Sound Phenomena: Doppler's Effect on Motorcycles and further queries

                                                 

                                                Sound waves inter looping
                                

Motorcycles or boda boda as they are fondly referred to as in Kenya are the most convenient means of transport over short distances both in towns and to and from market centers in upcountry.  Most of them have customized music systems to attract passengers especially youth. They are thereby blaring loud music as they ride along.

While walking or being near a busy road, I have observed a Peculiar behavior of sound of music from boda bodas. I can distinctly hear and know which song is playing and as well follow the lyrics word for word, from a motorcycle that is approaching from say 100 m or 50 m ahead depending on how load it is. However when the boda boda rides past me, the rhythm and words of that song Become Distorted for a few seconds before resuming normalcy. This phenomenon also occurs if the boda boda is approaching from behind and reaches a similar distance ahead of me.

Doppler’s Effect explains this occurrence by stating that it’s the Wavelength of the sound which Increases because “in a given time the sound at the end of a vibration has to travel an extra distance due to relative movement of the boda boda”. However this theory fails to state specifically at what point the sound distorts or thins out. 

I haven’t done any experiment on the phenomena but I opine that the point at which wavelength Increases and Decreases in split seconds is key to this occurrence. But I opine that at this Point, P, the sound waves either flattens or inter loops each other and hence distorts the sound of the music.

Furthermore I have thought of other questions regarding this phenomenon:

      i) If there is number of people walking one ahead of the other in a straight line at measured intervals at which distortion happens and a boda boda (source of sound) is approaching in front or behind them, would they all hear the song in its distorted form?

    ii) Also how would the song sound if one was running towards a stationary source of sound?

    iii)   And what if two boda bodas are approaching from Opposite direction playing the Same song at the Same time and reach the distances of distortion (say 5 m on either direction) Dd1 and Dd2 at Once. Would there be distortion or would the wavelengths Cancel Out and therefore the song sound Normal as if from a single source without distortion?