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What is an Air Motion Transformer (AMT) Ribbon Tweeter?

The Air Motion Transformer (AMT) is a type of electroacoustic transducer. Invented by noted physicist and scientist Dr. Oskar Heil (1908–1994). It operates on a different transduction principle from other loudspeaker designs, such as a moving coil, planar magnetic or electrostatically driven loudspeakers, and should not be confused with planar or true ribbon loudspeakers. In contrast to a planar ribbon loudspeaker, the diaphragm of the AMT is of pleated shape similar to a bellows. The AMT moves air laterally in a perpendicular motion using a metal-etched folded sheet made of polyethylene terephthalate (PET) film. The circuit path embossed on the PET membrane, acts as the voice coil unit. The diaphragm (now, as a unit) is then housed between 4 stacks of steel pole-plate pieces positioned at 45° within a high-intensity, quadratic, opposing magnetic field. The air motion transformer with its sheet film equally exposed at 180° behaves as a dipole speaker, exciting front and rear sonic waves simultaneously.



How it works?

The diaphragm pushes back and forward from itself in a physical motion similar to that observed when an accordion is pushed in and pulled out to pump air though the reed chambers, albeit over an exceedingly smaller motion range. The result is a dipole driver with an extraordinarily rapid response rate, enabled by the extremely low mass of the polyethylene substrate and the far smaller distance it travels on each "swing" compared to a dynamic driver. In this technical respect, it shares characteristics with an electrostatic driver.

The discernible motion of each diaphragm flexure is very small, but because of the folded structure, more air is moved than would be by a conventional cone or electrostatic driver of the same plotted surface area. As a matter of surface comparison, a standard 1-inch-wide (25 mm) AMT strip has a functional driver area comparable to an 8-inch-diameter (200 mm) circular dynamic cone. The folded driver design, combined with the small motion range, means the AMT acts like a point source version of a larger driver, inherently resulting in lower sound reproduction distortion. The speed of the air as it leaves the diaphragm is approximately five times faster than the speed of the actual driver structure, hence the name Air Motion Transformer.

 Aperion Audio Dual AMT Ribbon Tweeter




While suited very well for high frequencies, the AMT can reproduce sound down to 650 Hz. Consequently, the most common use for the AMT driver in consumer electronics today is as a midrange-tweeter or tweeter in high-end multi-driver speakers, sometimes paired with horns, or in the case of Precide's speaker products, with an upward-firing woofer driver.

In the tweeter market, the AMT competes against electrostatic, ribbon and electrodynamic tweeters. While apparently very good as a mid-tweeter or full tweeter, the AMT is not commonly employed in lower frequency speakers. This is due mainly to the AMT's characteristics of a dipole sound radiator, which makes enclosure in traditional speaker cabinets difficult without sacrificing sound quality or employing sound reflex baffles. Crossover points are design decisions (depending on the model application, using a cut-off frequency of 18 dB at 800 Hz, or 1 kHz).


Aperion Audio's new Flagship Dual AMT Super Tweeter delivers quick dynamics and an ultra-clear high frequency transient response, expanding the atmospheric sound stage like you've never heard before. The light, airy highs produced by our AMT super tweeter are incredibly smooth, providing an effect which transports you even further into the sonic abyss of your music and movies.

The AMT can be suitably matched with any speaker whose sensitivity is between 87-98 dB, so this higher SPL rating allows the Dual AMT to be matched with power hungry speakers. While we've received plenty of stunning feedback on the Dual AMT's predecessors, we had an AMT style design in mind from the start - after years of development, we are proud to announce the Dual Air Motion Super Tweeter.


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