Short answer: the ThieAudio Monarch MKII. It ranks #69 of 1291 in-ear headphones by sound quality, rated 4.6/5, at $999; the Symphonium Audio Helios ranks #93, rated 4.5/5, and costs $1,099, so there is little reason to consider the other one.
The case for the ThieAudio Monarch MKII: A preference score of 81 from crinacle’s measurement and just 1.45 dB of deviation make it one of the most accurate in-ears available. Watch for: Those measurements show a 5.6 dB dip near 6.5 kHz and treble about 2.6 dB below target, which softens cymbal attack slightly.
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. 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 MKII. It is rated higher for sound quality than the Symphonium Audio Helios and costs less, which makes it the one to get unless you need something the other one does better.
Still deciding? The full Headphones rankings cover every ranked option.
A preference score of 81 from crinacle’s measurement and just 1.45 dB of deviation make it one of the most accurate in-ears available.
AliExpress $999.00 eBay
One of the smoothest in-ears measured, with a 1.57 dB standard deviation from the Harman target and a preference score of 80.
Headphones.com $1,099.00 eBayPrices on this page were last checked October 16, 2026 at 5:46 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.
As an eBay Partner, we may be compensated if you make a purchase.
Specifications Side By Side
| ThieAudio Monarch MKII | Symphonium Audio Helios | |
|---|---|---|
| Price | $999.00 | $1,099.00 |
| Ranked | #69 of 1291 in In-Ear Headphones | #93 of 1291 in In-Ear Headphones |
| Form Factor | In-ear | In-ear |
| Back | Closed | Closed |
| Harman Preference Score | 81 (measured by crinacle, via AutoEQ) | 80 (measured by HypetheSonics, via AutoEQ) |
| Deviation From Target | 1.45 dB standard deviation | 1.57 dB standard deviation |
| Tonal Tilt | -0.22 (negative is warmer, positive brighter) | +0.02 (negative is warmer, positive brighter) |
| Connection | Wired | Wired |
| Driver Type | Hybrid (1 dynamic + 6 balanced armature + 2 electrostatic) | Balanced armature |
| Drivers | 1 x 10mm dynamic + 6 x balanced armature + 2 x electrostatic | - |
| Impedance | 36 ohms | 8.5 ohms |
| Sensitivity | 108 dB/mW | 104 dB/Vrms |
| Frequency Response | 20Hz - 20kHz (Manufacturer specified) | 12Hz - 24kHz (Manufacturer specified) |
| Sub-bass Extension | Within 6 dB of target down to 20 Hz (-0.3 dB at 30 Hz) | Within 6 dB of target down to 20 Hz (-1.3 dB at 30 Hz) |
| Built-in Microphone | - | No |
Frequency Response Compared
Both headphones’ measurements overlaid on the Harman target. Above the target sounds louder in that range, below it quieter. Each curve is the median of several independent measurements, shifted so its 500 Hz to 2 kHz average sits at 0 dB, so only the tuning is compared.
Measurement data: the ThieAudio Monarch MKII from aden, aftersound, audioamigo, bloomaudio, bukanaudiophile, dentreviews, dl, eliseaudio, gadgetrytech, harutohiroki, hbb, iemworld, jacstone, jaytiss, joshtbvo, joycesreview, lown-fi, mmagtech, musicafe, nymz, precog, recode, sai, seanwee, sl0the, smirk, superreview, tgx78, theaudiostore, therollo9, timmyv, tonedeafmonk, treblewellxtended and vsg; the Symphonium Audio Helios from achoreviews, aden, aftersound, animagus, banzai1122, bloomaudio, cqtek, eliseaudio, freeryder05, harutohiroki, hbb, nymz, precog, recode, smirk, superreview, tgx78, timmyv and vsg, all via squig.link.
Related Headphone Comparisons
More top alternatives to ThieAudio Monarch MKII: