The KZ PRX is 15Ω at 94.0 dB (no reference unit printed); the KZ ZSX is 24Ω at 111.0 dB (no reference unit printed). This page covers what they ask of an amplifier, not how they sound.
The PRX needs 17.0 dB more than the ZSX to reach the same loudness — 4.0 mW against 0.08 mW.
| Specification | PRX | ZSX |
|---|---|---|
| Impedance | 15 Ω | 24 Ω |
| Sensitivity | 94.0 dB | 111.0 dB |
| Sensitivity (voltage) | 112.2 dB/V | 127.2 dB/V |
| Power for 100 dB | 4.0 mW | 0.08 mW |
| Voltage for 100 dB | 0.24 V | 44 mV |
| Current for 100 dB | 16.3 mA | 1.8 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.88 Ω | 3.00 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
One caution before reading the rows. KZ PRX and KZ ZSX printed a decibel figure with no reference unit, so this page reads it as per milliwatt. If it is really per volt, each of them needs far more than the table says. Why the two readings differ by so much.
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.
3 sources are low enough in output impedance for the ZSX under the one-eighth rule but not for the PRX (Astell&Kern HC3, RME Fireface UFX II, RME Fireface UFX III).
16 sources stay below the audible-hiss threshold with the PRX but cross it with the ZSX (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 13 more).
280 of the 280 sources here reach 100 dB on both.
The PRX is more demanding than 66% of the 567 non-electrostatic models in this database; the ZSX than 8%.
| dB SPL | PRX power | PRX voltage | ZSX power | ZSX voltage |
|---|---|---|---|---|
| 80 | 0.04 mW | 24 mV | 0.8 µW | 4 mV |
| 85 | 0.13 mW | 43 mV | 2.5 µW | 8 mV |
| 90 | 0.40 mW | 77 mV | 7.9 µW | 14 mV |
| 95 | 1.3 mW | 0.14 V | 0.03 mW | 25 mV |
| 100 | 4.0 mW | 0.24 V | 0.08 mW | 44 mV |
| 105 | 13 mW | 0.43 V | 0.25 mW | 78 mV |
| Source | Price | Headroom, PRX | Headroom, ZSX | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 5.5 dB | 24.5 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 17.6 dB | 34.3 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 14.5 dB | 31.2 dB | 0.6 Ω | 1.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. 55 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 55 is the JadeAudio JA11, at $20. It leaves 5.5 dB of headroom on the PRX and 24.5 dB on the ZSX, its output impedance is 0.5 Ω against a one-eighth limit of 1.88 Ω and 3.00 Ω, and its noise figure puts the hiss floor 23 dB and 8 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| PRX | 20-40000Hz | not printed | not printed |
| ZSX | 7-40000Hz | not printed | not printed |
KZ prints 20-40000Hz for the PRX and 7-40000Hz for the ZSX.
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 have a page of their own. In full: KZ PRX and KZ ZSX. Each figure on this page is labelled on those pages with where it came from, including the ones KZ never published — what that maker publishes, counted.