<p>Electronic devices that use acoustic vibrations are of use in classical and quantum technologies. Such devices rely on transducers to exchange signals between electrical and acoustic networks. The transducers are typically based on piezoelectricity. However, conventional piezoelectric transducers are limited to either small efficiencies or narrow bandwidths, and usually operate at a fixed frequency. Here we report piezoelectric microwave–acoustic transduction operating close to the maximal efficiency–bandwidth product of lithium niobate. We use superconducting quantum interference device arrays to transform the large complex impedance of wideband interdigital transducers into 50 Ω. We demonstrate an efficiency–bandwidth product of around 440 MHz, with a maximum efficiency of 62% at 5.7 GHz. We use the flux dependence of superconducting quantum interference devices to create transducers with in situ tunability across nearly an octave at around 5.5 GHz. Our transducers can be connected to other superconducting quantum devices and could be of use in applications such as microwave-to-optics conversion, quantum-limited phonon detection, acoustic spectroscopy and fast acoustic coherent control in the 4–8-GHz band.</p>