The Secret Pin Stopper in Muro Box

The Secret Behind the Comforting Charm of Music Box

Have you ever wondered why music box melodies have such a comforting charm? It’s because each note has a sustaining sound effect. This unique sound is generated from the continuing vibration of the comb after it is plucked by the pins on a cylinder. 

You can imagine that if a piano loses its sustain pedal, each note will sound for a very short time because the damper has stopped its vibration. The similar device inside the Muro Box works like a car’s brake. It will stop the flexible pins from touching the comb right away in order to keep the vibration of previous notes stay longer in the air.

The following video will show a comparison of two Muro Boxes (one with the pin stopper installed, and the other one without it) when playing the same melody:

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Cylinder Design:Traditional Music Box vs. Muro Box​

The mechanical design of a traditional music box let all pins rotate at the same pace with the cylinder. Therefore, it can only play slow music in order to maintain the sustaining sound effect. 

the close shot of a traditional music box cylinder and its comb
This is a close shot of a traditional music box cylinder and its comb.

On the other hand, Muro Box can play as fast as 4 beats per second for the same note, which is consecutive eight notes at BPM 120. The basic unit of notes in Muro Box is eighth note (quaver). So what enables Muro Box to play faster songs?

The answer lies in our patented cylinder, which has 20 “ratchets”. It is a metal component that looks like a wheel with a set of 8 angled-teeth (also referred as the pins) to pluck the comb. This design allows the flexible pins to pluck the comb according to your programmed music, including fast songs.

However, when a pin touches the comb before the previous note ends, it will cause the loss of the sustaining sound effect of the previous note. After numerous hours of research and experiments, we came up with the “pin stopper”. This device works like a car’s brake because it can stop the pins on the cylinder for a while to ensure that the previous note has completed its vibration to maintain the sustaining sound effect.

The Challenge in Designing the Pin Stopper

Our design of the pin stopper is much more complicated than just a bar that allows all of the pins to align at a position after plucking the comb. In order to match the size of the comb and cylinder, the pin stopper is only 6 cm wide. In total, there are 27 components in one pin stopper.

To be able to insert so many components in such a small space, our pin stopper has become a metal art craft. The following paragraphs will introduce the complicated processes of how we make a metal spring before assembling the pin stopper.

The closed shot of a pin stopper.
The closed shot of a pin stopper.
This picture shows that there are 20 teeth on a metal spring.
There are 20 teeth on a metal spring.

The Key Component of the Pin Stopper : Metal Spring

The pin stopper has 20 teeth on a key component called the “metal spring”, which corresponds to the 20-note comb. The crucial function of the metal spring is to bounce back the pins so they will stand by at the right position when waiting for the right timing to pluck the following notes according to the programmed music.

Muro Box requires a high precision in both the size and shape of each component because any tiny error may cause unpleasant noise or even dysfunction of the Muro Box. Therefore, the metal spring went through a series of processes on different machines: cutting, ultrasonic cleaning,  drying with an air gun, roasting in an oven, bending, and applying oil. From a giant roll of flat iron sheets to the precise metal spring that can be perfectly installed inside the Muro Box, the process is very complicated and time-consuming.

The Processes of Making the Metal Spring

 

Step 1: Cut the iron sheet into the right size and shape. 
We use a semi-automatic precision machine to cut the giant iron sheets to make sure that both the shape and size of the metal spring can meet precise requirements.

Step 2: Cleaning and drying the metal spring.
Any remaining oil stains, iron filing powders, and dusts will create error in the sizing of the metal spring and also break down the lubrication, which can easily lead to the dysfunction of Muro Box.

 

The worker is using an air gun to dry the metal springs that has been washed three times in an ultrasonic cleaner machine.
The worker is using an air gun to dry the metal springs that has been washed three times in an ultrasonic cleaner machine.
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Therefore, before the assembling process, we must make sure they are completely cleansed. We use an ultrasonic cleaner to wash it three times. In the first round, we add a special metal cleanser liquid to the machine to wash the surface of the metal spring. In the second round, we use clean water to wash it again. In the third round, we use the amplified soft water to wash it. After three rounds of washing, we wipe off the residual moisture with an air pressure gun, and roast the metal spring with an oven.  

The video summarizes the whole process of how a metal spring is produced before attaching it to the pin stopper.

Step 3: Bend the metal spring to a perfect bend shape.
For this step, we also use a bending machine to ensure its angle is accurate and to maintain the stable quality of this important metal spring. 

Step 4: Apply our special solution of oil on the 20 claws of the pin stopper.
This step requires a small machine (a dispenser) to ensure each drop of the oil applied on the tooth is the same. This machine generates a unique sound when each drop of the oil is pushed out from the injector controlled by a worker.

Finding a workable solution is just the first step. We found that the small components of the stopper generate mechanical noise while it operates. Moreover, after the whole Muro Box is assembled, the noise is amplified by the wooden box when Muro Box is playing music. The “crack” sound became an unpleasant noise that interferes with the beautiful melodies played from Muro Box.

 

We have tested various kinds of acoustic pads and industrial lubricating oil. We also modified the shape of the baffle for pins on the ratchet to hit them from different angles. Our team has invested a lot of effort in reducing the mechanical noise. 

Can you imagine that, it requires such a complicated design for just a pin stopper to align the pins at a fixed position after they pluck the comb? Because the sustaining sound is the soul of music box music, we believe all of our effort in research and experiments for the pin stopper will not be wasted. Thanks to this unique device, Muro Box can maintain the sustaining sound effect when playing your favorite melodies.

The pin stopped installed on the Muro Box before installing the comb and cylinder
Muro Box in the user's hand

Why is Muro Box so Special?

The appearance of Muro Box is just a small music box, however, the design and production of each single piece of its components is very complicated. It requires a huge amount of time, money, and effort in the development of Muro Box. 

This is why playing your valuable memories from Muro Box is so special and precious. We hope that our customers will enjoy listening to the live music playing from Muro Box as we do.

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