Why have capacitors improved so much over the years?

Barjohn, that's the engineer's answer from 1980.

The book that changed all that was Horowitz and Hill, 'The Art of Electronics', which had a table of capacitors and their actual characteristics. With real information about the physical effect known as 'Dielectric Absorption', or DA, applied to everyday electronic components, the stage was set for a genuine improvement in sound quality.

There are a few topologies which sound good and don't much profit from better components, but the best ones can be much improved thereby. In my experience, anyway.

Build yourself a breakout box in which you can change an important cap from one technology to another with the flick of a switch. Get a book on psychology experiments to learn how to do a single-blind experiment, and recruit your lady as a test subject. I think you'll get quite a surprise.

Here is a person who has done a lot of subjective testing with many different brands and types of capacitors. Might be worth reading before diving headlong into capacitor rolling. It saved me a lot of time and money.

http://www.humblehomemadehifi.com/Cap.html

Since capacitors are ubiquitous in all electronics, the statement, “Why they got better is audiophiles obsessed with and driven to achieve exceptional sound quality” is inane. To suggest that  our niche industry would be the driver of such improvements is just silly. 

@terry9 thanks for your thoughtful replies. Can you give an example of great air dielectric capacitor?
@puffball08 - I used that database to pick new caps for one of my amps, very informative.  Quite an undertaking…

Obviously, better manufacturing in general will lift all boats, but clearly the audiophile niche is highly active and innovative to some degree beyond mere marketing.  The premium audiophiles will pay has to explain the R&D that goes into VCaps or Mundorf or Duelund or whatever, and there must be legit technical advances happening, whether proprietary or otherwise.

First off the capacitors of the past are not all around today.  Think Black Gate capacitors which I feel were the best capacitors back then and today but they are no longer manufactured.  Materials have not really changed but now manufacturers are using different materials then they did back in the day.  Same goes with cables.  Silver, copper, aluminum combinations, twisting, insultation, etc.  Even the cheap Sprague capacitors lasted a long time.

What is different is more of the wire used.  Dueland makes hybrid copper and silver capacitors.  Could not find that back in the day.

So to me it is more of the types of materials being used and yes, some are made better than others - think V-Caps.  They are a really good manufactured product.  As referred to above with parts swappers - you can change the sound by installing larger power supply capacitors think Nichicon and Mundorf.  Anyone of you can do this as there is generally two leads for solder wires onto - just make sure there is enough room for the larger caps.

So what has changed to me is the materials used, etc.  BUT some of these caps can elevate you systems sound considerably.  V-Caps especially.  

For resistors - Audio Note now only offers non-magnetic resistors.  A step up from their now discontinued resistors.  Plus they also are now manufacturing a Silver resistor.  Expensive but worth it.

Happy Listening.