Kerry Wong writes:
You can generate some pretty amazing patterns by shining a laser onto a mirror mounted on a vibrating speaker cone, a lot of people have experimented with this kind of laser show. But how about building a true laser oscilloscope that is capable of displaying signals? In this post, I will show you just that. For those who are impatient, I included a video towards the end.
Project info at Kerry Wong’s site.
Check out the video after the break.
Kind of like this – from 1936;
http://blog.modernmechanix.com/seeing-sound-with-a-home-made-oscillograph/
Could always use an old fax rotating mirror & laser for the same thing