Noise level reference for the masses.

[tragus]

MikeC, I'll put my hand up as one who understands and thinks your project has a great deal of merit, in principle. The devil, of course, lives in the details of implementation. I think the goal of obtaining and delivering accurately reproducible recordings of *very* quiet fans (e.g., Panaflo at 5.75V) poses an exceptional challenge, as you've pointed out. There are other challenges, like the frequency response of the microphone and any non-linearities or noise introduced by the electronics. Alas, there is no control over the speakers/headphones used by the end-user--both of which can be notoriously inaccurate even if "calibrated" to the same loudness/level.

Nonetheless, I support this heroic effort. I think the advantages far outweigh the pitfalls. The basic concept seems quite simple. As Putz mentioned, a side-by-side comparison[\i] of sounds allows for judging both quality and relative perceived loudness--even if "absolute loudness" may not be accurately reproduced.

For the record, on my lab's system, I calibrate a full frequency spectrum in a sound-attenuated booth (not quite an anechoic) to a pre-defined microphone voltage, taking into account the electronic noise floor. It's quite a finicky undertaking with, as MikeC points out, rather expensive gear.