Alex,

Thanks for posting the loudness curves; visuals always help.

And 3.5kHz is indeed the area we are best at hearing. At the risk of offending anyone's beliefs...
... one common explantion for this is that mankind, being social by nature and for survival, has gotten exceptionally good at recognizing each other's voices.

In any event, it is in fact this frequency area that is most critical in determing "clarity" of the human voice. We simply hear best in the area that is most important to us. Design or chance, that's pretty cool.

So if I were to look for the "perfect" whistle... that is indeed the frequency range I would look for. To Susan's point, all of us are better at hearing in this range. All that changes is how much better (or worse) depending on volume, age, gender, etc.

Hope this helps,

Keep in mind, however, that in a choice between decibel level and frequency, decibel level is usually the deciding factor. In most practical cases, the difference between one whistle's frequency and another will be minimal. (The Storm and Windstorm whistles produce a 3.15 KHz tone, if I remember correctly.) However, decibels are logarithmic, and 105 dB (Storm Whistle) is a little over 3 times louder than 100 dB (competition).

You are right on the money... assuming we are talking about signal whistles here. We got pretty far afield, but the thread started as a discussion of air horns vs signal whistles.

The fact is that both frequency and SPL matter. If the frequncy of the signaling device falls outside of the "sweet spot" of human hearing, the SPL level needs to be MUCH higher in order to be heard as well. Most airhorns run in the 500Hz to 250Hz range. At those frequencies, human hearing can be off 30dB or more when sounds are very faint. That's why you see SPL levels for things like boat horns at 125dB or more.

And while low frequencies do have a tendency to travel further, the energy requied to produce those super high SPLs at low frequencies is simply not practical/possible for portable devices.

So the bottom line for all these numbers is what exactly?

Just as JC suggests... get a whistle whose pitch falls into the human sweet spot of hearing (most do) and go for the loudest one of those you can carry comfortably.

Hope this helps,

A fantastic piercingly loud emergency whistle is simply an empty (fired) SKS rifle cartridge. You basically put it up against your lower lip and sort of blow into and across the top kind of like making sound by blowing into the top of a pop bottle.

One thing to also remember about cars with loud bass, those subwoofers are pushing lots of power. My four car speakers each get 40 watts, while, each of my two subs runs on 200 Watts. There's a lot of power shoved into the low freqs.