Overview

The Final Audio S4000 is a dual balanced-armature in-ear monitor listed at 329 USD in the US market, featuring a stainless-steel housing, a newly developed “tone chamber system,” and a repair-friendly structure. It ships with a soft 8-core silver-coated OFC cable using standard 0.78 mm 2-pin connectors, Fusion-G eartips, and supports either cable-down or over-ear wear. Key catalog specs include 48 Ω impedance and 112 dB sensitivity. [1][3]

Scientific Validity

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As of August 18, 2025, no credible third-party B&K 5128/IEC 60318-4 measurements of the S4000’s frequency response, distortion, or isolation are publicly available. Therefore, we default to a neutral 0.5 pending independent data. Manufacturer specifications confirm dual full-range BA drivers arranged in a horizontal opposition layout, 48 Ω impedance, and 112 dB sensitivity, but do not disclose THD or isolation figures relevant to audibility thresholds. This score will warrant revision when reliable lab data emerges. [1]

Technology Level

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The S4000 exhibits several thoughtful engineering choices: a “tone chamber system” to control the front-volume acoustics of the BA drivers, dual full-range BAs mounted in a horizontal opposition configuration aimed at reducing self-resonance, precision stainless-steel housings, and a repair-forward, adhesive-minimized assembly. Detachable 2-pin cabling and a two-year warranty are also positives. These are competent, mildly original implementations rather than industry-leading breakthroughs. [1]

Cost-Performance

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Basis price (denominator): 329 USD (current representative US price). [3]

Cheapest equivalent-or-better comparator: Moondrop Chu II (wired IEM with detachable 2-pin cable). Third-party graphs (B&K 5128) show a response closely tracking modern targets, and the manufacturer publishes a THD figure ≤0.5% at 1 kHz/94 dB. On user-visible functions (wired operation, passive isolation form factor, detachable cable) and audibility-relevant axes (target-conforming FR with low distortion at normal levels), Chu II is judged equivalent-or-better for fidelity. Market price: 19 USD. Calculation: 19 USD ÷ 329 USD = 0.06 → rounded to one decimal place = 0.1. (Provisional until S4000 third-party measurements appear.) [4][5][3]

Reliability & Support

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Final provides a two-year warranty for the S4000. The stainless-steel shell, standard 2-pin interface, and a design intended for disassembly/repair indicate sensible serviceability and durability considerations. No public failure-rate data was found; support quality appears typical for this segment. [1]

Rationality of Design Philosophy

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The development direction—mechanically controlling driver interaction (horizontal opposition), managing front volume via a tone chamber, and enabling repairability—is rational from an engineering perspective. However, without published independent measurements demonstrating transparent-level outcomes (e.g., target-conforming FR within tight tolerances, very low distortion), we cannot judge the approach as strongly validated. Hence a neutral score. [1]

Advice

If you specifically value a stainless-steel micro-shell, dual BA architecture, and a repair-friendly build, the S4000 offers a distinctive package. For measurable fidelity at minimal cost, proven budget IEMs like the Moondrop Chu II already deliver target-aligned response for a fraction of the price, which translates into dramatically stronger objective value until credible S4000 lab data becomes available. [4][5]

References

[1] final. “S4000 – Features/Specs (official product page).” https://final-inc.com/en/products/s4000 (accessed 2025-08-18). Specs: 2× full-range BA (horizontal opposition), stainless-steel housing, 0.78 mm 2-pin, sensitivity 112 dB, impedance 48 Ω, warranty 2 years.

[2] AV Watch (JA). “final、トーンチャンバーシステム採用の新BAイヤフォン『S5000/4000』.” https://av.watch.impress.co.jp/docs/news/1633825.html (2024-10-23; accessed 2025-08-18). Launch announcement; Japan prices S4000 44,800円, S5000 54,800円.

[3] Audio46. “Final Audio S4000 Earphones (US product listing).” https://audio46.com/products/final-audio-s4000-earphones (accessed 2025-08-18). Representative US price 329 USD.

[4] Moondrop (official). “MOONDROP CHU II – Specifications.” https://moondroplab.com/en/products/chu-ii (accessed 2025-08-18). THD ≤0.5% @1 kHz/94 dB; effective FR 20 Hz–20 kHz (IEC 60318-4).

[5] Crinacle / Hangout.Audio. “5128 Graph Tool – Chu 2.” https://graph.hangout.audio/iem/5128/?share=Chu_2 (accessed 2025-08-18). Third-party frequency-response measurement on B&K 5128.

(2025.8.19)