Overtones of Bells Over A Distance The hourly bell tower sound at Indiana University Bloomington sounds like a higher frequency when heard from ~1.4 km away, compared to standing right next to it. Is this effect likely due to the higher-frequency overtones not getting muffled over the distance? If so, is there a physical argument underlying this? This perception runs counter to the common-sense expectation that lower-frequency sounds should carry over a longer distance. 
It is not a doppler effect, because in both instances I was not moving relative to the clock tower.
 A: This is because the sound waves from the bell are being diffracted ('bent') as they propagate past an obstacle or through a gap in wall. The amount of diffraction depends on the size of the obstacle or the gap when compared to the wavelength.  Generally however, longer wavelengths (the lower frequencies) will experience a greater amount of diffraction than shorter wavelengths (higher frequencies).  In effect then, the longer wavelength/lower frequencies are filtered out from the overall sound you hear at a distance by the amount of bending they experience.  As you move in nearer to the tower you'll begin to hear the lower frequency sounds.  
A sound with frequency 130 Hz - one octave below "middle C" on a piano which is 260 Hz (source https://en.wikipedia.org/wiki/Piano_key_frequencies) will have a wavelength in air of about 2.54 m (assuming speed of sound is 345 m/s which is a reasonable approximation for an air temperature of around 22 deg C - source http://www2.siba.fi/akustiikka/?id=38&la=en).  The next octave lower frequency will have a wavelength of about 5.08 m.  Judging from the picture of the bell tower at https://www.flickr.com/photos/29445095@N05/14407371324 these wavelengths are comparable to the dimensions of the tower and so diffraction of sound waves in this frequency range will occur.
A simple example of sound diffraction is being able to hear peoples' voices round the corner of a building.  Human voice frequencies range from about 85 Hz (male) up to 255 Hz (female) or a range of wavelength from about 4 m to 1.4 m (source https://en.wikipedia.org/wiki/Voice_frequency) which, as the analysis above shows, will be diffracted by an obstacle of a comparable size like a wall or corner.
