Don Leslie loved the (then) new Hammond Organ, but found the tone a little “square’. He wished the Hammond to sound more like his beloved “Mighty WurliTzer” Theatre Pipe Organ. Being a seasoned and skilled inventor, he imagined utilizing a principle called the “Doppler Effect”-(It’s why a train whistle seems to go down in pitch when a train passes you). Don took a horn speaker, and developed an apparatus to make it spin around in a circle. Legend has it Don constructed the whole thing in a closet! His experiment bore fruit-The spinning horn gave the Hammond Organ what is called in the pipe organ world, a “tremulant”. Vibrato, Tremolo, and a little “whoosh” of air all put together. It made the Hammond Organ sound completely different. The Hammond’s life in all popular music-Jazz, Rock, Pop was born at that moment, and Don Leslie secured his place in the rare pantheon of immortal inventors.