swiss air motion transformer.


A tweeter should be able to reproduce the higher frequencies contained in music as flawlessly as possible. Ideally, it should be able to follow the input signal as closely as possible and neither omit nor add anything. In technical terms, we speak of linear behavior, low distortion (harmonic distortion and intermodulation distortion) and a large dynamic range. Likewise, a tweeter should have the broadest possible bandwidth, to enable a low crossover frequency from the midrange driver and transmit it beyond the audible range.

low distortion

air motion transformer.

There are many different designs of tweeters, but only one type could meet our requirements, the Air Motion Transformer, or A.M.T. for short. The A.M.T. was invented and patented by the German-American physicist Oskar Heil. The principle is based on a folded very light membrane, which is completely located in a homogeneous magnetic field. The ratio of the effcetic membrane area to the radiating area is about 5:1. This means that the A.M.T. has five times more diaphragm surface area than all other types with the same dispersion characteristics, allowing low-distortion reproduction down to low frequencies.

very light diaphragm
homogeneous magnetic field
large diaphragm area

airplain a.m.t.

In search of a way to meet our requirements as perfectly as possible, we found what we were looking for in Ticino (CH) at the company Precide SA. Its owner, Mr. D├╝rrenmatt, was a friend of Oskar Heil and still builds these fabulous tweeters with unique know-how. Precide SA also supplies the diaphragms for airplain’s large and small Air Motion Transformer. These are provided by airplain with an optimized neodymium magnet system and get a solid aluminum front.

Precide diaphragm
neodym magnet system
massive alu-front


The large airplain tweeter is called ap-AMT-L and will be used in the phli speakers for the time being. It is exceptionally broadband and low distortion and has very good horizontal dispersion characteristics. In the phli, it is used from 600 Hz and transmits well above 30,000 Hz. The transmission behavior even reaches up to around 180 Hz and the distortion behavior is already ideal above 400 Hz.

180 – 30’000 Hz
distortion factor <0.3%


At around 125 mm in diameter, the smaller airplain Air Motion Transformer ap-AMT-M is ideal for combining with 4 to 5″ midrange units. It has the same genes as its bigger brother and can be used from around 1000 Hz and is just as low in distortion above this frequency. It is also manufactured entirely in Switzerland and is used in the phli mini.

500 – 30’000 Hz
distortion factor <0.3 %