Short answer: a tie on sound quality. Both are rated 4.0/5 (#418 and #446 of 1291 in-ear headphones) at nearly the same price ($55 vs $53.99), so choose on features and fit.
The case for the Cozoy D2: The median of 16 hobbyist measurements gives it a solid Harman preference score of 74 with a 2.11 dB spread, and its mids sit within about 0.7 dB of target, so vocals and instruments sound natural. Watch for: Presence sits about 3.6 dB low with a 7.5 dB dip near 6.3 kHz, so vocals and instruments lose some bite.
What the KZ ZS12 Pro X does well: The median of 6 hobbyist measurements gives it a solid Harman preference score of 73 with a 2.01 dB spread, and its mids sit within about 0.5 dB of target, so vocals and instruments sound natural. The catch: An 8.7 dB peak near 10.9 kHz can make cymbals and sibilance sound sharp.
Buy the Cozoy D2 or the KZ ZS12 Pro X on features: they are rated the same for sound quality at close to the same price.
Looking for alternatives? See the complete Headphones rankings.
The median of 16 hobbyist measurements gives it a solid Harman preference score of 74 with a 2.11 dB spread, and its mids sit within about 0.7 dB of target, so vocals and instruments sound natural.
Cozoy $55 eBay
The median of 6 hobbyist measurements gives it a solid Harman preference score of 73 with a 2.01 dB spread, and its mids sit within about 0.5 dB of target, so vocals and instruments sound natural.
Amazon $53.99 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.
As an eBay Partner, we may be compensated if you make a purchase.
Specifications Side By Side
| Cozoy D2 | KZ ZS12 Pro X | |
|---|---|---|
| Price | $55 | $53.99 |
| Ranked | #418 of 1291 in In-Ear Headphones | #446 of 1291 in In-Ear Headphones |
| Form Factor | In-ear | In-ear |
| Back | Closed | Closed |
| Connection | Wired | Wired |
| Driver Type | Dynamic | Hybrid (1 dynamic + 5 balanced armature) |
| Drivers | 1 x 10mm dynamic + 1 x 6mm dynamic | 1 x dynamic + 5 x balanced armature |
| Impedance | 20 ohms | 25 ohms |
| Frequency Response | 10Hz - 50kHz (Manufacturer specified) | 20Hz - 40kHz (Manufacturer specified) |
| Harman Preference Score | 74 (median of 16 squig.link measurements, calibrated to AutoEQ) | 73 (median of 6 squig.link measurements, calibrated to AutoEQ) |
| Deviation From Target | 2.11 dB standard deviation | 2.01 dB standard deviation |
| Tonal Tilt | -0.09 (negative is warmer, positive brighter) | +0.53 (negative is warmer, positive brighter) |
| Sub-bass Extension | Within 6 dB of target down to 20 Hz (-2.9 dB at 30 Hz) | Within 6 dB of target down to 20 Hz (-3.1 dB at 30 Hz) |
| Sensitivity | - | 106 dB/mW |
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 Cozoy D2 from aftersound, ankramutt, audioamigo, bassaudio, digaoreviews, ducbloke, elrics, fahryst, fernandagunsan, hbb, jaytiss, musicafe, practiphile, soundcheck39, superreview and tonedeafmonk; the KZ ZS12 Pro X from audioamigo, eplv, obodio, pw, tdl and tonedeafmonk, all via squig.link.
Related Headphone Comparisons
How Cozoy D2 compares with other leading options: