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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.

Caveats

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].

Outro

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:

References

Etymotic ER2 series (ER2XR and ER2SE) dynamic driver size

I couldn’t find any info on the driver size of the ER2 series so I contacted Etymotic and got an official number from them.

The official response I got from them is that the driver size of the ER2 series is 5.8mm.

AUX extension cable mod for Sony MH755

After having tried many different AUX extension cables, I really like this short 0.5m 3.5mm male to female AUX extension cable from DTECH. The TPE material is nice and soft and blends well with the MH755 cable unlike the fabric ones that sorely stand out.

Please note that this is a 3.5mm 3 pole (TRS) cable and doesn’t work with 3.5mm 4 pole microphone (TRRS) connectors.

Tyll would have loved the ER2XR

While reviewing the Etymotic ER4SR and ER4XR here is what Tyll had to say about bass response:

For me, the bass level on the ER4SR simply isn’t enough. Frankly, even the ER4XR doesn’t have enough bass for me, but it’s much better. I believe quite strongly that bass response on headphone should have about a 5dB bass boost below about 150Hz.
Tyll Hertsens in 25 Years of Making a Good Thing Better: The Etymotic ER4sr and ER4XR on Page 2

Tyll would have loved the ER2XR 🙂:

When the ER4XR was launched, Tyll applauded Etymotic for making the brave move of catering to user preferences and deviating from that they believed to be technically “accurate”. I think Etymotic went further with the ER2XR (and it’s almost like they took his feedback into account) and for that I am grateful as the ER2XR has just the right bass response for my preferences 🤗.

For me, having over 20 years of close experience interacting with Etymotic and the ER4 product evolution, I find it an interesting example of corporate learning at work. On the one hand, Etymotic has very strong reasons to believe they have a grip on what “accurate” means, on the other, they have 20 years of experience with customer feedback about the desire for more bass. Adding bass willy-nilly is simply not something this audiometry company would do; but having strong feedback that customers want more bass can’t be denied either. Making the corporate decision to deviate from technically accurate to cater to user preference is actually a pretty brave move from their point of view. I applaud this development!
Tyll Hertsens in 25 Years of Making a Good Thing Better: The Etymotic ER4sr and ER4XR on Page 2

Seekers vs. Tinkerers

You can judge IEMs/headphones on whether they sound good to you out of the box or also on their potential.

People from the former camp (seekers) might go down the path of finding the ones that perfectly match their preferences. IMO, the probability of this is so low that it seems futile to chase the perfect match. At best they might find something that is close to some of their preferences, but not others.

People from the latter camp (tinkeres) recognize they might not find the perfect match and are willing to put in the work to take advantage of potential. They do this either via EQ or modding. A prerequisite for this is potential. You might be able to fix tonality to some extent but you can’t fix things like technicalities, coherence, etc. if there isn’t a potential for it. Even tonality might not be fixable in some cases.

Some good example of tinkeres are james444 and the folks over at audioreview.org and a great example of an IEM being recognized for it’s potential is the JVC HA-FD01 which was modded by james444 and eventually resulted in the now legendary Drop+JVC HA-FDX1.

Of course there are many other dimensions along which to categories ourselves in the hobby but I think this is an interesting dichotomy to highlight.

So which are you, a seeker or a tinkerer? Are there better terms for these?

Category: Stuff