The Kiwi Ears Halcyon is 29Ω at 109.0 dB/mW; the Kiwi Ears KE4 is 28Ω at 102.0 dB (no reference unit printed). This page covers what they ask of an amplifier, not how they sound.
The KE4 needs 7.0 dB more than the Halcyon to reach the same loudness — 0.63 mW against 0.13 mW.
| Specification | Halcyon | KE4 |
|---|---|---|
| Impedance | 29 Ω | 28 Ω |
| Sensitivity | 109.0 dB/mW | 102.0 dB |
| Sensitivity (voltage) | 124.4 dB/V | 117.5 dB/V |
| Power for 100 dB | 0.13 mW | 0.63 mW |
| Voltage for 100 dB | 60 mV | 0.13 V |
| Current for 100 dB | 2.1 mA | 4.7 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 3.62 Ω | 3.50 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
One caution before reading the rows. Kiwi Ears KE4 printed a decibel figure with no reference unit, so this page reads it as per milliwatt. If it is really per volt, that model 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.
9 sources stay below the audible-hiss threshold with the KE4 but cross it with the Halcyon (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 6 more).
280 of the 280 sources here reach 100 dB on both.
The KE4 is more demanding than 42% of the 567 non-electrostatic models in this database; the Halcyon than 17%.
| dB SPL | Halcyon power | Halcyon voltage | KE4 power | KE4 voltage |
|---|---|---|---|---|
| 80 | 1.3 µW | 6 mV | 6.3 µW | 13 mV |
| 85 | 4.0 µW | 11 mV | 0.02 mW | 24 mV |
| 90 | 0.01 mW | 19 mV | 0.06 mW | 42 mV |
| 95 | 0.04 mW | 34 mV | 0.20 mW | 75 mV |
| 100 | 0.13 mW | 60 mV | 0.63 mW | 0.13 V |
| 105 | 0.40 mW | 0.11 V | 2.0 mW | 0.24 V |
| Source | Price | Headroom, Halcyon | Headroom, KE4 | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 23.3 dB | 16.2 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 32.1 dB | 25.1 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 29.1 dB | 22.1 dB | 0.6 Ω | 1.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. 62 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 62 is the JadeAudio JA11, at $20. It leaves 23.3 dB of headroom on the Halcyon and 16.2 dB on the KE4, its output impedance is 0.5 Ω against a one-eighth limit of 3.62 Ω and 3.50 Ω, and its noise figure puts the hiss floor 11 dB and 18 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| Halcyon | 10-42kHz | not printed | not printed |
| KE4 | nothing printed | — | — |
Kiwi Ears prints 10-42kHz for the Halcyon and nothing at all for the KE4.
So one side of this comparison has a frequency-response number and the other does not — which changes less than it looks. The range printed for the Halcyon comes with no tolerance beside it, and a range without a ±dB figure says nothing about how loud the headphone is at either end of it: thirty decibels down at the bottom and the sentence would still be true. On the only reading that would have made it a specification, the two sheets say the same amount: nothing.
Not a measurement; maker by maker.
Both have a page of their own. In full: Kiwi Ears Halcyon and Kiwi Ears KE4. Each figure on this page is labelled on those pages with where it came from, including the ones Kiwi Ears never published — what that maker publishes, counted.