MartinLogan Expression ESL 13A Electrostatic Loudspeakers

Complimentary White Glove Delivery • Travel Reimbursement*

The MartinLogan Expression ESL 13A is a Masterpiece Series hybrid electrostatic loudspeaker combining a 44 × 13-inch XStat CLS electrostatic panel with two independently powered 10-inch aluminum-cone woofers. The electrostatic transducer provides 572 square inches of radiating area for the frequencies above 300 Hz, while the active bass system extends response to a specified 24 Hz.

Each 10-inch woofer operates in its own sealed chamber and is driven by a dedicated 300-watt Class D amplifier, providing 600 watts of internal bass amplification per speaker. MartinLogan's 24-bit Vojtko DSP manages the low-frequency system, while PoweredForce Forward controls the interaction between the opposing woofers and the wall behind the speaker. Anthem Room Correction provides further optimization of the powered bass section for the listening environment.

This combination gives the Expression ESL 13A the speed and controlled radiation of a large electrostatic panel with deep bass, substantial dynamic capability and far greater room adaptability than a traditional passive electrostatic design.

44 × 13-Inch XStat CLS Electrostatic Panel

The Expression ESL 13A uses MartinLogan's XStat Curvilinear Line Source electrostatic transducer, measuring 44 inches high by 13 inches wide with 572 square inches of radiating area.

The panel handles the entire spectrum above the 300 Hz crossover point.

Instead of dividing the midrange and treble among conventional cone, dome and crossover systems, a single extremely lightweight diaphragm reproduces this broad frequency range.

The conductive diaphragm is suspended between perforated stators. As the musical signal changes the electrostatic field, force is applied across the diaphragm's entire surface.

With very little moving mass and no conventional voice coil attached to the diaphragm, the XStat panel is capable of responding to extremely small signal changes.

Curvilinear Line Source Technology

Large flat electrostatic panels naturally become increasingly directional at high frequencies.

MartinLogan's Curvilinear Line Source, or CLS, geometry introduces a precisely controlled horizontal curvature into the panel.

The Expression ESL 13A provides 30 degrees of horizontal dispersion while maintaining a 44-inch vertical line source.

This controlled radiation pattern also influences how the loudspeaker interacts with the room. Relatively little acoustic energy is directed toward the side walls compared with a conventional wide-dispersion loudspeaker, reducing early lateral reflections that can interfere with stereo localization.

Dipole Electrostatic Radiation

The XStat panel is a true dipole transducer.

It radiates from both its front and rear surfaces, with the rear wave opposite in phase to the front. At the sides of the panel, these opposing wavefronts largely cancel.

The rear radiation remains an important part of the listening experience, contributing reflected energy from the wall behind the loudspeaker.

This makes positioning particularly important. MartinLogan recommends giving the electrostatic panel substantial distance from the wall behind it, allowing the rear wave to arrive sufficiently later than the direct sound from the front of the panel.

MicroPerf Stator Technology

The perforated stators surrounding the diaphragm must remain rigid while allowing acoustic output from the electrostatic membrane to pass through them.

MartinLogan's MicroPerf technology increases the amount of exposed diaphragm surface compared with earlier stator designs.

This allows a greater percentage of the electrostatic diaphragm to contribute directly to the acoustic output without requiring a physically larger panel.

For the Expression ESL 13A, the result is 572 square inches of active radiating area within a relatively slender 13-inch-wide panel.

ClearSpar Reinforcement

MartinLogan's transparent ClearSpar spacers reinforce the panel while maintaining the precise spacing and diaphragm tension required across its surface.

The narrow transparent structures provide mechanical support without substantially obstructing the radiating area or the characteristic visual transparency of the electrostatic panel.

This becomes increasingly important as panel dimensions increase because maintaining consistent geometry across the entire diaphragm is fundamental to predictable electrostatic operation.

AirFrame Blade Construction

The electrostatic panel is mounted using MartinLogan's AirFrame Blade, precision manufactured from aerospace-grade extruded aluminum alloy.

The structure is deliberately narrow from the front and considerably deeper when viewed from the side. This geometry creates a rigid structural support without unnecessarily obstructing the panel.

The AirFrame also mechanically separates the electrostatic assembly from the bass enclosure, reducing the transmission of vibration generated by the dynamic woofers into the panel structure.

Dual 10-Inch Aluminum Woofers

Low frequencies are generated by two 10-inch high-excursion aluminum-cone woofers.

Each driver uses a rigid aluminum diaphragm, cast basket and extended-throw motor system and operates within its own independent sealed enclosure.

The opposed driver arrangement is important because MartinLogan does more than simply use two woofers to increase bass output. Their physical orientation, dedicated amplification and DSP-controlled phase relationship form the basis of PoweredForce Forward technology.

The complete loudspeaker reaches a specified 24 Hz at ±3 dB.

600 Watts of Internal Bass Amplification Per Speaker

Each 10-inch woofer has its own 300-watt Class D amplifier, providing 600 watts of dedicated internal bass amplification in each Expression ESL 13A.

Peak capability is specified at 600 watts per woofer.

The external amplifier therefore does not directly supply the power required to drive the two large dynamic bass drivers. It drives the electrostatic section while the internal amplifier system handles the substantial power requirements of the woofer array.

This allows MartinLogan to optimize the woofer, amplifier and DSP as a complete low-frequency system.

24-Bit Vojtko DSP

The bass system is controlled by a 24-bit Vojtko Digital Signal Processing engine developed by MartinLogan.

DSP manages the low-pass filters, woofer equalization, phase relationships and limiting functions required by the active bass architecture.

This precise control is particularly important at the 300 Hz crossover, where two fundamentally different transducer technologies must operate as one loudspeaker.

Rather than relying exclusively on passive components to integrate the electrostatic panel with the dynamic bass drivers, MartinLogan can optimize the behavior of the powered woofer system in the digital domain.

PoweredForce Forward Bass

PoweredForce Forward uses the physical arrangement of the two woofers together with DSP-controlled phase relationships to reduce problematic bass energy radiating toward the wall behind the loudspeaker.

Bass reflected from the front wall can return toward the listener and interact with the direct output of the speaker, producing peaks and cancellations.

By controlling the phase relationship between the opposing woofers, MartinLogan reduces this rearward bass energy and creates a more controlled forward launch.

The technology also increases placement flexibility compared with a conventional omnidirectional bass system.

Anthem Room Correction

The Expression ESL 13A incorporates Anthem Room Correction compatibility for its powered bass section.

ARC measures the loudspeaker's low-frequency behavior in the actual listening environment and calculates correction filters to address room-induced response problems.

Importantly, correction is applied to the powered bass system rather than digitizing the signal sent to the electrostatic panel.

The ARC or PBK measurement microphone kit required for calibration is sold separately.

Adjustable Bass Response

Two physical controls provide additional low-frequency adjustment.

Deep Bass: ±10 dB below 75 Hz
Mid-Bass: -2 dB / 0 dB / +2 dB

These controls provide useful room and placement compensation without requiring a complete ARC calibration.

The deep-bass control offers substantial adjustment where room gain can have its greatest influence, while the mid-bass control allows finer optimization of the region approaching the electrostatic crossover.

Advanced Vojtko Crossover

The Expression ESL 13A uses MartinLogan's advanced-topology Vojtko crossover to integrate the electrostatic panel with the active bass system.

Its passive components include a custom-wound audio transformer, air-core inductors and polypropylene capacitors.

The electrostatic transducer requires the transformer because it operates at substantially higher voltage than the signal supplied directly by a conventional power amplifier.

The powered bass section combines this passive architecture with dedicated amplification and 24-bit DSP.

WBT nextgen Binding Posts

Loudspeaker-level signal connection is through WBT-0703Cu nextgen 5-way binding posts.

The terminals use gold-plated, nickel-free, non-ferromagnetic pure copper conductors designed to minimize unnecessary conductive mass and eddy-current effects.

They accommodate substantial loudspeaker cables while providing the mechanical connection expected in a system at this level.

Amplifier Matching

The powered bass system substantially reduces the burden placed on the external amplifier, but the XStat electrostatic panel remains a demanding electrical load.

Nominal impedance is 4 ohms, falling to 0.7 ohm at 20 kHz.

MartinLogan's current product specifications recommend amplification from 20 to 600 watts per channel and state compatibility with amplifiers rated for 4-, 6- or 8-ohm loudspeakers.

The wattage figure should not be considered in isolation. Stability into the electrostatic load, output-stage design and overall amplifier quality are critical when selecting electronics for the Expression ESL 13A.

Technical Details

Specification	MartinLogan Expression ESL 13A
Series	Masterpiece Series
Product Type	Powered Hybrid Electrostatic Floorstanding Loudspeaker
Frequency Response	24 Hz to 23 kHz ±3 dB
Electrostatic Transducer	XStat CLS
Panel Dimensions	44 × 13 in / 112 × 33 cm
Radiating Area	572 in² / 3,696 cm²
Panel Technology	XStat / CLS / MicroPerf / ClearSpar
Panel Structure	AirFrame Blade
Horizontal Dispersion	30°
Vertical Dispersion	44 in / 112 cm line source
Bass Drivers	2 × 10 in / 25.4 cm
Woofer Construction	Rigid aluminum cone
Woofer Basket	Cast
Woofer Enclosures	Independent sealed chambers
Bass Technology	PoweredForce Forward
Internal Amplification	2 × 300 W Class D per speaker
Internal Peak Amplification	2 × 600 W
Bass Processing	24-bit Vojtko DSP
Crossover Frequency	300 Hz
Room Correction	Anthem Room Correction Ready
ARC/PBK Microphone Kit	Sold separately
Deep Bass Adjustment	±10 dB below 75 Hz
Mid-Bass Adjustment	-2 / 0 / +2 dB
Sensitivity	91 dB / 2.83 V / 1 m
Nominal Impedance	4 Ω
Impedance at 20 kHz	0.7 Ω
Recommended Amplifier Power	20 to 600 W per channel
Amplifier Compatibility	4 / 6 / 8 Ω rated amplifiers
Crossover Components	Custom-wound transformer, air-core coils, polypropylene capacitors
Binding Posts	WBT-0703Cu nextgen 5-way
ARC Connections	RJ45 / Mini USB
Maximum Power Draw	500 W per speaker
Standby Power Draw	<1 W per speaker
LED Control	On / Dim / Off
Height	61.5 in / 156.1 cm
Width	13.4 in / 33.9 cm
Depth	27.5 in / 69.9 cm
Weight	103 lb / 46.8 kg each

MartinLogan Expression ESL 13A at The Grid HiFi

The Grid HiFi in Houston specializes in MartinLogan electrostatic loudspeakers and complete high-end two-channel systems.

The Expression ESL 13A benefits enormously from proper system design. Its 0.7-ohm high-frequency impedance, powered dual-woofer architecture and dipole electrostatic radiation make amplifier selection, speaker positioning and bass integration important parts of the final result.

We can match the Expression ESL 13A with appropriate amplification, optimize its PoweredForce Forward bass system, perform ARC calibration and establish the panel position and toe-in around the listening room.

The Grid can also design the complete system, including digital and analog sources, amplification, cabling, power infrastructure, equipment support, networking and final system calibration.

Complimentary White Glove Delivery • Travel Reimbursement*
Qualifying purchasers may receive airfare reimbursement for your private audition.
Considering the Expression ESL 13A? Experience it properly before you decide. Call The Grid HiFi at (713) 218-8120 to arrange your private consultation.
*Restrictions apply. Contact us for details.