OK, some updates. I allowed my recapped AR-58S speakers to play and burn in for about four weeks. The recap sounded very good, with a warm, rich balance, with a wide enveloping soundstage. But, for whatever reason, the Clarity ESA cap on the UMR dome, never opened up in the upper mids. The sound stayed rolled off and veiled, making vocals hard to understand. So, I opened the speakers up and added cascaded bypass caps. I added a 0.1uF Dayton film and foil cap, and a 0.01uF Russian K40Y-9 PIO cap. Why 2 bypass caps? Because I could, since I already had both. Plus, I was hoping the Russian paper in oil caps would help retain the rich sound of the Clarity's. Now, the speakers sound much more balanced through the mids. The veiling is gone too. I'm starting to finally like the speakers, post recap. Next time, I'll stick with Mundorf. But for now, I'm happy.
Now, a weird thing. Before finding the AR-58S speakers, I had picked up a set of AR-1MS minimonitors. Nice little speakers, with good midrange clarity. But, the 1MS speakers were very sibilant at times, with a pronounced 'ess' peakiness. So, I opened them up, and they had already been recapped by the previous owner. Poly TRW caps on the mids, and poly Dayton 5% caps on the tweeters. I added a 0.1uF Dayton F&F to the mids, and a 0.1uF Auricap to the tweeters. Sibilance gone.
Explain to me why a bypass cap can open up the response of one speaker, and tame the peakiness in another? Please help, 'cause I'm confused!