Sound level is power level, and power is a function of
voltage squared, so if sound level goes up by 2X or 3dB, the
output voltage of the microphone goes up by the square root
of 2 = (1.414). So, if you have say 4 millivolts of mic output
from some sound level and then double the sound level (+3dB),
the output voltage will be 1.414 times 4 = 5.7 millivolts.
Low sound: Sound too weak for the microphone to detect and
respond. This would be a 'minimum' or 'threshold' sensitivity of
Normal sound range: From quiet to loud. There will be some
relationship, say logarithmic (decibels) between the sound input
and the electrical power output of the microphone. Affected by
many factors such as direction and closeness to the source of the
sound etc. etc.
The relationship between low and high sounds may be called the
'Dynamic Range' of the microphone. It may vary with frequency.
For example mics broadcasting an orchestral music concert may
have a wide dynamic and a broad frequency range. The microphone
in a telephone handset will probably be more limited.
Very Loud: Sound input so loud that it exceeds the maximum output
capability of the microphone; at that 'maximum' or 'saturation'
point it doesn't matter how much louder the sound gets. It just
isn't capable of turning any more sound power into electrical
energy. Distortion may occur before reaching maximum output. This
is sometimes evidenced when a performer or user "Swallows the
mike" or yells into it at close range or when sometimes a mild
'thump' is heard when a loud explosion has actually occurred.