People often confuse air-motion speakers with ribbon loudspeakers, but they are rather different. To begin with, a ribbon one emits a sound when the whole diaphragm moves forward and backwards in a consistent way. Within this process, the plates never change their angles. In contrast, the air-motion transformer shifts its diaphragm in a very different way. The movement generates from drawing the air into the folds as they expand and expelling the air as they contract.
Air-motion Speakers: the Design
The original design of the heil air-motion speaker involved a diaphragm of a mylar ribbon which joined with conductive aluminium strips. This device includes a high-dynamic range as well as a broad-frequency range. The aluminium strips from the original design were accordion-folded for point-source dispersion.
The low-mass diaphragm suspends in a dipole magnetic field. When the signal runs through the aluminium strips, the movement of the folded ones passes at a speed five times faster than a conventional cone driver. The fast acceleration of the air-motion offers an enhanced sound reproduction.
Modern Designs
In modern heil air-motion speakers, the air flows through a conducting track connected to a diaphragm. The conductive strip is parallel to itself on the adjacent fold. When the air passes through one direction over the whole circuit, it usually travels in different directions within the conductors of the adjacent folds. When the circuit’s current reverses, the open folds close and vice versa. There is a specific ratio between the air particle speed in an out of the folds. This is relative to the speed of the movement of the plated diaphragm.
Permanent magnets can either attract or repel the magnetic field. It’s essential for magnet structures to be large since the plate diaphragm must fit inside the gap that appears to be between the poles. Diaphragms are made of several plastics, being polyethene the most common one. This material is great for damping. Modern heil air-motion speakers can operate from 500Hz to 20kHz.
