Why can't wave speed in a spring change, but frequency can?

[Nitric]

(a) Can the speed of the waves in the spring be changed?
I know it can't, but can someone explain why in a simple way?
(b) Can the frequency of a wave in the spring be changed?
I know it can, but again explanation

 

[mezarashi]

(a) The speed of waves in any medium is due to the properties of that medium. If if the property of the medium does not change, then you cannot change the speed of the wave. Same goes for sound in air.

(b) The frequency of any wave in any medium depends solely on the "creator" of that wave. For example you can choose to create high pitch or low pitch tones in air right? You cannot however, change the natural frequency of a configuration without changing the configuration itself.