By Dennis Bohn, Rane Corporation
Much confusion abounds regarding headphone power requirements. This RaneNote is intended to disperse some of the mist surrounding headphone specifications and hopefully give you a clearer understanding of how much power is really needed for your application.
Headphone manufacturers specify a sensitivity rating for their products that is very similar to loudspeaker sensitivity ratings. For loudspeakers, the standard is to apply 1 watt and then measure the sound pressure level (SPL) at a distance of 1 meter. For headphones, the standard is to apply 1 milliwatt (1 mW = 1/1000 of a watt) 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). For example, 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 don’t 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.
Take another moment and think about all those portable tape players. Ever hear one? They sound great, and loud. Why you can even hear the headphones ten feet away as the teenage skateboarder that ran over your foot escapes.
Power output? About 12 mW.
As an aid in finding out how much power is available from the MH 4 Headphone Console, we have compiled a listing of popular headphones. Included is a column giving the maximum SPL obtainable using the MH 4 and any particular headphone. Ultimately, it all gets down to actual SPL. The power rating really doesn’t matter at all. Either it’s loud enough or it isn’t (of course it has to be clean power, not clipped and distorted). The SPL numbers shown are for maximum continuous SPL; for momentary peak SPL add 3 dB.
Note that the maximum achievable SPL varies widely for different models and manufacturers, ranging from a low of 107 dB to a harmful 146 dB! The table also shows there is very little relationship between headphone impedance and sensitivity, and that power output alone means nothing, since in one case 80 mW produces a maximum SPL of 107 dB, yet in another case the same 80 mW yields an SPL of 124 dB!
Sensitivity dB is measured sound pressure level with 1mW of power. The Max Power mW columns are typical continuous average (RMS) power, 20 Hz-20 kHz, with THD less than .4%.
If headphones are not yet owned, or replacements are desired, use this listing as a guide for selecting headphones with sufficient sensitivity for the maximum desired SPL.
Table of Headphone Specifications
Disclaimer: The headphone specifications were supplied to us by the respective manufacturers, subject to change without notice.
|Audio-Technica||ATH-COM1, COM2, ATH-908||40||90||440||116|
|Koss Headphones||A/250, A/200, A/130, TD/80||60||98||320||125|
|R/90, HD/2, SB/15||60||100||400||126|
|R/80, R/35S, R/20, Porta Pro models||60||101||400||127|
|R/70B, R/55B, SB/50, SB/35||60||101||400||127|
|HD265, HD525, HD535, HD545, HD565||150||94||190||117|
|MDR-D33, MDR-D55, MDR-7504||45||104||435||130|
|Stanton||ST PRO, DJ PRO 1000||32||100||450||127|
c. 1983, Rane Corporation
c. 1983, Rane Corporation
From Rane Corporation Site. (Republished with permission.)