Several years ago, and soon after a couple of occasions when I’d wanted a whistle on very short notice but didn’t have one, I went out to buy a whistle to attach to my pack. With very little research I bought a Fox40 Classic whistle because it was easy to find and because their marketing said they were fantastic, and also that they were the "standard choice for personal safety and rescue professionals worldwide". Besides giving me greater opportunities to annoy people, I thought that maybe it’d be useful in a SAR situation some day, too.
Sadly I felt let down after some time. Despite the Fox40’s ability to momentarily deafen me any time I blew it, I found it often didn’t annoy people at a distance in an open space, or even reach their ears, as much as I hoped. I put this down to various issues in the bush, like the frequency of corners little hillocks around which sound probably wouldn’t be travelling well, and probably also some audio absorbing properties of thick vegetation. Recently though, I was pointed to some research that’s been done on whistles, and (even better) it’s about the effectiveness of different whistles in New Zealand back-country conditions.
Specifically, in 2006 a group of New Zealand Youth Search and Rescue members ran tests that compared a variety of whistles, as well as a giant honker and “yelling and screaming”. The tests have very recently been updated in 2012 to include comparisons of some extra whistles that were provided by Safety Whistles NZ. [Edit 9-Sep-2015: The above-linked page is no longer available, but it’s helpfully still hosted by the WayBack machine.]
From personal experience I’m not surprised in hindsight that the Fox40 whistle tested badly, coming 6th out of 7 whistles and (after the 2012 tests) being barely comparable with a newly tested Safety Whistle. I was surprised by a couple of things, though.
The first surprise, which maybe shouldn’t have been surprising if I’d considered the physics properly, was that the bush absorbs the sound from different whistles by different amounts. It’s not just a simple linear relationship, and two whistles being equally effective in the open doesn’t necessarily mean they’ll be equally effective in a bush environment. Presumably there’s something happening with the respective frequencies and how they interact with the environmental surroundings. As the testing notes, whilst “all whistles could be heard over a range of 600 metres or more in the open”, there are major differences between their relative effectiveness once muffled by dense bush. “The bush is very good at absorbing the sound and this really does reduce their range.”
The other surprise was that yelling and screaming was, in terms of effective distance, as good as any whistle tested, albeit with the riding issue that it’s hard to maintain extreme levels of yelling and screaming for long periods of time. In some respects you could say that whistle blowing’s also hard to maintain for too long, but probably not to the same extent. If you’re stuck without a whistle, however, and need to get some attention with noise, all is not necessarily lost.
Maybe I’ll look at buying a new whistle so as to see just how ultra-annoying I can really be. From the test results, it looks as if I should be looking at a Storm whistle, or an Acme Thunderer whistle. Both of these were audible at an average of 400 metres after 6 testing sessions… nearly as far as the yelling and screaming test. My poor old Fox40 whistle, by comparison, averaged only 238 metres. In considering these distances, be mindful that the testers also note that the effective range of a whistle might be halved if a recipient isn’t expecting to have to listen for a whistle.
The report is very interesting to read, and not just because the actual results of the testing contradict what manufacturers have sometimes claimed about their suitability for outdoor back-country use. Thank you, YSAR, for pushing some genuinely useful and interesting research.