The story behind Sony MDR-CD900ST and it’s unique design and tuning choices

As an owner of the Sony CD900ST and someone that absolutely loves it, I was very curious about the story behind this cult Japanese headphone and the reasons behind some of it’s design choices. So I did some digging and this is what I found.

What the CD for Digital?

The first Sony CD headphone was released in 1982 to faithfully reproduce the wide frequency band and dynamic range of Compact Disc (CD) sound sources in the “digital age” [1] that was ushered by the release of the Philips and Sony co-developed Compact disc (CD) format that same year [2].

So, if you’ve always wondered what the ‘CD’ in CD900ST signified and why the headphone has that famous “For Digital” sticker, now you know.

P.S. Someone please tell Zeos so this doesn’t haunt him forever.

The Driver-on-Ear Headphone

The MDR-CD900ST was jointly developed by Sony and Sony Music Studios originally for use at CBS/Sony Shinanomachi Studios. According to Koji Nageno the engineer behind the MDR-CD900ST, he worked together with the engineering team of Sony Shinanomachi Studio and it took him 3 years to tune it to the satisfaction of Sony Music who had very specific requirements around sound localization and sibilant sounds [3]:

It was very important that they (Sony Music) wanted the sound to come from the front. For example, when a singer sings 10 cm away from the mic, the sound coming out of the headphones must also be able to tell this 10 cm distance. While most headphones tend to have wide dimensions and sound distant. Which is quite different So I tried to get the sound from the driver to be as direct as possible to my ear.

To be able to do that I had to reduce the space between the headphones and the ears. Using a 40 mm driver and a not very thick headphone pad to reduce this area. I also put a small seal around the driver to direct the sound from the driver to the ear. When wearing headphones, the ears will be close to the driver, similar to wearing headphones over the ear half-ear. Which will make the sound from the driver go directly to the ear.

In addition, they also have very complex requirements, such as the style of the sound emanating from the teeth, such as the S, that must be tuned to the manner they want. Which I have to put in a lot of effort in tuning until the success of Sony Music.

Koji Nageno in this interview (translated using Google Translate)

A lot of people think the thin earpads on the CD900ST and the driver touching your ears are just bad design or some Japanese quirk but it was in fact a design choice to achieve a very specific sound goal: localization.

Built to last

The MDR-CD900ST is known as the de-facto standard for monitor headphones in Japan [4] for more than 30 years for good reason.

Sony thoroughly pursued the qualities (maximum input of 1,000 mW, replacement parts system [5], etc.) and durability required in the professional world to withstand the grueling requirements of regular use in recording studios and broadcasting stations [6].

Open to All

Since it’s launch, it’s durability along with the emphasis on sound quality required for monitoring ensured it gained the trust of not only studio personnel but also by artists, and had been featured on TV, radio, magazines, etc. This resulted in a flood of purchase requests from the general public so in 1995 it was made available to consumers.


After reading this article If you’re thinking about buying the MDR-CD900ST you should know the following caveats:

  • The MDR-CD900ST is officially available only in Japan [7].
  • Since it’s a professional headphone intended for business use by recording studios, it doesn’t come with any warranty [6].


That’s all for now. I really enjoyed researching and writing this post and found lots of other interesting information on the MDR-CD900ST that I’ll write about soon in future posts so subscribe to the blog with your email to get notified as soon as I make future posts:

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