Changing the staff size
Though the simplest way to resize staves is to use
#(set-global-staff-size xx), an individual staff’s size can be
changed by scaling the properties 'staff-space and
fontSize.
<< \new Staff { \relative c'' { \dynamicDown c8\ff c c c c c c c } } \new Staff \with { fontSize = #-3 \override StaffSymbol.staff-space = #(magstep -3) } { \clef bass c8 c c c c\f c c c } >>