[Dixielandjazz] Re: Columbia's echo

[Andy.Ling at Quantel.Com]

Dave Palmquist asks:-
>
Sometime in the late 1960's, a high school friend who was taking 
electronics showed me a gadget used to create reverberation.  It was 
mechanical rather than electronic,

snip....

Is anyone familiar with this gadget, and if so, can they explain the 
technology?  It seems obvious to me that I haven't got a clue what I'm 
talking about.
>

I assume what you are talking about is a spring delay line.

The way these work is to take the input signal and then using
something like a small loudspeaker make one end of the spring
vibrate. Then at the other end of the spring you have something
like a microphone to pick up the vibrations and convert them back
into a signal that can be mixed with the original.
(NOTE for the techies out there I know it's not a speaker
and microphone, but the analogy works to simplify things)
The delay is determined by how long the vibrations take
to travel down the spring, which, in part, is determined
by how long the spring is.

The reverb is achieved simply by mixing the original and
delayed signals. The delayed signal acts just like an echo.

The reason vibrations and springs are used is that vibrations
take a lot longer to travel down a spring than the electrical
signal takes to travel down a similar length of wire.

Interesting effects could be achieved by hitting the box
containing the spring and making it vibrate. This would
add to the vibrations caused by the original signal.

We used to have a PA with a spring delay line for the reverb
and if someone kicked it it produced some very odd sounds.


Andy Ling