Наушники — Stax SR-009S

The SR-009S is an open-air electrostatic earspeaker in the Omega series from Stax of Japan, a maker devoted to electrostatic headphones and the driver units needed to power them. Released in 2018, it is an evolution of the earlier SR-009 and uses a sound element with new fixed electrodes. It connects through the 5-pin Pro bias standard.

Key specs that matter

Stax describes the transducer as a push-pull electrostatic large circular element, mounted in an open-air housing. Its range extends from 5 Hz to 42,000 Hz. Sensitivity is 101 dB at an input of 100 V RMS at 1 kHz, and the bias voltage is DC 580 V. Electrostatic capacitance is 110 pF and impedance is 145 kohm at 10 kHz, both figures including the cable. Maximum sound pressure level is rated at 118 dB. The headphone weighs 583 g with its cable and 441 g without it.

Engineering and use context

For the diaphragm Stax uses a very low-mass, ultra-thin film of advanced super-engineering plastic. Stax reasons that thinner fixed electrodes lower air resistance and let sound waves pass more freely, but thin electrodes can lose rigidity. For the SR-009S the company answers this with after-etching processing and gold plating of the electrodes to reduce vibration. The element sits in a solid, precision-machined aluminium chassis that holds it firmly, and the case walls were kept as thin as possible to improve airflow. The guard mesh in front of the element is given a rounded shape, which Stax says increases its strength and lowers the influence of reflections. Hand-made ear pads use lamb leather where they touch the head and artificial leather on the rest of the pad. The headband arc adjusts through a 10-step slider. The cable uses silver-coated 6N OFC conductors of 99.9999 percent purity in a parallel 6-strand, low-capacity wide format and is 2.5 m long.

Pairing

Like all Stax earspeakers, the SR-009S needs a dedicated driver unit with a Pro bias output instead of a normal headphone amplifier. The current range offers the solid-state SRM-400S and SRM-700S, the hybrid tube SRM-500T and SRM-700T, the SRM-T8000 with E88CC dual triodes and up to 470 V RMS output, and the SRM-D50 with a built-in DAC for USB, optical and coaxial sources.

Alternatives

The Stax SR-X9000 is a newer open-air earspeaker with a large circular element and a weight of 432 g without cable.