The word decibel, abbreviated dB, seems to show up everywhere in acoustics: sound pressure levels, sound power levels, intensity levels, and even voltage levels. With so many usages, it is no surprise that a cloud of confusion lurks around the term. How could one unit describe so many different things? Shouldn’t different quantities have different units?

Well, the firstly it’s important to understand that the decibel is not an absolute unit like seconds or meters—it’s a relative unit. Absolute units can ...