Last month we looked at microphone polar patterns. However, that is just one characteristic of a microphone. So this month we will look at several other measuerments that define a microphone's character.
The frequency response is the range of frequencies of which a microphone is capable of capturing, within a given tolerance in decibels (db). It is often used interchangeably with frequency range, but frequency range does not specify the tolerance. For example, a microphone might have a frequency range of 20 to 20,000 Hz. However, if the response drops off rapidly by 20 dB above 15,000 Hz, its response should be specified something like 20 to 15,000 Hz ± 2 dB. The frequency response indicates how accurately the microphone will represent the sound it captures. The frequency response is often accompanied by a frequency response curve (a plot of amplitude vs frequency), which will indicate how and where the captured signal deviates from the true sound.
Sensitivity is a measure of how much voltage a microphone will generate for a given sound pressure level. IEC standard 268-4 specifies sensitivity to be measured in millivolts/pascal (mV/Pa) with a 1-kHz sine wave at 94 dB-SPL (the SPL equivalent of 1 pascal). A pascal is a unit of pressure equal to about 0.000145 pounds per square inch. However, in the US, sensitivity is often expressed in in dBV, relatively to 1 V/Pa.
Maximum SPL indicates the highest sound pressure level that a microphone can handle without distortion. It is typically specified with a maximum total harmonic distortion (THD) of 0.5% (sometimes 1%) at 1000 Hz. A THD of 0.5% is the point where the distortion can be measured, but cannot be heard. Frequently referred to as max SPL, it is an important spec to be aware of before placing a microphone in front of a loud source such as a kick drum or guitar amp.
Another specification is equivalent noise level. It is an indication of the self noise of a microphone. Self noise (sometimes called internal noise) is the intrinsic noise that occurs in all electronic devices when no signal is present. Equivalent noise level is the sound pressure level that creates the same voltage as the self noise produced by the microphone. A low noise level is desirable when working with low level sounds, so the sound will not be covered up by the microphone noise. Equivalent noise levels are typically measured using the dB(A) scale, which weights the sound level according to the ear's sensitivity. Good levels with this scale are considered to be below 15 dB(A).
Although there are a few other specification for microphones, these are the most important ones you are likely to encounter.
• When the Beatles first released the single “Ticket To Ride” in April 1965, the fine print under the title said “From the United Artists Release 'Eight Arms To Hold You.'” That was the original name for the movie “Help!”
• “Sugar, Sugar” by the Archies was recorded by a group of studio musicians playing the parts of fictional cartoon characters for the television series The Archie Show. Ron Dante sang lead vocals backed by Toni Wine. Although it sold over 13 million copies and was named Billboard magazine's Record of the Year for 1969, none of the musicians received any royalties, only musicians union scale wages.
• The 1958 hit song “Claudette” by the Everly Brothers was written by then unknown Roy Orbision, a tribute to his wife Claudette. It was his first major songwriting success.