The Symphonium Giant is 7.0Ω at 88.5 dB/mW; the Symphonium Helios is 8.5Ω at 83.3 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.
The Helios needs 5.2 dB more than the Giant to reach the same loudness — 47 mW against 14 mW.
| Specification | Giant | Helios |
|---|---|---|
| Impedance | 7.0 Ω | 8.5 Ω |
| Sensitivity | 88.5 dB/mW | 83.3 dB/mW |
| Sensitivity (voltage) | 110.0 dB/V | 104.0 dB/V |
| Power for 100 dB | 14 mW | 47 mW |
| Voltage for 100 dB | 0.31 V | 0.63 V |
| Current for 100 dB | 44.9 mA | 74.2 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 0.88 Ω | 1.06 Ω |
| Sources that reach 100 dB out of 280 | 252 | 179 |
73 of the 280 sources have the power for the Giant but not for the Helios — FiiO SnowSky Tiny A, FiiO SnowSky Tiny B, FiiO BTR11, 70 more.
34 sources are low enough in output impedance for the Helios under the one-eighth rule but not for the Giant (FiiO SnowSky Tiny B, FiiO BTR15, FiiO BTR5 2021, 31 more).
179 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 Helios is more demanding than 98% of the 567 non-electrostatic models in this database; the Giant than 76%. 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 | Giant power | Giant voltage | Helios power | Helios voltage |
|---|---|---|---|---|
| 80 | 0.14 mW | 31 mV | 0.47 mW | 63 mV |
| 85 | 0.45 mW | 56 mV | 1.5 mW | 0.11 V |
| 90 | 1.4 mW | 99 mV | 4.7 mW | 0.20 V |
| 95 | 4.5 mW | 0.18 V | 15 mW | 0.35 V |
| 100 | 14 mW | 0.31 V | 47 mW | 0.63 V |
| 105 | 45 mW | 0.56 V | 148 mW | 1.12 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, Giant | Headroom, Helios | Output impedance | Noise |
|---|---|---|---|---|---|
| FiiO KA11 | $29 | 8.8 dB | 4.4 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 5.7 dB | 1.3 dB | 0.6 Ω | 1.0 µV |
| FiiO KA3 | $79 | 5.7 dB | 1.3 dB | 0.5 Ω | 1.7 µV |
Of the 280 sources here, 179 reach 100 dB on both. That is the easy axis. 43 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 111 of them are in the second group.
The cheapest of the 43 is the FiiO KA11, at $29. It leaves 8.8 dB of headroom on the Giant and 4.4 dB on the Helios, its output impedance is 0.7 Ω against a one-eighth limit of 0.88 Ω and 1.06 Ω, and its noise figure puts the hiss floor 25 dB and 31 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 |
|---|---|---|---|
| Giant | 5Hz - 18kHz, ± 2 dB | ±2 dB | not printed |
| Helios | 12Hz - 24kHz, ± 2 dB | ±2 dB | not printed |
Symphonium prints 5Hz - 18kHz, ± 2 dB for the Giant and 12Hz - 24kHz, ± 2 dB for the Helios.
Both sheets print a tolerance, which is rare enough to be worth pointing at: only 58 of the 490 models with a printed range do. These two ranges can be set against each other, because each of them says how far down the response is allowed to be at the ends.
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: Symphonium Giant and Symphonium Helios. Every figure on this page comes from what Symphonium published, or is derived from it — what that maker publishes, counted.