The Softears RSV is 8Ω at 104.0 dB/mW; the Softears Studio4 is 12Ω at 103.8 dB/mW. This page is only about what they ask of an amplifier — not how they sound, which no specification on either sheet can tell you.
In amplifier terms these two are the same headphone. The gap between what they need for 100 dB is under half a decibel, which is smaller than the step between two clicks of most volume controls.
| Specification | RSV | Studio4 |
|---|---|---|
| Impedance | 8 Ω | 12 Ω |
| Sensitivity | 104.0 dB/mW | 103.8 dB/mW |
| Sensitivity (voltage) | 125.0 dB/V | 123.0 dB/V |
| Power for 100 dB | 0.40 mW | 0.42 mW |
| Voltage for 100 dB | 56 mV | 71 mV |
| Current for 100 dB | 7.1 mA | 5.9 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.00 Ω | 1.50 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
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.
7 sources are low enough in output impedance for the Studio4 under the one-eighth rule but not for the RSV (FiiO K11, FiiO BTR7, FiiO M11S, 4 more).
6 sources stay below the audible-hiss threshold with the Studio4 but cross it with the RSV (Lake People G103-S Mk II, Schiit Valhalla 3, Lake People G111 Mk II, 3 more).
280 of the 280 sources here reach 100 dB on both. That count is about power only — the output-impedance and hiss lines above are separate questions, and a source can pass this one and fail those.
The gap between these two in decibels does not change with volume — it is a property of the two headphones. What changes is the size of the numbers, and it changes fast: every 10 dB costs ten times the power. The row that matters is the one nearest the level you listen at, and for most people that is nearer the top of this table than the bottom.
The Studio4 is more demanding than 21% of the 567 non-electrostatic models in this database; the RSV than 14%. Both figures use the same measure as the rest of the site: whichever runs out first against a 2 V, 100 mW dongle, voltage or power.
| dB SPL | RSV power | RSV voltage | Studio4 power | Studio4 voltage |
|---|---|---|---|---|
| 80 | 4.0 µW | 6 mV | 4.2 µW | 7 mV |
| 85 | 0.01 mW | 10 mV | 0.01 mW | 13 mV |
| 90 | 0.04 mW | 18 mV | 0.04 mW | 22 mV |
| 95 | 0.13 mW | 32 mV | 0.13 mW | 40 mV |
| 100 | 0.40 mW | 56 mV | 0.42 mW | 71 mV |
| 105 | 1.3 mW | 0.10 V | 1.3 mW | 0.13 V |
105 dB is included because forum power figures are usually quoted there or higher. It is also a level that damages hearing in minutes — how many minutes is its own calculator.
| Source | Price | Headroom, RSV | Headroom, Studio4 | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 12.8 dB | 14.3 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 24.9 dB | 26.4 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 21.8 dB | 23.3 dB | 0.6 Ω | 1.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. That is the easy axis. 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 rest either fail one of those or never printed the number at all, and 208 of them are in the second group.
The cheapest of the 55 is the JadeAudio JA11, at $20. It leaves 12.8 dB of headroom on the RSV and 14.3 dB on the Studio4, its output impedance is 0.5 Ω against a one-eighth limit of 1.00 Ω and 1.50 Ω, and its noise figure puts the hiss floor 10 dB and 12 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
Cheapest that satisfies three published numbers is not the same as best, and none of it is about how either headphone sounds. To put either model against a source this page does not mention, or to change the target loudness, use the amplifier matcher.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| RSV | 5-40kHz | not printed | not printed |
| 20-20kHz | not printed | not printed | |
| Studio4 | 5-40kHz (1/4' free field, -3Db) | -3 dB | 1/4″ free field |
| 20-20kHz (IEC60318-4) | not printed | IEC60318-4 |
Softears prints two ranges, “5-40kHz” and “20-20kHz”, for the RSV and two ranges, “5-40kHz (1/4' free field, -3Db)” and “20-20kHz (IEC60318-4)”, for the Studio4.
Studio4: Softears puts the tolerance on the WIDE range and leaves the effective one without it — the opposite way round to every other maker here that prints both.
Only one of the two is a specification. The range printed for the Studio4 comes with a tolerance; the one printed for the RSV does not, and a range without a ±dB figure says nothing about how loud that model is at either end of it. The two cannot be compared number against number, however similar they look in the table. Of the 490 models whose maker prints a range, 58 print the tolerance.
None of this is a measurement. What each maker publishes, and what it is worth, is set out in the frequency response audit.
Each model has a page of its own with the full source list, the hiss estimate and the provenance of every figure above: Softears RSV and Softears Studio4. Every figure on this page comes from what Softears published, or is derived from it — what that maker publishes, counted.