The resonance/antiresonance measurements has been in the mm2 and .hivin.43m phase of Cu-Cl-B (-30 to +200 DegC) and Cu-Br-B (-130 to +100 DegC). The piezoelectric coefficients d31, d32, g31, g32 (mm2 phase) and d14, g14 (.hivin.43m phase), the elastic compliances SE11, SE22, SD11, SD22 (mm2 phase) and the electromechanical coupling factors k231, k232 (mm2) were determined. The relative sign of d31 and d14 is equal and opposite to that of d32. The sign was correlated with the orientation of the etch figures, optical indicatrix, spontaneous polarization and ferroelasticity. The free dielectric constant eT33 (1 MHz) of Cu-Br-B was measured in the mm2 and .hivin.43m phase. The temp. dependence of resonance frequency and elastic compliance reflects a softening of the lattice at the phase transition, being stronger for Cu-Cl-B than for Cu-Br-B.