Q. Does freezing really improve the quality of valves?

I’ve heard that some companies routinely freeze valves and certain electrical components to improve their performance. Would this technique actually have any effect on quality?

Clive Edmondson, via email

SOS Technical Editor Hugh Robjohns replies: 

There are certainly some people who claim that it can, but I’ve not experienced it personally and my knowledge of materials science isn’t up to giving a definitive view, I’m afraid.

However, the basic idea of ‘deep cryogenic treatment’ is to freeze the valve to an extremely cold temperature (well below the capability of any domestic freezer: typically, the valve is submerged in liquid nitrogen at about -195 degrees Celsius and stored like that for a day or so before gradually returning it to room temperature. This cryogenic process is claimed to allow the crystalline structure of the metals used in the valve plates to realign in a way that allows electrons to flow more easily (ie. resistance is reduced), and that’s what brings the claimed benefits to sound quality.

Assuming that it’s done slowly and in a controlled environment, valves can be frozen in liquid nitrogen for a while without being damaged. Some companies offer this as an option on the valves they sell, as it is said to improve long-term reliability.

Certainly, strange things can happen to metals at very low temperatures — like superconductivity — but these effects don’t usually last when the metal is returned to room temperature. NASA also apparently use cryogenic treatments to prepare materials for use in space. But whether the science behind their applications extends to the use of audio valves at room temperature, I’m not so sure. Allegedly, the benefits of the cryogenic process remain throughout the life of the valve, despite the heating and cooling cycles it will go through in normal use.

Given the natural variability in valve sets anyway, I think it likely that differences will be heard between normal and cryogenically treated tubes. However, whether those differences are really better or just different — and whether the cost is justified — I suspect comes down to personal choice.  

Published in SOS December 2010