It would very easy to setup. You would need an RTA (real time analyzer.) Computers can do it really easy with software such as TrueRTA (
http://www.trueaudio.com/rta_abt1.htm )
To get a decent idea all you need is the free version and any mic. Of course for more detailed results you would need at least te 1/3 octave program and a nice mic.
I migt mess around with this in a few days since i have the software on my laptop. If I do i will report back what i find when changing volume and tone.