Just as tube amplifiers appeal to guitarists yearning for the warmly overdriven tones they hear on old analog recordings, tube microphones hold a special place in the hearts of many singers keen to add a little vintage warmth to their vocals.
Prices for a tube microphone range from the affordable to cost prohibitive, depending upon the brand and the era in which it was manufactured. Like an antique and collectible car that holds its value, certain microphones can be quite an investment. In some cases, they may even cost almost as much as a small car.
History
The first microphones were primitive carbon transmitters of the type found in telephones, as far back as the 1800s. Although adequate for transmitting speech, their poor frequency response rendered them unsuitable for recording music. The concept of a condenser transmitter had been experimented with during this time, but the high impedence and low output on them made them impractical. The arrival of vacuum tube amplifiers solved that problem, and Bell Labs introduced the first condenser microphone in 1917. Improvements made to them, most notably by Western Electric, led to improved reliability and increased popularity.
In the United States, the bandwidth of broadcast radio was quite limited and since most microphones were made for this purpose, the development of condenser models was a little lackluster. Not so in Germany, where state-run radio insisted on the highest-quality broadcast sound. In 1928, Georg Neumann and Co. began developing very high-quality condensers. Among them was the legendary CMV3A. This microphone allowed the user to remove and exchange the condensor head according to his preference.
The Neuman U47 was released in 1948. This soon-to-be legendary microphone became the jewel in the crown of the top American recording studios in the 1950s, replacing the famed RCA ribbon microphones that had previously dominated recordings stateside. The U47 soon became the vocal microphone of choice for such luminaries as Frank Sinatra, Louis Armstrong, John Coltrane, Ella Fitzgerald and Nat King Cole.
Along with Neumann, the Austrian company AKG were major players in the condenser microphone field. Their famous C12 model had a remote-controlled pattern selector, enabling a switch from omni-directional to bi-directional function. This remained in production until 1963.
Function
What makes the sound of a tube microphone so pleasing and desirable? Condenser microphones have a very low electrical signal and need amplification. As such, they have a built-in amplifier that boosts the signal to the level of a regular microphone. Like any other microphone, it is then fed to a pre-amp. The tube in a tube microphone is just the amplification stage for inside the microphone itself.
The tube saturation produces harmonics that, in the case of high-quality tube microphones, sound very warm and musical. This is despite the fact that they tend to have more total harmonic distortion (THD) than solid-state models.
Theories/Speculation
Tube aficionados point to the vocal recordings of the 1950s, '60s and '70s, whether by Sinatra, Presley, Orbison, Lennon & McCartney or Wonder, as being the pinnacle of recorded vocal sound in popular music--and as proof that microphones with tubes are superior to those with transistors. It's hard to argue with the quality of the vocal performances of the aforementioned artists, but how much the microphones had to do with it is debatable. It's highly likely that singers of that caliber would wow listeners regardless of microphone choice. Maybe a better argument might involve the study of mediocre singers made to sound stellar thanks to an elite, top-drawer tube microphone.
Warning
Assuming that a microphone that has a tube in it is automatically a superior-sounding microphone to any solid-state model could lead to disappointment for a buyer. It's important to remember that the elite vintage microphones like Neumann and AKG had first-rate tubes in them and were hand assembled with the finest quality components. There are many companies keen to cash in on the resurgent interest in vintage tube microphones by offering budget tube models that use modern tubes that are of inferior quality.
Currently produced tubes are inferior because it's not cost effective to produce them to the standards of yesteryear. Vintage tubes had superior durability and sound quality, and were also less noisy. Consequently, there is a hugely competitive market for new old stock (NOS) tubes. These are tubes that were manufactured decades ago, but for various reasons have never been used. Obviously, the market is competitive because of the scarcity of these parts, and it pays to be cautious because there are unscrupulous dealers--especially on Internet auction sites--who are selling relabeled or even outright fake NOS tubes.
Considerations
The arrival of transistors sounded the death knell for the reign of tube condensers. Tube microphones were a little noisy, tended to be a little temperamental and were prone to distortion. Solid-state models were more reliable and required little maintenance and so began to dominate the market. As these microphones fell out of favor, many of them (and, as discussed above, the tubes that powered them) were snapped up at bargain prices to be sold at huge profits when quality vintage equipment became popular again. In the digital age, artists and engineers have rediscovered the beauty and warmth that a quality tube microphone can impart on a recording, and many are willing to pay extreme prices for them.
In the 1960s, the U47 was the go-to vocal microphone on practically every Beatles recording session, cementing its standing as one of the elite microphones of all time. Because these records are among the most revered pop recordings ever, it stands to reason that engineers and musicians--tired of the perceived harsh digital edge of modern microphones and recording mediums--would search out the gear that helped create these sonic masterpieces.
Of course, the gear can only take you so far. The fact remains that John Lennon and Paul McCartney could have sung into a tin can attached to a piece of string and still sounded fabulous; the performance is still key. It's important to remember when you're plunking down $10,000 for a microphone.
