A GA INSTRUCTOR PLT TURNED DOWN HIS RADIO VOLUME CTL TO EXPLAIN SOMETHING ABOUT THE LNDG PROCESS TO HIS STUDENT AND CONSEQUENTLY HE MISSED IMPORTANT INFO ABOUT ANOTHER ACFT FROM THE TWR. THE ATCT LCL CTLR THEN ASSUMED THAT HE WAS NOW NORDO. AFTER A CLOSE ENCOUNTER; THE INSTRUCTOR TURNED UP HIS VOLUME.

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WHILE TEACHING LNDGS (STAYING IN PATTERN) I WAS TRYING TO TEACH AN IMPORTANT ELEMENT OF LNDGS WHEN RADIO CHATTER BTWN TWR AND ANOTHER ACFT KEPT INTERRING. SO I TURNED DOWN VOLUME WITH THE INTENT TO TURN IT BACK UP AFTER A SHORT MOMENT HAD PASSED (LONG ENOUGH TO SAY WHAT I WANTED TO SAY; APPROX 15-20 SECONDS). THE INSTRUCTOR WAS CONCENTRATING TOO MUCH ON TEACHING INSTEAD OF FLYING BECAUSE THE INSTRUCTOR (ME) FORGOT TO TURN THE VOLUME BACK UP. ON DOWNWIND; I NOTICED AN ACFT PASSING ACROSS OUR FLT PATH; SAME ALT. I REMEMBER THINKING WHAT THE HECK IS HE DOING. THEN IT DAWNED ON ME THAT MY VOLUME WAS TURNED DOWN. I TURNED IT UP JUST IN TIME TO HEAR THE CTLR TELLING ME TO MAKE A FULL STOP DUE TO NO RADIO. I WISH I HAD REMEMBERED TO LOOK AT THE TWR TO SEE IF HE WAS USING THE LIGHT GUN. AFTER I ADMITTED THAT THE VOLUME WAS TURNED DOWN HE CLRED US FOR THE OPTION; THEN INSISTED WE KEEP VOLUME TURNED UP. I HATE BEING CAUGHT DOING SOMETHING THAT I KNOW I SHOULDN'T HAVE DONE. EVALUATING THIS; I DETERMINED THAT 1) MY PAST EXPERIENCE AT NON TWRED ARPTS HAS ALLOWED ME TO DEVELOP BAD TEACHING HABITS SUCH AS TURNING VOLUME DOWN; AND 2) I MAY BE DOING TOO MUCH TEACHING IN AIRPLANE INSTEAD OF ON THE GND. THE ACFT I SAW WAS APPARENTLY DOING A MISSED APCH AFTER A PRACTICE APCH.