Mono headphones?

I just got a Moog Etherwave last week and am excited to learn to make music with it! In order to spare my neighbors some of the pain of the learning process, I would like to do much of my practicing with headphones instead of an amp. Just hearing the sound in one ear is proving to be insufficient. Do I need mono headhphones and, if so, can anyone recommend a source/ type?

Actually, you might be able to find a mono-to-stereo adapter for your stereo headphones. Then you'll be able to hear the same signal in both ears. Check your local Radio Shack or similar store.

If you aren't afraid to do a little soldering, or know someone who can do it, you might replace the mono headphone 2 conductor jack with a stereo 3 conductor jack. Take the wire that connected to the "tip" of the mono jack, and connect it to both the "tip" and "ring" (left and right) contacts on the stereo jack. The other wire goes to the "sleeve". Thus the signal will be fed into both sides of your stereo phones.
Tip, Ring, and Sleeve are phone company terms which relate to the parts of the male plug. The "tip" is the pointy end of the plug, then there's a band of plastic that insulates from a "ring" of metal, then another band of insulation, then "sleeve", the base of the plug's shaft.
If you get a replacement stereo jack and plug your phones into it before you install it, you will see which contacts on the jack correspond to tip, ring, and sleeve on the jack