  We demonstrate the possibility of drastically reducing the velocity of
phonons in quasi one-dimensional Bose-Einstein condensates. Our scheme consists
of a dilute dark-soliton "gas" that provide the trapping for the impurities
that surround the condensate. We tune the interaction between the impurities
and the condensate particles in such a way that the dark solitons result in an
array of {\it qutrits} (three-level structures). We compute the phonon-soliton
coupling and investigate the decay rates of these three-level qutrits inside
the condensate. As such, we are able to reproduce the phenomenon of acoustic
transparency based purely on matter wave phononics, in analogy with the
electric induced transparency (EIT) effect in quantum optics. Thanks to the
unique properties of transmission and dispersion of dark solitons, we show that
the speed of an acoustic pulse can be brought down to $\sim 5$ $\mu$m/s, $\sim
10^3$ times lower than the condensate sound speed. This is a record value that
greatly underdoes most of the reported studies for phononic platforms. We
believe the present work could pave the stage for a new generation of
"stopped-sound" based quantum information protocols.
