PC Spectrum Analyser?

Great question. I asked this some time ago and was refered to the "audio toolbox", which was about $1000. More than I wanted to spend. But to answer your question there are inexpensive spectrum analyzers. HP works FFT spectrum analyzer at: http://www.hpw-works.com/ it's between $69 and $300 depending on options. Audua Speaker Workshop: www.audua.com. You can download an alpha product for free. Sample Champion is another that you can download a trial version for free at www.purebits.com. I wanted to do the same thing you are trying to do, but I can't find a linear microphone. Some of these programs have methods to calibrate the microphone for non-linearity, but if you don't have a flat source to do the calibration it's basically impossible. Hopefully, someone else will post some ideas on microphones or methods to calibrate them. If you get a set-up like this working, please post it--I'm sure many audiogoners would be interested.

Being unsure of the exact use you intend...you might want to check out the ETF 5 software package, which alows you to do MLS measurements on speakers, and on listening room acoustics, etc. You can find more info at their web-site http://www.etfacoustic.com/. It may do some of things you're hoping to accomplish. Good luck!

There is a program called "Spectra-Lab" or something of that sorts. I have used it briefly and it is quite versatile. Can't speak for how much it costs though as it was someone else's computer. As to finding a microphone that is quite excellent for the money, try contacting Old Colony Sound Labs. They have what is called "Mitey Mic" and they are on the second version of this. It is very linear and was designed by Joe D'Appolito if memory serves me right. Once you've gotten a good mic, you'll have to invest in a good sound card. If you've ever looked at the frequency response chart or specs for a typical "sound blaster" type of card, you'll realize that it is FAR, FAR below what you would want to do the job. Sean
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The street price for the Terrasonde Audio Toolbox is $750; it's not cheap, but still a very good value. It has a high quality built in microphone, test signal generator, and the RTA is selectable for 1, 1/3, 1/6 and 1/12 octave accuracy. Plus the Toolbox performs a number of other functions. Visit their website and see if it makes sense for you.