Sinusoidal tones have frequencies of 439 Hz and 443 Hz. One might still hear beats, but the effect would be reduced. All waves can propagate around obstacles to some extent as a result of diffraction. The distance is comparable with the wavelength, or at most a few wavelengths. This is why we can hear sound from an invisible source sound propagates around a corner while light, with its very short wavelength, does not.
Flutes produce generally higher frequencies, and thus shorter wavelengths , than French horns.
Thus, the sounds from a French horn should propagate around a corner more effectively than those from a flute. With this wavelength one could see body parts as small as a small grape, i.e. large stones, tumors, organs, parts of a fetus, etc. Ultrasonic imaging can also be used for materials such as plastics and metal alloys. It can detect flaws in the material of the various sizes indicated above, depending on the wavelength used. Note that while the apparent frequency is always higher when source and listener are in relative motion toward each other, the result is slightly different depending on whether the source or the listener is moving.