I found this article on how to build an acoustic radar using a computer speaker and a microphone. It uses a sound card for data acquisition and Labview for the real time display. They talk about the possibility of using Matlab or Octave though.
http://ajp.aapt.org/resource/1/ajpias/v79/i12/p1240_s1
http://ajp.aapt.org/resource/1/ajpias/v79/i12/p1240_s1