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1 − Sensitivity (new): dB re 1 V/Pa ← → Transfer factor: mV/Pa
| International standards have established 1 pascal (Pa) as 94 dBSPL. This reference point is now accepted for specifying the sensitivity of microphones. The μbar found in some non-European specifications refers to 74 dBSPL (20 dB less than 1 Pa) and the sensitivity or the transfer factor is not expressed in the usual form of "mV/Pa" as open circuit voltage rating. In the data sheets the sensitivity always applies to the frequency 1 kHz, unless otherwise noted. Microphones simply convert the sound pressure in audio voltage. Forget to mention the energy. |
2 − Sensitivity (old): dB re 1 V/dyne/cm2 ← → Transfer factor: mV/Pa
| Microphone firms in the USA are partly still using the old sensitivity of "dB re 1 V/dyne/cm2" or "dB re 1 V/µbar" (74 dBSPL) and do not show the usual form "mV/Pa". In the data sheets the sensitivity always applies to the frequency 1 kHz, unless otherwise noted. |
| 1 µbar = 1 dyne/cm2 = 0.1 Pascal and 1 pascal = 10 µbars = 10 dynes/cm2 1 mV/µbar or 1 mV/Pa = 0.1 mV/µbar = 10 mV/Pa and pascal = newton/m2 |
| Pascal is written in English with lower-case letter beginning: We have the pascal and we have the dyne, and the plural dynes which are microbars. A typical condenser microphone, having 10 mV/Pa is the same as 1.0 mV/µbar; but 10 Pa are 100 µbar. −40 dB "re 1V/Pa" equals to −60 dB "re 1V/microbar". There is a difference of 20 dB. |
| All field quantities, like voltage, or sound pressure are always RMS values in audio engineering, unless otherwise stated. |
| An often heard question: Why are microphone output levels expressed in negative decibels (dB)? Answer: Because all microphone produce a voltage which is less than 1 volt for the reference sound pressure of 94 dB or 74 dB. |
Note about power ratings
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Forget the power ratings. They have no relevance to microphones. The term "dB SPL" is a measurement of Sound "Pressure" Level (SPL) which is the force per area that acoustical sound waves apply to air particles. Microphones are sensors in the sound field which deliver an analogous voltage. Microphones measure sound pressure, or sometimes they may measure the particle velocity, but they never measure sound intensity directly. Intensity stereo is an unfortunate linguistic misnomer which has come to mean the recording of stereophonic signals that are distinguished only by level differences. In stereo the level differences have been called "intensity" differences, but sound intensity is a specifically defined quantity and cannot be sensed by a simple microphone, nor would it be valuable in music recording if it could "Intensity" stereophony is a misnomer and is better called level difference stereophony. Ears are directly only sensitive to sound pressure, like microphones. Forget both intensity and the power. A studio microphone is never attached to a load equal to its own internal resistance. The load resistor (impedance) should always to be at least ten times greater than the internal source resistor of the microphone (open circuit). Here only voltage is important and not the power. Sound intensity and energy are energy and power quantities and computational tools for acousticians and sound protectors (noise fighters), and not so important for sound engineers. Note: The output voltage of a microphone is proportional to the incident sound pressure. To obtain the microphone maximum output level in dBu, find your microphone's sensitivity rating on the left side and then move right until you are directly below your microphone's maximum SPL rating. As an example, for a microphone with a sensitivity rating of 20 mV/Pa and a max SPL equal to 130 dB. Table 1 tells us that the maximum output voltage is +4 dBu. You now have what you need to compare preamps regarding maximum input level. |
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Microphone Dynamic Range Calculation
| Enter any TWO of the following values, then press the calculate button. The missing value will be calculated. 10 μbar = 1 pascal ≡ 94 dBSPL rating is used here. |
| Self-noise may be entered using any weighting factor (A, CCIR 468 etc) but the dynamic range will be predicated by that weighting. "S/N re 94 dB SPL" is 94 dB minus self noise. The max. SPL for less than 0.5 % THD should be used. If you find there values for 1 % THD, then do a 6 dB subtraction, for a more correct comparison. |
| Note: There is no conversion formula for weighted dBA values to sound pressure level dBSPL or vice versa. |
| Words to the wise: Always wonder what a manufacturer is hiding when they use A-weighting. *) |
*) http://www.google.com/search?q=Always+wonder+what+a+manufacturer+Rane&filter=0
Readings of a pure 1 kHz tone should be identical, whether weighted or not.
Transfer factor in mV/Pa and sensitivity
| Enter a value in the left or right box, then press the TAB bar or make a mouse click at an empty space at the side, to get the solution. The calculator works in both directions of the ↔ sign. |
The sensitivity must be a negative dB value.
The sometimes found microphone "power level" in dB is wrong. It really means "sensitivity in dB re 1 V/Pa".
Interconnection of microphone and preamplifier Zout < Zin
| "Input sensitivity" is basically the same thing as sensitivity - putting the word "input" in front of it is somewhat redundant. Input sensitivity controls are commonly found on amplifiers and other audio equipment, but not on microphones. |
Conversion of sound units (levels)
Acoustic equivalent for Ohm's law
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