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Original Message

RE: Belay that, I was wrong!

Posted by josh358 on June 26, 2011 at 11:53:32:
Was the original MMG tweeter wider or narrower? I forget. In any case, I'm not sure what else they changed, besides the crossover. So it would probably make sense to take some measurements of wire length, number of runs, magnet spacing, etc. so we can compare without pestering Wendell.

AFAIK, the one thing we'll be changing is the woofer wire, unless we also add a supertweeter segment (which I'd do, heh, for a Mini 1.7, but it is more work). Obviously we can't change tension, compliance, magnet strength and spacing, diaphragm size, and the like. So basically mass is going to change, and DCR. Which is enough to see how the Thiele-Small equations will change, but measurement will give us a baseline. We'll need a new crossover which will probably have to be the single pole series design so the summed response will be flat despite varying DCR.

I don't know what the differences will be between the old MMG and new ones because as I said I don't know if they use the same tension, etc. But I'm guessing they'll be pretty similar after the mod. If mass changes, resonant frequencies will shift, but the harmonic series of the tuning dots shouldn't, that's fixed by geometry. Like a string on an instrument that can be tuned to different pitches but still plays a scale when you put your finger on the frets. In any case I don't think there's much leeway to change them, since there aren't that many reasonable ways to alter the height of the driver. What may go off is the tuning, I'd speculated that they were referenced to A-440 to make the resonances more euphonic, if you have a tuning fork or are near the computer you could test that hypothesis by tapping lightly on the segments. But I don't think it's practical to compensate for that, you'd have to trim the mass of the driver, it's the sort of thing that should be done with dimensions and tensioning.

I did a search for Thiele-Small calculators and came up with this, unfortunately they charge for it but it does provide a useful guide to the measurement technique:

http://www.purebits.com/appnote16.html

I'm sure there's something out there for free but don't have much time to look today.

Here's a picture of a tuning dot on a 1.7:

http://www.audioasylum.com/forums/MUG/messages/17/175474.html

So it looks like we can stick with round ones.