What do people actually mean when they are seeking sound proof headphones, they are probably looking for a set of headphones that block out ambient noise. Ambient noise is just a term for the normal noise in your environment.

This noise can include computer fans, noise from your air filter and/or heating and cooling equipment. It can also include noise from your landscapers, kids, etc. Whatever the source of noise, you want it eliminated so that you can enjoy the sound coming from the headphones without anything added to it.

There are two major types of sound proof headphones. There are active noise cancellation units and passive units. The active noise cancellation headphones use noise canceling technology which requires its own power supply, usually one or two AA batteries. They have a microphone on the outside of the headphones which monitors the noise. This noise is fed to a small amplifier and it creates the exact opposite noise to what is going on outside.

This “opposite” noise is fed into the headphones and the net effect is silence. The silence comes because the two sources of noise cancel each other out when they reach your ears. These type of headphones have two major disadvantages, the first being price and the second is the requirement for batteries to power the noise canceling circuitry. Some of them also don't work all that well. You should try the headphones at the store before buying.

 The passive type of sound proof headphones uses sound absorbing technology. This comes in the form of various sound dampening materials to isolate your ears from the outside. The ear cups typically fit all around the ear, surrounding it completely. This method can be very effective.

The disadvantages of this approach vary. First, the headphones tend to be heavy. Second, the rubber surround on the ear cups has to fit well, so pressure needs to be applied. This can cause ear fatigue. Another potential problem is that you tend to sweat on the rubber surround. Last, but not least, these headphones are anything but inconspicuous, so if you are a commuter, prepare for some odd looks here and there.