Short answer: the ThieAudio Monarch MKIII. It ranks #1 of 450 in-ear headphones by sound quality, rated 4.9/5, at $999; the Symphonium Audio Helios ranks #64, rated 4.5/5, and costs $1,099, which makes this an easy call rather than a real tradeoff.
The ThieAudio Monarch MKIII is the better-sounding choice. A preference score of 91 in HypetheSonics’ measurement, with an exceptionally smooth 0.77 dB standard deviation from target. The catch: The air band from 10 to 16 kHz sits about 5.7 dB above target with a 4.4 dB peak near 11.9 kHz, which can add a hint of glare on bright or sibilant recordings.
The case for the Symphonium Audio Helios: One of the smoothest in-ears measured, with a 1.57 dB standard deviation from the Harman target and a preference score of 80. Watch for: 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.
Buy the ThieAudio Monarch MKIII. It is rated higher for sound quality than the Symphonium Audio Helios and costs less, so only choose the other one for a particular feature it does better.
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Specifications Side By Side
| ThieAudio Monarch MKIII | Symphonium Audio Helios | |
|---|---|---|
| Price | $999.00 | $1,099.00 |
| Ranked | #1 of 450 in In-Ear Headphones | #64 of 450 in In-Ear Headphones |
| Form Factor | In-ear | In-ear |
| Back | Closed | Closed |
| Harman Preference Score | 91 (measured by HypetheSonics, via AutoEQ) | 80 (measured by HypetheSonics, via AutoEQ) |
| Deviation From Target | 0.77 dB standard deviation | 1.57 dB standard deviation |
| Tonal Tilt | -0.11 (negative is warmer, positive brighter) | +0.02 (negative is warmer, positive brighter) |
| Sub-bass Extension | Within 6 dB of target down to 20 Hz (-0.8 dB at 30 Hz) | Within 6 dB of target down to 20 Hz (-1.3 dB at 30 Hz) |
| Connection | Wired | Wired |
| Driver Type | Hybrid (2 dynamic + 6 balanced armature + 2 electrostatic) | Balanced armature |
| Drivers | 2 x 10mm dynamic + 6 x balanced armature + 2 x electrostatic | - |
| Impedance | 18 ohms | 8.5 ohms |
| Sensitivity | 99 dB @ 1kHz | 104 dB/Vrms |
| Frequency Response | 20Hz - 80kHz (Manufacturer specified) | 12Hz - 24kHz (Manufacturer specified) |
| Built-in Microphone | No | No |
Related Headphone Comparisons
How ThieAudio Monarch MKIII compares with other leading options:
- Moondrop Dark Saber vs ThieAudio Monarch MKIII
- ThieAudio Monarch MKIII vs Simgot EW100P
- ThieAudio Monarch MKII vs ThieAudio Monarch MKIII
- ThieAudio Monarch MKIII vs ThieAudio Monarch MKIV
- Symphonium Audio Helios vs Letshuoer Mystic 8
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
ThieAudio Monarch MKIII: $999.00 Linsoul eBay
Pros: A preference score of 91 in HypetheSonics’ measurement, with an exceptionally smooth 0.77 dB standard deviation from target. Everything from 20 Hz to 10 kHz stays within about 1.1 dB of target, so bass, vocals and treble all sound balanced and true. It rates above the pricier Symphonium Audio Helios and well above the SoftEars RSV.
Cons: The air band from 10 to 16 kHz sits about 5.7 dB above target with a 4.4 dB peak near 11.9 kHz, which can add a hint of glare on bright or sibilant recordings. It is a wired in-ear with no built-in microphone, so it is not suited to calls on the go.
Full ThieAudio Monarch MKIII review and specifications →
| Released | 2023 (3 years ago) |
|---|---|
| Back | Closed |
| Built-in Microphone | No |
| Connection | Wired |
| Deviation From Target | 0.77 dB standard deviation |
| Driver Type | Hybrid (2 dynamic + 6 balanced armature + 2 electrostatic) |
| Drivers | 2 x 10mm dynamic + 6 x balanced armature + 2 x electrostatic |
| Form Factor | In-ear |
| Frequency Response | 20Hz - 80kHz (Manufacturer specified) |
| Harman Preference Score | 91 (measured by HypetheSonics, via AutoEQ) |
| Impedance | 18 ohms |
| Sensitivity | 99 dB @ 1kHz |
| Sub-bass Extension | Within 6 dB of target down to 20 Hz (-0.8 dB at 30 Hz) |
| Tonal Tilt | -0.11 (negative is warmer, positive brighter) |
EQ preset to match the Harman target
Set a preamp of -1.0 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 | -0.1 dB | 0.70 |
| Peak | 742 Hz | +1.1 dB | 1.13 |
| Peak | 130 Hz | -1.1 dB | 1.51 |
| Peak | 1,584 Hz | -0.6 dB | 1.19 |
| Peak | 3,281 Hz | +0.9 dB | 4.08 |
| High shelf | 10,000 Hz | -7.9 dB | 0.70 |
| Peak | 8,077 Hz | +1.8 dB | 1.48 |
| Peak | 5,639 Hz | -1.4 dB | 6.00 |
| Peak | 9,669 Hz | +1.1 dB | 4.55 |
| Peak | 60 Hz | +0.1 dB | 2.11 |
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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