| 181 / | HD | ACOUSTICS |
| 175 | DF | SOUND-MODIFYING MEANS {12} |
| 198 | DF | .~ Housing or enclosure (e.g., sound confining and absorbing) {2} |
| 200 | ![]() | .~.~ Machine type enclosure {5} |
| 201 | DF | .~.~.~> Offfice type devices (e.g., typewriters, teleprinters, etc.) |
| 202 | DF | .~.~.~> Electical type devices (e.g., transformers, motors, etc.) |
| 203 | DF | .~.~.~> Reaction engine test chamber |
| 204 | DF | .~.~.~> Internal-combustion engine |
| 205 | DF | .~.~.~> Partial enclosure or shroud |