  Intrinsic defects in optomechanical devices are generally viewed to be
detrimental for achieving coherent amplification of phonons, and great care has
thus been exercised in fabricating devices and materials with no (or a minimal
number of) defects. Contrary to this view, here we show that, by surpassing an
exceptional point (EP), both the mechanical gain and the phonon number can be
enhanced despite increasing defect losses. This counterintuitive effect, well
described by an effective non-Hermitian phonon-defect model, provides a
mechanical analog of the loss-induced purely optical lasing. This opens the way
to operating random-defect phonon devices at EPs.
