this is what i tested with changing C3 and C4 .... both connected +12V DC supply respectively....
C3 and C4 positive polarity connected to Q1 , jumper wire was connected between both circuits Q1 Collector : Speak in mike 1 or mike 2 = Both Speaker voiced out
C3 positive polarity connected to Q1 , C4 negative polarity connected to Q1, jumper wire was connected between both circuits Q1 Collector : Speak in mike 1 or mike 2 = Both Speaker Voiced Out
C3 and C4 negative polarity connected to Q1 , jumper wire was connected between both circuits Q1 Collector : Speak in mike 1 or mike 2 = Both Speaker voiced out
(all the voiced out from Speaker 2 was not clearly....)
now i pull out the jumper wire and changing the C3 and C4 as 3 solution above, and you can guess the result as shown : Speak in mike 1 = Speaker 1 voiced out, Speak in mike 2 = speaker 2 voiced out(but very quietly....maybe i will change the R10 and R11 value or instead with potentiometer)