Waveforms

Amplified noise-canceling mike as used on David Clark type headsets Compare with FLYCOM

DC generic waveform 1

DC generic waveform 2

DC generic waveform 5

Low frequency signal
(voice sound "arrr" as in ark)
Mike on lips centre line

Mike 25 mm below lips centre line. (same sound as 1)
Only slightly less amplitude

Comparison background noise
110 dB, 100 mm behind the pilot's head (**see below)

DC generic waveform 3

DC generic waveform 4

For good noise cancellation the signals off the lips centre-line (2 & 4) should be a lot smaller than on the lips centre-line (1 & 3).
With this mike there is only a small reduction at both high and low frequencies.
Note the background noise (5) compared with all the signals 1 through 4.
In practice, very 'hissy'

High frequency signal
(voice sound "esss" as in six)
Mike on lips centre line

Mike 25 mm below lips centre line. (same sound as 3)
Only slightly less amplitude

FLYCOM NOISE-CANCELLING MIKE Compare these waveforms with David Clark type above

FLYCOM Waveform 6

FLYCOM Waveform 7

FLYCOM Waveform 10

Low frequency voice sound ("arrr" as in ark)
Mike on lips centre line

Mike 25 mm below lips centre line. (same sound as 6)
Much less amplitude

Comparison background noise
110 dB, 100 mm behind the pilot's head. (**see below)

FLYCOM Waveform 8

FLYCOM Waveform 9

Note the reduction in signal amplitude (size) when the FLYCOM mike is moved away from the mouth (off-centre) at both high and low frequencies. 7 & 9 are both a lot smaller than 6 & 8 respectively.
This is how a good noise cancelling mike should behave.
Compare the background noise 10 with all the signals 1 thru 9.

High frequency voice sound
("esss" as in six)
Mike on lips centre line

Mike 25 mm below lips centre line. (same sound as 8)
Much less amplitude

**The comparison background noise source was a very old and noisy electric drill which has a large proportion of high frequency noise similar to that produced by two-stroke engines, propellers and wind-rush or slipstream. The 110 dB was estimated (having to shout to make yourself heard at half a metre) More importantly, it was the same test noise at the same distance for both tests.		The comparisons were made with the oscilloscope set at the following calibrations for both mikes and for all the tests: Vertical scale, (y-axis amplitude) 0.2 v/cm Horizontal scale, (x-axis frequency) 2.0 ms/cm Measurements were made at the output to the speakers, after processing via the FLYCOM Mk2 intercom. What you see is what you hear. Note: In all the waveform pictures above there are faint or missing sections. This is a feature of the photographic process and the oscilloscope screen and nothing to do with the performance of either mike.
		Loud high frequency noise has been shown to be more damaging to hearing than loud low frequency noise.

PILOTS ARE CHANGING TO FLYCOM

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