  We use the AdS/CFT correspondence to study propagation of sound waves in
strongly coupled (2+1) dimensional conformal magnetic fluids. Our computation
provides a nontrivial consistency check of the viscous magneto-hydrodynamics of
Hartnoll-Kovtun-Muller-Sachdev to leading order in the external field.
Depending on the behavior of the magnetic field in the hydrodynamic limit, we
show that it can lead to further attenuation of sound waves in the (2+1)
dimensional conformal plasma, or reduce the speed of sound. We present both
field theory and dual supergravity descriptions of these phenomena. While to
the leading order in momenta the dispersion of the sound waves obtained from
the dual supergravity description agrees with the one predicted from field
theory, we find a discrepancy at higher order. This suggests that further
corrections to HKMS magneto-hydrodynamics are necessary.
