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audio amplification question & coupling ?

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New Member
Hi all,
hope iam noy making this forum a boring place for new visitor by asking the same old question again and again. ya you all got it...it is 2 wire door intercom question again but this time i have worked out lots of things and need help about the following:-

Considering the most simplified example.

Suppose :-

1) In your Bed Room you have

8 Ohms Speaker
a Condenser Mic
9 Volts Battery
bell circuit using KA2410.


2) At your Door side you have

8 Ohms Speaker
a Condenser Mic
it gets supply from the room side.
Push button which when ever pressed cause a bell to ring in your room using KA2419 circuit as mentioned above.

Now i which type of coupling should i do in order to create full duplex communication between above mentioned units considering that both units are connected with a single pair cable i.e. two wires are used to connect the room and the door intercom. Following web site contains coupling info related to audio amplification please guide me which should i use and how:-

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