Voltage from Ribbon Microphone

The signal from a ribbon microphone is generated as a motional voltage; the movement of the ribbon in the magnetic field generates a voltage proportional to the velocity of the ribbon.

Ribbon Microphone Use

Current applications of ribbon microphones exploit the "warmth" of these microphones for vocals and some instruments. Blair Jackson in "Off the Beaten Track", Mix, November 1994 p247 provides a recent comment from sound engineer Ed Thacker:

"We did a lot of experimenting on this record with ribbon mikes, mainly old RCA 44s and 77s. We wanted to keep it as warm and round as we could. Ribbon mikes are very rich-sounding, but they don't have a lot of top end ... so they're great on horn instruments. We also used them on several vocals to fatten and warm them up."

Condenser Microphone Signal

The flat, faithful frequency response of the condenser microphone arises from its mechanism. The charge on the membrane depends only upon the spacing and shows no appreciable resonances to skew the frequency response.

When the spacing changes, the charge changes, giving an electric current through the resistor R.

The voltage measured across the resistor is an electrical image of the sound pressure which moves the membrane.

Because the sensing element of a condenser microphone is a light membrane, it is capable of excellent transient response. The fact that the condenser has excellent high frequency response implies good transient response, since sharp transients have more high frequency content than the sustained sounds which follow them.

Because the condenser microphone must have a continuous, stable DC voltage to bias the membrane, it is common practice to supply that voltage from the sound mixing board. The voltage is applied via one of the microphone leads, typically 48 volts, and is commonly referred to as "phantom power". Since the alternative is a battery supplied bias, with the risk that a battery can go out in mid performance, the phantom power provision from mixing boards is useful.

Electret Condenser Microphone

Electret condenser microphones are not to be compared with the studio standard condenser microphones which have such excellent frequency response characteristics. The electret class of microphones are condenser microphones which use a permanently polarized electret material for their diaphragms, thus avoiding the necessity for the biasing DC voltage required for the conventional condenser.

They can be made very inexpensively and are the typical microphones on portable tape recorders. Better quality electret condensers incorporate a field-effect transistor (FET) preamplifier to match their extremely high impedance and boost the signal.

Recent technical literature is suggesting that with increased precision in manufacture, electret condenser microphones are being made with sufficient quality to be competitive with the dynamic and ribbon microphones for performance use.

Miniature electret condenser microphones have found productive application in hearing aids where their ruggedness and reasonable signal-to-noise ratio serve well.

Electret Microphone Diaphragm

The electret material of the diaphragm may be less than a thousandth of an inch thick. Even so, it is polarized enough to produce an active capacitive change in the voltage between the membrane and the back plate when it is moved by the pressure of a sound wave.