CPC Subgroup
G10K 11/22 for conducting sound through hollow pipes, e.g. speaking tubes
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 > Methods or devices for transmitting, conducting or directing sound (G10K11/02, G10K11/36 take precedence) > for conducting sound through hollow pipes, e.g. speaking tubes