There are other factors to consider when choosing headphones:
• Long-term wearing comfort — people might have to wear them for many hours in a row
• Spatially accurate sound field — that is, they accurately reproduce the stereo image you’ve created
• Extended, smooth frequency response — at least 20Hz to 20kHz
• Reliability and durability — people tend to toss around headphones like they’re indestructible
• The ability to produce high levels with very low distortion — some people like their headphones loud (see sidebar on noise levels)

Whatever headphones you buy, compare them to other products. Being aware of the characteristics of headphones will provide useful information during recording, critical listening, mixing, and mastering. (I’m not advocating using headphones to mix or master, however sometimes that might be the only option if your roommates, family, or neighbors are sleeping or otherwise sensitive to volume.)

For example, the headphones I use for recording sessions in my home studio are closed-ear, comfortable, loud, and bass-heavy. This information tells me that (a) I don’t need to worry about leakage into microphones, (b) I should be careful of the overall volume of the headphone mix, (c) I don’t need to pump the bass in the headphone mix, (d) I may need to bump up the mid and high frequencies in the headphones to compensate for the bass response, and (e) if I’m recording a bass part, I’ll know that what I record into Pro Tools isn’t as boomy as it sounds in the phones. I use a separate pair of headphones for critical listening that are closed-ear, extremely comfortable, and have a softer volume and flat frequency response.

[DON’T] STICK IT IN YOUR EAR
Listening to high levels of any type of sound (whether it’s music, jackhammers, or jet engines) can be dangerous if done even for short periods of time. OSHA (Occupational Safety and Health Act, 1970) has published the following data:

Permissable Exposure to Noise Levels
Decibels (dB) are the units used to measure the ratio of sound pressure level (SPL) of an audio source to the lower threshold of human hearing. An SPL of 130dB is the upper threshold of human tolerance; a noisy factory might have an SPL of 90dB and your house or apartment has an SPL of approximately 45dB. (Apparently some Who concerts reached a noise level of 120dB . . . it’s no wonder Pete Townsend is having difficulties hearing these days!)

Please be careful with listening levels and be sure to give your ears a break from time to time — allow them to recover from loud levels. If you must listen at loud levels try to protect your ears (using plugs, etc.), because permanent damage to your hearing could mean permanent damage not only to your career, but also to your basic enjoyment of music.