B737-200 FLC FLEW THROUGH THEIR ASSIGNED PARALLEL RWY LOC ON VECTOR BECAUSE THEIR RADIO COM VOLUME WAS TOO LOW TO HEAR ATC INSTRUCTIONS FOR TURNING INBOUND. THE OVERSHOOT ALSO CAUSED PENETRATION OF CLASS B AIRSPACE OF THE ADJOINING PRIMARY ARPT.

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ORD AIRSPACE INCURSION. AT XB45 I AND MY FO WERE FLYING FLT FROM MCI TO MDW. WE WERE AT AN ALT OF 2500 FT ON A HDG OF 040 DEGS. WE WERE FLYING ACFT B737-200. AS MY FO LOADED THE TWR FREQ INTO THE #1 RADIO'S STANDBY SIDE; HE INADVERTENTLY TURNED DOWN THE RADIO'S VOLUME KNOB WHICH IS LOCATED ON TOP OF THE TUNING KNOBS ON THE L SIDE OF THE COM #1. WE WERE CURRENTLY BEING VECTORED BY APCH FOR AN ILS LNDG ON RWY 13L AT MDW. AFTER ABOUT 60 SECONDS OF SILENCE; WE NOTICED WE WERE GOING THROUGH THE RWY 13L LOC. AT THIS POINT WE FOUND THE RADIO HAD BEEN TURNED DOWN. WE RE-ESTABLISHED COM WITH APCH AND WERE TOLD TO MAKE AN IMMEDIATE R TURN HDG 180 DEGS. WE WERE ALSO TOLD THAT THERE WAS A DC10; 3 MI AHEAD WHEN WE WERE GIVEN THE TURN. WE RECEIVED NO TCASII ALERTS. FROM THE 180 DEG HDG WE WERE VECTORED BACK ONTO FINAL FOR A NORMAL ILS LNDG ON RWY 13L AT MDW. MY CONCLUSION IS THAT THE NONSTANDARD FUNCTIONS INVOLVED IN FLYING THE -200 ACFT; ESPECIALLY THE COM RADIO SET-UP; MAKE THIS A POTENTIALLY DANGEROUS ACFT FOR THOSE OF US WHO DON'T FLY IT ENOUGH TO REMAIN PROFICIENT IN ITS DIFFERENCES.