How much do tweeters change over time?

[Conrad Hoffman]

I don't know how many decades ago I bought my Morel MDT-28 tweeters. They were clean and sticky. Now they're dry and a bit dusty on the top of the domes. They still sound great, but my hearing was better back when they were new. Has anybody compared new and old tweeters known to be of the same construction (as far as we can know such a thing)? Everybody re-cones woofers, but my guess is that as long as the T-S parameters come out the same, they sound about the same. Sticky coated tweeters I have more doubts about because it seems like the basic character of the dome would change unless the coating could be renewed somehow.

[J.R.Freeman]

Hi Conrad,

I can not speak from experience on this matter, but in the case of a sticky dome becoming dry, I would imagine it's damping properties would change. This is a big assumption, but IF the sticky treatment drys somewhat solid, the driver may exhibit properties closer to that of a hard-domed counterpart than the soft dome it once was. A break-up node that was previously tamed may appear, weather or not that be in band is anyone's guess.

If the treatment extends to the surround, the Fs of the driver may rise as the spring constant stiffens (I am guessing that it would stiffen as the treatment hardens). You may also lose a little excursion capability.

Anyway, you've brought up an interesting point. Perhaps you could measure the response of your aged tweeters, and see if there are any surprises to deal with in the crossover. Alternatively, if it is a standard sized dome, you could play around with finding replacement diaphragms. Of course you'd need to measure them once more following such a Frankenstein-ing!

Jim