Separating Stators - some tips

[wfissell]

I decided to have a go at separating the stators on the one panel of my Clarity that is dead. I wanted to pass on my experience.

1- not for faint of heart. ONLY do this if you have already decided that you are going to have to buy new panels anyway and want to try a Doug Flutie Hail Mary pass.
2- Like the old joke about the 911 operator who tells the woman to make sure her husband is really dead before starting CPR, if it wasn't dead before it sure is now.
3- I tried the sawing string approach and did not get anywhere. I used a discarded steel guitar string. It may have been too smooth.
4. I dribbled some acetone onto the 3M VHB tape to dissolve the solvent.
5. I then used some tiny wood wedges to try to ease the panels apart. It was clearly just tearing things up. I stopped.
6. I had a 'cellphone repair kit' lying around and I used one of the plastic triangles to pry two stators apart. I got them far enough apart that I could place a pry tool in the gap, long axis of the tool aligned with long axis of the panel. I did one on each end. I made a sketch and attached it.
7. I dribbled a few drops of acetone in the parting line, reefed on it by hand a lil, and then advanced the tool a few mm further.
8. The Mylar is pretty tough. Even though the struts were bonded to both the stator and the film, by moving very slowly I was able to give the adhesive time to relax and let go. Robin Renzetti, a machinist and precision freak, has some videos about using adhesives effectively. Hes on Youtube.
9. Working my way along I had about 95% done and I heard a pop and a corner of the Mylar had torn. Fumble and turnover at the 4 yard line.
10. I'm not sure why it failed as it did when it did. It looked to me as though there was some sort of breach (wedge-induced? most likely) in the mylar where it is bonded to the stator and the tool - essentially just a dowel - just entered the breach and propagated it into the active speaker area. If I had noticed I probably could have stopped it.

Its definitely a mess. Now Im going to try to decide if I want to try restretching new mylar myself. Hell, I made it this far.

 

[Jazzman53]

Hey, you have nothing to lose at this point so go for it!

I haven't tried wire for a string saw but 60-lbs braided fishing line works pretty well. It's thin, and it saws because it's braided, and it has a slick coating (to slide through the eyes of a fishing rod with minimal resistance), which minimizes the chances of tearing the diaphragm or binding when cutting through double-sided adhesive tape.

ML uses 12-micron polyester film (Mylar) for their diaphragms but many re-builders go back with 6-micron film and call it an upgrade. The thinner film rolls off at a higher frequency, so it can give somewhat better treble response, but it's more fragile and can't be tensioned as high.

I once rebuilt a ML Theater panel using 6-micron film, and was able to tension it high enough to achieve the same 200Hz drum-head resonance that the panel had originally.

When I rebuilt the Theater panel, I assumed the original diahragm would have to be replaced so I made no attempt to save it. In hindsight; I think there's a good chance the original diaphragm could have been saved and reused. If I have another opportunity, I will attempt to save the diaphragm rather than just tearing the panel apart willy-nilly.

I built a jig to tension the replacement diaphragm but not everyone does, and I'm sure you could get by without one. Tension should be predominantly perpendicular to the curvature, with only enough tension across the curve to pull out any wrinkles. Better to tension the film too high than too low!

In order to recreate the original diaphragm tension/resonance, I made a simple deflection gage and measured the deflection at a still-intact area on the original diaphragm, and then tensioned the replacement diaphragm to the same deflection, which then produced the same drum-head resonance.

To the extent that ML may have tuned the crossover to work with a specific diaphragm resonance, it's desirable to tension the replacement diaphragm to the same resonance.

For what it's worth; here's a link to my write-up on the ML Theater panel rebuild:
https://jazzman-esl-page.blogspot.com/2011/11/compensating-diplole-phase-cancellation.html

Good luck with your rebuild!

Charlie