CPC Main Group
H04R 21/00 Variable-resistance transducers (gaseous resistance transducers H04R23/00; magneto-resistive transducers H04R23/00)
2 direct subcodes
Child Classifications
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- H04R 21/02 Microphones
- H04R 21/04 Gramophone pick-ups using a stylus; Recorders using a stylus