Loudspeaker sensitivity (dB SPL / 1W / 1m) plus power ratio in dB gives maximum SPL at 1m

Loudspeaker sensitivity is typically specified as dB SPL measured at 1 meter on-axis with a 1 watt input signal (pink noise). To find maximum SPL, add the sensitivity to the power ratio in dB between the maximum power and 1 watt. Power ratio in dB = 10 · log(Power/1W). Combine with ISL to calculate SPL at any distance. For example: 93 dB sensitivity + 20 dB (100W) = 113 dB SPL at 1m; at 10m (ISL: –20 dB) = 93 dB SPL. Sensitivity and efficiency are often confused: sensitivity is measured in free field at 1m with 1W and represents output level; efficiency is the ratio of acoustic power out to electrical power in (typically 0.5–5% for direct radiators). High sensitivity does not always mean high efficiency (horn loading can increase both; larger woofers may have lower sensitivity but higher efficiency in terms of total output).

Examples

Woofer sensitivity: 100 dB / 1W / 1m; rated 100W continuous. Max SPL at 1m = 100 + 10·log(100) = 100 + 20 = 120 dB. At 10m (free field): 120 – 20 = 100 dB SPL.

Assessment

A loudspeaker is rated 97 dB / 1W / 1m, maximum 200W. Calculate maximum SPL at 1m and at 30m in free field.