YOU SAID:
People in the back need to speak louder so everyone can hear.
INTO JAPANESE
後ろにいる人は全員に聞こえるように、より大きな声で話す必要があります。
BACK INTO ENGLISH
People behind you must speak louder so that everyone can hear you.
INTO JAPANESE
あなたの後ろにいる人は、全員に聞こえるように、より大きな声で話さなければなりません。
BACK INTO ENGLISH
The person behind you must speak louder for everyone to hear.
INTO JAPANESE
あなたの後ろにいる人は、全員に聞こえるようにもっと大きな声で話さなければなりません。
BACK INTO ENGLISH
The person behind you must speak louder for everyone to hear.
That didn't even make that much sense in English.