Sound Power Level (SWL)

Sound Power Level (SWL or Lw) is the total acoustic energy radiated by a source per unit time, expressed in decibels relative to a reference power of 1 picowatt. Unlike Sound Pressure Level, SWL is an intrinsic property of the source and does not depend on distance, room size, or acoustic environment. It is defined in ISO 3741 and measured in anechoic or reverberant chambers. SWL is essential for acoustic modelling because it allows prediction of sound levels at any point in a room using propagation equations. Manufacturers of HVAC equipment, machinery, and building services typically publish SWL data in octave bands. Converting SWL to SPL at a given distance requires knowledge of room acoustics or outdoor propagation conditions.