Dunlavy SC IV A harsh high frequency

You may want to think about having your crossovers rebuilt.
Your Dunlavy's may be 15 years old. Capacitors generally have a ten year life cycle.
So depending on use, they may need replacing.
BTW, the SC IVA is on my "Top 5" favorite speakers list!

UNless there is a known defect with the tweeters, blowing them once a year would seem, (IMO) an indication that your amp is underpowered for your needs and that you are driving it into clipping, which will fry the tweeters pretty quickly.

What kind of SPL levels do you listen at? Are you concerned to any degree about retaining your hearing? If you are harming your ears, the "glassy" sound could be associated with hearing loss. Hopefully not, but if you already have tinnitus, you may want to reconsider what you are doing, besides simply replacing tweeters.

Hopefully I'm wrong about your situation.

OTOH, if the problem is not hearing loss, there is a figurative world of difference between cheap and high quality drivers. You admit it yourself when you state the manufacturer would not accept the tweeters you are using. You are likely hearing that qualitative difference. One can attain harsh sound quite cheaply.

Swampwalker makes a very good observation :-) especially with a first order crossover design like the Dunlavy where the crossover offers very little protection for the tweeter as far a power handling goes.

Dweller, I don't think Dunlavy used Electrolytic capacitors in at least the tweeter section of the crossover, I would assume that he used polypropylene capacitors which have a much longer lifespan than the 10 years you mention. Below is a link to a informative description on a XO modification the the speaker

Dunlavy X0 Modification

Best of Luck

Peter

I ended up using the Seas Excel T25CF-001 tweeter. It spec'd out to be a perfect match to the stock tweeter.