Shims, 30Hz or DC to align coil after a refoam ?

[Dave Cawley]

.
OK, I get shims but they only center the coil when they are in, the surround could easily pull the coil asymmetrically the moment the shims are removed ?

30Hz, the cone seems to exhibit a toppling effect due to it's weight and can resonate and flap, is this the way ?

DC seems to hold the coil ultra rigidly, almost vice like, but then you have the option of coil in or coil out.

So is DC a no-no or is it the answer ? And if so coil in or out ?

Dave

[grumpy]

If you glued one side of the surround under tension, sure. But why would you do that?

No. The tone tends to center the voice coil along axis and allows you to hear rubbing and adjust.

[Dave Cawley]

I do understand that 30Hz is successful, but how do we know it's better than DC, has anyone first hand experience of both ?

Thanks

Dave

[1audiohack]

Hi Dave;

DC wont do anything for you other than show you polarity. DC will not hold the coil centered radially which is what you are after. Only a shim will do that.

The LF (30Hz) will let you know audibly if the coil is rubbing or not, thats all.

My last out the door test for woofers is a 5Hz run with near Xmax motion. If you hear anything, there is a problem.

Barry.

[Dave Cawley]

Hi Dave;

DC wont do anything for you other than show you polarity. DC will not hold the coil centered radially which is what you are after.

Hi Barry

Well remarkable it does seem to do just that. But I may not test this next week as no one actually seems to have tried it !

Thanks

Dave

[Chris Brown]

30hz does tend to self-center the cone slightly, but any effect that it has in that regard would be easily negated by any force the foam is already applying to the cone. 30hz, as well as possibly DC, might be helpful if you are right at that stage where you have glued the foam to the cone but not to the frame yet. Beyond that, and once you have even one drop of glue connecting the foam to the frame, any "Self-centering" becomes irrelevant compared to other forces that are now being applied to the cone. The reason to keep testing frequently as you finish the glue process is to reveal voice coil rubbing only, which DC won't do. Shims are more precise in that regard, since they are still there and providing the best centering possible from the very beginning of the process to the very end, but like I mentioned in your other thread, the big deal with shims is the dust cap. I've yet to ever see even one single pair of speakers where the dust cap looked as good as stock after being removed and put back. Disturbingly often, you see woofers with larger dust caps than stock because the owner butchered the stock dust cap and needed something to cover up the mess. :(

[Dave Cawley]

I may be wrong, but DC exerts a vice like grip on the cone. I'll try gluing down tentatively with DC then immediately try 30Hz.

Thanks Chris for your inputs.

Regards

Dave

[1audiohack]

Hi Barry

Well remarkable it does seem to do just that. But I may not test this next week as no one actually seems to have tried it !

Thanks

Dave

Maybe, but only since the spider is straining to hold it centered radially. Nothing in the applied magnetic field works to center the coil radially.

Before I came back and opened my trap, I went out and dropped a 2121 conekit in a basket, put 1.5V to it and the coil moves vertically but is easily moved about radially making contact in the gap where ever you put it.

Curiously, you can hover the VC just above the gap in the fringe field, until it moves from center about an eighth of an inch and falls back to the top plate. If there was any centering force would it not hover on center in space?

None of this is meant to start or continue an argument. Purely academic.

Best of luck with your project! :)

Barry.

[gasfan]

30hz helps once the foam is already glued to the cone. Now that the vc is supported by the foam against the basket, it will right itself in the gap, pulling and centering the assembly. Glue applied under the lip serves as lubricant while still wet. Gently pressing down on randomly alternate locations until the lip stays put ensures center is maintained. Shims are needed only when gluing the spider in place. Using a turntable of some sort, even an old audio tt for applying glue cleanly is indispensable. Also those long thin nozzles for glue available at hobby stores. Nozzles on the tubes/containers are way too fat for precision.

[Dave Cawley]

Hi Barry

1.5V is not enough, but you may well be right, thanks for testing it.
Maybe, but only since the spider is straining to hold it centered radially. EDIT; I think you are 100% right, thanks !

And thanks for the turntable suggestion gasfan.

Dave

[Dave Cawley]

Fully sorted now, I used 3V RMS of 22Hz as the was the resonant frequency and worked well. But I have to say the cone is well and truly aligned by the spider and I'm not sure that anything except gross misalignment of the foam surround would make any difference ?

Dave