…I actually had several discussions with and helped with the protocol of the double blinded capacitor testing that was carried out by Dennis Murphy and Bob a couple of years ago on the DIY loudspeaker events. I had several discussions with Bob via email. Then Bob and Dennis constructed the final test system and carried out these tests at several DIY events. The results of those tests were that no one could reliably pick out a high end film capacitor from even an electrolytic(as long as the electrolytic was within a tight tolerance of value) when knowledge of the items listened to was removed. The only positive outcomes were with very limited trial numbers and when retested, came out as random…
I was one of the participants in that blind listening test. It took place over 4 years ago, and
I posted about it here. About 40 people in all, mostly DIY speaker builders, participated in that test. Some were newbies, like myself, and others had many years of experience.
Each person took a test which consisted of 12 individual trials listening to short selections of music over very high quality speakers that contained two crossovers inside. The crossovers were identical except for one capacitor - one used an expensive film capacitor and the other used either a non-polar electrolytic or cheap polypropylene. A listener could instantly switch between the two crossovers while listening, and record whether they heard a difference or not.
The result was that no one there could successfully identify the different crossovers by sound. The results were no different than if people were guessing randomly.
A similar version of this whole test was repeated at the Dayton Ohio DIY meeting about a month or two later. It had nearly identical results.
Now those who wish can quibble that this was never published in a scientific journal. True, but for a variety of different reasons, that will probably never happen. Real science journals aren't interested in this (for good reason). There is no scientific reason to explain why capacitors made with different materials or construction should behave differently, nor is there any credible listening test data to suggest that people CAN hear a difference. End of story.
It would be wise to ignore unsubstantiated claims that passive devices such as capacitors (or wires, etc.) can generate different sounds, and spend more time reading the reports of such real scientists as Floyd Toole or Sean Olive who have spent their careers studying just how listeners impressions (usually of speakers) can be influenced by such things as appearance, brand identity, price, etc. It is a genuine psychological phenomena not limited to hearing. Too many people in audio just plain ignore this or pretend that they are immune to such influences.