The 60Hz hum in the subs may be from poorly shielded or oriented power supply transformers in the sub cabinet. I belive the Avantgardes use internal amps for the subs, yes? If they do, have you tried running them straight off the wall socket with no filtering? If you get a similar 60 cycle hum, you've got an inernal noise source--that is, the mains transformer. Opening the speaker (yikes!) and carefully shielding the transformer with ERS cloth (*don't short anything*) or similar could help. A more simple method of banishing such hum from a component builder's perspective is to change the orientation of the transformer. In other words, unmount it from whatever it's attached to and simply turn in from it's origial mounting position and listen for changes.
If the mains transformer is in a separate chassis from the subs, you can try similar things and it's easier since you don't have to open the speaker.
Not sure about the sound from the horn, but it doesn't sound like a tube issue as the volume doesn't increase with settings.
Hope this helps--we all can get a bit neurotic about this. As I recently said to my audio bud, this sometimes seems more like a support group than a hobby group.
Enjoy.
If the mains transformer is in a separate chassis from the subs, you can try similar things and it's easier since you don't have to open the speaker.
Not sure about the sound from the horn, but it doesn't sound like a tube issue as the volume doesn't increase with settings.
Hope this helps--we all can get a bit neurotic about this. As I recently said to my audio bud, this sometimes seems more like a support group than a hobby group.
Enjoy.