Acoustics is the experimental and theoretical science of sound and hearing, and especially the phenomena of sound in space, such as buildings.
Acoustics teaches the cause, nature, and phenomena of such vibrations of elastic
bodies as affect the organ of hearing; the manner in which sound is produced, its transmission through air and other media, the doctrine of reflected sound or echoes, the properties and effects of different sounds, including musical sounds or notes, and the structure and action of the organ of hearing, etc. The propagation of sound is analogous to that of light, both being due to vibrations which produce successive waves, and Isaac Newton was the first to show that its propagation through any medium depended upon the elasticity of that medium. Regarding the intensity, reflection, and refraction of sound, much the same rules apply as in light. In ordinary cases of hearing the vibrating medium is air, but all substances capable of vibrating may be employed to propagate and convey sound. When a bell is struck its vibrations are communicated to the particles of air surrounding it, and from these to particles outside them, until they reach the ear of the listener. The intensity of sound varies inversely as the square of the distance of the body sounding from the ear. Sound travels through the air at the rate of about 332 metres per second; through water at the rate of about 1433 metres.
Sounds may be musical or non-musical. A musical sound is caused by a regular series of exactly similar pulses succeeding each other at precisely equal intervals of time. If these conditions are not fulfilled the sound is a noise. Musical sounds are comparatively simple, and are combined to give pleasing sensations according to easy numerical relations. The loudness of a note depends on the degree to which it affects the ear; the pitch of a note depends on the number of vibrations to the second which produce the note; the timbre, quality, or character of a note depends on the body or bodies whose vibrations produce the sound, and is due to the form of the paths of vibrating particles. The gamut is a series of eight notes, which are called by the names Do, Re, Mi, Fa, Sol, La, Si, Do, and the numbers of vibrations which produce these notes are respectively proportional to 24, 27, 30, 32, 36, 40, 45, 48. The numerical value of the interval between any two notes is given by dividing one of the above numbers corresponding to the higher note by the number corresponding to the lower note. The intervals from Do to each of the others are called a second, a major third, a fourth, a, fifth, a sixth, a seventh, and an octave respectively. The interval from La to Do is a minor third. An interval of nine eights is a major tone; ten ninths is a minor tone; sixteen fifteenths is called a limma.
In music, a Neapolitan sixth is a chord composed of the subdominant of the key, plus a minor third and a minor sixth. Harmonically it is equivalent to the first inversion of a major chord built upon the flattened supertonic. Research Neapolitan Sixth
An oboe d'amore is a type of oboe pitched a minor third lower than the oboe itself. It is used chiefly in the performance of baroque music. Research Oboe d'amore
Abbreviations
Research Acoustics
