Hey Mitch,
Thanks for rotating the pics. Somewhere in the process of going from iphone to gmail to my PC the file gets "grumpy" and won't allow changes to be saved. It works on my trusty mac, but that is in FLA with my wife until Thursday.
Your question about the tom L-arm direction effecting resonance/sustain is an interesting one. My first thought is placebo effect, but hmmmmmm...
Typically we think of the resonant characteristics of an object as being determined entirely by it's construction and the environment that it is oscillating in. If you replicate every minute detail of a Stradivarius violin and play it in the same room, it should sound like the original. When you connect objects together, like the tom drum to the L-arm to the mount to the bass drum, they become one oscillating system whose overall resonance and sustain is a complex combination of the vibrational characteristics of the parts. In the case of the tom drum/L-arm/mount/bass drum system the connecting points between them play a big role in how well the vibrational energy is transferred/shared between the parts in the system as well. If the connections are tight then the parts act more like a whole, if they are loose the opposite is true, and dampening occurs. So let's assume the connections are all tight with minimal dampening effect. In this system the two main oscillators are the tom and bass drum, the tom being the source and the bass acting as a passive radiator, the other heavy steel parts do not resonate or sustain much on their own.
So lets do a series of Gedankens (thought experiments)...
First, strip it down to just the tom and the L-arm.
Attach the up pointing L-arm securely to an immovable object, attach tom drum securely to the L-arm, have your robot drummer hit drum with a precise impulse, measure the sustain. Repeat for down pointing L-arm. The only physical difference in the trials is that a small section of the steel L-arm is under compression due to the weight of the tom in trial one, and it experiences tensile (pulling) stress in trial two. I can't imagine that would have any noticeable effect, and to rule it out completely we could set the whole thing up with the drum heads facing sideways rather than up and down. If we do that, trial one looks just like trial two viewed from behind. (Note: You may have to reprogram your robot to use Taiko techniques.)
Now let's include the tom mount...
Stick the tom mount down into the immovable object, attach the up pointing L-arm and tom drum, have your robot drummer hit drum, measure sustain, repeat for down pointing L-arm. What changed between trials this time? The center of mass of the system is lower for trial 2. How much lower depends on how long the L-arm is, and where exactly the tom makes connection to the L-arm. If the tom is connected near the elbow of the L-arm then the center of mass only shifts downward by a few millimeters. If the tom is connected an inch or two away from the elbow then the shift would be more significant. Would this shift in the center of mass effect sustain? Surely it could have some effect, but I doubt it would be much. If we turned this experiment sideways there is still a change in the geometry of the parts. It goes from a stretched out Z shape to more of a U or J shape. In the end, the energy is vibrating the same overall mass, I doubt that changing the geometry of the heavy steel parts would make them more "sympathetic" to the tom drum's vibration in any significant way.
Finally, let's include the bass drum...
Replace the immovable object with the bass drum and repeat the previous Gedanken. What is different between the trials now? Well, now the change of the geometry associated with the L-arm pointing down brings the tom drum closer to the bass drum which should increase the sustain to some extent. The bass drum receives vibrational energy though the tom mount, but also through the air. The wave energy traveling through the air from the tom to the bass would roughly follow an inverse square relationship with distance. i.e. If you double the distance between them, the bass would receive only 1/4 as much wave energy. BUT...as a practical matter drummers set the height of the tom drum with respect to the floor or the top of the bass drum, to their playing preference. SO...when the L-rod is pointing up he/she would shift the whole tom mount assembly downward to get the tom head to the desired playing height, and vise versa for the L-rod pointing down. In either case the tom and bass end up the same distance apart, so all that inverse square stuff is moot.
In summary...
If it is anything more than a placebo effect (started by some guy named Gary "stix"" Jones at a Guitar Center drum clinic back in 1989) I think it comes back to physics similar to what I expressed in my previous post. The mass and length of the mount tube that extends down into the bass drum could have a dampening effect the transfer of vibrational energy from the tom to the bass. In the previous post was thinking in terms of it mitigating a large force/torque that would possibly damage the acrylic shell, but the same would be true of smaller repeating vibrational forces.
So if you take the advise of Gary "stix" Jones and set up your kit with the L-rod pointing down, you are probably also adjusting the mount tube upward to set the playing height of the tom, if my theory holds, that would make the bass shell less damped and more sympathetic to the vibrations coming to it from the tom though the mount assembly. So in that way, my theory seems to fit with the urban legend.
Alas, all this is pure conjecture, the only true answer would come from actual controlled experiments. I didn't go as far as getting out the oscilloscope, and charging up the Tokai robot, but to my (tinnitus riddled) ears I hear no difference between L-Rod up and L-Rod down.
Thanks a lot Mitch! I was suppose to get some trim painted in the kitchen today before my wife gets home...I guess I'll be working late
tonight.
P.S.
These thoughts brought to mind a local musician/inventor friend of mine. He invented and patented something he calls "Jet Fretz" http://www.jetfretz.com/ that allow a guitar to have double the sustain, and it's entirely mechanical. He can prove on an oscilloscope that the sustain is actually tripled, but it drops below the threshold of hearing after a while so he advertises it as a doubling effect. Anyway, he removes the regular frets from your guitar neck and routs out a dove tail channel where the fret used to be. He then slides in the Jet Fret from the side. The Jet Frets are much more massive, they look like a little piece of railroad track or something. So the added sustain results due to the string being fretted against a more massive object that is more securely connected to the mass of the rest of the guitar, so the vibrational energy stays in the string longer. I have played some Jet Fretz guitars and it really is a noticeable difference, but he charges like $800 to do the retrofitting...alas he has not gotten rich from the idea yet, but the guy from Dream Theater and a few other celeb guitar guys have used them.
AL
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-69 Ludwig Standard
-72ish Star Acrylic
-Taiko drumming robot
-immovable object
