Transducer selection initially requires consideration to the operating environment. If the transducer module will be exposed to the outdoors, positioned in an active warehouse or production floor, or is highly mobile, such that water droplets, dirt, or airborne debris are present, a closed-top or closed-face transducer is recommended. Closed-top transducers are typically hermetically sealed to prevent the piezoelectric membrane from being damaged by environmental debris or alien particles, and are able to tolerate a wider temperature range. As a result of the additional protective overhead from closed-top transducers, the piezoelectric membrane must be excited with a sinusoidal voltage averaging 100 V_PP. If the protective overhead is not required, and the transducer will be operating in a controlled, indoor environment, open-top transducers are available as an alternative. Open-top transducers offer an increase to driver and receiver sensitivity since the piezoelectric membrane is directly exposed to air, and less acoustic impedance mismatch exists at the face of the transducer. Open-top transducers typically require ten times less in their driving voltage requirement, averaging 10 V_PP.