Overview

The STAX SR-X9000 is a new flagship model announced in 2022 by STAX, a Japanese electrostatic headphone specialist manufacturer. It adopts the newly developed MLER-3 (Multi-Layer-Elect-Rods) 4-layer fixed electrode technology and features an ultra-thin engineering film diaphragm that is 20% larger than the previous SR-009S. It employs a push-pull electrostatic driver with 5-42,000Hz frequency response, 145kΩ impedance, and 580V DC bias voltage, weighing 432g. The market price is 4620 USD (dedicated amplifier sold separately), and the manufacturing period requires approximately 8 months.

Scientific Validity

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The SR-X9000 demonstrates excellent performance close to transparency level in measurement results. The nominal specifications indicate THD+N below 0.01% and S/N ratio above 100dB. The frequency response is designed within ±3dB for 5-42,000Hz, with excellent flatness targeting ±1dB within the mid-high range. Crosstalk is designed to achieve -70dB or below, and improvements have been made to the 6kHz vicinity dip pointed out in the predecessor SR-009S. The improvements through MILER-3 technology are expected to enhance measurement transparency, indicating potential for scientifically effective sound quality improvements.

Technology Level

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The MLER-3 (Multi-Layer-Elect-Rods) technology represents a groundbreaking design at industry-leading standards. It integrates a 4-layer structure combining mesh electrodes with conventional etching electrodes through thermal diffusion bonding, dramatically reducing air resistance. The 20% larger diaphragm and adoption of ultra-thin engineering film achieve significant improvements in both transient characteristics and frequency response. The adoption of machined aluminum enclosures and 6N OFC silver-coated cables is also technically advanced. These technological innovations directly contribute to measurement performance improvements, representing a new pinnacle in electrostatic driver technology.

Cost-Performance

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The SR-X9000 employs a specialized electrostatic driver system, requiring a dedicated, expensive amplifier (e.g., SRM-700S at 3100 USD) to perform optimally. This brings the total system cost to 7720 USD.

For this evaluation, we compare its “pure acoustic performance” against alternatives that can achieve equivalent or superior results for less, regardless of driver technology. The planar magnetic HiFiMan Arya Stealth Magnet (500 USD) has been shown in multiple third-party measurements to exhibit extremely low distortion, rivaling or even surpassing the SR-X9000 in that regard.

When comparing the SR-X9000 system to the performance offered by the Arya combined with a standard high-quality amplifier like the Fosi Audio V3 (133 USD), for a total of about 633 USD, the SR-X9000’s twelve-fold price increase is not justified by an overwhelming superiority in acoustic performance. Therefore, based on the calculation of 633 USD ÷ 7720 USD = 0.082, its cost-performance is rated as extremely low.

Reliability & Support

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The SR-X9000 has reported reliability issues. Multiple cases of channel imbalance occurrence have been reported and are drawing attention within the industry. The warranty period is standard at 1 year, but out-of-warranty repair costs are set at approximately 2333 USD, which is expensive. The manufacturing period is long at 8 months, and there are challenges with supply capacity relative to demand. STAX’s technical support system is limited, and these factors result in industry-average evaluation for reliability and support aspects.

Rationality of Design Philosophy

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While electrostatic driver technology is a rational approach that contributes to measurement performance improvement, the design requiring dedicated amplifiers significantly impairs convenience. Considering that equivalent measurement performance can be substituted with planar magnetic headphones, the necessity as dedicated equipment is questionable. The 580V DC bias voltage poses challenges from a safety perspective, and reliability issues suggest fundamental design flaws. While technological advancement is appreciable, the design philosophy that sacrifices practicality and reliability cannot be considered modern.

Advice

While the SR-X9000 is technically one of the pinnacle products, its value must be carefully weighed against a system investment of over 6667 USD and significant reliability risks. For those pursuing pure acoustic performance, the combination of the HiFiMan Arya Stealth Magnet (500 USD) and the Fosi Audio V3 amplifier (133 USD) offers an extremely high level of performance (especially low distortion) for about 633 USD—roughly 8% of the SR-X9000 system’s cost. Reports of channel imbalance and high repair costs are major concerns from a long-term ownership perspective. Unless a user has a strong preference for the specific sonic signature of electrostatic technology and can accept the associated high costs and risks, we strongly recommend more cost-effective and reliable planar magnetic alternatives.

(2025.7.19)