ESS - The well known Air Motion Transformer (AMT) was developed by Dr. Oscar Heil as an outstanding tweeter. Because of the extremely low moving mass his sound is characterized by impulsiveness and high efficiency. The diaphragm works like an accordion and therefore is able to displace a lot of air with a minimum of diaphragm movement. Being used as a normal tweeter or as a dipole, the AMT surely is one of the best tweeters on earth.