I have been tasked with designing a sound level meter (I am an electrical engineer) that can measure accurate sound levels down to ~18 dB SPL. However, part of the task is that my microphone should be relatively inexpensive (perhaps <= $150).
There are a number of other specifications I need to consider when looking at mics, but as a high-level opinion, is this possible or is my boss crazy?
Everything about the electronics/amplifier design, etc, I am fine with, but I've never done much high-performance stuff with microphones before. From the myriad of specs I've seen, hardly any mic in my price range will be useful for signals below ~25-26 dB SPL.
[Edit: Each octave band from 125 Hz - 8 kHz (my freq range) can be band-limited and measured separately, which should offer some small noise improvement from the 20 kHz BW in most microphone specs.]