The science of reverb springs

[JWBarlow at aol.com]

In a message dated 2/23/99 7:22:39 PM, will7370 at tao.sou.edu wrote:

>Do reverb springs have to hang freely in order to work
>right?  Why can't they be coiled (with separators) inside
>something round like a Skoal can?  Or can they be tie
>wrapped snug to a board to avoid that SPROINGGGG! when you
>drop them?

A reverb unit is a transducer system. It is changing electrical energy into a
physical form (mechanical energy) and then back to electrical energy. The
initial change into mechanical energy is done in order to induce a slight
delay and (more importantly) multiple reflections of the original signal in a
simple and somewhat elegant fashion. It was, of course, a one dimensional
reflective system intended to provide a cheap alternative to echo chambers and
plate echoes (in the 1930's?) which have respectively 3 dimensional and 2
dimensional reflective properties.

It is easy to imagine how the waves travel through the spring (in the ideal
case) if you think of one side of the spring as having a speaker element which
forces the spring back and forth (in a longitudinal manner) at the same freq.
as the input signal. A small section of the spring will be compressed or
expanded, and will "travel" towards the other side of the spring, when it
comes to the end of the spring, it will travel back towards the driver element
(see any good physics book on longitudinal waves). It will continue reflecting
back and forth until all the inital energy is dissipated through friction,
heat, etc. 

At the end of the spring opposite the driver is a microphonic element which
translates the energy back into electrical energy.

So if you screw up the reflective properties of the springs, you'll screw up
the sound (man). Of course that may be the sound you want! But the thing that
makes it go "SPROINGGGG!" is the same thing that makes it work.

John B.