Short answer: the Letshuoer S12 Ultra. Both are rated 3.6/5 for sound quality (#707 and #720 of 1291 in-ear headphones), and the Letshuoer S12 Ultra costs $152.10 against $164.99 for the FiiO FD15, with sound quality a draw, the lower price decides it.
What the FiiO FD15 does well: A large 13.8mm dynamic driver with 32 ohm impedance and 112 dB/mW sensitivity makes it easy to drive loud from a phone. Watch for: Presence sits 5.8 dB below target with an 8.4 dB dip at 6.5 kHz, so vocals lose clarity and cymbals sound dull, and treble from 6 to 10 kHz is down 4.1 dB as well.
The case for the Letshuoer S12 Ultra: The median of 12 hobbyist measurements gives it a solid Harman preference score of 69 with a 2.18 dB spread, and its mids sit within about 0.5 dB of target, so vocals and instruments sound natural. The tradeoff: Presence sits about 4 dB low with a 6 dB dip near 3.4 kHz, so vocals and instruments lose some bite.
Buy the Letshuoer S12 Ultra. Both are rated the same for sound quality, and it costs $12.89 less than the FiiO FD15.
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A large 13.8mm dynamic driver with 32 ohm impedance and 112 dB/mW sensitivity makes it easy to drive loud from a phone.
Amazon $164.99 eBay
The median of 12 hobbyist measurements gives it a solid Harman preference score of 69 with a 2.18 dB spread, and its mids sit within about 0.5 dB of target, so vocals and instruments sound natural.
Amazon $152.10 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.
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Specifications Side By Side
| FiiO FD15 | Letshuoer S12 Ultra | |
|---|---|---|
| Price | $164.99 | $152.10 |
| Ranked | #720 of 1291 in In-Ear Headphones | #707 of 1291 in In-Ear Headphones |
| Form Factor | In-ear | In-ear |
| Back | Closed | Closed |
| Harman Preference Score | 69 (median of 7 squig.link measurements, calibrated to AutoEQ) | 69 (median of 12 squig.link measurements, calibrated to AutoEQ) |
| Deviation From Target | 2.52 dB standard deviation | 2.18 dB standard deviation |
| Tonal Tilt | -0.30 (negative is warmer, positive brighter) | -0.68 (negative is warmer, positive brighter) |
| Sub-bass Extension | Within 6 dB of target down to 20 Hz (-3.9 dB at 30 Hz) | Within 6 dB of target down to 20 Hz (+2.1 dB at 30 Hz) |
| Connection | Wired | Wired |
| Driver Type | Dynamic | Planar |
| Drivers | 1 x 13.8mm dynamic | 1 x 14.8mm planar magnetic |
| Impedance | 32 ohms | 16 ohms |
| Sensitivity | 112 dB/mW | - |
| Weight | 0 lbs (12 g) per earbud | - |
| Frequency Response | 10Hz - 40kHz (Manufacturer specified) | 20Hz - 40kHz (Manufacturer specified) |
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 FiiO FD15 from boizoff, breampike, ekaudio, iemocean, jaytiss, pw and timmyv; the Letshuoer S12 Ultra from aden, atechreviews, audioamigo, cqtek, eplv, flare, hbb, jaytiss, pw, soundignity, superreview and tonedeafmonk, all via squig.link.
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