Tweeters

The Air Motion Transformer goes back to the physicist Oskar Heil. His idea was as simple as it was ingenious: instead of a rigid dome pushing air ahead of itself like a piston, a folded diaphragm moves the air like a bellows. Folding makes it possible to accommodate a large effective diaphragm area in a small space. This also explains the name Air Motion Transformer: a sound-emitting area of the desired dimensions is combined with a larger effective diaphragm area.

Because sufficient diaphragm area is available, the diaphragm as a whole only needs to travel a small distance – considerably less than with classic dome tweeters. This means: fewer nonlinear effects, less mechanical stress – and thus the basis for impulse accuracy and very low distortion. What matters here is not only the principle but equally the diaphragm material: combined with high internal damping, the reproduction remains calm, clean and precise – without hardness, without sharpness, without listening fatigue.

An obvious and yet extremely ambitious idea: in the professional field, the line array became the dominant standard in the 2000s – a concept, however, that also requires a line source in the high-frequency path. In this context, the following thought suggests itself: by principle, the AMT is the ideal line source. No detour from a point- or ring-shaped sound source to a line source. No complex waveguide that only works approximately!

Advantages of our AMTs

• Exceptionally good-natured electrical and acoustic behavior: the very flat impedance curve and the only slightly pronounced impedance rise around the diaphragm’s natural resonance make integration into passive as well as active crossovers considerably easier.
• The exemplary behavior of electrical and acoustic phase. Together, these make voicing not only easier but also safer. This stability of impedance and phase has a direct effect on reproduction. Especially in comparison with compression drivers: where impedance jumps and unsteady phase behavior often lead to temporal blurring, an AMT with good phase behavior reproduces the temporal course of the signal with particular precision. This is a foundation for spatiality, imaging focus, stage layering and fine texture in the harmonic spectrum.
• A further special feature of our AMTs is that – unlike what is common with other tweeter principles – they can be operated close to the resonance frequency. The widespread rule of thumb “crossover frequency = twice the resonance frequency” expressly does not apply here. This opens up additional degrees of freedom in passive and active designs alike: crossovers can be set lower, more elegantly and with high tonal homogeneity – without the typical side effects known from other principles in the vicinity of resonance.

Back to the challenge: it was the extreme conditions of the intended professional use: the diaphragm material, the geometry and the magnet drive had to be developed further so that they would permanently withstand the very high stresses of professional sound reinforcement without distorting or compressing in use.

This is where the uniqueness of the Mundorf AMT lies: our diaphragm technology, developed and produced in-house, consistently designed for durability, minimal distortion even at high levels, and a reproduction that remains both impulse-precise and practically three-dimensionally rich in detail.

Another important point is the magnet drive: due to its construction, the extremely stable, damped diaphragm entails a higher moving mass compared with other AMTs. To guide this diaphragm precisely, we use particularly strong magnet drives in our AMTs – usually neodymium N50 (N50 is a specification for the magnet material and the strength of magnetization). This not only ensures high sensitivity (sound pressure at 1 W / 1 m) but above all very tight control of the diaphragm motion. As a result, distortion drops even further, and reproduction remains clean and stable even at high levels.

A milestone – and a true accolade for us – was the installation of our AMTs in the Royal Albert Hall environment in London in 2012. Sound engineers who have worked there with the most varied systems described, in essence, exactly what we had set as our development goal: exceptional speech intelligibility, naturalness and clarity, even coverage and large reserves – as well as a transparency one would not think possible even in such a demanding room.

“Having heard almost every conceivable combination of loudspeaker manufacturers installed in this house by the best in the PA world, I can confirm: even though this system may be deceptive in its size, it delivers considerably more than any other system in terms of speech intelligibility and clarity, evenness of coverage and headroom.”

Stephen Hughes

Project engineer at Sound By Design for all of the company’s Royal Albert Hall concerts

“I can say without any doubt that HALO Compact is quite simply the best-sounding system I have ever mixed on. The transparency, linearity and headroom that EM Acoustics have achieved with this product are simply impressive.… With these new drivers they have hit the nail on the head … the result is by far the most even system coverage we have ever achieved in the Royal Albert Hall”

Phil Wright

one of the best-known sound engineers, worked in the Royal Albert Hall with our AMT 197F1

From the field

These voices from the field are so valuable to us because they show: the AMT is not just “audiophile” – it can do live sound at an entirely new, unique level.

Today, almost 20 years after the market launch of our proAMT, two things have been proven: first, in professional use the Mundorf AMT enables exceptionally natural music reproduction under high loads. Second, many years of field use have allowed us to dispel the early concerns about the durability of what was then a new technology: we look back on an exceptionally robust track record with longevity well above the industry average and virtually no failures over the entire service history. This is no coincidence, but the result of consistent work on materials and construction.

From this “Formula 1” DNA – developed under the maximum demands of professional sound reinforcement – the further series emerged: compact, universal designs for home and studio, specialized solutions for dipole concepts, and variants for directional radiation, line arrangements and point sources.

We started where the demands are toughest – and that is exactly where the quality comes from that can be heard today in every field of application.

With this development work, which began in the 2000s and became visible with our proAMT solutions, we are convinced that we have opened up a true renaissance for the AMT. Today, numerous AMT variants can be found on the market, including many designs modeled on Mundorf AMTs. The decisive difference is hard to see and easy to hear. It lies in the diaphragm technology and in a diaphragm material designed for high-performance and professional applications, which works with low distortion and remains stable even at high levels.