Tuesday, December 05, 2006

The Microphone Part 7

Despite improvements, in both carbon and condensner microphone design audiotechnicians in radio and recording wanted something better. With the popularity of the radio there was even a genuine cash market for the product. There was a need as they say...

In 1924 the ribbon microphone was invented by Walter Schottky and Erwin Gerlach (of Siemens.) This first ribbon mic consisted of an extremely thin (0.002 mm!) concertina ribbon of aluminum placed between the poles of a permanent magnet. The directional pick up pattern was a very useful quality since it makes it possible to eliminate acoustic feedback. http://www.coutant.org/ribbons.html

Many articles claim that Harry F. Olson of RCA invented the Ribbon Mic. this is not so. He did pioneer many of the early popular Ribbon Mic designs. But ac much credit as he and RCA deserve for the success of Ribbon mics in the market place, even these early commercially successful models were bulky and eventually fell out of favor.

The moving element of the ribbon microphone is a thin corrugated aluminum ribbon suspended between the poles of a strong magnet. In this arrangement sound moves air particles vibrating the ribbon in the magnetic field. This motion causes an alternating voltage to be generated in the ribbon, the amplitude of which is proportional to the velocity of the air particles. The output voltage and the electrical impedance of the ribbon are raised to a value suitable for transmission of the signal to an amplifier, by a transformer built into the microphone case. The transformer is well shielded against stray magnetic fields by multiple shields of mu-metal and copper. Article here.

While it was (and is) widely considered to be the most natural sounding microphone ever made, it had a down side. The first ribbon mics were very heavy, about 8 lb. they were very susceptible to moisture damage and also could easily be damaged by shock or blowing into it. Simply blowing into a Ribbon mic ruined them. Great article on modern Ribbon Mics here.

In 1932 RCA introduced the RCA Type 44-BX, A bi-directional velocity mic. This is a classic robbon mic. more information here: http://www.coutant.org/2.html Ribbon mic technology improved slowly moving toward smaller chassis and less delicate hardware. In 1958 Eugen Beyer changed all that with his introduction of the world's first robust, 'short diaphragm' ribbon mic. Its capsule shared dimensions similar to the moving coil transducers of the time and his original designs are still manufactured today.

The 44BX pic to right is from the illustrious K-BAY Microphone Collectors Website. Mr. James U. Steele over there knows more about mics than the rest of us radio geeks combined. http://www.k-bay106.com/photos.htm