SR/Live Fri, July 04, 2008

That however, has now changed, and as technology moves forwards and becomes increasingly affordable, more and more condensers are making their way onto the world stages, both in vocal and instrument applications. The reasons are varied, but to understand this, one has to take a look at some of the history and practicalities of the technology.

The condenser microphone was developed in 1916 by E. C. Wente at Bell Labs in the USA to translate sound waves into electrical waves that could be transmitted by a vacuum tube amplifier. His patent 1,333,744 “Telephone Transmitter” was filed December 20, 1916 and granted March 16, 1920. This design was improved over the next 10 years and became in 1926, the Western Electric 394-W microphone used to produce the first generation of sound motion pictures.

Condenser is actually an obsolete name for a capacitor, as the microphone uses a capacitor to convert acoustical energy into electrical energy. The capacitor has two plates with a voltage between them. In the condenser microphone, one of these plates is made of very light material and acts as the diaphragm. The diaphragm vibrates when struck by sound waves, changing the distance between the two plates and therefore changing the capacitance. As such, condenser microphones require an electrical source to establish the capacitor plate voltage, and for internal amplification of the signal to a useful output level, which can be provided by an internal battery or external source.The good news was that condensers tend to be more sensitive and responsive to transients and have a flatter response, especially at higher frequencies. But the downside was the power requirement (batteries can run down and power was not always readily available), delicate capacitors and a reaction to humidity between the plates that can create an audible “fizzing” of the audio output.

One answer was the development of the electret condenser microphone, (the foil-electret courtesy of Gerhard Sessler and James West at Bell Labs in 1962) which incorporates a permanent voltage applied to the capacitor during manufacture.

This was advanced through the “back electret” design, which applies the electrostatic charge to a rigid back plate, thus allowing a thinner diaphragm front plate. As such no power is required. It is this design that features heavily in today’s condenser microphones for stage use, however note that models may incorporate an internal preamp, which still needs power, and although some can work on batteries, phantom power (provided by a mixing console for example) is always a better option.

In addition to back electret designs, another option is the pressure gradient transducer, where the incoming pressure wave reaches both sides of a single diaphragm that is externally charged with a negative polarity at the rear and a positive polarity at the front. The result is that the pressure at the rear is subtracted from the front. The bigger the difference in pressure, the bigger the voltage output. Another word for “difference” is “gradient” and thus the name of the design.

Today manufacturers are also creating more rugged microphones, especially for vocal stage use. They are also actively and successfully combating the humidity issue, a major problem on hot stages, although care is still required. The result for today’s live sound engineer is an increase in reproduction quality across the board on stage, thus allowing some of the nuances captured in the studio to be translated to a live audience.

This issue’s Real World Gear offers 24 models: 12 suitable for vocals and a further 12 with instrument potential, and are divided in that order. And as always, the normal caveat applies that this is not an exhaustive list, just our representation of some of the products on sale now… call it a condensed selection if you will.