I thought I'd look at the Electrovoice RE20 and the SM7B, both coming from the broadcast industry where radio in particular needed mics where the talent could move around a fair bit without the tone of the mics changing very much.

Refers to the effect caused by a sound source being very close to a directional microphone. The net result is that low frequencies become boosted as the source comes closer. For vocalists, the effect can be used creatively, while for others the effect can cause problems, where distortion can occur from the diaphragm being stressed from the signal boost.

I know what proximity effect is, what I am wondering is what, from a physics standpoint, causes it.

Also perhaps why some similar mics seem to have more proximity effect than others.

I am having a little trouble understanding the cancelling of high frequencies due to closeness of directional mics to the sound source. what's the relation between high freq and it's wavelenghts coming from 0 degrees cancelling at the mic diaphragm? and why does the dual capsule omni mode exhibit so little effect?