Acoustics (Gr. akouo, 'I hear') is sometimes used for the science of sound in general, which in this work is treated at SOUND, but more commonly for the special practical branch of that science which deals with the construction of public halls, churches, &c. so as to secure the accurate hearing of speech or music. It must be confessed that, in this practical sense, the science is still in its infancy. It is very easy, in general, to point out the causes of acoustic defects in a building once it has been erected and tried; it is quite another matter to predict from the plans what are likely to be its defects; except, of course, when some flagrant violation of simple principles has been perpetrated. One reason for this is obviously the want of data on which to reason, due to the enormous cost which would be involved in a thorough experimental treatment of the subject. The consequence is that when by chance one successful attempt has been made, architects prefer to copy it rather than to attempt some new form, which might probably entail complete failure.
The improvement of the acoustic properties of a building must be determined by the ascertained defects, so that no general rules can be laid down. One great point is the prevention of echoes, unless these reach the ear almost at the same moment with the original sound. This can be effected in many cases by lowering the ceiling so as to expedite the echo; also by hanging carpets or heavy tapestry on the walls, and especially in the corners of the building. These have the effect of abolishing it. Idiomatic attempts are constantly being made nowadays to secure the same results by stretching wires about in various directions. Such devices betray absolute ignorance of the mode of propagation of sound.