LE10 recone Problem

[Guido]

I need your help!

Yesterday I reconed one LE10H of course with an original cone kit. The cone kit is an older one with paper voicecoil former.
Driver works perfect, no rub. Dustcap is still open
When starting to break it in I noticed a strange smell. It came from the voice coil that gets very hot. Even the center pole piece gets warm very fast.
DCR is around 5 Ohms
Power for break in I don’t know but not to high excursion at 20 Hz. Appr. +/- 1 or 2mm

What is wrong? Anybody else had this?

[Guido]

You would never guess what happened.

I bought this LE10H Basket BRANDNEW with loose cone assembly from a guy who said it was some kind of demo.

Call me stupid but while gluing the cone in I didn't realize that the magnet isn't magnetized Well it is a little magnetized but flux is close to zero. Why this is? I don't know. Anyhow I didn't realize.

When it comes to break in the speaker I put in 20 Hz via my big amp and again didn't wonder how much energy I had to put in to bring the cone into movement. Then I had this smell from the hot voice coil (see my post above)

Today I did measure the voltage at the speaker terminals while break in and hell 18 V and only few cone movement......

And then I realized that it must be the flux. Hold a screwdriver to the magnet and BINGO
When -first time- putting music to the driver I got only distortion. CLEAR NOW!


So this is crazy. Now I have to find a magnet spezialist.

[johnaec]

Be aware that you can hold a screwdriver near to most JBL alnico assemblies and not feel anything - that's how well JBL designed these magnetic structures - almost all the magnetic energy is focused in the gap.

John

[Guido]

Hey John


I know this, but H means Ferrite!

[johnaec]

Originally posted by Guido
I know this, but H means Ferrite!

Oops - I missed that.

I was under the impression it was almost impossible for ferrite to lose magnetism, short of dropping them....

But CLEAR NOW? Are you saying after a little run-in it seems to be OK? (I might suspect curing glue to account for the smell...)

John

[Guido]

Nothing is ok!

This driver seems to have never been magnetized. The flux is zero (or close to). That was the reason for needing excessive power to move the cone a bit.

I need to magnetize it!