Shell Thickness

In a nutshell, the thicker the shell, the more higher it will sound. The thinner the shell, the lower it will sound.
Don't get caught up in plies. You can't always judge a shell's thickness by how many plies it has. Some companies cut their plies thinner or thicker than others. The density of the wood also determines how thin a ply can be cut. Lauan plies will be much thicker than Birch, for example, because Birch is stronger and can be cut thinner. Or one company's 9 ply shell could be thinner than another company's 6 ply shell. There are many variables.

Making shells from many plies, instead of one thick piece of wood, adds strength and stability to the shell. By alternating the grain of each ply, a thinner shell can be made that ends up being stronger than a thicker, solid piece of wood. It also will resist warping, as each ply has a different direction to the grain.

Gene Okamoto at Pearl Drums, provided the following information about how shell thickness effects the sound of a drum: The number of plies effects how readily energy is transferred from the heads to the shell. This single factor has a profound affect on the tonal characteristics and projection of the drum.

Thin shells (4 ply, 5mm) enable relatively easy energy transfer from the heads to the shells thus causing the shells to vibrate. This vibration imparts a very rich "wood" tone to the overall sound that can be most appreciated in near-field applications and especially in recording.

Medium thick shells (6 ply, 7.5mm) have greater stiffness and resist energy transference from the heads. With less shell vibration, a trade-off is achieved: the sound is slightly "cooler" than thinner shells but projection is greater. Drums made to this thickness are ideal for general-purpose applications and / or situations requiring more "horsepower."

Thick shells (8 ply, 10mm and 10 ply, 12.5mm) are extremely "efficient" and allow most of the player's energy to be focused to the audience. These drums are ideal for coliseum-type venues and other applications requiring high sound pressure levels. Snare drums made in this thickness rival metal snare drums in intensity and projection.