To make your very own parabolic microphone you will need a tape recorder, a microphone and a large bowl.
// Plug the microphone into the tape recorder
Hold the bowl on its side, with the bottom facing you. Hold the microphone towards the inside of the bowl at the center.
// Aim the microphone and the bowl towards the subject you wish to record.
// The bowl will magnify the sounds of whatever is directly in front of it so make sure you have a clear view of your sound source.
Yep...the theory works. Back in my experimenting days, I made a parabolic dish..about the size of a garbage can lid with a focal point of about 100 yards..stuck a mic in the center and pointed the thing at a corner near by where kids gathered after school. I got some fairly decent recordings..but not the best..some was understandable and some not..but, this was in the early days of such technology and my 'equipment' was elcheapo and homemade..but..hey, it worked and proved (to me) that it would work.
Ever hear of a device called "Whisper 2000"? A friend of mine had one of those when we were young lads. He cut the outer rim of a funnel and attached it to the front of the mic and it helped boost reception. Didn't have a recording feature though, too bad.
I saw some X-Ray specs once, they didn't work.
You could always put a glass up to the wall and listen through that as well!