Rafowell made a good point in one of his posts (which I pasted below.) People have to keep in mind that there is no best whistle for every application/environment and that every person hears sounds and frequencies differently. What you think is the best whistle for your hearing does not necessarily mean it will be for SAR when they are searching for you. I carry Fox 40 Classic whistles and do not fret that it may not be the best whistle for my hearing or my environment, otherwise I would be carrying a dozen different whistles around just in case..

That does highlight the importance of testing for the expected application. The best whistles for forest, desert and sea could well be different, and different frequencies are likely to be absorbed at different rates. Storm thinks their choice of 3150 Hz is particularly effective.

Another factor is the hearing of the listener - in this whistle test, the kids thought the Fox 40 was louder than the Nexus Whistle, the adult thought the Nexus whistle louder than the Fox 40. He speculated it could be due to his hearing loss in the high frequencies.