Originally Posted by
aa777888
Things do get really weird, often unusable even, when you cup or cover the external noise sensing microphone with your hand. Not being a helmet user I wonder how the ANR helmet installations handle the placement of those microphones? That by itself may be the source of some of the reported issues.
In the original military design for the Mk4A helmet (entered service in 1997), the two low profile transducers in each helmet capsule sat just in front of your earhole about an inch apart, fitted to a printed circuit board.
The design highlighted the need for properly fitted helmets. Hitherto, many aircrew had chosen to have a slightly oversized helmet, for comfort. But the airgap, especially when wearing spectacles, caused feedback; exacerbated by the acoustic chamber being smaller due to the PCB. The solution included a new design of earshell padding, and made to measure helmet fitting. (Which should be the norm anyway). The company had a laser mapping system, which was simply fed to the machine that formed the helmet shell. Added a few quid to the cost, but worth every penny.
Edited to add image. There's a small rectangular thing sitting at 45 degrees to the tels transducer. That's the upper ANR transducer. This is the prototype, before the low profile one was fitted.
