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Shure KSE1200

Electrostatic In-ear Monitors By Hugh Robjohns

Shure KSE1200

If you thought earbuds were a compromise, think again...

We all like to listen to music on the move, and many of us also appreciate the benefits of in-ear monitoring when performing. Both applications require high-quality earphones, and the market is awash with wired and Bluetooth designs at prices ranging from under a tenner to several thousand poundsdollars.

Shure are one of the most respected and familiar manufacturers of earphones, with their own range of sound-isolating models starting at under £50 (for the SE112GR), and extending up to nearly £900 for the SE846. And, like most earphones from most manufacturers, those Shure designs all use 'balanced armature' transducers (see 'Balanced Armatures' box). However, not all manufacturers choose to use balanced armatures. For example, Sennheiser applied its considerable expertise in moving-coil headphone drivers to develop a miniaturised version just 7mm in diameter, for use in their top-of-the-line IE800 earphones, which I reviewed a few years ago — see www.soundonsound.com/reviews/sennheiser-ie800.

Static Conversion

Another sophisticated transducer technology that's occasionally used for high-end loudspeakers and headphones is the electrostatic transducer. This works a bit like a capacitor microphone in reverse: an incredibly light but strong plastic film carrying a static-electric charge is suspended between a pair of conductive grilles. When a high AC voltage (carrying the audio signal) is applied across the grilles, the film is attracted and repulsed by the changing electric charges, and by moving back and forth it acts as a diaphragm to reproduce the acoustic audio signal.

One of the advantages of this technology is that the diaphragm is virtually mass-less — it certainly weighs less than the air surrounding it, unlike a moving-coil transducer design — so it has negligible inertia and can respond virtually instantly to the subtlest nuances within a signal. It's also inherently driven across its entire surface to act as a true piston, and can reproduce the entire audio bandwidth, so there's no need for multiple drivers. Moreover, there are no inherent resonances or energy storage artifacts in the diaphragm, the transient response is incredibly accurate, and the transducer's harmonic distortion is typically an order of magnitude lower than that of an equivalent-sized moving-coil device at mid and high frequencies, and two orders better in the lowest octaves. In short, there is (currently) no better method of reproducing sound!

The obvious question, then, is why hasn't this technology already taken over the monitor speaker and headphone market? Well, one of the reasons is that the electrostatic transducer requires a very high biasing voltage — typically several hundred Volts...

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Published August 2020