A crash helmet for use by motorcycle drivers or riders has a rigid shell; a first flexible acoustic tube a first section of which extends into and has a bell horn in the region of the mouth-protecting part of the shell, and a second section extending from the shell through the opening in the neck-surrounding part of the shell; a second flexible acoustic tube a first section of which extends into and has a sound-intensifying terminal portion in the region of an ear-protecting part of the shell, and a second section extending outwardly through the aforementioned opening of the shell; first and second additional flexible acoustic tubes respectively corresponding to the second and first tubes and having first sections installed in the shell of a second crash helmet; and a quick-release coupling respectively connecting the second sections of the first and second tubes with the second sections of the second and first additional tubes. The first sections of the tubes are embedded in or secured to the padding at the inner side of the respective shell.