\version "2.19.82"
\pointAndClickOff

mymusic = \relative c{
  \clef bass
  <b d g>4 <c e a> <d f b> <e g c> | <f a d> <g b e> <a c f> <b d g> |
}

\score {
  \new Staff { 
    \mymusic
  }
  \header { piece = "default staffsize" }
  \layout {}
}

\score {
  \new Staff { 
    \mymusic
  }
  \header { piece = "staffsize 16" }
  \layout {
        #(layout-set-staff-size 16)
  }
}

\score {
  \new Staff { 
    \mymusic
  }
  \header { piece = "staffsize 14" }
  \layout {
        #(layout-set-staff-size 14)
  }
}

\score {
  \new Staff { 
    \mymusic
  }
  \header { piece = "staffsize 12" }
  \layout {
        #(layout-set-staff-size 12)
  }
}