The spring’s the thing
With its weird, twangy sound and distinct upward pitch envelope, spring reverb has long been a popular effect among producers of dub and reggae – in which it’s simply part of the genre vocabulary (think King Tubby and Lee ‘Scratch’ Perry) – but it also helped to define the sound of surf rock in the 50s and 60s (Dick Dale, The Beach Boys).
Originally invented as an onboard effect for the Hammond organ in 1940, it quickly found its way into guitar amps by Fender and other manufacturers. The mechanical principle on which it works is really quite straightforward: one or more tensioned springs are suspended within a metal case, each one connected to an electromagnetic transducer at each end, and in some cases, divided into ‘separate’ springs using metal joints, for extra diffusion. The transducer at the ‘input’ end turns the incoming signal into vibrations along the spring, while the ‘output’ transducer converts the vibrations back to an electrical signal, which exits the loudspeakers at which it eventually arrives as a characteristically dark and ‘springy’ reverberation. This reverberation is anything but linear, with a fairly defined (but very fast) oscillating rhythm to it, influenced by the spring length and source material.