Overview

The Superlux HD681 is a semi-open professional monitor headphone from the Taiwanese manufacturer Superlux. Positioned as an entry-level product, it features a 50mm neodymium driver, 32Ω impedance, 98dB SPL, and a claimed frequency range of 10-30,000Hz. While its price point under 4,000 JPY in the Japanese market is appealing, a technical review reveals significant issues, particularly in its treble response, and its overall competitive advantages are limited.

Scientific Validity

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According to measurement data, the HD681’s frequency response is relatively good in the midrange from 100Hz to 2.5kHz. However, there is a bass boost of approximately +5dB, and more critically, multiple sharp peaks above 6kHz. This is a clear flaw, perceived as harsh sibilance that significantly compromises fidelity to the master recording. The THD (Total Harmonic Distortion), while increasing in the low frequencies, is within an acceptable range for its price. However, considering the problematic treble and the limited isolation 이슈 from its semi-open design, its overall performance remains at an intermediate level, a clear step down from transparent reproduction.

Technology Level

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The use of a 50mm neodymium driver is a standard industry approach and offers no particular technical advantage. The 32Ω impedance is designed for compatibility with general-purpose devices, but this is also a common specification. The semi-open enclosure design remains conventional, with no discernible acoustic engineering innovations. No technical papers or patents related to its internal structure or circuit design were found, suggesting it is likely based on an OEM design. With no proprietary technologies contributing to improved measurement performance, its technology level is assessed as industry average.

Cost-Performance

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The HD681 is priced at approximately 4,000 JPY in the Japanese market, but the Koss KSC75, which offers superior acoustic performance, is available for about 3,080 JPY. The KSC75 lacks the harsh treble peaks of the HD681 and has received better evaluations for its natural and faithful sound quality. Although the form factor is different, the KSC75 is an equivalent or superior option in terms of core performance, which is sonic fidelity. Based on the calculation (3,080 JPY ÷ 4,000 JPY = 0.77), the score is 0.8. The numerical data clearly shows that the HD681 is in an inferior position regarding pure acoustic performance for the price.

Reliability & Support

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While Superlux is an established audio equipment manufacturer in Taiwan, its support system in Japan is limited. The product warranty period is at the industry standard level, with no notably excellent support confirmed. The lack of public data on RMA rates or MTBF makes an objective assessment of reliability difficult. As an entry-level product, quality control is presumed to be at a standard level, but long-term durability and the comprehensiveness of after-sales service may be inferior to products from more established manufacturers. It is evaluated as having a typical risk level for a product from an emerging brand.

Rationality of Design Philosophy

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The design philosophy of aiming for intermediate characteristics between open-air and closed-back types with a semi-open design is rational in theory. The relatively flat midrange response, intended for monitoring applications, is also commendable. However, the multiple sharp peaks above 6kHz represent a tuning that is inconsistent with a scientifically-grounded pursuit of high-fidelity sound, thus undermining the rationality of the design. Furthermore, the existence of a competitor that offers superior acoustic performance at a lower cost diminishes the rationale for this product’s existence. The design follows basic acoustic principles, but the pursuit of modern rationality is judged to be incomplete.

Advice

The Superlux HD681 is an option for users who prefer a traditional headband design and want to keep their budget under 4,000 JPY. It is particularly worth considering for those who are averse to the ear-clip design of the Koss KSC75. However, if pure sound quality—specifically a natural and non-fatiguing sound—is the top priority, we strongly recommend spending the extra 1,000 JPY for the KSC75. If you choose the HD681, you should be aware that equalization to tame the harsh treble peaks will likely be necessary. For more serious monitoring environments, it is wise to expand the budget and consider higher-tier products.

(2025.7.23)