Acoustics is the science of sound, dealing with its production, transmission, and effects. Engineering acoustics deals with the design of sound-systems and their components, such as microphones, headphones, and loudspeakers; musical acoustics is concerned with the construction of musical instruments, and ultrasonics studies sounds having frequencies too high for the human ear to detect.
Architectural acoustics gives design principles of rooms and buildings having optimum acoustic properties. This is particularly important for auditoriums, where the whole audience must be able to hear the speaker or performers clearly and without echoes. Also, the reverberation time (the time taken for the sound to decay to one millionth of its original intensity) must be matched to the intended uses of the hall; for speech it should be less than 1 second; for chamber music between 1s and 2s; for larger scale works, from 2s to 3.5s. All this is achieved by paying careful attention to the geometry and furnishings of the hall and incorporating the appropriate sound absorbing, diffusing, and reflecting surfaces.
Anechoic chambers, using for testing acoustic equipment, are completely surfaced with diffusing and absorbing materials so that reverberation is eliminated. Noise insulation engineering is a further increasingly important branch of acoustics.