Floorstanding loudspeakers — ELAC Expression ESL 13A

The Expression ESL 13A is a floorstanding hybrid electrostatic loudspeaker from MartinLogan's Masterpiece Series. It joins a 13-inch wide XStat CLS electrostatic transducer to a compact woofer cabinet with its own built-in amplification, so the bass section is self-powered while the panel is driven by an outboard amplifier.

Key specs that matter

Quoted bandwidth spans 24 Hz to 23 kHz, sensitivity is 91 dB and nominal impedance is 4 ohms, and MartinLogan quotes 20 to 600 W as the suitable amplifier power. The cabinet stands 156.1 cm tall, 33.9 cm wide and 69.9 cm deep, and each speaker weighs 46.8 kg. Speaker cables attach to 5-way WBT binding posts with a pure copper contact plate.

Engineering and use context

The panel uses MicroPerf stator technology, which leaves nearly double the exposed diaphragm area of a conventional stator panel with equal outer dimensions, and rigid ClearSpar spacers hold tension on the vacuum-bonded diaphragm. A gentle horizontal curvature is built into the Curvilinear Line Source panel, and as a true dipole it sends little energy to the side walls while radiating strongly to the rear. The panel is joined to the cabinet by an AirFrame Blade rail extruded from an aerospace aluminium alloy, and this rail also isolates it electrically and acoustically from the woofer section. Bass comes from two 10-inch aluminium cone woofers, each in its own sealed chamber and driven by a dedicated 300 W Class D amplifier. A 24-bit Vojtko DSP engine handles low-pass filtering, woofer equalisation and limiting in the digital domain, and MartinLogan states that it lets the woofer section reach down to 22 Hz. The PoweredForce Forward alignment adjusts the phase of the rear-firing woofer so that bass energy radiated towards the front wall is reduced. The passive Vojtko crossover uses air-core inductors and polypropylene capacitors and is assembled by hand, and a toroidal transformer couples the amplifier to the panel.

Pairing

Because the woofers are self-powered, the external amplifier sees mainly the panel and crossover, and a stable 4 ohm load capability is the main requirement. Two level controls at 75 Hz and 200 Hz trim bass integration.

Alternatives

In the same Masterpiece Series, MartinLogan also offers the larger Renaissance ESL 15A with 12-inch woofers.