The Shure 520DX Green Bullet is a legendary high-impedance, dynamic microphone renowned for its distinctive sound and iconic industrial design, originally developed for communications and later embraced by musicians. Its most famous application is in blues and rock harmonica (blues harp) performance, where its unique tonal characteristics have become a defining element of the genre's sound. The microphone's body is a durable, cylindrical metal case with a green crinkle-finish paint, housing a unidirectional dynamic element. This element is inherently loud and capable of handling extremely high sound pressure levels, which is perfect for the close-miking, cupping technique used by harmonica players. The microphone produces a gritty, mid-range heavy, and naturally distorted tone when driven hard, a sound that cuts powerfully through a band mix and is difficult to replicate with other microphones.

The 520DX operates as a high-impedance microphone, designed to be plugged directly into guitar amplifiers or simple PA inputs without the need for a preamplifier or impedance-matching transformer, though such devices are often used in professional settings for greater flexibility and to prevent signal loss over long cables. Its unidirectional (cardioid) polar pattern helps reject some ambient stage noise, but its classic sound is truly achieved when the performer completely encloses the microphone in their hands, creating a resonant chamber that emphasizes low-end feedback and harmonic distortion. This interactive, tactile relationship between player and microphone is a key part of its appeal and performance technique. The microphone includes a finger-operated push-to-talk switch on its body, a remnant of its communications origins that some musicians incorporate for rhythmic, staccato mute effects.

Beyond harmonica, the Green Bullet has found a niche for vocal applications where a raw, lo-fi, or aggressive tone is desired, often used by punk, rockabilly, and alternative vocalists. Its rugged, all-metal construction makes it nearly indestructible on the road. While it lacks the flat frequency response and clean output of modern studio microphones, the Shure 520DX Green Bullet is cherished precisely for its colored, characterful sound. It is less a transparent audio tool and more a musical instrument in its own right, delivering a specific, iconic sonic texture that has shaped the sound of American blues and rock for decades, remaining a staple on stages worldwide for musicians seeking that authentic, aggressive, and unmistakable "bullet" tone.