Speaker sensitivity measures how efficiently a speaker converts electrical power into sound, typically represented in decibels (dB) at a specified distance with a given input power. Higher sensitivity speakers require less power to produce the same volume level as lower sensitivity speakers, making them more suitable for use with low-powered amplifiers or in larger rooms. Impedance, on the other hand, affects the interaction between the speaker and amplifier, influencing power transfer and system compatibility. Matching sensitivity and impedance ratings ensures optimal performance and compatibility within a Hi-Fi system.