Sound-Power Level. This is a measure of the noise energy emitted by the equipment. It is a basic characteristic of the equipment and therefore does not vary with distance or the reverberant nature of the surroundings. The actual radiated acoustic power is small, so it is international practice to use the ratio of this power to 10-12 watt. It is then expressed in decibels so that it can be related to sound-pressure level in appropriate equations. For the same equipment the sound-power level in decibels is usually numerically greater than the sound-pressure level and it is important not to confuse the two terms.