Overview

The Fostex TH909 is an open-back dynamic headphone derived from the company’s flagship TH900MK2. It features 50mm Biodyna drivers and a unique dual-layer metal grill structure, with a beautiful Urushi lacquer finish on Mizume cherry wood. Fostex, established in 1973 as a subsidiary of Foster Electric, has a long track record in speaker unit development and manufacturing. This product combines traditional lacquer techniques from the Sakamoto Urushi Kogei workshop with modern acoustic technology.

Scientific Validity

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According to measurement data, the THD is 0.16%, which is a good level, but it does not reach the standard of top-tier products, which is below 0.05%. The frequency response covers a wide range of 5Hz-45kHz, and the sensitivity of 100dB/mW is excellent, indicating it is easy to drive. The 25Ω impedance is also low, enabling use with a wide range of equipment. Phase characteristics are excellent, remaining within approximately 10 degrees, which is better than the Sennheiser HD800S (approx. 20 degrees) and Focal Utopia (approx. 50 degrees). However, as the THD value is not at the highest standard, it does not achieve full transparency.

Technology Level

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The Biodyna driver technology, combining biocellulose and inorganic fibers, achieves excellent transient response and dynamic range with its powerful 1.5 Tesla magnetic circuit. In addition to the 50mm driver inherited from the TH900MK2, the newly developed dual-layer metal grill structure optimizes acoustic characteristics by varying the size and shape of each opening. Despite its light weight of 390g, it has a robust construction that excels at preserving phase information. These technologies show originality and a level of technology above the industry standard, though they are not exceptionally innovative.

Cost-Performance

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Against the TH909’s typical price of 2,000 USD, the Hifiman Edition XS, which offers equivalent or superior performance, is available for around 400 USD. The Edition XS features a planar magnetic open-back design, 18Ω impedance, 92dB sensitivity, an 8Hz-50kHz frequency response, and exhibits excellent THD performance that surpasses the TH909. The calculation is: 400 USD ÷ 2,000 USD = 0.2. Even considering the lacquer finish and minor performance differences the TH909 provides, the 5x price difference is not justified. Multiple high-performance headphones are available at the same price point, making its cost-performance extremely poor.

Reliability & Support

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Fostex provides a 1-year product warranty, which is standard for the industry. As a subsidiary of Foster Electric with over 50 years of experience, the company has an established sales network both domestically and internationally. Repair support is available for a fee after the warranty expires, and proper after-sales service is provided for purchases made through authorized dealers. However, the warranty period and repair system do not lead the industry, and there is no data to confirm superior reliability compared to emerging manufacturers. We evaluate it as being at an industry-average level.

Rationality of Design Philosophy

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The scientific approach of improving measurement performance through Biodyna driver technology and an open-back design is commendable. The acoustic optimization via the dual-layer grill structure and improvements in phase characteristics also indicate a rational design direction. However, the high price is irrational when competing products can achieve equivalent or better measurement performance at a much lower cost. The focus on decorative elements like the lacquer finish deviates from the pure pursuit of sound quality and lacks a commitment to achieving breakthrough performance at a disruptive price. While the science-based design is recognized, there is a clear inclination towards luxury specifications that ignore cost efficiency.

Advice

While the TH909 is an attractive product that combines excellent measurement performance with traditional craftsmanship, it cannot be recommended from a cost-performance perspective. For those considering a purchase in this price range, we strongly recommend combining the Hifiman Edition XS (around 400 USD) with a high-quality headphone amplifier and DAC. This setup will achieve a level of sound quality and overall system transparency that far exceeds the TH909 alone. Unless you find special value in the lacquered appearance or have a strong attachment to the Fostex brand, numerous more rational choices exist. If sound quality is your priority, consider other options; if aesthetics are your priority, consider it a purchase of an art piece.

(2025.7.27)