(DI) The directivity index is the value in dB of ten times the common logarithm of the directivity factor. The directivity factor is the ratio of the sound intensity produced by a test transducer on a specific axis to that of a point source that is emitting the same acoustic power. Since the specific axis is usually one of maximum radiation, the directivity index is usually greater than zero.

See also dB/dt.

The acoustic power of sound and ultrasound is the energy delivered per unit of time. The power is measured in Watt (W) and is proportional to the square of the amplitude.
1 W = 1 joule/second.

See also Directivity Index, Spatial Average Intensity, and Source Level.

(d B/d t) Definition: The ratio between the amount of change in amplitude of the magnetic field (dB) and the time it takes to make that change (dt). Because changing magnetic fields can induce electrical fields, this is one area of potential concern for safety limits.
The value of dB/dt is measured in Tesla per second (T/s).

See also Directivity Index, Phon, and Decibel.