I just peeked at the data sheet. Yes, it's spec'd down to 20 Hz.
That's a real honey of a part, Andrew. 90 dB of dynamic range from audio to 500 MHz is nothing to sneeze at. $10.18 (in PDIP) or $7.42 (in SOIC) from DigiKey, qty 1, in stock.
Many thanks for the tip!
Tom
It depends how it's coupled. You can actually use it at DC, but you have to be VERY careful about your input matching and filtering, otherwise it gets wonky (experience here). Also, I've used it even past the 900mhz "top end" so to speak with careful matching. The response drops off like a rock off a blimp above, say, 6 or 7 hundred mhz, but if you're not looking for anyhitng super accurate, and just want to see some relativity, it'll work. The whole lineup is fantastic.
Go the OP (craig your name is I think?)- Instead of saying to yourself "I'm going to build a DB meter"...say to yourself soemthing like "I'm going ot build a relative SPL meter to see if the driver is in danger" sort of thing. That right there cuts your workload in half (if you can do this, of course). 3-5 DB is quite a large difference, and if that's your accuracy, I say scrap the DB idea.
Second: Dont think of this entire project as a single entity. A professional designer wouldn't sit down and design an spl. They would design a microphone pre-amp, a level detection circuit, and a display driver. oh..and a display. You could evenn break that down further...
1) mic. power supply (if it's an electret mic)
2) filter (couple resistors and caps)
3) amp (op amp to bring mic level up)
4) filter (output filter for preamp..again, couple resistors and caps)
5) amplifier (for filtering, level setting, detector impedance matching, etc)
6) detector (a full wave rectifier if you've brought the level up high enough)
7) post detection filter (again, res and caps)
8) display driver (something like the above mentioned bargraph chip)
9) extra circuits needed to make blinkies blink and lighties light
10) the blinkies and lighties.
Every single one of these steps really shouldn't take more than 5 or 6 parts a piece for the most complex, and being in very small stages, you wont get overwhelmed with "oh my god I have to build an entire meter", but instead "oh this will be easy, I jut have to make a filter, or an amp" and just string them all together.
Then, down the line, when you need a particular section for a different project, you dont have to say "how did it work in the sound meter" you can say "oh..I can just use this amplifier, or this filter". It will expand your repetoire of basic circuits, and be a smaller headache int he long run as well.
--Andy P