| 381 / | HD | ELECTRICAL AUDIO SIGNAL PROCESSING SYSTEMS AND DEVICES |
| FOR 127 | DF | HEARING AIDS, ELECTRICAL (381/68) {15} |
| FOR 140 | | .~ With acoustic wave modifying structure (381/153) {5} |
| FOR 141 | DD | .~.~> Including sound conducting tube (381/154) |
| FOR 142 | DD | .~.~> Directional (381/155) |
| FOR 143 | DD | .~.~> Sound intensifying or spreading element (381/156) {1} |
| FOR 145 | DD | .~.~> Absorbing or attenuating element (e.g., baffle, obstruction, damping) (381/158) |
| FOR 146 | DD | .~.~> Enclosure or resonant cavity (381/159) |