We investigated the influence of CuO amount (0.5-3.0mol%), sintering temperature (900 degrees C-1000 degrees C), and sintering time (2-6h) on the low-temperature sintering behavior of CuO-added Bi-0.5(Na0.78K0.22)(0.5)TiO3 (BNKT22) ceramics. Normalized strain (S-max/E-max), piezoelectric coefficient (d(33)), and remanent polarization (P-r) of 1.0mol% CuO-added BNKT22 ceramics sintered at 950 degrees C for 4h was 280pm/V, 180pC/N, and 28C/cm(2), respectively. These values are similar to those of pure BNKT22 ceramics sintered at 1150 degrees C. In addition, we investigated the performance of multilayer ceramic actuators made from CuO-added BNKT22 in acoustic sound speaker devices. A prototype sound speaker device showed similar output sound pressure levels as a Pb(Zr,Ti)O-3-based device in the frequency range 0.66-20 kHz. This result highlights the feasibility of using low-cost multilayer ceramic devices made of lead-free BNKT-based piezoelectric materials in sound speaker devices.