Music boxes are a popular gift for many occasions. However, few people know how they actually work. In this article, we're breaking down the internal workings of a common music box.
The evolution of music boxes has been such a fascinating journey. They began as cumbersome sets of bells struck by hammers, but over the course of several hundred years, they've evolved into compact devices that can fit in your pocket and provide you with melodies whenever needed! Inside a music box, the drum and comb work together. The comb works like a tuning fork because it vibrates to produce sound. A clock spring with a wind-up mechanism turns gears in the music box. A governor in the clockwork controls how fast all of the parts move, and slows down when it is running too quickly.
The drum and comb are two of the most important parts which play a song. There are two main parts that work together to pluck the song: the drum and the comb. The drum is the rotating cylinder with little spikes and the comb is the set of notes that can be plucked. The melody is programmed into the drum by placing the pins in a particular pattern. As the drum rotates, the pins pluck the teeth of the comb. The comb is made of steel and has eighteen teeth. Each tooth is a note. Longer teeth are lower notes and shorter teeth are higher notes.
The comb works like a tuning fork because it vibrates to make a sound. The teeth each vibrate with a different tone, and the shorter teeth vibrate faster than the longer ones, producing higher frequency musical notes. When you look at the bottom of the comb, the teeth don’t have the same thickness. The longer teeth — the lower notes — are weighted more on the ends. This added weight lowers their resonant frequency even more. Because of this added weight, the comb is more compact. If the comb were unweighted it would have to be roughly 40 percent longer to produce the same range of frequencies. Another advantage of the weighting is that the combs can be manufactured in a single size, you just cut away the proper amount of material to tune the instrument to play a unique set of notes. For example, although each comb has eighteen notes, the specific notes vary for a particular song.
The part that moves the entire mechanism is a clockspring. It is 40 centimeters long when it's not wound up. One end of the spring attaches to the casing of the music box and holds it in place. The other end of the spring is attached to the winding key. There are also some ratchet mechanisms on this axle so that it can turn independently from its plastic gears. This happens when you wind up your music box, but when you unwind your clock spring, these gears turn too! As the spring unwinds, it rotates the gears and turns the drum. But there’s a problem with this setup — the spring will unravel quickly and the music will play too fast.
In the clock, there is a part called the governor. This controls how fast everything moves. It works like a fan that spins really fast. If you stop this, nothing will move. The machine uses a multiplying gear system to make the fan spin over 3000 times per minute! The governor slows down the unwinding of the spring using air resistance. Air resistance increases with velocity squared - so if things move a little bit faster, there is a lot more air resistance. When you start the governor, it will go fast without difficulty, but when the governor is spinning quickly, air resistance slows it down and limits how fast it can go.
For a hundred years music boxes were the way a family listened to music in the home. However, by the turn of the twentieth century, the phonograph and radio had displaced them. Music boxes were shoved into attics or, more often, left to rot in junkyards. Over time, they became less and less common and now real clockwork music boxes have become an emotionally powerful collector's item.
These modern music boxes, then, are a charming vestige of a past filled with brilliant engineering and craftsmanship. One last thing, if you hold a music box in your hand, it’s not very loud. However, if you place it on top of a hollow container, it’s much louder and richer. The vibrations of the comb are transferred through the metal base, into the container where they resonate. This resonance amplifies the sound. Also, if you rest the music box gently against your teeth, the music will resonate inside your skull. So, the next time you listen to a music box appreciate its sound, but also think of the centuries of innovation and design that led to it.