Tuesday, July 28, 2009

Mike's Mic

Microphones should be simple.

Of course, in the best of all possible worlds, everything should be simple. As a former radioman might tell you though, nothing is ever as simple as it seems, and not all microphones are the same.

The M1-DC headset mic shown above has a built in amplifier. The small screw visible in the picture is a gain adjustment screw. Turning the screw "up" makes the wearer "louder". A better use for this adjustment is to balance the microphone output to match other microphones or systems requirements. A technician can match A radio to A microphone, or in the case of the microphone above, A microphone to A radio. When you start mixing a bunch of different mics with a bunch of different radios, you don't always get good results. That is where standardization becomes necessary.

The recent installation of a new radio/intercom system in the Mi-2 brought attention to cabin noise levels and balancing different microphone inputs. One pilot's mic (Mike's mic) had significantly more gain than the others and background (turbine) noise was strongly amplified during the flight.

Recent experience with piston helicopters at the Cold War Air Museum has been at much lower ambient noise levels and hot mikes or voice activated intercoms have given good performance. Because of high noise levels, most military helicopters have push to talk intercoms. But we are still working towards the convenience of voice activated systems in the Mi-2, at least for the pilots.

Although a subjective evaluation can be made during flight tests, it is expensive to experiment with different settings and equipment while burning 2-3 liters of Jet-A per minute. So evaluation and testing is done on the ground when possible.

Although classic shop equipment is available, testing has been made easier by the availability of plug in analyzers for laptops computers. After a series of ground tests, we can focus further in-flight tests on specific noise issues associated with the Mi-2.

This gaggle of headsets represents some of the headsets used by our associates. ANR's from Bose and Lightspeed as well as passives from Peltor and David Clark, including the 10-46, 10-56 and 10-66 are shown. Each has a different microphone.

Although all are "GA Helicopter" headsets, microphone outputs varied by 3:1 across the group. While the human ear can easily compensate for this kind of difference, an automatic squelch or background noise adjusting circuit has a much more difficult time.

No comments:

Post a Comment