[Editorial] Electrostatic speakers for car audio?

Electrostatic loudspeakers, such as Quad ESL, Martin Logan CLS and several others, have always been highly praised by expert audiophiles for their detailed, airy and low-distortion music reproduction. They have their weaknesses, especially their sometimes weak bass range reproduction, but certainly they are something to be listened to, at least once in a lifetime.

How do they work? The principle is simple: they use a thin flat diaphragm, usually a plastic sheet coated with a conductive material, sandwiched between two electrically conductive grids, with a small air gap between the diaphragm and grids. The diaphragm is usually made from a polyester film (thickness 2-20 um). By means of the conductive coating and the external high voltage supply the diaphragm is maintained at a DC potential of several kV with respect to the grids. The grids are then driven by the audio signal. Hence, a uniform electrostatic field proportional to the audio signal is produced between both grids, causing a force on the diaphragm which is, in turn, forced to move/vibrate, more or less like a standard driver membrane. There's no moving coil nor magnets. Hence, these drivers can be extremely lightweight, unobtrusive and eco-friendly, because they don't use rare earth metals. In a word, they seem ideal for modern, eco-friendly automotive use.

This is exactly what motivated an electrostatic headphones company, Warwick Audio, located in Nuneaton, Warwickshire, UK, to enter the automotive market.

Their electrostatic panels are claimed to save up to 75% of the weight and power consumption of comparable traditional transducers. Moreover, their ElectroAcoustic Panels can be manufactured in almost any shape (see pics) and placed almost everywhere, considering their depth is just a fraction of conventional transducers. The EST is stretched across open cell (honeycomb) spacers, creating small, individual “drums” that deliver sound at different frequencies.

The Warwick Audio ElectroStatic Transducer module vibrates air using a thin (15um), conductive multi-layer membrane centred between two thin, electrically conductive stators. The membrane is kept at a high DC potential relative to the stators and the audio signal is applied across the stators. Moreover, the panels are driven by the so-called EDM (ElectroAcoustics Drive Module) that provides bias power and audio signals. The EDM can be powered by the vehicle's standard 12V power rail. The EDM supplies a transducer bias voltage of between 1,300V - 2,000V depending upon the system requirement and the audio output signal. The audio input signal can range between 100mV - 2.2V, which is standard for car audio sources. In case you're concerned with safety (at such high voltages!) inertia and other safety devices can be connected to the vehicle's CAN at system or A²B level to disconnect power in the event of a crash.

Will this become the future of OEM car audio systems? Who knows! Certainly, the technology seems promising, the “green”, low-impact factor is definitely a plus nowadays.

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November 2022 Editorial

Electrostatic drivers, the future for car audio?