You can use Labeled or Panel using the second and third arguments to specify the labels and their positions:
Labeled[Slider[Dynamic[f], {f1, f2}], {"frequency", Row[{Dynamic[f], "Hz"}, Spacer[2]]}, {Left, Right}, LabelStyle -> style] 
Panel[Slider[Dynamic[f], {f1, f2}], {"frequency", Row[{Dynamic[f], "Hz"}, Spacer[2]]}, {Left, Right}, LabelStyle -> style] 