Clinical and other applications of ultrasound Ultrasonic waves are being increasingly used in medical and surgical diagnosis by a technique based on the fact that different types of tissue, e.g., bone, fat, and muscle have different reflective properties for very high-frequency waves. When a portion of the body is scanned by an ultrasonic beam, the varying echoes are […]
Echo sounding An echo sounder or fathometer is a device used on a ship for the purpose of measuring the depth of the sea. A detailed explanation of the apparatus is beyond the scope of this book, but the basic principle involved is comparatively simple. An electrical device fitted to the bottom of the ship sends out regular […]
To measure the velocity of sound by an echo method In places where a clear space extends for about 100 m from a high wall the velocity of sound may be found by measuring the time taken for a sound to travel to the wall and back again. The experiment is best carried out by two persons […]
Anechoic and soundproof rooms For certain special purposes, e.g., investigation of the properties of loud-speakers and other sound equipment, it is necessary to have rooms whose walls absorb completely all sound energy falling upon them. This is achieved by lining the walls, ceiling, and’ floor with anechoic (= without echo) wedges composed of glass fibre, or plastic foam, encased […]
The acoustics of buildings Reverberation is particularly noticeable in cathedrals and other large buildings where multiple sound reflections can occur from walls, roof and floor. For example, in St. Paul’s Cathedral, London, it takes about 6 seconds for the notes of the organ to die away after the organist has stopped playing. Excessive reverberation in a concert hall […]
The echelon echo Another effect explained by the reflection of sound is the high-pitched ring of short duration heard when one stamps on the pavement near to a fence made of equally spaced iron bars or wooden palings, or indeed, near any series of regularly spaced reflecting surfaces such as a flight of steps. Thus, in the case of […]
Echoes Echoes are produced by the reflection of sound from a hard surface such as a wall or cliff. Let us suppose that a person claps his hands when standing some distance from a high wall and listens for the echo. The time which elapses before the echo arrives will depend on the distance away of the wall. […]
An experiment on the reflection of sound Two metal or cardboard tubes are set up, inclined to one another in a horizontal plane, and pointing towards a vertical flat surface of any hard material, e.g., a drawing-board (Fig. 27.5). A ticking watch is placed near the end of one tube and the ear is placed at the […]
To construct a longitudinal wave model [Crova’s disc) The manner in which oscillatory motion of the air layers gives rise to the compressions and rarefactions of a sound wave may be illustrated by a simple device known as Crova’s disc. A circle of radius about 7.5 mm is drawn on a piece of stout paper or thin […]
Sound waves Sound waves in air differ from the transverse waves described in the previous chapter in that the wave particles oscillate in the same direction as the wave instead of at right angles to it. Waves of this type are called longitudinal waves. Owing to the longitudinal motion of the wave particles, sound waves consist of a […]