You not only have to use headphones but you have to make sure that what comes thru on the left speaker doesn't also come thru on the right. You can tell in the beginning when he says "If you're listening to this in stereo, this voice should be in the right ear, and this voice should be in the left ear." I had a cheap set of headphones that played both sounds on both so I had to get different ones. "Non compliance will result in your head exploding." I think.
