  Common envelope evolution is a fundamental ingredient in our understanding of
the formation of close binary stars containing compact objects which includes
the progenitors of type Ia supernovae, short gamma ray bursts and most stellar
gravitational wave sources. To predict the outcome of common envelope evolution
we still rely to a large degree on a simplified energy conservation equation.
Unfortunately, this equation contains a theoretically rather poorly constrained
efficiency parameter ($\alpha_{\mathrm{CE}}$) and, even worse, it is unclear if
energy sources in addition to orbital energy (such as recombination energy)
contribute to the envelope ejection process. In previous works we reconstructed
the evolution of observed populations of post common envelope binaries (PCEBs)
consisting of white dwarfs with main sequence star companions and found
indications that the efficiency is rather small
($\alpha_{\mathrm{CE}}\simeq0.2-0.3$) and that extra energy sources are only
required in very few cases. Here we used the same reconstruction tool to
investigate the evolutionary history of a sample of observed PCEBs with brown
dwarf companions. In contrast to previous works, we found that the evolution of
observationally well characterized PCEBs with brown dwarf companions can be
understood assuming a low common envelope efficiency
($\alpha_{\mathrm{CE}}=0.24-0.41$), similar to that required to understand
PCEBs with main sequence star companions, and that contributions from
recombination energy are not required. We conclude that the vast majority of
PCEBs form from common envelope evolution that can be parameterized with a
small efficiency and without taking into account additional energy sources.
