Pressure field and SPL in the closed back-volume configuration with an excitation of 1 V at an atmospheric pressure of 100 kPa. (a) Acoustic pressure field at f = 5 kHz. (b) (b) Sound pressure level (SPL) at distance of 13 mm. The experimental results are shown as mean (dashed line) ±2σ (shaded region) using the standard deviation σ of the 8 individual measurements (full thiner lines).