The main categories of trademarks related to audio are as follows:
Class 9 Scientific Instruments
0908-Audio and Video Equipment
090015: Audio Conduit
090015: Audio tube
09182: Diaphragm (audio)
090593: Audio connector
0920-Alarm device, Electric bell
090014: Audio alarm
Class 20 Furniture
2001-Furniture
C200004: Audio stand
Class 41 Educational Entertainment
4105-Recreational and Sports Activity Services
410085: Rental of Audio Equipment