You may be aware that dogs have a hearing range well above that of human beings – they are capable of hearing high frequencies that humans simply are not able to hear. But, did you know that dolphins have a hearing range that far exceeds that of humans and even dogs? In fact, dolphins are able to hear, and to produce, some of the highest frequency sounds of all mammals. Let’s put this into perspective. Humans have a hearing range of around 20 Hz to 20kHz. (that is, 20,000Hz) The Hertz scale is a measure of how many times a second a sound wave is produced.. Here is an example of a 60 Hz sound [play sound] – that is, 60 sound wave cycles per second. The human voice produces a range of frequencies when we speak, but the main frequencies are between 500Hz and 2 kHz. Here is an example of a 1 kHz tone [play sound] – a tone that is pretty easy for humans to hear. The top range of human hearing is up around 18 or 20 kHz – depending on your age and gender. As humans get older, we begin to lose our ability to hear these higher frequencies. I will now play an example of a 15kHz tone [play sound]. Did you hear it? If not, it might be an indication that you are getting on in years. Of course, it is possible that your speakers or headphones are not able to produce a tone that high, so for now, let’s blame it on the speakers. So what about dogs? Well, dogs are able to hear frequencies more than twice as high as humans – up around an impressive 45 kHz. But dolphins can do even better than that! For the species whose hearing has been researched the most, the bottlenose dolphin, we know that they can hear frequencies as high as 150kHz. Yes, that’s right – 150kHz! If a jump from 1 kHz to 10 kHz sounds like this [play sounds], can you imagine how much higher 150kHz must be? Dolphins use high frequency click sounds as part of their echolocation, producing and listening to sounds in these high frequency ranges. These clicks can sometimes be heard by the human ear because they contain frequencies below 20kHz, but the loudest frequencies produced in a click are up around 120 kHz. These high frequencies help a dolphin to pick out fine detail when is uses its echolocation to investigate an object. There is one other mammal that can best the dolphin when it comes to producing and hearing high frequencies: the bat. Bats can produce and hear frequencies as high as 250kHz! Now that is a frequency response that not even the most expense 5.1 surround sound home cinema would be able to cope with.
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