First, let's think about sound in terms of a loudspeaker. If you put your hand up to a loudspeaker, you can feel vibrations. As it vibrates, it compresses the air around it, raising the pressure. This disturbance in the air flows outward as a traveling sound wave that eventually reaches your ear. The number of vibrations moving per second is called the frequency, measured in Hertz, which determines the pitch of a note: the higher the frequency, the higher the note.


The four strings on the bass, E, A, D, G have the following frequency: 41.2Hz, 55Hz, 73.4Hz, and 98Hz. This proves the relationship between frequency and pitch, showing that E, the string with the lowest pitch also has the lowest frequency, while the vice versa is true of the G string. The lowest frequency that can be played on the bass is the open E at 41.2Hz and the highest is the harmonic G on the G string at 392Hz.


The following formula for finding the lowest frequency of a string instrument with dimensions Lx and Ly and thickness h is approximately, but not exactly correct due to the complicated shapes of string instruments and their vibrational modes:


                                                   


Photo from the book:  The Physics of Musical Instruments