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Most commercial headphones are advertised to have sensitivity greater than 90 dB/mW. But to my understanding, even with 100% efficiency that's not possible (if we use 10 log (I/I0) where I = 1 mW, we get 90 dB). So, is this an exaggeration or am I missing something?

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  • \$\begingroup\$ the distance is about 2cm (or even zero, if buds), compared to 1 meter testing distance for speakers. \$\endgroup\$ – analogsystemsrf Jul 22 '19 at 15:17
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You are mixing things up. When the specification says 90 dB per milli watt it is referring to a sound pressure level of 90 decibels being produced close to your ear and you cannot imply any measure of power efficiency at all.

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