Part 19
Altec M11 System.
Altec-Lansing Corporation billed it as “The mike that became a must!” when it came out around 1949. I’m talking about the Altec 21B condenser microphone capsule which was part of the M-11 Microphone system. This capsule was an amazingly small mike for that era.
This mike was a revolutionary development at the time because condenser mikes had fallen out of favor way back in the 1930s. Ribbon and dynamics had taken over the professional audio field and many thought the condenser would never come back. Altec engineers had a different idea…a new approach to the problem: not “redesigning what was already available, but starting from scratch with a dual specification: “The best quality and the smallest size.”
More than 20 “man-years” were spent in the design and engineers of the 21B. The result wasn’t just a “better mike” – smaller in size – but a mike, smaller in diameter than a dime…that set a new standard in microphone performance…with new pickup techniques as well. The condenser mikes of the 1920s and 30s were big and had bulky amplifiers that had to be in close proximity to the pickup capsule and were powered by large battery packs.
The new smaller size capsule mated with the new “miniature” vacuum tubes developed during WWII made possible the come back of the condenser unit. Altec used an A/C power supply box instead of bulky battery packs. The result was the M-11 microphone system. The capsule itself was 5/8ths of an inch in diameter and just a quarter inch thick. It had a sound entrance opening that was a tiny slot around the top edge of the capsule.
People referred to this mike as the “coke-bottle” because of its unique and stylish shape. The small 21B capsule was mounted at the top of the slender “coke-bottle” “150A” base which contained a 6AU6 miniature vacuum tube which converted the very high impedance of the capsule to a low impedance by use of a cathode-follower circuit. The unit used a multi-conductor cable connected through a Cannon “P” 8-pin connector which was at the bottom of the “coke-bottle”. The mike could be separated from the power supply by as much as 400 feet.
This cable mated with the power supply box which supplied both filament and high voltage to the vacuum tube and condenser capsule. The power supply box also had an output cable that connected the system to the audio equipment it was to be used with. There was an optional matching transformer that plugged into the power supply box to provide a balanced output for professional audio systems.
The 21B capsule produced an extremely smooth and extended response over the entire audio range and was omnidirectional. Later modifications were the 21C and D which only changed the way the sound entered the mike at the top. Its graceful, slender shape made it possible for artists to “get out from behind the mike” and be seen with a minimum of obstruction when used on a mike stand and it also fit comfortably in the hand for mobile use.
The M-11 mike system became an instant sensation in the audio industry and saw wide use in broadcasting, public address motion picture production and recording. Later Altec used the same capsule with an even smaller base that used printed circuits and a sub-miniature vacuum tube…this was dubbed the “lipstik” M-20 microphone system. It was literally no larger than a lipstick and was practically invisible on a regular mike stand. It was also equipped with a fountain pen clip so that it could be put on a coat lapel or tie or hidden underneath the tie, corsage or other ornaments.
Altec went on to develop other condenser mikes including uni-directional units. This was the start of the resurgence of the condenser microphone in the US. Shortly after the Altec was introduced the industry saw the importing of the very fine German condenser mikes that continued the condenser comeback. Today condenser mikes of all kinds are used universally in everything from telephones to high end recording. Altec-Lansing was considered one of the premiere electronics manufacturers of the 20th century.
