K240 MKII vs K872: which needs more amplifier?

The AKG K240 MKII is 55Ω at 91.4 dB/mW; the AKG K872 is 36Ω at 97.6 dB/mW. This page covers what they ask of an amplifier, not how they sound.

The K240 MKII needs 6.2 dB more than the K872 to reach the same loudness — 7.2 mW against 1.7 mW.

Side by side

The numbers that decide it

Specification	K240 MKII	K872
Impedance	55 Ω	36 Ω
Sensitivity	91.4 dB/mW	97.6 dB/mW
Sensitivity (voltage)	104.0 dB/V	112.0 dB/V
Power for 100 dB	7.2 mW	1.7 mW
Voltage for 100 dB	0.63 V	0.25 V
Current for 100 dB	11.5 mA	6.9 mA
Highest source impedance that leaves them alone (one-eighth rule)	6.88 Ω	4.50 Ω
Sources that reach 100 dB out of 280	280	280

What separates them

Where the two part company

Every source in the database that drives one of them drives the other. On power, the choice between these two changes nothing about what amplifier you need.

1 source is low enough in output impedance for the K240 MKII under the one-eighth rule but not for the K872 (Shanling H5).

1 source stays below the audible-hiss threshold with the K240 MKII but crosses it with the K872 (Schiit Mjolnir 3).

280 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 K240 MKII is more demanding than 92% of the 567 non-electrostatic models in this database; the K872 than 67%.

dB SPL	K240 MKII power	K240 MKII voltage	K872 power	K872 voltage
80	0.07 mW	63 mV	0.02 mW	25 mV
85	0.23 mW	0.11 V	0.05 mW	44 mV
90	0.72 mW	0.20 V	0.17 mW	79 mV
95	2.3 mW	0.35 V	0.55 mW	0.14 V
100	7.2 mW	0.63 V	1.7 mW	0.25 V
105	23 mW	1.12 V	5.5 mW	0.44 V

What drives both

The cheapest source that satisfies both

Source	Price	Headroom, K240 MKII	Headroom, K872	Output impedance	Noise
JadeAudio JA11	$20	3.8 dB	11.9 dB	0.5 Ω	1.7 µV
FiiO KA11	$29	12.1 dB	20.1 dB	0.7 Ω	1.7 µV
FiiO BTR11	$36	3.8 dB	11.9 dB	0.5 Ω	8.0 µV

Of the 280 sources here, 280 reach 100 dB on both. 69 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 69 is the JadeAudio JA11, at $20. It leaves 3.8 dB of headroom on the K240 MKII and 11.9 dB on the K872, its output impedance is 0.5 Ω against a one-eighth limit of 6.88 Ω and 4.50 Ω, and its noise figure puts the hiss floor 31 dB and 23 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
K240 MKII	15 - 25000	not printed	not printed
K872	5 - 54000 Hz	not printed	not printed

AKG prints 15 - 25000 for the K240 MKII and 5 - 54000 Hz for the K872.

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: AKG K240 MKII and AKG K872. Every figure on this page comes from what AKG published, or is derived from it — what that maker publishes, counted.