Rhythms with no staff lines but with bar lines

[Adam Orris]

Hello,

I want to display rhythms without the staff, but with
bar lines.

I removed the Staff_symbol_engraver from the context of the Staff and
attempted to add the Bar_engraver to the context of the Voice.  The
staff lines are gone but there are no bar lines.

I am using version 2.11:

\new Staff \with {
 \remove Staff_symbol_engraver
 \remove Time_signature_engraver
 \remove Clef_engraver
}

<<
 \new Voice \with {
   \consists Bar_engraver
 }
 \relative c'' {
   a8 a4 a8 a4 a \bar "|" r8 a4. a2
 }
>>