What is the Sensitivity Reduction Specification of a Microphone?

Sensitivity Reduction of a Microphone

The Sensitivity Reduction Specification of a microphone is the amount of gain that a microphone would lose if the voltage powering the microphone were decreased to a certain level. Normally on datasheets, it is standard to specify the voltage level that a microphone would be for its gain to fall by 3dB. Thus, the sensitivity reduction voltage is the voltage level for the gain of the microphone to fall by or be within -3dB of its sensitivity rating.

Let's go over a practical example of this specification so you can understand better using the data from the chart above which is the data for an omnidirectional electret microphone:

Normally a microphone records a certain gain (its sensitivity rating) at a certain voltage (its standard operation voltage). Looking at the example of the specifications of the microphone on the chart above, it has a sensitivity rating, or gain, of -45dB ±4dB at a standard operation voltage of 2V. This means that with 2V powering the microphone, the microphone will have a gain of -45dB ±4dB; thus, the gain can vary from as high as -42dB to as low as -49dB with a voltage of 2V. Now, let's lower the voltage powering the microphone to the voltage specified in the sensitivity reduction specification. In this case, the gain of the microphone will drop by 3dB if lowered to 1.5V. Thus, with 1.5V powering the microphone, the microphone's sensitivity would now be -45dB +1/-7dB; so the gain of the microphone can vary from as high as -38dB to as low as -46dB. If the gain of the microphone is exactly -45dB with 2V powering it, it will drop to about -48dB with 1.5V powering it.

Why is this specification included in a datasheet? To many, it may seem useless but it isn't. Why would one want to drop the gain of a microphone by 3dB? When the gain of the microphone is dropped by 3dB, the level of the gain is dropped still to an acceptable amount of gain while at the same time power is saved, since less voltage is used. In a scenario with the microphone above, a half a volt of power is saved. If other microphones are used, as such with a standard voltage of 4.5V and a sensitivity reduction voltage of 1.5V, the microphone uses a third of the power with only a 3dB gain loss. Thus, in an application in which an engineer is creating a low-power device, saving voltage is critical, even if some gain must be sacrificed, which an engineer may or may not consider vital. Why would an engineer want to create a low-power device? Because the lower the power that the device runs on, the longer it can last without having to be recharged. The less quickly, it drains batteries. Thus, the sensitivity reduction specification has tremendous application to engineers trying to save power on their devices.

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