Re: Bonham tuning
I also love this type of tuning as it reduces excess resonance, throws the sound back up at you and is real punchy. It works great in a number of situations that I have been involved in with tuning drums, my own and other artists. If you got the 18" tom sounding good, to me that would be the toughest. Here's what I know from my experiences with this type of tuning.
When you say the 16" tom sounds horrible, what exactly do you mean? Too much sustain? Too floppy? Too high pitched? There is no exact answer to how much tighter the bottom head should be, but as a general rule, it usually works if the heads are in a relationship that is complimentary to one another. What I mean is, the bottom head usually works well on floor toms a third (4 notes) higher on the bottom than on the top. That's how Frankie Banali from Quiet Riot, who is a huge Bonham fan and has a vintage 1969 kit in the Bonham sizes, tunes his floor toms, with the top heads at a slightly higher tension than one would think. (Coated emperors over coated ambassadors)
Then, the drums are in tune with each other in that the two floor toms are in a complimentary relationship as well, (probably thirds or fourths) which eliminates weird overtones when you strike them together and avoids frequency cancellation, which enables each drum to project to it's fullest, making the floor toms sound huge.
It sounds to me like you're almost there, you just need to tweak the drums a bit. I would forget about the other drums for a second and start over with the 16" tom, getting it to sound good, and then try to compliment that drum with the others. You should make out OK. If you have any specific questions you can always email me and we can put our heads together to get those puppies sounding monstrous..