Though the initial concept of the face-mounted resonator was ahead of fabrication technology, the solidly-mounted resonator (SMR) is now a practical resonator design yielding high Qs in a space-efficient and robust mounting configuration. An agile tunable piezoelectric SMR is now provided with a resonator and alternating stacks of high mechanical impedance and low mechanical impedance, piezoelectric layers advantageously stacked on a substrate with the piezoelectric layers connected to an adaptive circuit that alternates with an external electrical impedance having values anywhere between an open circuit and a short circuit. The piezoelectric Bragg stacks with alternating layers of high and low mechanical impedance and properties made variable via the additional piezoelectric properties of the stack materials overcomes difficulties caused by the limitations of manufacturing techniques, acoustic power leakage and inability to meet the single-frequency, quarter-wavelength criterion due to manufacturing deviations.