An enclosure that intensifies those audio frequencies at which the enclosed air is set into natural vibration.
"Just want to thank you for setting up the order form so it can be used to calculate without actually ordering. It is SO refreshing to be able to estimate the cost of a service without having to register and log in and accept cookies and all that nonsense. In fact, I often leave a site if I have to go through all that just to find out my costs. ..."