Five is the right number for me:
2 IEMs: 1 hi-fi and 1 beater
3 Cans: 1 closed, 1 open, and 1 beater
a couple too many for me, but totally makes sense.
I ride a bike, and hate carrying crap to work and back, so that explains two of my three pairs. I have two over-ear, closed-back sets at home, one for my main rig and another pair works better on my laptop do to impedance. That doesn't mean I want more -- mostly different kinds, like open-back to try them out, a low-impedance travel pair and maybe electrostatic some day.
Besides, they're smaller than speakers and less scary to collect than other things people in my area collect
1. Buy new headphone
3. Rediscover whole library
4. Get bored of it
4. Go on Head-fi.org
5. Sell, and read reviews
Slowly killing my wallet profiting; one can at a time.
Currently I have 4 headphones.
1. Open Full Size for home listening
2. Closed Full Size at my workplace
3. two IEMs for mobile use. (One of them gets hardly used. Could do without it)
Though I'm always lusting for more.
It just happened one day. One minute its a life of floor standing speakers then next its mainly computer speakers. Suddenly its 2014 and my brother inlaw is telling me how he sees at least fourteen headphones in his view in my living room. That's when I realized I had at least five more stored away in the closet. Thank goodness he didn't see my collection of bookshelf speakers.
As for using all of them its mainly the HiFiMan HE-400 followed by the Sennheiser HD 280 Pro and the Audio Technica Ath AD 700 all for gaming, music and movies. A lot of my headphones are open which leads me to use my bookshelf speakers frequently due to a noisy environment. I use some Shure IEM's for when am outside or when I want extreme isolation even the Sennheiser HD 280 Pro cant give me.
My collection is growing lol i like my gadgets so i get tempted by new headphones also. While I've got 2 pairs of in-ears i find these are used for specific uses, Bose IE2 for early morning podcast listening on the train and my MF EB50's used for music use when i don't have my on-ears with me lol.
Ive got a pair of Marshall Majors (i liked the look) and these are my just chuck in my bag pair. My good listen are my Yamaha Pro500 but the are uncomfy so on my upgrade list.
My Mrs does think i have issues though lol
The most headphones I've had at once is probably about 4 or 5. I've sold several of my headphones over the past year mainly because I just wasn't listening to them that much. I think I've really found my "desert island" headphone in the SR-009. Chances are though after I while I'll get the bug again to buy new cans, especially with new and better ones coming out all the time.