Are your hoops round ? Flat ? Tuning problems will Ensue...
Most drummers are making sure their drums are round. And drummers might place a drum (without a head on it) on a perfectly flat surface to check for evenness of the bearing edge.
But have you measured your hoops diameter from several places to see if they are round ? Tuning is easier with round hoops.
Do your hoops lie flat on a flat surface ? Even tensioned tuning can be impossible if your hoops are not "flat". Did you ever have the head near one tension rod keep going up in pitch when you tune some other tension rod ? If the hoop does not lie flat, when it is mounted on a drum, one part of the hoop will press down on the head more than other sections of the hoop. Endless amounts of fine tuning, going back and forth around the head may or may not resolve the unevenness of the hoop. But it would be easier with a flat hoop.
I have seen new die cast hoops that were not "flat". Try tuning one of those evenly.
Think of a hoop shaped like the outer edge of a potato chip (only not so exaggerated). When you tune down the high ends, the low ends are pressed down even more, hence a pitch change when you didn't even touch that tension rod.
Another defect that will cause the same problem is if (where the hoop was welded together) there is a rough (or uneven) spot on the underside of the hoop.
I have some vintage Slingerland snare drums, I was able to bend the rims back into being round and back into being flat. It took time and patients, but the drum (with original hoops) became nice to tune.
Round flat hoops are a pleasure to tune. Check them when you change heads.
