An Air Motion Transformer, often abbreviated to AMT, is a type of loudspeaker driver designed primarily to reproduce high frequencies. It provides an alternative to the conventional dome tweeters found in many loudspeakers and uses a distinctive folded diaphragm to create sound.

Instead of moving backwards and forwards like the diaphragm of a conventional tweeter, an Air Motion Transformer uses a lightweight diaphragm formed into a series of folds. Conductive elements are incorporated into the diaphragm, which is positioned within a magnetic field.

When an electrical audio signal passes through the conductive elements, sections of the folded diaphragm move towards and away from each other. This action squeezes air out from between the folds and draws air back in as the diaphragm moves in the opposite direction. It is this movement of air that gives the Air Motion Transformer its name.

The diaphragm of an AMT is extremely lightweight and can respond rapidly to changes in the audio signal. This makes the technology particularly suitable for reproducing high frequencies, where a driver needs to move quickly and accurately.

Air Motion Transformers are commonly used as tweeters, although larger versions can sometimes reproduce frequencies extending further into the midrange. As with other drivers in a multi-way loudspeaker, a crossover controls the range of frequencies sent to the AMT.

One of the characteristics of an AMT design is that the movement of its folded diaphragm can produce relatively high air velocity without requiring the entire diaphragm to move over a large distance. This allows an AMT to combine a relatively large diaphragm surface area with small physical movements.

The Air Motion Transformer was developed by physicist and engineer Oskar Heil and has since been adopted and adapted by numerous loudspeaker manufacturers. Modern AMT drivers vary considerably in their materials, dimensions and construction, but they continue to use the same basic principle of moving air through a folded diaphragm.

Ultimately, an Air Motion Transformer performs the same fundamental job as other tweeter technologies: reproducing the high-frequency portion of an audio signal. Its unusual method of moving air, however, makes it one of the more distinctive driver technologies used in modern loudspeaker design.