hammyman wrote:

It works in both ears!It's a doddle to convert to full headphones.You must use the existing speakers from the backphones though.The impedence is important!

The Impedance is in fact not that important at all (within reason) if it was then all XP headphones would be the same, but they aren't. Backphones for instance use 32 Ohm whereas the WS 3 use 16 OHM.
The important aspect is the tone of the speakers (and whether you have got used to the tone from the supplied backphones). When using the Backphones the speaker is directly connected to your ear without any reverb but when you allow a cone for reverb to build up then the sound will totally change. This can be seen in headphones such as those from the States ie; Nugget Busters, Pro Golds, Grey Ghosts etc. All of these models share identical speakers, switches and potentiometers but the sound is slightly different in each soley because the outer "shells" are of a different shape.
So if you are converting be prepared for a slightly bassier finished product
