Purpose <p> Inspired by the structural properties of DNA, this study develops a multi-oscillator coupled piezoelectric phononic crystal beam to achieve low-frequency broadband vibration suppression. The research aims to establish a systematic design method for tunable metamaterials, elucidate the underlying bandgap formation mechanisms, and propose an effective optimization strategy for bandgap expansion.</p> Method <p>The proposed locally resonant phononic crystal beam is designed and analyzed using the PWE/FE hybrid method. Geometric parameters of the local oscillators are optimized via the MOCOA-CPO-SVR multi-objective algorithm. Bandgap characteristics are investigated through detailed modal analysis and piezoelectric tuning under external voltage excitation.</p> Results <p>The structure exhibits a broad bandgap spanning 1401.8–2682.3 Hz along with four narrower low-frequency bandgaps between 700 and 1100 Hz, demonstrating a maximum transmission loss of 279.5 dB. Optimization by MOCOA-CPO-SVR multi-objective optimization algorithm yields a 15.13% reduction in the starting frequency and a 32.11% increase in the termination frequency of the widest bandgap. Modal analysis reveals that bandgap initiation is governed by co-directional vibration of local resonators, while termination correlates with counter-directional motion. Additionally, applied voltage actively tunes bandgap properties through enhanced electromechanical coupling, and reduced coating density increases the termination frequency by approximately 4.15%.</p> Conclusions <p>This work presents a comprehensive design and optimization methodology for low-frequency broadband phononic crystals. The demonstrated synergy between oscillator geometry, material properties, and piezoelectric effects provides a viable pathway for developing advanced tunable metamaterials and intelligent acoustic devices.</p>