Micro (from the Greek word mikros) means “small,” and phone (from the Greek word phone) means “sound” or “voice.” This translates microphone to “small sound,” which is accurate, as the microphone deals with small audio signals, changing mechanical wave energy (sound) into electrical energy (audio signal). It is used in many applications such as telephones, tape recorders, hearing aids, motion picture production, live and recorded audio engineering, radio and television broadcasting, and in computers for recording voice. IEC 61094-4 Ed. 1.0 b:1995—Measurement Microphones – Part 4: Specifications For Working Standard Microphones specifies guidelines for working standard microphones.
The IEC 61094-4 Ed. 1.0 b:1995 Standard for Microphones
IEC 61094-4 Ed. 1.0 b:1995 specifies mechanical dimensions and certain electro-acoustical characteristics for working standard microphones. These microphones are specifically used in measuring systems for the determination of sound pressure to enable them to be used as transfer standards in the calibration of acoustic measurement instruments. The microphone in IEC 61094-4 Ed. 1.0 b:1995 should be capable of being calibrated by at least one of the following:
- A method specified in IEC 1094-2 or IEC 1094-3
- By comparison with a calibrated laboratory standard microphone
- By a sound calibrator as specified in IEC 942
This standard establishes a system for classifying working standard microphones into a number of types according to their dimensions and properties in order to facilitation the specification of measurement systems, the calibration of measuring systems and microphones by sound calibrators, and the interchangeability of microphones in given measuring and calibration systems.
IEC 61094-4 Ed. 1.0 b:1995 does not specify the transduction principles by which working standard microphones operate.
What Is the History of Microphones?
The microphone was initially introduced in 1877 by Emile Berliner, who had been working with Thomas Edison. It was a drum-like device consisting of a carbon button microphone. In 1878, David Edward Hughes independently developed the microphone into a different model—the crude carbon rod microphone. Alexander Graham Bell bought the patent to Berliner’s microphone in 1878 that consisted of a wire which conducted electrical direct current (DC). Audio signals were generated and received by a moving armature transmitter and its receiver, and transmission was possible from both directions.
In 1915, the vacuum tube amplifier was invented, helping improve the volume output for devices, including the microphone. In 1916, condenser microphone, also known as a capacitor or an electrostatic microphone, was introduced by Edward Christopher Wente of Bell Laboratories and was patented by inventor E.C. Wente while working at Bell Laboratories. Wente had been tasked to improve the audio quality for telephones, but his innovations also enhanced the microphone. In 1928, the commercial production of condenser microphones began. Condenser microphones are used today for recording purposes including vocal tracks, pianos, live strings, acoustic guitars, and more.
After the development of radio broadcasting, ribbon microphones were invented in the early 1920s to assist in broadcasting. A ribbon microphone is a very fragile microphone and is rarely used, but its ability to capture higher frequencies of sound gives it the edge when recording certain instruments that require detail in that frequency department. Moreover, the first dynamic microphone, the electrodynamic moving-coil microphone, was invented in 1931 by Western Electric. Dynamic microphones are used for bass guitar, drums and amplifiers due to their high volume levels. In 1957, the first recorded patent for a wireless microphone happened, and it was filed by Raymond A. Litke, an American electrical engineer.
An electret microphone came about in 1964, invented by Bell Laboratories, completely transforming the microphone industry because it offered greater reliability at a lower cost. In 1970s, condenser and ribbon microphones were further improved to enhance the audio quality of sound systems and allowed for clear volume and reduced sound level sensitivity. Finally, in 1983, the first clip-on microphones were invented, which are still being used to this day. Now, microphones that are composed of higher quality microphones are being used regularly.
Characteristics of Working Standard Microphones
IEC 61094-4 Ed. 1.0 b:1995 details characteristics of microphones, such as:
- Sensitivity: The sensitivity of a microphone is defined in IEC 1094-1.
- Effective Front volume: This is an important quantity when the microphone is calibrated with a sound calibrator and when used in small couplers such as ear simulators
- Upper limit of the dynamic range of microphone: This should be stated in terms of the sound pressure level which, throughout the frequency range of 160 Hz to 1,000 Hz, results in total harmonic distortion of 3%.
- Linearity range of the microphone sensitivity level: The sensitivity level of the microphone reference conditions should not vary by more than 0.2 dB at any frequency in the range from 160 Hz to 1,000 Hz when the sound pressure level varies.
- Static pressure dependence of microphone sensitivity: The sensitivity of a microphone depends on the static pressure which influences the impedance of the air enclose din the cavity behind the diaphragm
- Temperature dependence of microphone sensitivity: Small and slow temperature variations usually cause reversible changes in sensitivity; large or rapid temperature changes (temperature shock) can lead to a permanent change of microphone sensitivity
- Humidity dependence of microphone sensitivity: : The sensitivity of a microphone can depend on relative humidity
- Stability of microphone sensitivity: The sensitivity of a microphone can change over a period of time even when stored under typical conditions
- Pressure equalizing leakage: The cavity behind the diaphragm is normally fitted with a narrow pressure equalizing tube to permit the static pressure to be the same on both sides of the diaphragm, so at very low frequencies, this tube also partially equality the sound pressure
IEC 61094-4 Ed. 1.0 b:1995—Measurement Microphones – Part 4: Specifications For Working Standard Microphones is available on the ANSI Webstore.