When Hammond introduced the first home organ in 1935, most people had only heard such instruments in churches and theaters. So, when they purchased a Hammond for their homes, they expected the same room-filling sound, but in their thickly carpeted living rooms with low ceilings, furniture, and drape-covered windows, they didn’t hear it. So Hammond needed to find a way to add reverberation to the living room. Bell Labs had developed an electromechanical device that could be modified to create reverb, but that unit stood four feet high! Initially, this was not a problem, as the Hammond cabinet was huge. But in 1960, an engineer named Alan Young was assigned with the task of developing a more compact reverb unit. Young was also a musician who frequently took projects home to experiment with at night and on weekends. He wanted a unit that was smaller than his briefcase, and eventually his efforts resulted in what is now called the Accutronics Type 4 spring reverb, which quickly caught on with organ makers and anyone else requiring reverb. One customer was Leo Fender, who introduced the Fender Reverb Unit in 1961, then added the Type 4 to his now famous Twin Reverb. After that, the Accutronics quickly became the industry standard.
Spring reverb units use a combination of electromagnetic and mechanical elements to simulate paths of delayed sound. An audio signal drives the coil of the input transducer, which applies a twisting force to miniature cylindrical magnets attached to a set of precision stainless steel transmission springs. The twisting motion travels as a wave impulse down the length of the springs until it is rebounded by the output transducer, which also uses magnetic components to generate a delayed output signal. (This is a simplification, of course.) In any case, by 1990, the reverb division had outgrown its original facility and was moved to a new 37,000 square foot plant in Cary, Illinois, and still makes the world-famous Accutronics Reverb for such major amplifier manufacturers as Fender, Marshall, Peavey, and others, though it is no longer part of the Hammond Organ Company. Despite the introduction of digital reverb several years ago, Accutronics’ reverb business continues to grow because the sound of the spring reverb is such an integral part of the overall sound of most classic guitar amplifiers.