[jules]

Anybody tried this?

The obvious challenge is to get the voice coils truly concentric with the magnet but I have no idea how that's done or if it needs very special alignment tools.

[FullRangeMan]

I made some in pro-audio woofers with a assembled recone kits which gap was wide 6mm or more, it was made at naked eye, very important have a suited glue.

EDIT:  Before doing anything you must know how much is the driver gap to see if it is a hard job or so.

[jules]

Thanks FRM. I'll do a check on the gap.

I was wondering if a set of spacers, say cardboard or thick paper could be used around the perimeter to set the gap. 

[S Clark]

Thanks FRM. I'll do a check on the gap.

I was wondering if a set of spacers, say cardboard or thick paper could be used around the perimeter to set the gap.

Yes. Shims work well. 

[FullRangeMan]

It depend on the basket and the recone kit, do you already have the kit ?

[jules]

Yes. Shims work well. 

Thanks, good to know.

It depend on the basket and the recone kit, do you already have the kit ?

No, I don't have the re-cone kit. I've got a Rythmik sub that was made at a time when they used Aluminium cones. I'm not a huge fan, plus I understand these were heavier than the paper cones used before and after that time. So I'm weighing up whether it might be worth having a go at re-coning the sub.

[AVnerdguy]

If not very carefully aligned shims may shift during set time and the voice coil could scrape under load when completed. Another method to ensure centering is to apply an audio signal (single frequency relative to the response of the speaker) to the driver and glue the edges carefully without disturbing the centering. I have been reconing or repairing edge foam rot with this method for over 30 years without failure.

Use an audio signal generator at low (almost inaudible) volume - if you do not have access to one you can download an app for your phone and use a adapter cable, 1/8" mini stereo to a pair of clip leads, from the headphone jack. Depending on the speaker cone/basket edge, pre glue the outer edge of the cone and/or gasket material but do not press into place at this time. After setting the cone into the basket, apply the signal to the speaker at a low volume until the speaker centers itself. For a typical woofer I use 50Hz SINE wave and slowly bring up the volume until the cone snaps to center. Carefully apply pressure to the surround edges until a complete seal is formed. Depending on the adhesive used you can remove the signal after a few minutes after the the glue has set. A typical cone glue starts out cloudy/milky white and turns clear as it cures which is a good indication that you may safely remove the signal from the speaker. Allow the adhesive to completely set overnight before applying full signal to the speaker.

I've seen YouTube videos showing this method. Do a search on reconing speakers with an audio generator and it will direct you appropriately. Springfield Speaker Repair has a very good video tutorial for the beginner.

[jules]

I hadn't thought about the concept that current through the voice coil actually tends to centre the coil in the speaker's magnetic field. Logical enough and very useful tool when used as you've outlined.

Many thanks for the very well described technique. I'll search out the YouTube video.