Why do spring verbs work?

[soggybag]

I've had this question in my head for a few years now: why do spring reverbs sound the way they do and how does spring reverb work?

I assume that it has something to with sending the signal through a metal coil and vibrating that coil. The audio output has to have an effect on the coil by physically moving it.

Is there something in that the signal is going through a coil and inductance comes into play? But the coil is changing shape effecting the sound?

[antonis]

If you like to go into Physics:
http://www.guitarscience.net/papers/guibook.pdf

Ch. 6.15 - page 454..

[imJonWain]

Good Rod Elliott article too.
https://sound-au.com/articles/reverb.htm

[Rob Strand]

I'd read the links the otherw posted first.  The drive side can be current driven or voltage driven.

As to what's under the hood:

The springs have small cylindrical magnets attached at each end.

At the drive end there is a coil which creates a magnetic field and a small cylindrical magnet in the magnetic field.  The field causes a torque to move the spring.  It's basically a motor.

At the receive side you have a similar coil and magnet set up.  In this case the moving magnet produces a voltage in the coil.   Basically a pickup.

Exactly how it all looks and works is in this thread.   If you want to read over the thread you can see mac's design evolve.   The key point is you can do the motor part and pickup part different ways.
https://www.diystompboxes.com/smfforum/index.php?topic=120207.msg

The pic in reply #51 shows different ways the motor might work,
https://www.diystompboxes.com/smfforum/index.php?topic=120207.msg1127046#msg1127046

The pic #55 it shows what really happens.  The motor spins,
https://www.diystompboxes.com/smfforum/index.php?topic=120207.msg1127164#msg1127164

The reverb spring detailed in the thread has two parallel springs.

[PRR]

Speed of sound in air is about air's mass and stiffness.

We want a sloooww speed of sound to get long delay in small package.

Solid metal is a little more massy but much stiffer. Speed of sound is high.

The coiled metal adds mass but reduces stiffness. Also gets more length in the box. (It does not have to be coiled to work, but then it would be much-much longer.)

[soggybag]

Thanks this makes more sense. I was not aware of the magnet and coil! I had no idea that there was more to those springs.