Question aboutt speaker's efficiency

[markw]

Impedance refers to how "easy" a load a speaker represents to an amp. Amps generally "like" a higher impedance and respond by producing less distortion, less heat and living a long, happy life.

A low impedance speaker puts more strain on an amp. The amp works harder, produces more distortion and, in the long run, may not last as long. Some amps simply aren't designed for low (4 ohm) impedance speakers. It takes a very well designed amp to handle very low (< 4 ohms) impedance anyway.

Sensitivity is merely a rough guideline as to how "loud" a speaker will play in relation to other speakers at the same "power" level. Sensitivity ratings are done by feeding the speaker the same voltage (2.83?) and a decible reading is taken at 1 meter from the speaker. That reading is the sensitivity spec you see touted.