SRH145 vs SRH840A: which needs more amplifier?

The Shure SRH145 is 34Ω at 100.0 dB/mW; the Shure SRH840A is 40Ω at 97.0 dB/mW. This page covers what they ask of an amplifier, not how they sound.

The SRH840A needs 3.0 dB more than the SRH145 to reach the same loudness — 2.0 mW against 1.0 mW.

Side by side

The numbers that decide it

Specification	SRH145	SRH840A
Impedance	34 Ω	40 Ω
Sensitivity	100.0 dB/mW	97.0 dB/mW
Sensitivity (voltage)	114.7 dB/V	111.0 dB/V
Power for 100 dB	1.0 mW	2.0 mW
Voltage for 100 dB	0.18 V	0.28 V
Current for 100 dB	5.4 mA	7.1 mA
Highest source impedance that leaves them alone (one-eighth rule)	4.25 Ω	5.00 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.

1 source is low enough in output impedance for the SRH840A under the one-eighth rule but not for the SRH145 (Shanling H5).

1 source stays below the audible-hiss threshold with the SRH840A but crosses it with the SRH145 (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 SRH840A is more demanding than 71% of the 567 non-electrostatic models in this database; the SRH145 than 55%.

dB SPL	SRH145 power	SRH145 voltage	SRH840A power	SRH840A voltage
80	0.01 mW	18 mV	0.02 mW	28 mV
85	0.03 mW	33 mV	0.06 mW	50 mV
90	0.10 mW	58 mV	0.20 mW	89 mV
95	0.32 mW	0.10 V	0.63 mW	0.16 V
100	1.0 mW	0.18 V	2.0 mW	0.28 V
105	3.2 mW	0.33 V	6.3 mW	0.50 V

What drives both

The cheapest source that satisfies both

Source	Price	Headroom, SRH145	Headroom, SRH840A	Output impedance	Noise
JadeAudio JA11	$20	14.5 dB	10.8 dB	0.5 Ω	1.7 µV
FiiO KA11	$29	22.7 dB	19.0 dB	0.7 Ω	1.7 µV
FiiO BTR11	$36	14.5 dB	10.8 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 14.5 dB of headroom on the SRH145 and 10.8 dB on the SRH840A, its output impedance is 0.5 Ω against a one-eighth limit of 4.25 Ω and 5.00 Ω, and its noise figure puts the hiss floor 21 dB and 24 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
SRH145	25 to 18,000 Hz	not printed	not printed
SRH840A	5 to 25,000 Hz	not printed	not printed

Shure prints 25 to 18,000 Hz for the SRH145 and 5 to 25,000 Hz for the SRH840A.

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: Shure SRH145 and Shure SRH840A. Every figure on this page comes from what Shure published, or is derived from it — what that maker publishes, counted.