Spring Reverb without Electricity

[Demonstration]

This is a spring reverb. Usually a spring reverb unit has an electrical driver and a pickup. But this one does not use electricity.

The mechanism is simple. Two paper cups are connected using three chopysticks. (It looks two in the picture but there's actually the third one behind the spring.) Between the bottoms of the cups is a spring.

Cut the edge of the lower cup so that it can be set at the speaker of the synthesizer.