By George Petersen
With this month’s launch of the next-gen Sennheiser MD 421 KOMPACT microphone (visit https://fohonline.com/blogs/new-gear/sennheiser-unveils-md-421-kompakt-dynamic-microphone/ for more details and the first product review), we thought we would look back at the amazing 64-year history of the original Sennheiser MD 421…
Introduced in 1953, the Sennheiser MD 21 dynamic microphone was perhaps one of the company’s most successful products. Rugged, reliable, good sounding and available in available in five colors, it was a hit with European broadcasters and remains in production today.
However, the MD 21 was a basic, no-frills omnidirectional model, so in 1959, company founder Dr. Fritz Sennheiser worked with his design engineers Paul-Friedrich Warning and Johann-Friedrich Fischer to take the design to the next step.
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, along with the capability to handle extremely high sound pressure levels, a hum compensation coil to prevent EMI/RFI interference and a 5-step low-frequency attenuation circuit for tweaking bass response. Note: One rare (and short-lived) variant was the MD 421-2, which had a Tuchel output connector and NO bass roll-off filter. Do NOT confuse this model with the similarly named “second series” MD 421-II that came out in 2002 and remains in production today.
The MD 421 also 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 most studio (or live sound) mic designs, 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. Below, the cutaway diagram of the mic reveals the complexity of a design that resembles a jet engine more than a dynamic microphone.
The body was made of DuPont Delrin polymer resin, which had just become available the year before and four decades later, the MD 421 remains one of the few professional audio microphones featuring a molded body.
The MD 421 debuted 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 version followed years later. But in any version, the MD 421 was an instant success.
In fact at one time, the backorder situation was so extreme that Sennheiser ran ads with a bakery worker posing with trays of mics coming out of the oven, to assure customers and dealers that more MD 421s were on the way.
Today, 64 years after its introduction, the MD 421 remains in use worldwide in broadcast as a vocal microphone and on live stages and studios mostly as an instrumental microphone. The current incarnation, 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 distinction of an audio classic. And no, I have never met ANYONE who is a fan of the 421’s fragile mic clip!
MD 421: The Next Gen
Some 64 years later, on October 1, 2024, Sennheiser launched the next-gen MD 421 KOMPACT microphone (visit https://fohonline.com/blogs/new-gear/sennheiser-unveils-md-421-kompakt-dynamic-microphone/ for more details and the first product review).
