Vintage Sennheiser MD-421

THERE AREN’T MANY LIVE SOUND MIC DESIGNS that are still being used a half-century later, but the Sennheiser MD-421 is just as useable today as it was on its debut in 1960. And now, some 50 years later, it’s still a favorite mic for drums, percussion, horns, guitar cabinets and vocals.

THE PREDECESSOR… Introduced in 1953, Sennheiser’s MD-21 dynamic microphone was rugged, reliable, good sounding and available in available in five colors. It remained in production for decades. However, the basic, no-frills MD-21 was an omnidirectional model, so in 1959, company founder Dr. Fritz Sennheiser worked with design engineers Paul-Friedrich Warning and Johann-Friedrich Fischer to take the design to the next step.

NEW MIC ON THE BLOCK… The project was the MD-421, a rugged dynamic mic that could provide a tight cardioid directivity pattern that was consistent at nearly all frequencies. It also featured the capability to handle extremely high sound pressure levels (up to 175 dB!), a hum compensation coil to prevent EMI/RFI interference and a 5-step low-frequency attenuation circuit for tweaking bass response.

The MD-421 had to provide studio-quality frequency response (30 Hz to 17 kHz) and be able to be manufactured in relatively large quantities. It was a tall order, but the development team went to work.

In any pro mic design, the capsule and electronics are the most difficult part of the design process, but with the MD-421, extreme attention was also paid to controlling low frequency directivity and assuring consistent polar response. This was accomplished using four rear vents near the rear of the mic, felt damping at the rear of the mic body, internal damping within the capsule and a bass pre-emphasis tube that provided airflow between the capsule interior and a large air chamber within the mic body. A cutaway diagram of the MD-421 reveals the complexity of a design that resembles a jet engine more than a dynamic microphone, with multiple air chambers, venting tubes and dampening material used inside the body cavity. Download this cutaway diagram of the MD-421 for a look into the complexity of the mic’s design.

The MD-421′s body was made of DuPont Delrin polymer resin, which had just become available the year before, and 50 years later, the MD-421 remains one of the few professional audio microphones featuring a molded (now glass composite) body.

The MD-421 was launched at Germany’s Hannover Fair in 1960 and carried a price tag of 180 Deutschmarks (about $45 USD). The original version was available with Tuchel or DIN output connectors; an XLR model followed years later. But in any version, the MD-421 was an instant success.

THE PRESENT AND BEYOND… Today, the next-generation MD-421-II incorporates improvements such as a metal inner chassis for better weight distribution, a shorter, sleeker housing and self-sealing (non-adhesive) acoustic connections for improved serviceability. And with some 500,000 units in use since 1960, the MD-421 has definitely earned the well-deserved distinction of an audio classic. Read about the current Sennheiser MD-421-II.
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George Petersen’s most recent project is co-producing Chelle and Friends’ “Voodooville: A Celebration of New Orleans,” a surround-audio DVD of funk/blues/jazz insired from The Big Easy.