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Headphones & Headsets
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Headphones Power Requirements
Headphone manufacturers specify a sensitivity rating for their products that is very similar to loudspeaker sensitivity ratings. For loudspeakers, the standard is to apply one (1) watt and then measure the sound pressure level (SPL) at a distance of 1 meter.
For headphones, the standard is to apply one (1 ) milliwatt and then measure the sound pressure level at the earpiece (using a dummy head with built-in microphones). Sensitivity is then stated as the number of dB of actual sound level (SPL) produced by the headphones with 1 mW of input; headphone specifications commonly refer to this by the misleading term dB/mW. What they really mean is dB SPL for 1 mW input.
Think about these sensitivity definitions a moment: headphone sensitivity is rated using 1/1000 of a watt; loudspeaker sensitivity is rated using 1 watt. So a quick rule-of-thumb is that you are going to need about 1/1000 as much power to drive your headphones as to drive your loudspeakers since both of their sensitivity ratings are similar (around 90-110 dB-SPL).
If your hi-fi amp is rated at 65 watts, then you would need only 65 mW to drive comparable headphones. (Actually you need less than 65 mW since most people donít listen to their loudspeakers at 1 meter.) And this is exactly what you find in hi-fi receivers. Their headphone jacks typically provide only 10-20 mW of output power.
"Understanding Headphone Power Requirements", Dennis Bohn, Rane Corporation
© 1983, Rane Corporation, From Rane Corporation Site. (Republished with permission.)
Additional information is available on headphone and headset selection ... LEARN MORE
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