet.

Maybe someone will have an idea for a mod without completely disassembling a driver what is not practical or economical.

 

[Freedom666]

@Arthur Jackson

I used gasket copper rings

 

[Freedom666]

if the loudspeaker will suffer humidity its good to laquer the copper before putting it onto the pole plate because if it corrodes with green patina it can loosen the glue and the ring will fall off

 

[Freedom666]

here some discussion

https://www.diyaudio.com/community/threads/faraday-rings.62247/