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:

See Also



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.

QKZ VK4 vs Sony MH755 (SBH56) Measurements (Frequency Response Graphs)

So I took out the QKZ VK4 today to measure (using my DIY-tube rig) and I was pleasantly surprised to see why I remember liking them.

Note: The graphs don’t accurately represent what you might hear and are only representational. Improving them is an ongoing process.

Measurements taken using pre v0.1 of my DIY IEM measurement rig

Where to buy original Sony MH755 in India (might also be applicable to other countries)

If you’re looking at buying a Sony MH755, you already know why it’s special, so I won’t get into that here. Let’s dive right in and look at all the options you have for buying a genuine one. I’ll be focusing on India but some of these may apply to other countries as well.

Sony SBH56 and SBH24

The most risk-free way to get an original Sony MH755 is to buy the Sony SBH56 or Sony SBH24. These are Bluetooth headsets that the Sony MH755 comes bundled with. This is how I got my first one (I think I got the last listed one at You can still (as of February 2020) find them in authorized Sony Centers in Mumbai and very likely in other parts of India. I have also walked into smaller shops selling mobile phones and electronics and found them (as of February 2020). I also occasionally find them online, for e.g., I’ve seen them on as recently as February 2020.

This is obviously an expensive option (compared to the next one) because you’re also paying for the Bluetooth receiver (SBH56 is Bluetooth 4 and SBH24 is Bluetooth 4.2, and both only supports SBC and AAC) but you can find them on discount and even negotiate a cheaper rate in some places.

Standalone MH755 (OEM Version)

If you just want the standalone MH755 (OEM version) and have searched online, you will come across this list of confirmed genuine Sony MH755 eBay sellers that is a great starting point (though not all of them ship to India). I’ve bought MH755s from the following three sellers from that list and can confirm the units I got were legit:

  1. kanoya (Japan)
  2. xirui_01 (China)
  3. rwtf3024 (China)

Note 1: I have ordered many white units from kanoya and they were all legit but the one and only black unit I got from them was not, and they promptly issued a refund and unlisted the black one after realizing it wasn’t legit. So there’s still a chance you could get fake ones (I’ll be making another post soon about how to detect fake ones).

Note 2: The tips of the OEM version are slightly different from the ones you get with SBH56/SBH24 and there is a very very minor difference in the sound quality because of it (I’ll talk about this in another post soon) but the difference is so minor that it shouldn’t be of concern for most people and the OEM version is just as good as the one that comes with the Sony Bluetooth headsets.

Pre-modded MH755

If you’ve done your research on the MH755, you’ll know that it was meant to be used with Bluetooth headsets and therefore has a very short J-cable, i.e., the right-side cable above the y-split is longer than the left-side (designed to wear around the back of your head which was (is?) apparently popular in Japan). This makes them very inconvenient and annoying. Most people generally end up modding it (I’ll be doing a separate post on the different ways in which you can mod the MH755).

If you don’t want to go through the hassle of modding it yourself, you can find people that sell pre-modded MH755s online. I’ve bought a pre-modded MMCX MH755 from mh755seller on ebay and can vouch for the one I received. He has many options that also include upgrade cables.

Pre-owned MH755

Lastly, you can try asking in the Pre Loved Gear for Sale – by The Indian Audiophile Forum (or similar selling and trading groups in your country), to see if someone wants to part ways with their MH755.

And… that’s all I got. If you know of any other way to buy a legit Sony MH755, let me know in the comments. Happy listening.

Sony MDR-EX800ST/MDR7550 – Brief Encounter

Thanks to someone from the Indian Audiophile community, I got to try the Sony MDR-EX800ST/MDR7550 for about 20 min and really loved them.

Here are my quick and dirty notes:

  • Treble was rolled off and I was missing some treble detail.
  • Bass was slower compared to my ER2XR (couldn’t A/B) but in general the bass (had punch but didn’t sound boomy) and especially the sub-bass was such a treat.
  • The sense of space, air and the natural timbre gave me goosebumps on some songs.
  • The cable wouldn’t sit on my ear (twists away from the ear) but it didn’t affect the fit as much and overall the fit was not bad.

Blon BL-03 vs. Sony MH755 – Initial Impressions

  • BLON03 is more efficient than MH755
  • I experience driver flex on both of them
  • I get slightly better isolation on MH755
  • BLON03 is more brighter than MH755
  • MH755 has more sub-bass/rumble and feels more viseral
  • BLON03 is more punchy/boomy than MH755 and sounds more “fun”
  • Bass is slightly faster on MH755
  • Vocals sound slightly veiled on MH755
  • String instruments, high hats and cymbals sound more natural and have more detail on MH755