However since it is a Modern horn, I don't think that it seems likely that it is the split bell problem. I think we still need to know what moutphiece/reed combo you are using. Wide moutphiece could be the problem as well, espicially if you are using a strong reed. I'd say take it to the tech, or get a light. If their is not a leak then it could be the mouthpiece and reed combo.saxismyaxe said:Problems in the low end bow and bell notes are usually traceable to a leak in the horn nine times out of ten, as others have noted.
A well sealing horn will play easily top to bottom provided your chops and mouthpiece setup up are also up to snuff, which is why a good adjustment and tuneup of the horn is worth it's weight in gold.
The cork or mouthpiece cap in the bell trick is particularly helpful for certain peculiar issues that seem inherent with split bell key horns.