The following video is a brainwave entrainment for theta meditation using isochronic tones. It is a low theta wave frequency using two solfeggio tones carrier frequency. The first tone which is 639 hz is for breathing in which is approximately 4 seconds and the second tone which is 528 hz is for breathing out which is 10 seconds in length. You'll experience a better brainwave entrainment if you keep your breathing in step with the tones.
You can download a 'wav' version of this isochronic tones theta meditation at the brainwave entrainment blog.