DVDdoug:
Anything that's home-built isn't acceptable for legal purposes. It gets rather complicated to make a calibrated A-weighed SPL meter, and of course it has to be professionally calibrated by a certified lab. Most labs won't calibrate homemade equipment.... You can only make something that's approximately accurate if you can calibrate it to a particular "kind" of noise.The kind of timed & logged measurements you want to do require some expensive equipment. You might be able to rent it... I don't know...
Typically there is a range control (sometimes auto-ranging) that adjusts the sensitivity or the gain of the amplifier. You also don't need 130dB of dynamic range to read up-to 130dB SPL because you're not reading down to zero dB SPL.
I understand what you're saying about the dynamic range. I think that's something I could process from the ADC output.
As far as legal purposes, I'm not looking for something I can use in a legal battle. I need a smoke detector, not a smoke analyzer. I want to get approximate dB levels while logging the times they occur at over 365/24/7. If I can show there's sufficient 'annoyance', I would have the regulatory agency place sophisticated equipment at the monitoring site to make the legal case. Right now they stand by their "noise contour" analysis which has very simplistic and best case assumptions.