Sound waves: frequency, speed, and wavelength I need to understand the relationship between the three. When does the wavelength stay the same as there is a change in one of the other two variables? When does it change as there is a change in one of the other variables? 
My understanding is this: If the speed changes due to a shift in the medium, let's say increases, only frequency increases.
But if the frequency changes due to a change in the source of vibrations, wavelength would change to compensate for it, since there is no change in medium, correct? 
I just need to know if this is right, because I am not sure if I am getting it, and if there is anything about this relationship that I am missing. Thank you:)  
 A: The frequency of a sound wave will stay the same when sound passes from one medium to another because each compression or rarefaction in the first medium will produced exactly one compression or rarefaction in the second medium.  Typically the speed of a wave depends mainly on the properties of the medium so in this case speed and wavelength would change while the frequency stays constant.
A number of sound sources produce specific frequencies based on standing waves in some medium - for example most musical instruments or the human voice.  When we want to change these frequencies we typically change the length of the resonating system, say by effectively shortening a guitar string or sliding a trombone to change the length of an air column.  In that case the medium is unchanged (except for length) meaning the speed of the sound is fixed.  In this case as the wavelength changes the frequency changes as the speed stays constant.
As for a case where the wavelength would stay constant while the frequency and speed change consider tuning a guitar.  The wavelength is determined by the length of the string which is constant but the tension of the string changes which changes the speed of the wave.  This results in a changing frequency.  Drums can be tuned in a similar way by adjusting the tensing in the drum skin.  In some drums, for example the tabla, the tension in the drumskin is manipulated while playing to change the frequency of the sound.
