Intensity and Loudness

Two sounds can carry exactly the same measurable physical energy and yet be judged very differently "loud" by two different listeners, or by the same listener in two different surroundings -- the sound of a balloon bursting in a silent, closed room seems far louder than the identical burst happening in a noisy, crowded market, even though the physical sound energy released is the same in both cases. This everyday observation is why two related but genuinely distinct quantities, intensity and loudness, are needed to describe how "strong" a sound actually is: intensity is a purely objective, physically measurable property of the sound wave itself, independent of any particular listener, while loudness is instead a subjective sensation that additionally depends on the listener's own individual ear and its sensitivity. This section defines each quantity precisely, in turn, and then introduces …