Overview

The final GRID01 (model number: RE-MAKE05-01) is the debut product from REB, a community-oriented sub-brand launched by S’NEXT Co., Ltd. — the parent company of final audio. Released in November 2023 and co-developed with final’s E3000 driver engineering team, it is positioned as an entry-tier wired IEM at approximately 40 USD in Japan, with no official US retail presence confirmed [1]. The product centres on two pillars: the proprietary REB-Core Gen1 dynamic driver and the MAKE Nozzle interchangeable filter system, which enables passive acoustic tuning via screw-in nozzle filters without tools. It received a VGP 2024 divisional award in the wired earphone category. REB’s brand philosophy emphasises user maintainability and community engagement through a dedicated tuning-recipe sharing platform called “MAKER’S.”

Scientific Validity

The manufacturer publishes only sensitivity (97 dB) and impedance (17 Ω); no frequency response range, THD, or other audio performance specifications are disclosed [1]. No credible professional third-party measurements are available for the GRID01.

An informal frequency response measurement obtained using an IEC711 clone coupler and REW analysis software [2] shows treble roll-off beginning around 9 kHz, with the measurement author describing poor high-frequency extension overall. A separate informal comparative measurement corroborates a closely similar tuning profile to the final E3000 [2]. Based on this qualitative FR data, the frequency response deviation from the Harman target is conservatively estimated at approximately ±4 dB — between the acceptable and problematic ranges. No THD data exists from any source. S/N ratio is not applicable to a passive IEM. Given that the sole available FR data points to deviation in the between-acceptable-and-problematic range and no additional metrics are available to assess overall performance, measured performance is below standard.

Technology Level

The GRID01 is a fully in-house design, co-developed by final’s established f-Core driver engineering team and the REB brand [1]. The REB-Core Gen1 dynamic driver employs adhesive-free thermal bonding of the silicone surround to the diaphragm — a specific manufacturing process carried forward from final’s f-Core development lineage, representing genuine accumulated process know-how that differentiates it from commodity driver construction. No patents were independently confirmed for either the REB-Core Gen1 driver or the MAKE Nozzle system. The tunable nozzle filter concept and single dynamic driver architecture are established technologies as of 2023; comparable tunable-nozzle IEMs exist across the industry. The product is entirely analog and mechanical with no DSP integration, app control, or software component [1]. Overall, the in-house process know-how supports a slightly above-average technology score, while the absence of confirmed patent differentiation or digital integration keeps the evaluation moderate.

Cost-Performance

This site evaluates based solely on functionality and measured performance values, without considering driver types or configurations.

The GRID01 provides wired stereo IEM playback via a fixed 3.5mm cable with no DSP, ANC, or wireless capability. The market price used for this review is 40 USD [1].

The 7Hz Salnotes Zero is available at 20.99 USD at Linsoul US [4] and delivers equivalent-or-better user-facing functions: wired IEM stereo playback with 3.5mm connectivity, additionally providing a detachable 0.78mm 2-pin cable — a functional advantage the GRID01 does not offer. Audio Science Review measurements [3] confirm the following performance for the Salnotes Zero:

• Frequency response deviation from Harman target: approximately ±2–3 dB (ASR: “compliance with our target is excellence”; minor peak around 12.7 kHz) vs. GRID01’s estimated approximately ±4 dB [2] — Salnotes Zero better
• THD: impressively low per ASR measurements (conservatively ≤0.1% at typical listening levels; ASR: “impressively low distortion”) vs. GRID01 THD, which has no available measurement data from any source

This comparison is provisional due to the absence of credible professional measurements for the GRID01. Based on currently available data, the Salnotes Zero shows confirmed measurement-backed performance that is equal or better across both evaluated metrics, while the GRID01 has no verified measurement baseline and an informally estimated FR deviation that is inferior.

CP = 20.99 USD ÷ 40 USD = 0.52 → 0.5

Reliability & Support

The standard warranty is 1 year from date of purchase — below the 2-year category average — with an optional extension to 2 years available only at time of purchase via the official REB store [5]. The GRID01 is a passive wired IEM with no active electronics; the stainless steel housing is robust and mechanically simple, giving it inherent structural advantages against component degradation. Post-warranty paid repair is available through final Inc.’s authorized service system. No failure rate statistics (RMA ratio, MTBF) are available for this inaugural REB product. Cable microphonics noted by users in informal reviews are an inherent characteristic of the thin OFC cable and do not represent a manufacturing defect. REB has no long-term reliability track record as a newly established sub-brand. The shorter warranty and limited brand track record are balanced by the simple passive construction, so the reliability and support score remains neutral.

Rationality of Design Philosophy

The GRID01’s design philosophy targets entry-tier acoustic performance combined with a user-driven tuning ecosystem via passive acoustic filter swapping. The core driver engineering rationale — adhesive-free thermal bonding for reduced assembly-variance and claimed lower distortion — is mechanically sound, though independent data validating these distortion claims is unavailable. Cost allocation includes a stainless steel housing and final TYPE E earpieces that serve build quality and user experience rather than directly improving measured acoustic performance. The MAKE Nozzle filter system achieves passive acoustic tuning through mechanical means that a software DSP implementation would accomplish more precisely, more flexibly, and at lower marginal cost; the primary value proposition of the physical filter approach is tactile community engagement rather than measurable acoustic transparency improvement. No manufacturer audio performance specifications are published, limiting independent verification of any acoustic claims. Overall, the design direction is neither measurement-first nor scientifically irrational, which supports a neutral rationality score.

Advice

The GRID01 is best suited to users who are specifically interested in the REB MAKE ecosystem and the hands-on experience of passive filter tuning as a hobbyist activity. Users whose primary goal is maximising verified acoustic performance per dollar will find better-supported options with confirmed professional measurement data at a lower price — the 7Hz Salnotes Zero at 20.99 USD is the clearest alternative [3][4].

Buyers should note that realising the full tuning capability of the MAKE Nozzle system requires purchasing additional filter sets separately (approximately 17 to 20 USD in Japan per set), raising the effective total system cost beyond the 40 USD body price. The 1-year base warranty is shorter than the category average; purchasing the optional 2-year extension at time of order is advisable. No confirmed US retail presence exists; international buyers should verify availability through authorized channels before purchasing.

References

[1] REB Audio - GRID01 Official Product Page - https://reb-audio.com/products/grid-01 - Accessed 2026-05-26

[2] Yurufuwa Audio Diary (personal blog) - “REB FES vol.01 / GRID01 周波数特性” (informal FR measurement) - https://el-snow.hatenablog.com/entry/2023/07/31/150631 - Accessed 2026-05-26 - IEC711 clone coupler (IEC60318-4), REW V5.20.13, MOTU M2 interface, 192kHz/24-bit, Final TYPE E Black M ear tips; personal blog, not a professional measurement lab

[3] Audio Science Review - “7Hz Salnotes Zero IEM Review” - https://www.audiosciencereview.com/forum/index.php?threads/7hz-salnotes-zero-iem-review.50226/ - Accessed 2026-05-26

[4] Linsoul - “7Hz Salnotes Zero” (3.5mm, no microphone version) - https://www.linsoul.com/products/7hz-salnotes-zero - Accessed 2026-05-26

[5] final Audio - “Warranty and After Service FAQ” - https://snext-final.com/en/series/faq/id=770 - Accessed 2026-05-26

(2026.5.31)