Overview

The SP601 is Fosi Audio’s first HiFi passive bookshelf speaker pair. Per the manufacturer it uses a 6.5-inch HybridCone woofer (paper inner cone with aluminum outer layer) and a 1.5-inch silk dome tweeter in a rear-ported MDF enclosure, with claimed 44Hz–20kHz response, 4Ω nominal impedance and 85dB sensitivity [2][3]. It requires an external amplifier and is positioned for desktop, stereo and home-theater use.

Scientific Validity

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Independent Klippel NFS measurements reveal audible response issues. Erin’s CTA-2034 data shows a “dip-boost-dip-boost” tonality: midrange ~3dB down, followed by a 4–6kHz treble rise of ~3–4dB, and directivity behavior implying side-wall reflections stronger than the direct sound from roughly 2–7kHz—likely worsening in-room balance without treatment [1]. Burst decay indicates mild resonances around 4–5kHz at about −27dB [1]. Dynamic-range and multitone tests further show elevated upper-mid distortion at 96dB SPL and a practical single-speaker max of ~95dB before compression; in-room bass rolls off near ~70Hz despite the 44Hz catalog claim [1][3]. Substantial EQ (e.g., a gentle boost around ~400Hz and a cut near ~4kHz) is needed to approach neutrality [1].

Technology Level

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The HybridCone woofer and silk-dome tweeter are established choices rather than novel advances [2][3]. Cabinet construction appears basic, with third-party inspection noting minimal internal damping/brace choices—cost savers that don’t elevate sophistication [1]. Overall implementation is industry-average with no clear innovation that would materially raise the performance ceiling.

Cost-Performance

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At 399.99 USD per pair [2], an equal-or-better alternative is the Polk Monitor XT20 at 225 USD (pair) on the official site, with published CTA-2034 data and generally more even response/directivity than the SP601’s irregular mid/treble behavior [4][5]. Calculation: 225 ÷ 399.99 = 0.563 → 0.6 (first-decimal rounding). Given the measured shortcomings of the SP601, the Polk offers a stronger value proposition.

Reliability & Support

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Fosi is well known for compact amplifiers, but this is its first passive loudspeaker; real-world reliability data in this category is limited. The company lists a 24-month limited warranty and a 30-day return policy, which is decent for the price bracket, but speaker-specific support track record is not yet established [2][6]. Construction choices (light damping/bracing) raise some durability/performance questions [1].

Rationality of Design Philosophy

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From a transparency-first standpoint, the voicing and radiation pattern choices are counterproductive: the measured upper-mid/treble emphasis, irregular directivity through 2–7kHz, and cabinet resonances work against neutral, reflection-robust in-room sound [1]. Investment in enclosure damping and crossover behavior would likely have yielded larger, measurable gains than the materials mix touted in marketing [2][3].

Advice

If you want neutral reproduction around this budget, prioritize designs with clean CTA-2034 curves and controlled directivity. The Polk Monitor XT20 is a safer bet at a lower price and with published Klippel data [4][5]. If you already own the SP601, use side-wall absorption, add a subwoofer crossed ~80Hz, and apply corrective EQ (boost around ~400Hz and cut near ~4kHz) to tame the mid/treble imbalance [1].

References

[1] Erin’s Audio Corner, “Fosi SP601 Bookshelf Speaker Review,” https://www.erinsaudiocorner.com/loudspeakers/fosi_sp601/ (2025-07-22). Klippel NFS; CTA-2034; tweeter reference; no grille; distortion at 86/96dB; multitone at 70/79/87/96dB; dynamic-range sweeps 76/86/96/102dB.
[2] Fosi Audio (official), “SP601 Bookshelf Passive Speakers (product listing),” https://fosiaudio.com/products/sp601-orange-version-passive-bookshelf-speakers (accessed 2025-08-20). Price and sales terms; 30-day money-back.
[3] Fosi Audio (official), “SP601 Orange Version – Specifications,” https://fosiaudio.com/pages/sp601-orange-version-bookshelf-speakers (accessed 2025-08-20). Driver materials/sizes; FR 44Hz–20kHz; 4Ω; 85dB.
[4] Erin’s Audio Corner, “Polk Monitor XT20 Bookshelf Speaker Review,” https://www.erinsaudiocorner.com/loudspeakers/polk_xt20/ (2022-01-08). CTA-2034 dataset published.
[5] Polk Audio (official), “Monitor XT20,” https://www.polkaudio.com/en-us/product/system-products/monitor-xt20/300151.html (accessed 2025-08-20). Current pair price shown as 225 USD.
[6] Fosi Audio (official), “24-Month Warranty,” https://fosiaudio.com/pages/fosi-audio-warranty (accessed 2025-08-20). Warranty terms.

(2025.8.21)