A tweeter is a relatively small loudspeaker optimizied to reproduce upper mid- and high frequencies. It is usually applied from around 2kHz (depending on the design approach) up to 50kHz (in some cases). The tweeter is a key component in bigger loudspeaker systems, consisting of additional woofers for the midrange and / or bass. There are all kinds of design approaches for tweeters, each with their own talents and weaknesses. The most common designs are cone- and dome-tweeters made of textile, honeycomb-sandwich-compound, aluminium and sometimes even ceramics. When a musical signal is applied, these tweeter’s diapghragms simply move back and forward towards the listener in a piston-like manner, meaning that the air velocity simply equals the speed in which the diaphragm itself is moving. The same is true for so-called ribbon tweeters and more esotheric designs to be found in electro- and magnetostatic speakers. A different approach was introduced by the German-American physicist Oskar Heil who invented the Air Motion Transformer in the 1960s. Heil proposed a folded elastic diaphragm, where single folds open and close in an alternating pattern and thus “breathe” air in and out, with the special charm that the air driven through the folds is accelerated to a ratio four times as fast as the diaphragm itself. As a consequence, Air Motion Transformers excel in reproducing musical signals with rich and fast transients (classical instruments, acoustic guitars, percussion, voice). In the early 1990s, the man behind ADAM Audio and HEDD, Klaus Heinz, was so intrigued by Heil’s idea that he used it to build a compact and reliable tweeter based on the exact same principle.

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