The Structure of the Timpani
Construction of the timpani

Calfskin has been used from long ago for the head of the timpani, as cowhide was said to be too thick. The skin from one animal was used to make one drumhead. The hard backbone part of the skin passes through the center, and acts as the node of the vibrations. The timpanist of the Vienna Philharmonic orchestra, for instance, uses goatskin heads.

When viewed under a microscope, heads made of animal skin show a more uniform and detailed pattern than that of a plastic head. Animal skin also offers better tone and sound quality, and what's more, even after putting stress on certain part of an animal skin drumhead by drumming and causing it to stretch out, it will eventually revert to just the right shape. Even though the animal that the skin is made from might not be alive, its skin lives on in the head of the timpani.
That said, animal skin is susceptible to changes in humidity and temperature; and the skin becomes taut when exposed to light, which raises the pitch. This means that heads made of animal skin require constant adjustment.

Calfskin heads, which naturally snap back into shape even when stretched

Calfskin heads, which naturally snap back into shape even when stretched

Plastic heads are easier to take care of, since they are not as susceptible to changes in humidity and temperature. As with animal skin, plastic heads need to be attached to the timpani shell in a specific direction. When the plastic sheet that forms the timpani drumhead is stretched out during manufacturing, tiny long grains that are invisible to the eye are formed at a molecular level in the direction that the sheet is stretched. From the standpoint of making the ideal sound, these grains should be facing the horizontal direction of the timpani. The mark that is printed on the drumhead shows the direction in which the head should be attached. Usually, it should be right in front of the player.

The manufacturer's logo is parallel to the grains

The manufacturer's logo is parallel to the grains

The method used to change the tension on a drumhead depends on the style of the timpani.
Hand-tightened timpani are tightened in the same way as ordinary drums, by tightening each tuning bolt, one at a time. Timpani with handles are tightened by tightening the tuning handle, which tightens all of the tuning bolts at the same time to adjust the head. Also, the pedal-type timpani that was invented in the 20th century can be tightened by moving the pedal with one's foot to change the head tension, thus changing the pitch.

On pedal-type timpani, the head will tighten when the pedal is depressed (producing a higher pitch), and the head will loosen when the pedal is loosened (producing a lower pitch). For performance, a feature to hold or maintain the tightness (pitch) of the head, according to the adjustments made using the pedal is necessary.

In the case of the pedal timpani that uses balanced action, the spring inside of the base tightens at the same time that the pedal is depressed. This makes the spring tension and the head tension equal, which silences (holds) the pedal.
Another type of system uses a clutch system to stabilize (hold) the pedal, which is used to adjust the pitch.

Pedal-type pitch change mechanism

Pedal-type pitch change mechanism

When the kettle of the timpani moves, it makes it harder to change the pitch. For this reason, a metal hoop called a suspension ring is used to firmly support the kettle. Also, the fewer parts that the kettle touches, the less the vibrations will be interfered with. The suspension ring supports the kettle by hanging it in air, so that it does not touch any other parts.

Yamaha's pedal balance spring mechanism uses an appropriate amount of friction to stabilize the tension of both the head and the pedal spring. Further, five different linking mechanisms that apply the principle of leverage are used to achieve a smoother pedal action.

How the head tension changes

How the head tension changes

The reason timpani can create pitched sounds whereas drums cannot is because they are constructed differently. Drums use two cylindrical heads, one on the top and one on the bottom. When the top head is struck, the vibration strikes the bottom head and is then transmitted back and forth from top to bottom, changing in various ways. As there are a variety of ways in which the vibration changes, a stable pitch cannot be produced.

On the other hand, the bottom of the timpani is closed off with a lid, and is round, which is why the timpani can create specific pitches and musical tones. The air trapped inside the round kettle blocks the complex vibrations that are normally produced by a drum; and it is said that this makes it easier to create regular, integral multiple harmonics from the membrane of the drum.

How the head tension changes

How the head tension changes

The difference between cylindrical and round-bottomed timpani lies in whether or not they are airtight.
Although we say that the timpani is airtight, there is actually a tiny hole at the bottom of the instrument. When the hole is smaller, the sound has a longer sustain; and when the hole is larger, the sound has a shorter sustain, with a lighter touch when played. When you put your hand under the hole, you can feel that the air is coming out.

The hole at the bottom of the kettle

The hole at the bottom of the kettle