A reverberation device is developed using coiled springs, which would be desirable for an electronic organ to add smooth reverberant sound to the musical tone. But it has its faults; (1) difference in loudness at every key, (2) pulsating sensation immediately after depressing the key, (3) similar sensation in the transient after releasing the key, and (4) appreciable change of the frequency in the same transient. Experiments show that (1) the free torsional vibrations build up when the key is

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... pressed and also when the key is released, (2) there is some difference between the frequency of the free vibration and excitation frequency of the musical tone of the key, and (3) the intensity of the free vibration of the key depends on the difference. This paper describes that these free vibrations are the cause of the four faults.