An acoustic collection system for handheld electronic devices is disclosed having a fitted casing with a chestpiece, and a passageway for conducting sound from the chestpiece to a microphone. In one embodiment, the configuration of the passageway can be actively varied by the user to selectively transmit frequencies of interest to the device. In another embodiment, materials with different sound propagation properties may be used to augment or dampen sound within the passage. In another embodiment, a microphone may be placed within the passageway and its position therein varied by the user.