FA19 vs FX15: which needs more amplifier?

The FiiO FA19 is 10Ω at 106.0 dB/mW; the FiiO FX15 is 24Ω at 103.0 dB/mW. This page covers what they ask of an amplifier, not how they sound.

The FX15 needs 3.0 dB more than the FA19 to reach the same loudness — 0.50 mW against 0.25 mW.

Side by side

The numbers that decide it

Specification	FA19	FX15
Impedance	10 Ω	24 Ω
Sensitivity	106.0 dB/mW	103.0 dB/mW
Sensitivity (voltage)	126.0 dB/V	119.2 dB/V
Power for 100 dB	0.25 mW	0.50 mW
Voltage for 100 dB	50 mV	0.11 V
Current for 100 dB	5.0 mA	4.6 mA
Highest source impedance that leaves them alone (one-eighth rule)	1.25 Ω	3.00 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.

8 sources are low enough in output impedance for the FX15 under the one-eighth rule but not for the FA19 (FiiO KA13, Schiit Vali 2+, Astell&Kern HC3, 5 more).

14 sources stay below the audible-hiss threshold with the FX15 but cross it with the FA19 (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 11 more).

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 FX15 is more demanding than 36% of the 567 non-electrostatic models in this database; the FA19 than 11%.

dB SPL	FA19 power	FA19 voltage	FX15 power	FX15 voltage
80	2.5 µW	5 mV	5.0 µW	11 mV
85	7.9 µW	9 mV	0.02 mW	20 mV
90	0.03 mW	16 mV	0.05 mW	35 mV
95	0.08 mW	28 mV	0.16 mW	62 mV
100	0.25 mW	50 mV	0.50 mW	0.11 V
105	0.79 mW	89 mV	1.6 mW	0.20 V

What drives both

The cheapest source that satisfies both

Source	Price	Headroom, FA19	Headroom, FX15	Output impedance	Noise
JadeAudio JA11	$20	15.7 dB	16.5 dB	0.5 Ω	1.7 µV
FiiO KA11	$29	27.9 dB	26.3 dB	0.7 Ω	1.7 µV
FiiO BTR13	$59	24.8 dB	23.2 dB	0.6 Ω	1.0 µV

Of the 280 sources here, 280 reach 100 dB on both. 53 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 53 is the JadeAudio JA11, at $20. It leaves 15.7 dB of headroom on the FA19 and 16.5 dB on the FX15, its output impedance is 0.5 Ω against a one-eighth limit of 1.25 Ω and 3.00 Ω, and its noise figure puts the hiss floor 9 dB and 16 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
FA19	20Hz-40kHz	not printed	not printed
FX15	20Hz-40kHz	not printed	not printed

FiiO prints the same thing for both the FA19 and the FX15: 20Hz-40kHz.

Neither range has a tolerance printed beside it, so the matching numbers say little.

Not a measurement; maker by maker.

Both pages in full

Both have a page of their own. In full: FiiO FA19 and FiiO FX15. Every figure on this page comes from what FiiO published, or is derived from it — what that maker publishes, counted.