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Allison convex midrange drivers


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On 11/4/2019 at 4:27 PM, teknofossil said:

I am testing some Allison drivers, made in 1984. I noticed the Q measured with a DATS v2 is considerably different. I know the ferro fluid gets gummy with age and /or heavy use. Any thoughts on this?




Hi Tom,

I have only used “ear measurements” on that wonderful convex driver, ever since I first owned them in 1977, in the Allison:One.

A few guys on the Yahoo forum years ago, talked about “renewing” the fluids, both the silicone grease in the tweeters, (3 way) and the ferrofluid here, but there were never posted completed, before and after test measurement results. I missed them if they are out there.

Back in 2012, I sent 3 of the newer midrange units out to Bill Legall to re-center the voice coils (slight rubbing). I never asked him if he touched or did anything with the cooling material.

Once you get continuity and sound out of that midrange, there are only two things I’ve noticed that radically impact the sound.

A damaged voice coil, which sounds typically like any other blown driver, and the voice coil rub, which is awful when it happens....adding distortion that kills the show.

Actually, there is one other, and that is over tightening, or unevenly securing the midrange into the cabinet. 
This problem, I believe, is unique to the midrange with the newer plastic bezels. Over tightening that one stresses the voice coil and reduces the drivers normal output volume.



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