Direct answer
A waterproof acoustic membrane adds acoustic impedance to the sound path, so its effect depends on membrane construction, active area, adhesive opening, cavity geometry and the microphone or speaker. The finished assembly must be measured across the required frequency range.
Main acoustic variables
Smaller active area, restricted adhesive openings and narrow cavities can increase acoustic loading. Membrane mass, pore structure and support layers also influence insertion loss, frequency response and distortion. Compare candidates using the same fixture and device geometry.
Validate after environmental exposure
Measure both initial performance and recovery after representative water, sweat, dust or temperature exposure. A membrane that meets an isolated material target may perform differently after it is bonded into the final acoustic path.