LE20-1 driver replacement question

[mike762]

If I have 1 LE20-1 with a blown driver and a good cone and another with a torn cone and a good driver, can I create one whole good speaker?

I removed the 3 front center screws from one and it looked like it might require a little hammer persuasion to get the thing apart, so I stopped there and decided to ask for help. help please. Hmmm, there's a thin band around the point where the aluminium face piece ends and the driver continues. The band is a poly like substance about 1/8in thick. And are there alignment issues? Thanks in advance.

Sincerely,
mike

[edgewound]

Hi Mike...

To answer your question....yes you can make one good one. It's been awhile since I've done one of these, but I believe there is locating pins on the alnico magnet top plate to align the cone/voice coil/frame assembly, and holes in the frame. Use a little...and I mean LITTLE...penetrating solvent such as "Liquid Wrench" or Ronsonal Butane Lighter Fluid to separate the magnet from the cone frame, then wipe off the excess. Use a knife edge or something similar to pry/separate the two halves....I wouldn't hit it with a hammer, as you might bend it out of shape.

Hope this helps,

Edgewound

[Don C]

The terminology here is not precice enough. Is sounds as though you may have an open voice coil on one tweeter, and a torn cone on the other. That's not a repair that most people would want to try at home. Swapping the cone usually takes the voice coil as well.

[mike762]

Yes, I believe it's a damaged voice coil. However, before declaring defeat, I will try Edgewound's procedure to see how this baby comes apart.

Mr Edgewound: the poly band along the joining line. It looks like I have to cut this off. This begs the question: do I need a replacement band there when I put it back together?

Mike

[edgewound]

Mike..

Sounds like it's just electrical tape(?)....not necessary to replace that. If it's the rubberband like O-ring seal that goes behind the mounting flange, it's a good idea to save it for sealing against the baffle. Just peel it off and save it...if that's what it is.

Edgewound

[mike762]

Don C, you are correct. The mating of the coil and cone is quite a delicate fusing of materials. Coil replacement does not look like something I should do. And thanks guys.

Could you guys help me make a definitive diagnosis here. I show no continuity between the coil wires, with a wiggy continuity meter. Does that prove that the coil is broken? I'm afraid my simpson vom is unable to read ohms now. I need a new battery back plate.

One other speaker question. I have read the surround (foam) replacement instructions from the place I intend to get my surrounds from, and it makes no mention of applying a signal to the speaker during the alignment process. Yet I have heard something about applying a voltage to center up the cone forward and aft. Do you guys think it's necessary to apply a signal during the alignment process? If so, how would that work?

Thanks

[pelly3s]

In the refoaming department, the way I learned and the way I do it at work is to apply a small DC voltage to the coil to lift the cone (or lower it in some cases) in order to center it. I have never used the method of a 30hz tone.

[mike762]

Yes, a dc voltage. I heard that too, but what voltage? I should be able to rig it up with a car battery and a potentiometer and likely another resistor. In messing around, I have found that the speaker signal wires, to the woofers of my cv d7's, seems to show a couple hundred millivolts dc, on my simpson vom, when an audio signal is applied. Since I'm reading that voltage from an open circuit (speakers awaiting surrounds) that might not be the proper centering voltage.

mike762

[Zilch]

Lessee. 12 Volts into 8 Ohms gonna be about 18 watts continuous. I'd say that'd be a bad idea on a tweeter.

9 Volts would be 10-1/8 watts, and move an 8-Ohm woofer cone "substantially."

Can't put that kind of current through a potentiometer without smokin' it. Think "rheostat."

Audio signal is AC. Should be no DC there except some minimal offset voltage (<100 mV) coming from the amp, which would be there even if nothing's playing.

A slow meter might read something that's not there when audio signal is applied.

Tweeter should be swept through its operating frequency range to make sure there's no buzzing or rubbing from improper alignment. That requires an audio signal generator or a test disk with the requisite frequencies on it, and a crossover or capacitor of the proper value to protect against audio "mishap."

In woofer reconing, application of low-volume 30 Hz tone has been described often here as helpful in centering the assembly while the adhesive dries....