Jada-jada...
Når vi først er på indremedisinsk:
Knowing Dr Heil as I do (he lives in Burlingame, an hour away, is in our SF AES Section, and we have spoken on numerous occasions, including when I visited him at home) I can say that the Heil AMT is an interesting departure from typical ribbon design with both pros and cons from a sonic standpoint.
In the AMT the magnetic field is highly focused on a central air gap where the pleated diaphragm is suspended. This gives a much greater force field and higher sensitivity than is typical of ribbons. The diaphragm motion is unorthodox in that it "squeezes" air in a kind of accordion bellows motion. This is higher acceleration than is typical of ribbons.
The disadvantages of the AMT are, primarily: the pleats tend to slap together when overdriven, producing startling breakup noise; the supporting film has a low melting point, leading to thermal breakdown (attempts made with teflon film backings were less than successful, due to the stiffness of the material); impedance tended to be quite low, due to the short trace; attempts to make bigger diaphragms with lower resonance frequencies ran into difficulties with undamped high frequency resonances caused by the material mass limiting and cavity resonances between the pleats.
The ribbon panels in our Ribbon Monitor series are fundamentally different. They are transformerless and push-pull, with drive magnetics front and back of the diaphragm. They are low resonant, they are high impedance (3 to 6 Ohms) due to the length of the trace. They are not very prone to thermal breakdown, separation of conductor from backing film, or diaphragm noise.
Problems include mass limiting and cavity resonances caused by the magnet structure in front of the diaphragm (the rear cavity is filled with foam), which we control with a simple series 6 dB network. Bass resonance is pronounced, but fairly high Q and controllable with a simple 12 dB crossover with one pole centered on the low frequency resonance and another pole about 1/3 octave below.
