Under controlled listening tests, humans judge that a 10-dB change in sound pressure levels in the mid- and high-frequency ranges represents approximately a halving or a doubling of the loudness of a sound. Yet a 10-dB reduction in a sound source means that 90 percent of the radiated sound energy has been eliminated. Table 1-2 shows the approximate relationship between sound level changes, the resulting loss in acoustic power, and the judgement of relative loudness of the changes. Toward the bottom of the table, it becomes clear that tremendous portions of the sound power must be eliminated to achieve impressive amounts of noise reduction in terms of perceived loudness.

Loudness Comparisions