Short answer: the Symphonium Audio Helios. It ranks #64 of 450 in-ear headphones by sound quality, rated 4.5/5, at $1,099; the ThieAudio Monarch MKIV ranks #105, rated 4.4/5, and costs $1,149, so there is not much of a tradeoff to weigh.
What the Symphonium Audio Helios does well: One of the smoothest in-ears measured, with a 1.57 dB standard deviation from the Harman target and a preference score of 80. The catch: The presence region from 3 to 6 kHz sits 3.5 dB below target, with a 6.3 dB dip near 6.95 kHz, so vocals and guitars lose a little bite and detail.
The case for the ThieAudio Monarch MKIV: Across 14 squig.link measurements it posts a preference score of 79.0 with a very smooth 1.31 dB spread. Watch for: Presence sits 2.7 dB below target with a 3.7 dB dip near 6.4 kHz, so vocals and strings lose some immediacy.
Buy the Symphonium Audio Helios. It is rated higher for sound quality than the ThieAudio Monarch MKIV and costs less, so it is the default pick unless a specific strength of the other one matters more to you.
Looking for alternatives? See the complete Headphones rankings.
Specifications Side By Side
| Symphonium Audio Helios | ThieAudio Monarch MKIV | |
|---|---|---|
| Price | $1,099.00 | $1,149.00 |
| Ranked | #64 of 450 in In-Ear Headphones | #105 of 450 in In-Ear Headphones |
| Form Factor | In-ear | In-ear |
| Back | Closed | Closed |
| Harman Preference Score | 80 (measured by HypetheSonics, via AutoEQ) | 79 (median of 14 squig.link measurements, calibrated to AutoEQ) |
| Deviation From Target | 1.57 dB standard deviation | 1.31 dB standard deviation |
| Tonal Tilt | +0.02 (negative is warmer, positive brighter) | -0.43 (negative is warmer, positive brighter) |
| Sub-bass Extension | Within 6 dB of target down to 20 Hz (-1.3 dB at 30 Hz) | Within 6 dB of target down to 20 Hz (-0.2 dB at 30 Hz) |
| Connection | Wired | Wired |
| Driver Type | Balanced armature | Hybrid (2 dynamic + 6 balanced armature + 2 electrostatic) |
| Impedance | 8.5 ohms | - |
| Sensitivity | 104 dB/Vrms | 100 dB |
| Frequency Response | 12Hz - 24kHz (Manufacturer specified) | 10Hz - 44kHz (Manufacturer specified) |
| Built-in Microphone | No | No |
| Drivers | - | 2 x 8mm dynamic + 6 x balanced armature + 2 x electrostatic |
Related Headphone Comparisons
How Symphonium Audio Helios compares with other leading options:
- ThieAudio Monarch MKIII vs Symphonium Audio Helios
- Simgot EM6L vs Symphonium Audio Helios
- Symphonium Audio Helios vs DUNU Glacier
- Symphonium Audio Helios vs Letshuoer Mystic 8
- ThieAudio Monarch MKII vs ThieAudio Monarch MKIV
Prices on this page were last checked October 11, 2026 at 4:59 PM UTC. Product prices and availability are accurate as of that date/time and are subject to change; the price and availability shown on Amazon at the time of purchase will apply to the purchase of this product.
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The Two Headphones In Full
Symphonium Audio Helios: $1,099.00 Headphones.com eBay
Pros: One of the smoothest in-ears measured, with a 1.57 dB standard deviation from the Harman target and a preference score of 80. Bass reaches all the way down, sitting only 1.3 dB under target at 30 Hz, so kick drums and synth bass keep their rumble from an all balanced armature design. Overall tilt is essentially flat, and listeners who like a warm, bass-forward balance are the best match. It earns a higher rating than the SoftEars Twilight and the HIFIMAN RE2000.
Cons: The presence region from 3 to 6 kHz sits 3.5 dB below target, with a 6.3 dB dip near 6.95 kHz, so vocals and guitars lose a little bite and detail. The ThieAudio Monarch MKIII costs about the same and carries a higher rating.
Full Symphonium Audio Helios review and specifications →
| Released | 2021 (5 years ago) |
|---|---|
| Back | Closed |
| Built-in Microphone | No |
| Connection | Wired |
| Deviation From Target | 1.57 dB standard deviation |
| Driver Type | Balanced armature |
| Form Factor | In-ear |
| Frequency Response | 12Hz - 24kHz (Manufacturer specified) |
| Harman Preference Score | 80 (measured by HypetheSonics, via AutoEQ) |
| Impedance | 8.5 ohms |
| Sensitivity | 104 dB/Vrms |
| Sub-bass Extension | Within 6 dB of target down to 20 Hz (-1.3 dB at 30 Hz) |
| Tonal Tilt | +0.02 (negative is warmer, positive brighter) |
EQ preset to match the Harman target
Set a preamp of -2.8 dB, then add these filters in any parametric equalizer (Wavelet, Equalizer APO, Peace, or a player with parametric EQ). Calculated by AutoEQ from its measured frequency response.
| Filter | Frequency | Gain | Q |
|---|---|---|---|
| Low shelf | 105 Hz | -2.6 dB | 0.70 |
| Peak | 1,245 Hz | -1.7 dB | 0.50 |
| Peak | 71 Hz | +3.6 dB | 0.56 |
| Peak | 6,561 Hz | +3.7 dB | 4.67 |
| Peak | 3,355 Hz | +2.2 dB | 2.99 |
| High shelf | 10,000 Hz | -7.3 dB | 0.70 |
| Peak | 276 Hz | +0.5 dB | 1.70 |
| Peak | 533 Hz | -0.4 dB | 2.28 |
| Peak | 4,907 Hz | +1.5 dB | 6.00 |
| Peak | 139 Hz | -0.3 dB | 2.01 |
- Reviews, Comparisons and Sound Samples
- Head-to-Head Comparisons
ThieAudio Monarch MKIV: $1,149.00 Linsoul eBay
Pros: Across 14 squig.link measurements it posts a preference score of 79.0 with a very smooth 1.31 dB spread. Sub-bass and bass sit within half a dB of target, so the dual 8 mm dynamic drivers give clean, accurate low end, and a 5 dB air lift near 12 kHz from the electrostatic tweeters adds shimmer and space. It rates above the SoftEars RSV.
Cons: Presence sits 2.7 dB below target with a 3.7 dB dip near 6.4 kHz, so vocals and strings lose some immediacy. The Moondrop Dark Saber rates well above it for less money, and the Symphonium Audio Helios rates higher at a similar price.
Full ThieAudio Monarch MKIV review and specifications →
| Released | Jul 2025 (1 year ago) |
|---|---|
| Back | Closed |
| Built-in Microphone | No |
| Connection | Wired |
| Deviation From Target | 1.31 dB standard deviation |
| Driver Type | Hybrid (2 dynamic + 6 balanced armature + 2 electrostatic) |
| Drivers | 2 x 8mm dynamic + 6 x balanced armature + 2 x electrostatic |
| Form Factor | In-ear |
| Frequency Response | 10Hz - 44kHz (Manufacturer specified) |
| Harman Preference Score | 79 (median of 14 squig.link measurements, calibrated to AutoEQ) |
| Sensitivity | 100 dB |
| Sub-bass Extension | Within 6 dB of target down to 20 Hz (-0.2 dB at 30 Hz) |
| Tonal Tilt | -0.43 (negative is warmer, positive brighter) |
- Reviews, Comparisons and Sound Samples
- Head-to-Head Comparisons