  Observations indicate that in plage areas (i.e. in active regions outside
sunspots) acoustic waves travel faster than in quiet sun, leading to shortened
travel times and higher p-mode frequencies. While it is clear that the ultimate
cause of any difference between quiet sun and plage is the presence of magnetic
fields of order 100 G in the latter, the mechanism by which the magnetic field
exerts its influence has not yet been conclusively identified. One possible
such mechanism is suggested by the observation that granular motions in plage
areas tend to be slightly ``abnormal'', dampened compared to quiet sun.
  In this paper we consider the effect that abnormal granulation observed in
active regions should have on the propagation of acoustic waves. Any such
effect is found to be limited to a shallow surface layer where sound waves
propagate nearly vertically. The magnetically suppressed turbulence implies
higher sound speeds, leading to shorter travel times. This time shift Dt is
independent of the travel distance, while it shows a characteristic dependence
on the assumed plage field strength. As a consequence of the variation of the
acoustic cutoff with height, Dt is expected to be significantly higher for
higher frequency waves within the observed regime of 3-5 mHz. The lower group
velocity near the upper reflection point further leads to an increased envelope
time shift, as compared to the phase shift. $p$-mode frequencies in plage areas
are increased by a corresponding amount, Dnu/nu = nu*Dt. These characteristics
of the time and frequency shifts are in accordance with observations. The
calculated overall amplitude of the time and frequency shifts are comparable
to, but still significantly (factor of 2 to 5) less than suggested by
measurements.
