6

Whistles are often used for emergency signalling, it would be good to know how far that signal can travel and still be recognized.

There are plenty of factors that would affect the distance, so how far would it travel under optimal conditions and then one could figure that real world conditions would be less.

As starting point,

Charlie Brumbaugh
  • 69,253
  • 35
  • 217
  • 423
  • I would refer to this answer from physics.stackexchange. https://physics.stackexchange.com/a/415426/9338 –  Nov 09 '18 at 19:12
  • At first I thought your two facts contradicted each other, as it appears the sports referee whistling beat the world record, in which case the sport referee would be the record. But the first point probably implies "without a device to aid the whistler" - ie: which just the mouth as the whistle device. – Loduwijk Nov 09 '18 at 21:14
  • I was going to provide an answer, however: I don't remember the formula for this, so I went to use an online calculator for it, and using the Storm Whistle (measured at 130 decibels, distance not provided in the source I read so I assumed 2 meters), the calculator I used provided an estimate of more than 2000 miles when I provided it the hearing threshold for the second point!!! Something is not right there (and it might be me), since I highly doubt it could be heard at more than 2000 miles. So no answer; but feel free to use this info in other answers. – Loduwijk Nov 09 '18 at 21:22
  • https://www.outdoors.org/articles/amc-outdoors/survival-essentials-the-worlds-loudest-whistle – Loduwijk Nov 09 '18 at 21:23
  • Yeah, there are probably things that can be heard at 2000 miles, but they're things like large nuclear bombs going off, as heard across a sea. – Monster Nov 10 '18 at 14:42
  • 1
    Optimal conditions probably involve the right thermal layers resulting in a wave guide and could theoretically be 100s of miles. I think it makes more sense to look at typical comditions. – StrongBad Nov 12 '18 at 01:28
  • The simple physics approximation would be a 1/r^2 decay, so at 10 times the distance the intensity drop by 100 fold (the whistles energy is spread out over a bigger spherical shell) a drop of 10 decibels (dB) is the drop of a tenth power. So looking up the minimum hearing level would give a best estimate - in reality you need to know how noisy it is at the recipient. And there are other factors. – Philip Oakley Nov 12 '18 at 23:05
  • 1
    I used a whistle this summer and I can definitely say that the lower the pitch of the whistle, the better. We lost a hiker in a dense boreal forest bushwhack and started a search. The 'lost' hiker simply angled slightly to our left and was descending past a small ridge. When she arrived at the trailhead, we started trying to get the further guys back down. I could hear the furthest guy loudly calling with his deep voice. He and the guy below him never heard my Fox40 whistle even though I called for over 5 minutes. I ended up climbing and shouting at them. It was not even 500m away. – Gabriel Nov 14 '18 at 15:15

2 Answers2

1

The simplest, as opposed to the optimal, approximation is to assume the inverse square law holds such that there is a 6 dB drop in the pressure for every doubling of distance. If we assume that the whistle needs to be 35 dB to be heard outside in this "optimal" scenario, the pressure needs to drop by 90 dB (or 15 doublings of distance). 2^15*2.5m is about 82 km. If it is really quiet and you have excellent hearing, maybe you could handle another 6 doublings or 5000 km.

There are a lot of factors that will affect the actual distance. With the right thermal layers, the atmosphere can act as a wave guide allowing sound to propagate 1000s of kilometers. While this seems far fetched, it is pretty common underwater. Wind, acoustic absorption, and scattering, will likely shorten the distance. Less acute listeners may need a whistle to be louder than 35 dB, especially if there is any background noise.

I touched on a number of these concepts in my answer about highway noise.

StrongBad
  • 10,663
  • 1
  • 37
  • 62
-1

Practically, I don't know how far, but a lower pitch will generally carry farther. Also, one's hearing works better if the sound pattern is unusual or personally known to the listener. (A loved one's voice across a crowded party.) Fog horns are low pitched to reach farther. A ululating sound pattern is often used to catch one's attention. I like the sports type whistle with a free-traveling ball inside to warble. Also consider listeners: as we age our hearable frequency range shrinks.

Sue Saddest Farewell TGO GL
  • 15,608
  • 8
  • 54
  • 130
David Reichard
  • 75
  • 4