| 381 / | HD | ELECTRICAL AUDIO SIGNAL PROCESSING SYSTEMS AND DEVICES |
| FOR 127 | DF | HEARING AIDS, ELECTRICAL (381/68) {15} |
| FOR 152 | DD | .~ Electromagnetic (e.g., dynamic) (381/192) {5} |
| FOR 154 | DD | .~.~ Movable voice coil (381/194) {3} |
| FOR 155 | | .~.~.~ Multiple (e.g., double) (381/195) |