  Synthetic magnetism has been recently realized using spatiotemporal
modulation patterns, producing non-reciprocal steering of charge-neutral
particles such as photons and phonons. Here, we design and experimentally
demonstrate a non-reciprocal acoustic system composed of three compact cavities
interlinked with both dynamic and static couplings, in which phase-correlated
modulations induce a synthetic magnetic flux that breaks time-reversal
symmetry. Within the rotating wave approximation, the transport properties of
the system are controlled to efficiently realize large non-reciprocal acoustic
transport. By optimizing the coupling strengths and modulation phases, we
achieve frequency-preserved unidirectional transport with 45-dB isolation ratio
and 0.85 forward transmission. Our results open to the realization of acoustic
nonreciprocal technologies with high efficiency and large isolation, and offer
a route towards Floquet topological insulators for sound.
