A large cylindrical chamber has a massless piston fitted at the top. An acoustic source is situated at the centre of the bottom of the cylinder, while an observer is situated at the bottom circumference (inside the chamber). The observer is moving directly towards the source with constant velocity and hears a frequency `f`.
If the chamber were to be isochorically cooled then the observed frequency will be :

Options

A. same as `f`
B. higher than `f`
C. lower than `f`
D. Date insufficient