The science of sounds, teaching their nature, phenomena, and laws.
The effect of the environment on sounds. Indoors, the effect is caused by the materials used in construction and can range from 'acoustically dead' (no reverberation or echo) to 'acoustically live' (with a long reverberation time or many echoes). In churches, 'good' acoustics means at least one second of reverberation time and no echo. This causes musical sounds to blend together and permits good intelligibility for speaking with a minimum of amplification.
The science of sound and its perception, involving physics (oscillations, wave lengths, etc.), anatomy of the ear and brain, and psychology.