HD 550 vs HD 600: which needs more amplifier?

The Sennheiser HD 550 is 150Ω at 98.5 dB/mW; the Sennheiser HD 600 is 300Ω at 91.8 dB/mW. This page covers what they ask of an amplifier, not how they sound.

The HD 600 needs 6.7 dB more than the HD 550 to reach the same loudness — 6.6 mW against 1.4 mW.

Side by side

The numbers that decide it

Specification	HD 550	HD 600
Impedance	150 Ω	300 Ω
Sensitivity	98.5 dB/mW	91.8 dB/mW
Sensitivity (voltage)	106.7 dB/V	97.0 dB/V
Power for 100 dB	1.4 mW	6.6 mW
Voltage for 100 dB	0.46 V	1.41 V
Current for 100 dB	3.1 mA	4.7 mA
Highest source impedance that leaves them alone (one-eighth rule)	18.75 Ω	37.50 Ω
Sources that reach 100 dB out of 280	280	261

What separates them

Where the two part company

19 of the 280 sources have the power for the HD 550 but not for the HD 600 — Apple USB-C dongle (US), Apple USB-C dongle (EU), JadeAudio JA11, 16 more.

2 sources are low enough in output impedance for the HD 600 under the one-eighth rule but not for the HD 550 (Schiit Valhalla 3, Arturia AudioFuse Rev2).

261 of the 280 sources here reach 100 dB on both.

At the level you actually listen at

What each one needs from 80 to 105 dB

The HD 600 is more demanding than 99% of the 567 non-electrostatic models in this database; the HD 550 than 85%.

dB SPL	HD 550 power	HD 550 voltage	HD 600 power	HD 600 voltage
80	0.01 mW	46 mV	0.07 mW	0.14 V
85	0.04 mW	82 mV	0.21 mW	0.25 V
90	0.14 mW	0.15 V	0.66 mW	0.45 V
95	0.45 mW	0.26 V	2.1 mW	0.79 V
100	1.4 mW	0.46 V	6.6 mW	1.41 V
105	4.5 mW	0.82 V	21 mW	2.50 V

What drives both

The cheapest source that satisfies both

Source	Price	Headroom, HD 550	Headroom, HD 600	Output impedance	Noise
FiiO KA11	$29	14.9 dB	5.2 dB	0.7 Ω	1.7 µV
FiiO BTR13	$59	11.7 dB	1.8 dB	0.6 Ω	1.0 µV
iBasso DC03 Pro	$69	11.7 dB	2.0 dB	0.12 Ω	0.9 µV

Of the 280 sources here, 261 reach 100 dB on both. 68 of them also publish an output impedance low enough for both under the one-eighth rule and a noise figure that stays below the audible-hiss threshold with both.

The cheapest of the 68 is the FiiO KA11, at $29. It leaves 14.9 dB of headroom on the HD 550 and 5.2 dB on the HD 600, its output impedance is 0.7 Ω against a one-eighth limit of 18.75 Ω and 37.50 Ω, and its noise figure puts the hiss floor 29 dB and 38 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.

Try any other source.

Frequency response

What each sheet prints, and what it is worth

Model	As printed	Tolerance	Standard
HD 550	6 Hz – 39.5 kHz	not printed	not printed
HD 600	12 Hz - 40,500 Hz	not printed	not printed

Sennheiser prints 6 Hz – 39.5 kHz for the HD 550 and 12 Hz - 40,500 Hz for the HD 600.

Neither range has a tolerance printed beside it, so a wider range on one sheet is not deeper bass or more treble.

Not a measurement; maker by maker.

Both pages in full

Both have a page of their own. In full: Sennheiser HD 550 and Sennheiser HD 600. Every figure on this page comes from what Sennheiser published, or is derived from it — what that maker publishes, counted.