C172 IN PRACTICE AREA NEAR HSV ARPT EXPERIENCED CONFLICT WITH C172 AT 4500 FT AFTER TURNING ATC FREQ DOWN TO INSTRUCT STUDENT.

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WE HAD RECEIVED CLRNC FROM HUNTSVILLE CLRNC TO DEPART TO THE NW PRACTICE AREA VFR AND REQUESTED 3000 FT AS OUR INITIAL ALT. ONCE ESTABLISHED IN THE NW PRACTICE AREA; AND AFTER PERFORMING SOME CLRING TURNS; WE BEGAN PRACTICING THE MANEUVERS. WE REMAINED ON THE SQUAWK CODE GIVEN TO US BY HUNTSVILLE CLRNC AND DID NOT CANCEL RADAR SVCS. THIS IS STANDARD PROC FOR OUR FLT SCHOOL. AFTER SOME PRACTICE AT SLOW FLT; IT BECAME APPARENT THAT A LAYER OF CLOUDS; THAT COULD BE CONSIDERED SCATTERED TO FEW AT APPROX 3000 FT; WAS GOING TO INTERFERE WITH THE MANEUVERS. I HAD THE STUDENT CLB TO 4000 FT TO CONTINUE. DURING THE NEXT FEW MANEUVERS; IT BECAME DIFFICULT TO TALK OVER HUNTSVILLE APCH AND I ELECTED TO TURN THE VOLUME DOWN ENOUGH THAT MY STUDENT AND I COULD CONVERSE. I HAVE DONE THIS IN THE PAST AND HAVE ALWAYS BEEN VERY CAREFUL NOT TO TURN IT DOWN SO MUCH THAT I COULDN'T HEAR ATC. THIS TIME; HOWEVER; I MUST HAVE TURNED IT DOWN A LITTLE TOO LOW. I COULD STILL HEAR ATC COMMUNICATING WITH OTHER ACFT BUT I WAS NOT AT FIRST AWARE THAT THE VOLUME WAS SO LOW THAT IT WOULD BE DIFFICULT TO HEAR ATC OVER MY OWN VOICE AS I TALKED THE STUDENT THROUGH THE MANEUVERS. OVER THE NEXT SEVERAL MINS; WE CONTINUED CLRING TURNS AND PRACTICE MANEUVERS AT 4000 FT. AFTER A PWR-OFF STALL ON A HDG OF 360 DEGS; I DIRECTED THE STUDENT TO TURN R TO 180 DEGS AND PERFORM A PWR-ON STALL. AS WE TURNED; WE CLRED THE AREA AND BEGAN TO SET UP FOR THE MANEUVER. THE STUDENT BEGAN THE MANEUVER INCORRECTLY. I HAD HIM STOP THE MANEUVER AND LEVEL OFF AGAIN AT 4000 FT ON THE SAME HDG SO I COULD TEACH IT TO HIM CORRECTLY. THIS IS WHERE I BELIEVE THE SECOND FACTOR THAT CONTRIBUTED TO THE OCCURRENCE CAME INTO PLAY (THE FIRST BEING THAT THE VOLUME ON THE RADIO IN USE WAS TOO LOW); IE; THAT WE REMAINED TOO FOCUSED TOO LONG ON A MANEUVER WHILE STAYING ON A CONSTANT HDG WITHOUT CLRING THE AREA FIRST AND BEGINNING AGAIN. BEFORE REDOING THE MANEUVER; I NOW FEEL I SHOULD HAVE HAD THE STUDENT (OR EVEN BETTER THE STUDENT SHOULD HAVE ELECTED) TO DO ANOTHER CLRING TURN TO THE R BEFORE BEGINNING AGAIN. THIS TIME; AT MY DIRECTION; HE BEGAN THE PROCS FOR A PWR-ON STALL CORRECTLY BUT HE BEGAN TO HAVE TROUBLE WITH COORD AND PRODUCING A FULL STALL. THIS CAUSED THE MANEUVER ON THE SAME HDG TO BE EVEN MORE PROLONGED WHILE I ATTEMPTED TO SHOW THE STUDENT HOW TO CORRECTLY CTL HIS HDG AND HOW MUCH NOSE-UP PITCH WAS NECESSARY TO PRODUCE A FULL STALL. DURING THIS PERIOD WE CLBED APPROX 500 FT TO 4500 FT MSL. AFTER THE STALL AND DURING THE RECOVERY WAS WHEN I HEARD HUNTSVILLE APCH SAY 'NXXXXX; DO YOU READ ME?' I REPLIED WITH 'NXXXXX; YES WE JUST DIDN'T HEAR YOU THE FIRST TIME.' THE CTLR REPLIED WITH 'YOU DIDN'T HEAR ME THE FIRST 7 TIMES; THIS IS THE 8TH TIME I'VE CALLED YOU TRYING TO TELL YOU TO MAINTAIN VFR AT OR BELOW 4000 FT FOR TFC; ARE YOU HAVING A PROB WITH YOUR RADIOS?' I SAID 'NXXXX; NO SIR.' ABOUT THAT TIME HE SAID 'TFC ALERT AGAIN! 2 O'CLOCK POS LESS THAN 1 MI SAME ALT!' I IMMEDIATELY LOOKED AND SAW THE OTHER ACFT WHICH APPEARED TO BE ANOTHER C172 IN CRUISE AT 4500 FT SBOUND; APPROX 1 MI AND ABOUT 100-200 FT ABOVE. I REPLIED WITH 'NXXXXX HAS THAT TFC IN SIGHT.' THE CTLR REPLIED WITH 'MAINTAIN VISUAL SEPARATION WITH THAT TFC AND MAINTAIN VFR AT OR BELOW 4000 FT.' I READ BACK AND COMPLIED WITH THE CLRNC. HE THEN ASKED 'ARE YOU A STUDENT PLT ON A SOLO; OR IS THERE AN INSTRUCTOR ON BOARD?' I REPLIED 'THERE IS AN INSTRUCTOR ON BOARD.' THE NEXT THING I SAID TO HIM WAS 'HUNTSVILLE APCH; NXXXX; I TELL YOU WHAT WE ARE ESTABLISHED IN THE NW PRACTICE AREA; WE'D LIKE TO CANCEL WITH YOU AT THIS TIME AND CALL YOU BACK ON THE WAY BACK INBOUND.' THE CTLR REPLIED WITH 'RADAR SVCS TERMINATED; SQUAWK VFR; FREQ CHANGE APPROVED.' AFTER THAT; I TURNED THE VOLUME UP AND CONTINUED TO MONITOR BOTH HUNTSVILLE APCH AND NEARBY PRYOR FIELD'S CTAF. THE REST OF THE FLT WAS UNEVENTFUL. I BELIEVE THIS SITUATION WOULD HAVE BEEN AVOIDED BY THE OBVIOUS; LEAVING THE VOLUME UP AND LISTENING BETTER TO ATC AND PERFORMING ANOTHER CLRING TURN AFTER THE FIRST MANEUVER ATTEMPT WAS UNSUCCESSFUL.