Short answer: the EarAcoustic STA Pro. It ranks #854 of 1291 in-ear headphones by sound quality, rated 3.4/5, at $49.90; the KZ ZSX ranks #901, rated 3.3/5, and costs $49.99, which makes this an easy call rather than a real tradeoff.
Why pick the EarAcoustic STA Pro: A broadly balanced tuning with a preference score of 67 against the Harman target. The catch: An uneven response, 2.4 dB standard deviation from target.
Why pick the KZ ZSX: 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.
Buy the EarAcoustic STA Pro. It is rated higher for sound quality than the KZ ZSX and costs less, so it is the default pick unless a specific strength of the other one matters more to you.
Still deciding? The full Headphones rankings cover every ranked option.
A broadly balanced tuning with a preference score of 67 against the Harman target.
Linsoul $49.90 eBay
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 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
| EarAcoustic STA Pro | KZ ZSX | |
|---|---|---|
| Price | $49.90 | $49.99 |
| Ranked | #854 of 1291 in In-Ear Headphones | #901 of 1291 in In-Ear Headphones |
| Form Factor | In-ear | In-ear |
| Back | Closed | Closed |
| Harman Preference Score | 67 (median of 3 squig.link measurements, calibrated to AutoEQ) | 65 (measured by crinacle, via AutoEQ) |
| Deviation From Target | 2.41 dB standard deviation | 2.73 dB standard deviation |
| Tonal Tilt | -0.55 (negative is warmer, positive brighter) | -0.63 (negative is warmer, positive brighter) |
| 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 (-0.9 dB at 30 Hz) |
| Connection | Wired | Wired |
| Driver Type | Dynamic | Hybrid (1 dynamic + 5 balanced armature) |
| Drivers | 2 x dynamic drivers (1 x 10mm graphene + 1 x 6mm titanium-plated) | 1 x dynamic + 5 x balanced armature |
| Impedance | 18 ohms | 24 ohms |
| Sensitivity | 113 dB | 111 dB |
| Frequency Response | 10Hz - 30kHz | 7Hz - 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 EarAcoustic STA Pro from avishai, lumerion and pw; the KZ ZSX from aden, bassyalexander, eplv, harutohiroki, lown-fi, melatonin, pw and vortexreviews, all via squig.link.
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