It can be seen in the picture that if the length of the pipe is „l”, and the wavelength of the sound created in the pipe is , then
• in the case of a closed pipe: l='/ 4, '=4l
• in the case of an open pipe:: l=/ 2, =2l

The frequency which determines the sound pitch of the pipe is:
• in the case of a closed pipe: f= c /'=c/4l
• in the case of an open pipe: f= c /=c/2l

So the sound pitch of an open pipe is twice as high (with an octave higher) as the sound pitch of a closed one. The formula also shows that a longer pipe produces lower frequencies in both cases, and accordingly its sound is deeper.