According to research findings from Fletcher and Munson (1933) human hearing has a frequency range response which varies with the intensity of the sound. That means that bass frequencies are heard less prominently than higher frequencies, when music is played at a low level of volume. At a given intensity, it’s easier to hear high frequencies than low frequencies. This seems to have an evolutionary explanation. So, if you don’t play music at a high level (within the pain threshold) you don’t hear all the music. Music is more engaging when played at a higher magnitude (or is it volume?). This isn’t just because it better grabs attention, it’s because the music is fuller in tone. Listening at low volume is to distort (unnaturally bias) the music presentation! It’s an interesting effect: when the sound is “turned up” a lot with the “volume” control, the lower frequencies sound much louder, but the higher frequencies not so much. The sound is bigger (i.e. the volume of sound waves emanating in three dimensions from the speakers is expanded).
Why “volume” in audio? Do we mean the magnitude of a sound wave in three-dimensional space as it impinges on our ears? Thus, increasing the volume means increasing the sound pressure in a given space? I found a definition: “the volume is the perception of loudness from the intensity of a sound wave”. But, why is it almost universally referred to as “volume”? The term “volume” is easily understood as quantity, and this is applied to the volume of air moved by loudspeakers which determines the distance at which the propagated sound can be heard comfortably. So, volume refers to the amount of space filled with sound! Thus, the amplifier control is a gain control, and volume equates (through a linguistic slight of reasoning) to loudness.
Some amplifiers have a so-called “loudness” button that switches in and out a circuit that boosts the intensity of bass frequencies, intended for use at low volume. Some audiophiles baulk at this idea as a corruption of the recorded sound.
In addition, amplifiers, and presumably speakers, perform differently when driven at high or low levels, too. With amplifiers, it’s about current and electrical power applied to devices, whereas for loudspeakers it’s related to space volume and air movement (coupling).
More explanation at http://www.testing1212.co.uk