Microphone sensor for picking up voice from across the room
Normal microphones are not very sensitive .Speak in to them while monitoring the output volts on a scope and you will see what I mean .The Carbon microphone which was in my 1970s junkbox did have a high output level but lots of distortion .I have not tried a parabolic microphone .What would always work was a loudspeaker backwards .I tried a horn type speaker backwards and that worked even better . Most speakers are low impedence like say 4 or 8 ohms .What I did in 1975 was to use an output transformer backwards to provide a better match to the preamp .Mains hum pickup was an issue and output transformers were becoming harder to find so I used a simple common base transistor stage biased at about 1 mA and then fed it into a more conventional AF amp .I could hear stuff 30 feet away with junkbox Ge 1960s transisters .Things were easy in the mid 1970s .Modern minature    microphones do not put out much voltage .I have used speakers from   4 inch dia to 8 inch dia with good results .I have not used this approach with any crossover speaker   systems because they were not in my junk box in 1972 .I have tried phillips 800 ohm Hi Z speakers directly and they work well but would be hard to find now .