Shell Vibrational Modes- how they work and how they affect drum shell design
This video is a big one- the main focus is vibrational modes, and the way shells vibrate. Just to be clear- our goal is to educate drummers and builders on the design factors that relate to sound. Here’s the summary":
-Drum shells vibrate in many ways, called “modes”
-The fundamental mode, which many builders often “tap” to hear is minimized by the addition of hoops/heads/tension, and is NOT a prominent tone in a completed shell
-Drum shell builders/designers should focus less on this fundamental, and instead focus on the shell’s flex and stiffness along it’s length, which is more relevant to the modes that vibrate in a completed drum.
Drum Shell Design 101
(why our ultra-thin shells are so versatile)
It is not easy to develop a great drum shell. It takes a lot of experimentation, time and cost. We all have preconceived ideas about what makes a shell sound a certain way, often developed by reading marketing blurbs, and online discussions. And most of it is wrong. The easy way to market a drum design is to focus on the wood species, number of plies, and bearing edge angles- all of these are the wrong details to consider. The way you build a shell (ply thickness, grain orientation, glue type) all influence the sound of a drum far more than the difference between wood species. When you design a shell, you are really trying to manipulate 3 physical attributes that define the sound:
1. STIFFNESS: THIS DEFINES THE PITCH OF THE SHELL- STIFFER IS HIGHER PITCHED, MORE FLEXIBLE IS LOWER PITCHED. THIS IS DIRECTIONAL, SO STIFFNESS PARALLEL TO THE AXIS OF THE DRUM EFFECTS THE DRUM DIFFERENTLY THAN AROUND IT'S CIRCUMFERENCE
2. ELASTICITY: THIS DETERMINES HOW VIBRATIONAL ENERGY SUSTAINS IN THE SHELL- A HIGHLY ELASTIC SHELL SUSTAINS LONGER, A SHELL WITH LOWER ELASTICITY CONVERTS ENERGY (TO HEAT) MORE QUICKLY, PROVIDING SHORTER DECAY, AND SOUNDING MORE "DEAD".
3. MASS: THE MASS OF THE SHELL AFFECTS HOW SENSITIVE THE SHELL IS TO VIBRATIONAL ENERGY. A LIGHTER SHELL REACTS EASILY TO THE VIBRATION OF THE HEAD, A HEAVIER SHELL REQUIRES MORE ENERGY TO EXCITE, REDUCING THEIR RESPONSIVENESS.
Different wood certainly have different traits, but the differences are very small compared to the effect of changing thickness or grain orientation. A 1mm thick piece of maple will have very different physical properties than a 2mm piece, but compared to a 1mm thick piece of birch, or even mahogany, it will be very similar.
We currently only offer ONE wooden shell design. And it kicks ass. It does exactly what we set out to do- offering incredible responsiveness and versatility. We didn’t get it right the first time, or the second. It took a while to figure out how to do it. But the result is consistently great.
Here are couple of the important things we learned:
1. Low mass is the key to versatility. Since heavy shells take more energy to resonate, they can either absorb a lot of energy and sound very controlled and thuddy, or keep the energy in the head and sound very open and bright, based on shell and edge designs. A low mass shell takes much less energy to vibrate, so you can let the heads and shells resonate together without killing the sustain. They can do everything well, and let you decide how you want them to sound with head choice and tuning.
2. Stiffness is directional. You want drum shells to vibrate along the length of the shell- keeping it more flexible along the length gives a lower pitch, and allows it to vibrate with less energy, yet you need the shell to be strong enough around it’s circumference to support head tension. You know that “tap test” that everybody does to show a shells tone? Yeah, that only tests the stiffness around the circumference, which is NOT the way shells vibrate in the context of a drum.
So these learnings helped us come up with our shell design. We were looking for Low Mass, High Elasticity, with a stiff circumference and axial flexibility. Therefore, we use 3 thick horizontal plies. This gives us the circumferential stiffness we need. In order to keep the shell strong, we use 2 thin vertical plies, just enough to keep the shell structurally sound. This combo lets us keep the shells ultra-light, with flex in the right directions.