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Stax Ltd. (有限会社スタックス Yugen-gaisha Sutakkusu) is a Japanese company that makes high-end-audio equipment. Stax is best known for their electrostatic and electret headphones, which they call “earspeakers.” Electrostatic headphones work similarly to electrostatic loudspeakers, but on a smaller scale.
Stax Ltd. was founded in 1938. Twenty-two years later, in 1960, Stax released their first electrostatic earspeaker, the Stax SR-1. Over the following thirty-six years Stax produced a variety of amplification, earspeaker, tonearm, CD player, DAC, phono cartridge and loudspeaker products. In 1995, fifty-seven years after the company’s foundation, it became insolvent. The company was revived in 1996 as the new STAX company. In December 2011, Chinese loudspeaker manufacturer Edifier announced the acquisition of 100% equity in Stax.
As of January 2016, the current Stax product lineup consists of nine electrostatic earspeakers, five electrostatic amplifiers and accessories for these products including extension cords and a headphone stand.
Eight current models of earspeaker are based upon Stax’s classic “Lambda” design. These are the SR-207, SR-307, SR-407, SR-507, SR-L300, SR-L300 Limited, SR-L500 and SR-L700.
Two models are of small-sized in-the-ear earspeaker type. The SR-003 is terminated with a standard “Pro-Bias” plug and is designed for use with a standalone electrostatic amplifier. The S-001 MK2 is terminated with a proprietary plug and is designed for use with its matching battery powered electrostatic amplifier for use as part of a high end portable audio system.
One model, the 4070, is a closed back electrostatic earspeaker, primarily targeted at studio and broadcast application.
Stax’s flagship earspeakers are the SR-009 (a model in the “Omega” series), which has an MSRP of $4,450 in the United States. Its predecessors are the SR-007 and SR-007A.
There are two different bias voltages for Stax earspeakers. The first earspeakers have a 230 volt bias, referred to as “Normal” bias. The later earspeakers have a 580 volt bias, referred to as “Pro” bias. The Normal bias earspeakers use a 6 pin plug, while the Pro bias ones use a 5 pin plug, which is like the 6 pin plug with one pin not present. Pro bias (5 pin) earspeakers can be plugged into a Normal bias (6 pin) socket, and will work with a limitation to maximum volume. Normal bias earspeakers cannot be plugged into Pro bias sockets since the bias voltage is too high. All current Stax earspeakers are Pro bias, as the last Normal bias earspeaker went out of production around 1992.