Update: Use the option DefaultOptions in Slider to change the ImageSize of InputField:
defaultoptions = {InputField -> {BaseStyle -> style, ImageSize -> {{30, 100}, 36}}}; Row[{Style["Frequency ", style], Framed[Slider[Dynamic[f], {f1, f2}, Appearance -> {"Labeled", "DownArrow"}, ImageSize -> {5 72, 0.5 72}, DefaultOptions -> defaultoptions]], Style["Hz", style]}, Spacer[1]] 
Original answer:
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] 