Acoustic Probe

a device for measuring the sound pressure at a given point in a sound field, it ensures minimum distortion of the field by the measurement process. An acoustic probe usually consists of a narrow wave guide connected to an acoustic receiver. The end of the wave guide is inserted into the area of the sound field being studied. Depending on the conditions of measurement, the wave guide may be a tube containing a column of gas or fluid or a solid rod that is insulated from the surrounding medium—for example, by a gas jacket. The acoustic insulation of the wave guide guarantees that only the energy from the test area of the field reaches the receiver. Special measures are taken to eliminate resonance phenomena and produce a traveling wave in acoustic probes. Thus, in probes designed for operation in air over the audible frequency range, the metal guide tube is connected to a rubber tube of the same diameter fIIIed with a sound-absorbing material to increase attenuation. The acoustic receiver, a microphone, is mounted on the side close to the tubing joint.

In acoustic probes for the ultrasonic range, the wave guides are solid metal coated on the outside with a sound-absorbing material; the acoustic receivers are plates or cylinders made from a piezoelectric ceramic.