The other day my younger brother was using a new dog whistle app on his phone to make tour dog (and me!) go crazy. However, my dad was in the same room and he couldn’t hear the annoying high-pitched sound at all, so my brother was able to get away with continuing the high-frequency dog whistle sound.
The highest frequency dogs can hear is 45 kHz, while a child’s limit is 20kHz, and a middle-aged adult’s is 15kHz. Dog whistles range from about 20 to 54 kHz, so it makes sense that I was able to hear the whistle while my dad was not. The equation for frequency is 1/period of the soundwave, or velocity/wavelength. So, higher frequencies are created by a greater velocity of the wave and a decreased wavelength. Waves with different velocities can still have the same frequency if the wavelengths are proportional, and waves with different wavelengths can have the same frequencies if their velocities are proportional. In the video below, it shows the sound waves at different lengths, illustrating the differing velocities and wavelengths at different frequencies – and the different sounds we are able to hear.