Abstract: In prior art acoustic test boxes, which can function as small anechoic chambers, it has been difficult to attain a frequency-independent pressure field at the test point without simultaneously increasing the frequency dependency of the velocity field, whereby tests of objects which are partly pressure sensitive and partly velocity sensitive are vitiated by errors. An elongated acoustic test box provided exclusively with curved surfaces and with space for an effective sound absorbent behind the test object overcomes this problem and at the same time provides improved acoustic insulation against low-frequency ambient noise. In a particularly appropriate embodiment the box (1) is shaped like an egg supported at its narrow end on a support (2) and divided about two-thirds of the way up into a bottom part (4) and a cover (5), the latter containing a sound source (10).

Abstract: A lightweight accelerometer in a casing or housing, having a very small base member to mechanically contact a surface, vibrations of which are to be determined; a piezoelectric element connected to the base, a seismic mass connected to the piezoelectric element, at least one thin circular diaphragm peripherically fixed to the housing, and with the base, the piezoelectric element, and the seismic mass fixed on, and axially symmetric to, the center of diaphragm and a soft pad member on the housing providing support on and dynamically isolating the housing from the vibrating surface. Several embodiments are disclosed and in each embodiment vibrations are directly transmitted from the vibrating body or surface to the piezoelectric element through the base, a very small half of a steel sphere.