We know that violins make high sounds, and basses low sounds. This is because of the boundary conditions. A large instrument like a bass lets the wavelengths be large.

 

Wavelength times frequency equals speed. This we see from dimensional analysis. Wavelength has units of distance, which is meters. Frequency has units of per second. Speed of sound has units of meters per second. Since all sound waves, that is, sound waves of all wavelengths travel with the same speed, it means that larger wavelengths have smaller frequencies. This is why basses produce sound with large wavelengths which implies small frequencies (low sounds).

 

See Why do elephants have large ears?