Overview

The STAX SR-009S is one of the flagship models developed by STAX, a Japanese manufacturer specializing in electrostatic headphones. It employs the company’s proprietary push-pull electrostatic driver with a frequency response of 5-42,000Hz and 145kΩ impedance. Featuring improved MLER 2 electrodes and ultra-thin engineering plastic film diaphragm from its predecessor SR-009, measurement results show extremely low distortion and excellent frequency response. It requires a dedicated electrostatic amplifier and has a market price of 3036 USD.

Scientific Validity

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The SR-009S achieves near-transparent level performance in measurement results. THD+N shows extremely low values below 0.01%, with Stereophile’s measurements rating it as “the best measured.” Frequency response stays within ±3dB from 5-42,000Hz, with particularly excellent flatness within ±1dB in the mid-high range. S/N ratio exceeds 100dB and crosstalk achieves transparent levels below -70dB. However, a sharp dip around 6kHz due to internal reflections has been measured, presenting minor challenges to complete transparency.

Technology Level

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The MLER 2 (Multi-Layer-Elect-Rods 2) electrode technology represents industry-leading design. Smooth processing of electrode opening edges reduces air resistance, while gold plating improves conductivity. The ultra-thin engineering plastic film diaphragm achieves excellent transient characteristics, and the push-pull electrostatic driver design represents a technical level difficult to achieve by other manufacturers. The 580V DC bias voltage control and 101dB/100V r.m.s sensitivity design also demonstrate advanced technical capabilities.

Cost-Performance

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Against the SR-009S market price of 3036 USD, competitive products with equivalent or superior measurement performance include the Sennheiser HD 800 S (1219 USD). Comparing with the HD 800 S as the most affordable equivalent-performance product: 1219 USD ÷ 3036 USD = 0.40. Since a dedicated electrostatic amplifier is required (minimum SRM-D10 at approximately 893 USD), total system cost reaches approximately 3929 USD. Compared to an HD 800 S with high-quality amplifier combination (approximately 2219 USD), cost-performance receives moderate evaluation.

Reliability & Support

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STAX has over 50 years of experience as an electrostatic headphone specialist manufacturer, with standard 1-year product warranty. Due to electrostatic driver characteristics, humidity management is important, and long-term stable operation can be expected under proper usage conditions. However, the requirement for dedicated amplifiers increases overall system failure risk compared to conventional headphones. Domestic repair support is satisfactory, but overseas support structure is limited.

Rationality of Design Philosophy

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Electrostatic driver technology is a rational approach contributing to measurement performance improvement. However, the design requiring dedicated amplifiers significantly compromises convenience, and considering that equivalent measurement performance can be achieved with dynamic headphones and general-purpose amplifiers, the necessity as dedicated equipment is questionable. The 580V DC bias voltage also presents safety concerns and raises questions as a modern design approach.

Advice

While the SR-009S demonstrates excellent measurement performance, its cost-performance ratio remains challenging. For equivalent sound quality, a combination of Sennheiser HD 800 S (1219 USD) and high-quality amplifier (approximately 1000 USD) can achieve equivalent performance at approximately 2219 USD total cost, compared to the SR-009S system cost of 3929 USD. The electrostatic system costs approximately 77% more than the dynamic alternative. Unless there is specific interest in electrostatic technology itself or special attachment to the STAX brand, the dynamic alternative offers better value. This product suits enthusiasts who prioritize electrostatic technology and can accept higher system costs.

(2025.7.18)