Kevin - Thanks for all the backround info. I re-ran the hiss test using an analog source and yes at a 0db setting I can hear a very faint hiss but again I have to physically stick my ear in the horn to hear it. I believe your right in that the digital signal may be getting muted. I also stuck my SPL in the horn but the hiss was still under 50db and didn't register on the meter.

Tom