Grid[{{LogLinearPlot[0,{f,10.,50000}
,PlotRange->{{10.,50000.},{-40,10}}
,Frame-> True,GridLines->Automatic
,AspectRatio->1
,FrameLabel->(Style[#,18,Black,FontFamily->"Arial"] &
/@ {"frequency (Hz)","relative amplitude (dB)"})
,LabelStyle->{14,Black,FontFamily->"Calibri"}
,ImageSize->400]
,LogLinearPlot[0,{f,10.,50000}
,PlotRange->{{10.,50000.},{-1.1,1.1}}
,Frame-> True,GridLines->Automatic
,AspectRatio->1
,FrameLabel->(Style[#,18,Black,FontFamily->"Arial"] &
/@ {"frequency (Hz)","phase shift (π)"})
,LabelStyle->{14,Black,FontFamily->"Calibri"}
,ImageSize->400]}}]