Julian Parker and Stefan Bilbao

Spring Reverberation: A Physical Perspective

DAFx-09 Companion Page

This page contains the measurements and recordings of two spring reverberation units, as discussed in the paper Spring Reverberation: A Physical Perspective accepted for publication at the 12th International Conference on Digital Audio Effects (DAFx-09), Como, Italy, September 1-4, 2009.

Spring Reverberation

Spring reverberation was conceived in the 1930s by Laurens Hammond, the inventor of the electric organ, as a method of counteracting the 'dry' sound of his instruments. The simple, inexpensive, and compact design made this method of artificial reverberation attractive in a number of contexts. Larger spring reverbs were used in studios where cost or available space precluded the use of reverberation chambers or plate reverberation units. Smaller spring reverberators quickly found their way onto the stage via their inclusion in guitar amplifier designs. By the 1950s and 60s spring reverberation was a widely used effect, integral in the aesthetic of a number of musical movements.

Spring reverberation units consist of a number of helical metal springs connected in parallel or in series. An electromagnetic coil is used to excite vibrations in these springs based on an input signal. The vibration of the springs induces a signal in the output coil. This output signal has a reverberation-like quality, but with distinctive features unlike those of acoustic spaces.

Geometry and Impulse Response Measurements of Spring Reverberation Units

Presented below are two typical small spring-reverberation units. A brief description of each is given, along with a table containing measurements of their geometry. Hotlinks within the tables lead to the measured impulse responses of each unit and its individual springs.

Olson X-82

Olson X-82
Photo of Olson X-82 Spring Reverberation Unit

The X-82 is a small device from the early 1960s, manufactured by Olson Electronics. It consists of two small springs in parallel,and according to the manufacturer's literature it is intended for use in small instrument amplifiers or in a car audio system. The spring geometries appear to have been chosen in order to provide different dispersion characteristics but similar delay times. This design is very similar to the popular Accutronics Type 1.

Olson X-82 Spring 1 Spring 2
Helix Length (cm) 6.5 6.5
Helix Diameter (cm) 0.54 0.61
Number of Turns 148 133
Wire Diameter (cm) 0.035 0.035
Magnet Length (cm) 0.5 0.5
Magnet Diameter (cm) 0.21 0.21

Leem Pro KA-1210

Leem Pro KA-1210
Photo of Spring Reverberation Unit from Leem Pro KA-1210 Guitar Amplifier

This is a spring reverberation unit taken from a Leem Pro KA-1210 guitar amplifier, built in the early 1990s. It is larger than the Olson unit, and employs three springs in parallel. The spring geometries appear to have been chosen to provide similar dispersion characteristics but different delay times. This design is similar to the popular Accutronics Type 8.

Leem Pro KA-1210 Spring 1 Spring 2 Spring 3
Helix Length (cm) 16.3 16.3 16.3
Helix Diameter (cm) 0.44 0.45 0.46
Number of Turns 303 280 351
Wire Diameter (cm) 0.035 0.035 0.035
Magnet Length (cm) 0.4 0.4 0.4
Magnet Diameter (cm) 0.15 0.15 0.15

Measurement Methods

Physical measurements were taken using a micrometer and vernier calipers. Impulse response measurements were taken using a sine-sweep method. The units were driven with a power-amplifier of suitable impedance, with the output recorded via an appropriate pre-amp.

Julian Parker (julian.parker@tkk.fi) Modified: 28.08.2009