Benchmark HPA4 vs SPL Phonitor x

Short answer

More power: the Benchmark HPA4, with 3.35 W into 32 Ω; the SPL Phonitor x has 1.00 W (balanced: 3.35 W against 700 mW). The Benchmark HPA4 drives 1 headphone to 100 dB that the SPL Phonitor x cannot (Symphonium Titan).
Quieter with sensitive IEMs: the Benchmark HPA4. 65 headphones stay below audible hiss on it but not on the SPL Phonitor x (64 Audio Nio, 64 Audio U12t, 64 Audio U18s, 62 more).
Price: the Benchmark HPA4 costs $299 more; what that buys on these numbers is set out further down, under What the price difference buys.

Both are desktop amplifiers, $3499 against $3200.

The Benchmark HPA4 reaches 100 dB on 567 of the 567 models here, the SPL Phonitor x on 566.

Specification	Benchmark HPA4	SPL Phonitor x
Power into 32Ω	3.4 W	1.0 W
Power into 150Ω	829 mW	3.1 W
Power into 300Ω	440 mW	4.2 W
Power into 600Ω	220 mW	2.1 W
Output impedance	<0.1 Ω	0.18 Ω
Output noise	2.45 µV	5.48 µV
Price	$3499	$3200
Headphones it reaches 100 dB on out of 567	567	566

Specification

Benchmark HPA4

SPL Phonitor x

Power into 32Ω

3.4 W

1.0 W

Power into 150Ω

829 mW

3.1 W

Power into 300Ω

440 mW

4.2 W

Power into 600Ω

220 mW

2.1 W

Output impedance

<0.1 Ω

0.18 Ω

Output noise

2.45 µV

5.48 µV

Price

$3499

$3200

Headphones it reaches 100 dB on
out of 567

567

566

The 4.4 mm or XLR socket, rated on its own

Balanced	Benchmark HPA4	SPL Phonitor x
Socket	balanced	balanced
Power into 32Ω	3.4 W derived	700 mW
Power into 300Ω	440 mW	2.9 W derived
Output impedance	<0.1 Ω	0.36 Ω
Output noise	2.45 µV	9.75 µV
Headphones it reaches 100 dB on out of 567	567	566

Through the balanced sockets the Benchmark HPA4 reaches 100 dB on 567 of the 567 models here and the SPL Phonitor x on 566. Derived figures are worked out from the loads the maker did publish.

Where each power figure comes from

Load	Benchmark HPA4	SPL Phonitor x
32 Ω	Derived	Published
150 Ω	Derived	Derived
300 Ω	Published	Derived
600 Ω	Derived	Derived

Both makers publish a power rating. Benchmark HPA4 publishes at 300 Ω; SPL Phonitor x at 32 Ω. The other rows are worked out from those.

So the two columns are not equally firm row by row: at 300 Ω only the Benchmark HPA4 figure is the maker’s own and at 32 Ω only the SPL Phonitor x figure is the maker’s own. On those rows the derived number is the one to doubt first.

What the labels mean.

The headphones that tell them apart

1 headphone reaches 100 dB on the Benchmark HPA4 but not on the SPL Phonitor x — Symphonium Titan.

65 headphones stay below the audible-hiss threshold on the Benchmark HPA4 but cross it on the SPL Phonitor x (64 Audio Nio, 64 Audio U12t, 64 Audio U18s, 62 more).

566 of the 567 models here reach 100 dB on both.

Headroom and hiss on 8 models, both sources

Headroom is at a 100 dB SPL peak.

The widest gap on the list is the Shure SE846: Benchmark HPA4 has +49 dB of headroom there against +38 dB. 11 dB is about 12 times the power, which matters for peaks rather than for how loud the music sits.

Hiss below about 20 dB SPL is inaudible in a quiet room.

Headphone	Impedance	Needs	Benchmark HPA4 headroom	SPL Phonitor x headroom	Benchmark HPA4 hiss	SPL Phonitor x hiss
Shure SE846	9 Ω	0.04 mW	+49 dB	+38 dB	22 dB	29 dB
Campfire Audio Andromeda 2020	9 Ω	4.0 mW	+29 dB	+18 dB	2 dB	9 dB
Audeze LCD-2 Classic	70 Ω	0.79 mW	+33 dB	+33 dB	0 dB	7 dB
Beyerdynamic DT 1990 Pro (250Ω)	250 Ω	0.63 mW	+29 dB	+39 dB	-4 dB	3 dB
HiFiMAN HE400se	25 Ω	7.9 mW	+27 dB	+20 dB	-5 dB	2 dB
Audio-Technica ATH-R70X	470 Ω	1.6 mW	+22 dB	+32 dB	-11 dB	-4 dB
Sennheiser HD 600	300 Ω	6.6 mW	+18 dB	+28 dB	-15 dB	-8 dB
HiFiMAN Susvara	60 Ω	50 mW	+16 dB	+15 dB	-17 dB	-10 dB

The gap in dollars, against the gap in numbers

The Benchmark HPA4 costs $299 more than the SPL Phonitor x. Out of the 567 models here, that difference buys 1 more model driven to 100 dB and 65 more models kept below the audible-hiss threshold.

Nothing runs the other way: there is no axis here on which the cheaper of the two does better.

Only published figures count here; blank axes are counted separately.