Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Publication of BE407422ApublicationCriticalpatent/BE407422A/xx
H04M1/00—Substation equipment, e.g. for use by subscribers
H04M1/02—Constructional features of telephone sets
H04M1/19—Arrangements of transmitters, receivers, or complete sets to prevent eavesdropping, to attenuate local noise or to prevent undesired transmission; Mouthpieces or receivers specially adapted therefor