Sapporo Subway 9000 series EMU set 9001 at Odori Station on the Toho Line (Image Source: Wikipedia). Photo by bellz_asamidou
We’ll uncover the mystery of the chirping sound that reverberates on Sapporo’s subway. Why is it making the sound? A major experiment at a train depot!
There, we’ll discover a surprising secret that is normally hidden from view. Client (Koara-san, in her 50s, resident of Sapporo): “I can hear a chirping sound on the Tozai Line platform. What is it? And please find out why I can’t hear it on the Namboku Line.”
Sapporo’s subway has three lines: the Namboku Line, the Tozai Line, and the Toho Line. According to the client, he can hear the sound on the Tozai Line, but not on the Namboku Line.
What on earth is that sound? Could it be that they keep sparrows as pets? We immediately went to Nijuyonken Station on the Tozai Line…
Investigator: “I can hear it! There’s a chirping sound going on right now.” When we actually checked on the platform, we could hear a mechanical chirping sound when a train approaches and after it has left.
What is the true nature of this sound? 、 働くやんがきたな。 English: Subway user: “I don’t know. I’ve never heard it.” “When you enter? Sorry, I don’t know.” “Isn’t it this kind of sound? Isn’t it something from the subway?” As expected, users have noticed the sound, but don’t seem to know the details.
Next, on the Namboku Line… Investigator: “I can’t hear the chiming sound on the Namboku Line platform.” Just as the client said, the chiming sound could not be confirmed on the Namboku Line.
So what about the Toho Line? Investigator: “The chiming sound can be heard on the Toho Line as well.” As a result, the chiming sound could be heard on the Tozai Line and Toho Line, but not on the Namboku Line.
What on earth is going on here? We requested an interview with the Sapporo City Transportation Bureau, and were given permission. They said they would show us an experiment, so we headed straight to the Toho Line’s rolling stock depot…
Sapporo City Transportation Bureau’s Hara Seiya: “So, I’d like to try making a chiming sound.” Standing far away from the investigator, he hit the guide rails, otherwise known as subway rails, with a hammer. And then… Hara Seiya of the Sapporo City Transportation Bureau says, “Here we go.”
*Chun chhun chhun, indeed! It’s the same chiming sound that can be heard on the Tozai Line and Toho Line!
What on earth is this? The secret to the sound lies underneath the carriage, and this time we were given a special look.
Hara Seiya of the Sapporo City Transportation Bureau says, “This is the negative current collector.” This device is the source of the chiming sound – the negative current collector.
In a typical subway, electricity is passed from the steel wheels to the rails, but as the Sapporo subway uses rubber tires, electricity does not flow. That’s why electricity is passed to the rails through the “negative current collector.”
So why is there that chiming sound? Hara Seiya of the Sapporo City Transportation Bureau said, “The chiming sound is heard when a device called a negative current collector separates at a joint in the guide rail or around a curve, then comes back together again.”
In other words, this negative current collector separates at a rail joint or curve, then comes back together again, making a clanging sound.
Furthermore, this sound reverberates underground and can be heard as a chiming sound. So why wasn’t it heard on the Namboku Line? We spoke to a train depot on the Namboku Line. Investigator: “Why doesn’t the Namboku Line make the chiming sound?”
Kaito Makino of the Sapporo City Transportation Bureau said, “The sound is heard. The structure of the negative current collector on the Namboku Line is different from that on the Tozai Line and Toho Electric Railway.” The chiming sound is heard on the Namboku Line as well! The secret lies in the negative current collector, after all.
Kaito Makino of the Sapporo City Transportation Bureau said, “This is the negative current collector. It bounces up once at the rail joints, etc., and then hits the top of the guide rail when it falls.” That’s right. While the Tozai and Toho lines make contact from the side, the Namboku Line’s negative current collector makes contact from above. That’s why… Kaito Makino of the Sapporo City Transportation Bureau said, “The sound resonates differently on the side and top, so I think that’s why it’s hard to hear the chiming sound.”
So, he experimented again! This time, he hit the side and top of the rail with a hammer and listened for the difference in sound. First from the side. *Chi-chi-chi-chi-chi, chi-chi-chi. Then from above. *Chi-chi-chi-chi-chi. There is definitely a chiming sound, but it’s quieter! Hitting from above makes the sound less resonant than hitting from the side! That’s why the sound wasn’t noticed on the Namboku Line.
So why are the negative current collectors shaped differently on the Namboku Line and the Tozai and Toho Lines? Makino Kaito of the Sapporo City Transportation Bureau says, “The shape of the guide rails is different on the Tozai Line, Toho Line and Namboku Line.” The answer lies in the shape of the rails. The rails on the Namboku Line are shaped like a horizontal H, while the rails on the Tozai Line and Toho Line are shaped like an inverted T. In fact, when the Tozai Line was being constructed, this method was adopted because changing to a negative current collector that makes contact from the side would allow for more space in the carriages. As a result, the shape of the rails was also changed.
Kaito Makino of the Sapporo City Transportation Bureau says, “The shape of the guide rails may also change the way the sound resonates.” This was the true nature of the “chunking sound.”
