Saying Biurchat hatora before you hear a Torah shiur. Why

Shulchan Orach OC: # 47
Does anyone know where is Shulchan Orach we learn out that listening to a shiur - for example on line or a tape - requires one to say Birchat Hatora beforehand.
A common occurence would be
Driving to shul to daven shachris and you plan to say Birchat Hatora in shul. In the meantime you are listening to a shiur online.


What did the Rabbi tell you? :slight_smile: