True Blast Volume

[Earl in Midlothian VA]

I have several WBB locomotives and they all run great!!!  My concern is that the volume of some of the True Blast Horn systems vary in volumes by engine---but most are not as loud as sound from other manufacturers that have a volume control onboard the unit.  Several of my WBB locos have their horn and bell drowned out by the sounds of the wheels of long trains that they are pulling or especially when more than one train is running too. The sound of these units are fine, but I wish I would make it louder.  Is there any way to do this---or have I missed something obvious? 

Thanks for your advice here. 

ES