Short answer: a tie on sound quality. Both are rated 4.2/5 (#260 and #270 of 1291 in-ear headphones) at nearly the same price ($99.99 vs $99.99), so choose on features and fit.
What the Fosi Audio IM4 does well: The median of 18 hobbyist measurements gives it a very good Harman preference score of 76 with a 1.77 dB spread, and its mids sit within about 1.2 dB of target, so vocals and instruments sound natural. The catch: A 4.6 dB peak near 8.2 kHz can make cymbals and sibilance sound sharp.
Why pick the Moondrop Concerto: The median of 9 hobbyist measurements gives it a very good Harman preference score of 76 with a 1.74 dB spread, and its mids sit within about 1.4 dB of target, so vocals and instruments sound natural. Watch for: Presence sits about 4.7 dB low with a 5.9 dB dip near 4.7 kHz, so vocals and instruments lose some bite.
Buy the Fosi Audio IM4 or the Moondrop Concerto on features: they are rated the same for sound quality at close to the same price.
Still deciding? The full Headphones rankings cover every ranked option.
The median of 18 hobbyist measurements gives it a very good Harman preference score of 76 with a 1.77 dB spread, and its mids sit within about 1.2 dB of target, so vocals and instruments sound natural.
Amazon $99.99 eBay
The median of 9 hobbyist measurements gives it a very good Harman preference score of 76 with a 1.74 dB spread, and its mids sit within about 1.4 dB of target, so vocals and instruments sound natural.
Amazon $99.99 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
| Fosi Audio IM4 | Moondrop Concerto | |
|---|---|---|
| Price | $99.99 | $99.99 |
| Ranked | #260 of 1291 in In-Ear Headphones | #270 of 1291 in In-Ear Headphones |
| Form Factor | In-ear | In-ear |
| Back | Closed | Closed |
| Harman Preference Score | 76 (median of 18 squig.link measurements, calibrated to AutoEQ) | 76 (median of 9 squig.link measurements, calibrated to AutoEQ) |
| Deviation From Target | 1.77 dB standard deviation | 1.74 dB standard deviation |
| Tonal Tilt | -0.23 (negative is warmer, positive brighter) | -0.21 (negative is warmer, positive brighter) |
| Sub-bass Extension | Within 6 dB of target down to 20 Hz (-0.7 dB at 30 Hz) | Within 6 dB of target down to 20 Hz (-2.5 dB at 30 Hz) |
| Connection | Wired | Wired |
| Driver Type | Dynamic | Hybrid (1 planar magnetic + 1 xMEMS) |
| Drivers | 1 x 10mm dynamic | 1 x 13mm planar magnetic + 1 x xMEMS solid-state |
| Impedance | 21 ohms | - |
| Sensitivity | 109 dB | - |
| Weight | 0 lbs (7 g) per earbud | - |
| Frequency Response | 20Hz - 20kHz (Manufacturer specified) | 20Hz - 20kHz (Manufacturer specified) |
| Built-in Microphone | No | Yes |
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 Fosi Audio IM4 from atechreviews, audioamigo, boizoff, digaoreviews, elrics, hu-fi, jaytiss, joycesreview, musicafe, practiphile, pw, samreviews, soundcheck39, soundignity, superreview, theaudiostore, tonedeafmonk and treblewellxtended; the Moondrop Concerto from boizoff, csi-zone, gadgetrytech, hu-fi, jaytiss, soundignity, superreview, timmyv and vsg, all via squig.link.
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