A couple of interesting points I learned from the article. I've always been concerned that the Coghlan's four-function whistle (whistle, compass, thermometer, magnifying class) was too much of a toy to be a good buy, but it turns out that the whistle part, at least, is actually pretty good and loud - in the top 3 of the 15 tested, and louder than any of the Fox whistles. Also, the Fox micro whistle, which has been part of my EDC due to its convenient small size, ranked among the lowest in carrying distance in a forest. This may be due to its higher pitch:

"From these results, it
is clear that the sounds produced by the sources
with the higher frequencies (pitch) – such as
sources one, four, five, six and twelve – did not
carry as far as those with a similar magnitude,
but lower frequency. It is possible that the
difference is due to the environment’s ability to
absorb different frequencies."