Short answer: a tie on sound quality. Both are rated 3.3/5 (#917 and #959 of 1369 in-ear headphones) at nearly the same price ($49.99 vs $45), so choose on features and fit.
What the KZ ZSX does well: A one dynamic plus five balanced armature hybrid at a budget price, with sub-bass within 1 dB of target and midbass about 2.4 dB above it, so electronic and hip hop tracks get punchy, full lows. Watch for: Across eight hobbyist measurements on squig.link a 10 dB peak near 11.9 kHz stands out, which can make cymbals and hi hats sound splashy and tizzy, while a 6.8 dB dip near 6.5 kHz leaves the treble uneven.
Why pick the qdc x FitEar Superior EX: A published AutoEQ preset corrects its response toward the Harman target, so a few minutes of EQ setup closes most of the gap. The catch: Treble about 4 dB below target from 3 to 10 kHz, which can sound dull or veiled next to brighter headphones.
Buy the KZ ZSX or the qdc x FitEar Superior EX 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.
A one dynamic plus five balanced armature hybrid at a budget price, with sub-bass within 1 dB of target and midbass about 2.4 dB above it, so electronic and hip hop tracks get punchy, full lows.
Linsoul $49.99 eBay
A published AutoEQ preset corrects its response toward the Harman target, so a few minutes of EQ setup closes most of the gap.
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Specifications Side By Side
| KZ ZSX | qdc x FitEar Superior EX | |
|---|---|---|
| Price | $49.99 | 45.00 |
| Ranked | #917 of 1369 in In-Ear Headphones | #959 of 1369 in In-Ear Headphones |
| Form Factor | In-ear | In-ear |
| Back | Closed | Closed |
| Harman Preference Score | 65 (measured by crinacle, via AutoEQ) | 65 (median of 4 squig.link measurements, calibrated to AutoEQ) |
| Deviation From Target | 2.73 dB standard deviation | 2.57 dB standard deviation |
| Tonal Tilt | -0.63 (negative is warmer, positive brighter) | -0.72 (negative is warmer, positive brighter) |
| Connection | Wired | Wired |
| Driver Type | Hybrid (1 dynamic + 5 balanced armature) | Dynamic |
| Drivers | 1 x dynamic + 5 x balanced armature | 1 x 10mm coaxial dual-magnetic dynamic driver |
| Impedance | 24 ohms | 16 ohms |
| Sensitivity | 111 dB | 100 dB SPL/mW |
| Frequency Response | 7Hz - 40kHz (Manufacturer specified) | 10Hz - 40kHz |
| Sub-bass Extension | Within 6 dB of target down to 20 Hz (-0.9 dB at 30 Hz) | Within 6 dB of target down to 20 Hz (-0.7 dB at 30 Hz) |
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 KZ ZSX from aden, bassyalexander, eplv, harutohiroki, lown-fi, melatonin, pw and vortexreviews; the qdc x FitEar Superior EX from aden, ekaudio, faxepremium and smirk, all via squig.link.
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