Tweakers' Asylum: Capacitor technology has advanced so far since then by Slider

Technology has advanced to allow the dielectric to be etched with finer and finer patterns, and metallurgy advances have lead to cases that can be deep drawn thinner and thinner, making the capacitors much smaller and much higher density and much lower esr. But these advances have made electrolytic capacitors that sound worse and worse in my comparisons against those antiques from 20 or 30 years ago. Listen to an old surplus Sprague 672/673D sometime, with the thick and soft aluminum case, and thick aluminum plates inside, and internal damping tar, and sealed copper leads. They sound much better than anything available today. Panasonic has historically made some of the worst sounding electrolytic caps in my opinion. Very brittle edge to the sound, usually accompanied with an overall softening. Delayed resonance plots show awful behavior for most modern electrolytics. Subjective for sure, but esr means almost nothing in audio applications unless your power supply or amp is unstable, and those low numbers are almost never realized in a practical layout anyway. Much better off judging a capacitor by weight.