In 1959, company founder Dr. Fritz Sennheiser worked with design engineers Paul-Friedrich Warning and Johann-Friedrich Fischer to take its successful MD-21 omnidirectional microphone to the next step. The project was the MD 421, a rugged dynamic mic with a tight cardioid pattern that was consistent at nearly all frequencies, with high SPL handling (up to 175 dB) and a five-step LF attenuation circuit for tweaking bass response.
Low-frequency directivity was accomplished using four vents near the rear of the mic, felt damping within the mic body, internal damping in the capsule and a bass pre-emphasis tube for airflow between the capsule and an air chamber in the mic body. A cut-away diagram of an MD 421 resembles a jet engine more than a dynamic mic. The body was molded of DuPont Delrin resin, and 50 years later the MD 421 remains one of the few pro audio mics featuring a molded (now glass-composite) body. The MD 421 was launched at Germany’s Hannover Fair in 1960; five decades later, it remains in use in studios, stages and broadcast facilties worldwide.