Loudspeakers

Where is it written that a loudspeaker driver must 'pump' an acoustical wavefront by moving axially, fore and aft? In practice most do, but other more innovative ideas exist for how a driver might displace the air around it. Just one such variation is the AMT (Air Motion Transformer), an increasingly popular alternative to the dome tweeter, although the technology could conceivably be expanded into low midrange and bass units. Patented by German engineer Dr Oskar Heil in 1973, the AMT uses a pleated, accordion-like substrate onto which is bonded an aluminium foil 'voice coil'. The polymer/alloy strip is bathed in a magnetic field so the applied signal current causes it to compress and expand along its length, squeezing the air out from its folds.

AMT drivers offer a resistive impedance, the potential of lower distortion and better power handling than an 'equivalent' dome tweeter, but the physical mounting and clamping of the AMT strip within its frame is critical in tackling resonances and otherwise managing the uniformity of its output. ELAC has long been a proponent of this technology with its JET tweeter but we've seen other AMT refinements courtesy of the FinkTeam KIM [HFN Feb '21], GoldenEar BRX [HFN Sep '22], Scansonic M20 [HFN Sep '21], Neat Acoustics Iota Explorer [HFN Jul '18], Monitor Audio PL500 II [HFN Jun '16] and MartinLogan Motion 35XT [HFN Oct '15]. PM