Headphones — Stax SR-L300

The SR-L300 is an electrostatic earspeaker from the Japanese maker Stax, built as an entry point into its Lambda family of open headphones. It works on the push-pull electrostatic principle and places an oval sound element inside a housing left open at the rear. Like all of the brand's earspeakers it cannot be driven from an ordinary headphone socket, so a separate electrostatic amplifier is always part of the purchase.

Key specs that matter

The frequency response is given as 7 Hz to 41,000 Hz. Capacitance is 110 pF with the attached cable included, and impedance is 145 kilohm measured at 10 kHz, again counting the lead. Sound pressure sensitivity is 101 dB for an input of 100 V rms at 1 kHz, and the diaphragm needs a polarising bias of 580 V DC from the driver unit. The attached lead is a parallel 6-strand, low-capacitance OFC cable with a full length of 2.5 m. The headphone weighs 322 g on its own and 448 g with the cable, and the ear pads use flexible, high-grade artificial leather.

Engineering and use context

Stax makes the fixed electrodes of the SR-L300 from stainless steel, machined by a photo etching process, and places the thin diaphragm between them so that the film is pulled from both sides at once rather than pushed from one. The oval shape of the sound element follows the outline of the outer ear, which is the defining trait of the Lambda line. Behind the element the enclosure is open, so the unit neither isolates the wearer from outside noise nor keeps its own output from leaking into the room. Height is set with a stepless slider that moves the headpad in fine increments instead of through a stepped click mechanism. The cable uses a special wide, flat parallel layout whose purpose is to hold down capacitance between the individual wires, since an electrostatic headphone is driven by voltage and extra cable capacitance loads the amplifier. Because the lead is fixed to this model, it cannot be swapped for another cable.

Pairing

A separate electrostatic headphone amplifier is required, and the SRM-353X from Stax is named as a suitable partner. Any Stax driver unit with a matching bias output will serve, and these units take line-level signals from a DAC, streamer or preamplifier rather than feeding off another headphone amplifier.

Alternatives

The Stax SR-L500 MK2 is the next Lambda model, with a detachable HiFC cable and aluminium case holders around its oval element.