Design and Build: The SR-009 features an open-back design, which is typical for electrostatic headphones to offer a broader soundstage. It has a lightweight aluminium enclosure, contributing to both rigidity and sound quality. The headphones come with hand-crafted lamb leather earpads for comfort during extended listening sessions. The headband has a 10-click slider mechanism for optimal fit.

Sound Element: The SR-009 utilises a push-pull electrostatic circular sound element. It incorporates a newly developed diaphragm made from super engineering plastics, which are much thinner than conventional engineered plastics and contribute to a high transient response across the audio spectrum. The electrodes are part of a Multi-Layer-Elect-Rords (MLER) design, which improves sound permeability and reduces air resistance due to enhanced finishing and etching processes. Additionally, these electrodes are gold-plated to minimise resonance and reduce electrical resistance.

Frequency Response and Sound Quality: The SR-009 has a frequency response from 5 to 42,000 Hz. It’s praised for its vast dynamic range, excellent tone quality, and the ability to produce detailed sound with clarity and speed. However, some users have noted that the bass might be less pronounced compared to dynamic driver headphones, though it’s still tight and deep when properly amped.

• Capacitance: 110pF (including cable)
• Impedance: 145kΩ (including cable, at 10kHz)
• Sound Pressure Sensitivity: 101dB / input 100Vr.m.s. / 1kHz
• Bias Voltage: DC580V
• Cable: Silver-plated 99.9999% (6N) OFC parallel 6-strand, low-capacity special wide cable, 2.5m full length
• Weight: 596g (including cable), 454g (without cable).
• Comfort and Usability: The SR-009 is noted for its comfort, thanks to the lambskin ear pads and the adjustable headband. However, like all electrostatic headphones, it requires a dedicated electrostatic headphone amplifier to function, which can add to the overall cost of the system.
• Comparison and Reception: Many audiophiles consider the SR-009 among the best headphones for detail retrieval, speed, and overall musicality, often drawing comparisons with other high-end models like the Sennheiser HD-800 or Audeze LCD series. The SR-009 is often described as setting a benchmark for what’s achievable with headphone technology at the time of its release.

These details highlight why the Stax SR-009 has earned its reputation in the audiophile community for delivering an unparalleled listening experience.