Non-electric sound-amplifying devices, e.g. non-electric megaphones (amplifying by horns G10K11/02; amplifying by focusing G10K11/26)

Full Title

Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general > Non-electric sound-amplifying devices, e.g. non-electric megaphones (amplifying by horns G10K11/02; amplifying by focusing G10K11/26)