A Leslie speaker is a type of loudspeaker that uses a rotating horn to create a unique sound effect. It is commonly associated with the Hammond organ, which produces rich, warm tones. The rotation of the horn creates a Doppler effect, giving the music a swirling, three-dimensional quality that is highly sought after in various music genres, especially in jazz and rock. Invented in the 1940s by Donald Leslie, the Leslie speaker has become an iconic part of many keyboard setups. It typically features two speakers: one for high frequencies and another for low frequencies. The combination of these elements allows musicians to achieve a distinctive sound that enhances their performances.