Understanding Headphone Power Requirements.

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 SENSITIVITY

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.

THE LIST

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. 

Manufacturer	Model	Impedance (Ohms)	Sensitivity (dB)	Max Power (mW)	Max SPL (dB)
AKG	K141M	600	98	80	117
	K240M, K240DF	600	88	80	107
	K270S	75	92	380	118
	K301	100	94	285	119
	K401, K501	120	94	290	119
Audio-Technica	ATH-COM1, COM2, ATH-908	40	90	440	116
	ATH-910	40	92	440	118
	ATH-P5	40	100	440	126
	ATH-M40	60	100	400	126
	ATH-D40	66	102	295	127
	ATH-M2X, ATH-M3X	45	100	435	126
Beyerdynamic	DT150	250	97	175	119
	DT211, DT311	40	98	440	124
	DT250	80	98	360	123
	DT411	250	102	175	124
	DT531	250	95	175	116
	DT431, DT331	40	86	440	112
	DT770PRO, DT990PRO	600	96	80	115
	DT801, DT811,DT511	250	94	175	116
	DT901, DT911	250	98	175	120
Fostex	T-5	44	96	435	122
	T-7	70	98	385	124
	T-20	50	96	425	122
	T-40	50	98	425	124
Hosa	HDS-701	40	91	440	117
Koss Headphones	A/250, A/200, A/130, TD/80	60	98	320	125
	R/200	60	84	400	110
	R/100, R/45	60	85	400	111
	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
	R/40	60	90	400	116
	R/30S	60	106	400	132
	R/10	60	103	400	129
	TD/75	60	95	400	121
	TD/65	90	101	340	126
	TD/61	38	93	440	119
Sennheiser	HD433, HD435	32	94	450	121
	HD25	70	120	380	146
	HD445	52	97	390	123
	HD25SP	85	100	350	125
	HD265, HD525, HD535, HD545, HD565	150	94	190	117
	HD455, HD475	60	94	400	120
	HD465	100	94	285	119
	HD580, HD600	300	97	80	116
Sony	MDR-V100MK2	32	98	450	125
	MDR-85	40	102	440	128
	MDR-V600, MDR-D77	45	106	435	132
	MDR-CD10	32	96	450	123
	MDR-CD550, CD750	45	100	435	126
	MDR-CD6	45	110	435	136
	MDR-CD850, CD950	32	102	450	129
	MDR-CD1000, CD3000	32	104	450	131
	MDR-D33, MDR-D55, MDR-7504	45	104	435	130
	MDR-7506	63	106	400	132
	MDR-7502	45	102	435	128
Stanton	ST PRO, DJ PRO 1000	32	100	450	127
Telex	PH-6	600	105	80	124
Yamaha	RH5M	32	98	450	125
	RH1	32	90	450	116
	RH2	32	95	450	122
	RH3	60	95	400	121
	RH10M	40	102	440	128
	RH40M	32	103	450	130

c. 1983, Rane Corporation

Understanding Headphone Power Requirements PDF version.

c. 1983, Rane Corporation
From Rane Corporation Site. (Republished with permission.)

 

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