Western Electric did a lot of work on audibility when they designed those carbon mic elements, their work is where the 300-3000Hz "voice" bandwidth came from.?
What kind of readability reports have you been getting???
I think those carbon mics were designed for 6V power; it might be a bit starved with 3.3V behind 2.2KΩ since the elements are about 200Ω IIRC.??
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73, (other) Don N2VGU?
Donald S Brant Jr