Speakers and mics

Reader David Blank pointed out something interesting to me in yesterday's post. There are, in fact, two nearly perfect speakers that are full range: a headphone and a microphone. A headphone, like the excellent sound Audeze LCD2X that I am going to purchase, has a single planar driver that covers the entire range of frequencies we need to reproduce sound. So why does this work when a loudspeaker driver trying to do the same thing struggles? The simple answer is the amount of movement. The headphone diaphragm moves very little as a piston and has a very small overall area of movement. This works in a headphone because your ear is only a couple of inches away from the diaphragm and it sounds quite loud. Try moving an entire room full of air and you have a very different set of requirements. I mentioned also microphones. A microphone is actually the same as a loudspeaker diaphragm, only it is being used in the opposite manner. I remember the first time I understood this was when my father was working on a design of a hands free intercom system. His design had a single 3 inch speaker driver that doubled as a microphone. Tomorrow the 2-way as promised.