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Interview with the Engineers of the Sony Signature Series


Our Editor Beng Yeow with the Engineers of the Sony Signature Series

Sony Engineers:

  • Koji NAGENO [KN], Senior Acoustic Architect, Sony Video & Sound Products Inc.
  • Tomoaki SATO [TS], Walkman® Project Leader/Senior Electrical Engineer, Sony Video & Sound Products Inc.
  • Hiroaki SATO [HS], Walkman® Sound Quality Design Leader, Sony Video & Sound Products Inc.
  • Eiji KUWAHARA [EK], Acoustic Engineer of headphones, Sony Video & Sound Products Inc.

First and foremost, I would like to express my heartfelt appreciation to be able to have a one-to-one or should I say a one-to-four interview with Nageno-san, Tomoaki Sato-san, Hiroaki Sato-San and Kuwahara-san. Welcome to Singapore.

[BY] Our readers would like to know from each of you, how many times you been to Singapore? And what is your favourite local food?

[KN] I first came to Singapore in 1985, since then I have visited no less than twenty times. I have to say that my favourite is the Singapore Chicken Rice, the white version. When I first came to Singapore, I could only eat the Singapore Chicken Rice in Singapore, now I can get Singapore Chicken Rice in Tokyo and also when I visit the factory in Penang, Malaysia. However, the Chicken Rice in Singapore is still the best.

[EK] I have visited Singapore 7 times; however, 5 times are on transit mainly to the factory in Penang, Malaysia. My favourite local food is Bak Kut Teh, the Singapore version. I have also tried the Malaysia version, but I think the Singapore version is better.

[TS] This is my 2nd time to Singapore, the first time was two years ago. I not only like the Singapore Bak Kut Teh, but I am also a Bak Kut Teh Spices collector and I cook Bak Kut Teh at home in Japan. I have also experimented cooking using different types of meat with the spices and in my opinion, adding tomato to the Bak Kut Teh makes it better.

[HS] This is my 4th visit to Singapore. Similar to Nageno-san, I also like the Singapore Chicken Rice, the white version.

[BY] What are your impressions of the Singaporean audiophile community? And do they differ in any way from the audiophile communities of Japan? or even the US?

[TS] The Singaporean audiophile community is unique impression-wise, while we do not recommend modification, there is a group of NW-WM1A/1Z users who goes as far as modifying the components of the device all, in pursuance of better sound quality.

[HS] I have received many feedbacks from customers from Singapore, particularly during the One Signature Sound event at the Sony Store at Wisma Atria in October last year. The one I met during the event are Sony fans, I am so surprised by the passion they showed for the Sony products, they love Sony so much, much more than our fans back in Japan.

[EK] Singapore has a very good audiophile community; I think they are positive. Sometimes, in Japan, the fans are a little bit negative. Probably because we are Sony, they probably had an expectation, a high one for Sony. Japanese audiophiles have a dream for the Japanese brand to be well represented globally.

[KN] Each country’s audiophile fanatics has a slight difference, These fanatics can be segregated by the countries they represent but my impression is that Japanese and Singaporean are almost the same with similar thinking and behaviour.

[BY] I have observed that there seems to be a renewed focus on audio in Sony, particularly in the last 5 to 6 years, why is this so? What has changed?

[KN] About 10 years ago, audio categories were divided across several Sony internal companies, Walkman was under a computer company while Home Audio and Personal Audio were divided. Each team only focused on their own products. What follows is an organizational change which saw the unification of the audio categories – what we meant by unification is to start identifying a new common area of development for the audio categories, for example Hi-Res audio, a comprehensive strategy was developed to open up a new market by simultaneously launching a group of Hi-Res (High-Resolution) audio playable products, from mobile devices through to home entertainment systems. This was a very big change for us, allowing us a unified effort which has since produced Hi-Res Walkman and Headphones from the two teams represented today.

[TS] Especially for Walkman products, we started on the Hi-Res Walkman in 2013. Starting on the same concept for Hi-Res. Prior to the focus on Hi-Res, the focus of the new model has to be small and light-weight, the product also delivers high-quality sound, but it is high quality for general consumers, not for audiophiles. Since 2013, the team must design with the focus of delivering high-quality sound leveraged higher for audiophiles.

[EK] I think we noticed that the customers want more high-end products, particularly in the last 5 years. So, we decided to create more high-end in-ear headphones, this is a big change.

[BY] Ex-CEO Kaz Hirai stepped down on April 1, 2018, succeeded by Kenichiro Yoshida. Has anything changed in Sony’s focus on audio?

[KN] Yoshida-san basically continues Hirai-san’s focus on the relationship between the Creator and Customers, however, he places a higher emphasis for the company’s profile to be greater to the customer. Essentially, the emphasis is placed on ensuring that the Customers experience is what the Creators intended it to be. A good example is a collaboration with artists and engineers during the development of the IER-M7 and IER-M9, the team lacked the knowledge regarding stage monitor usage and the required audio quality, the assistance of artists and engineers who specialise in Sound Reinforcement (SR) was invaluable, thanks to the introduction by Sony Music.

[BY] Nageno-san, you led Sony’s development of in-house balanced armatures. The development has led to the creation of BAs that made the IER-M7, IER-M9 as well as the signature IER-Z1R possible. When did Sony decide to develop their own BA drivers? Can you share with us the challenges faced by the team over the years and your most memorable moment?

[KN] The development of Sony balanced armature drivers started in the summer of 2008, I co-developed the first engineering prototypes with Takayuki Ishii (Ishii-san), the former project leader of dynamic driver unit in 1990. Ishii-san and I met in 2008 and spoke about many topics which included headphone drivers, I then mentioned about balanced armature drivers and I want to try to make that kind of drivers and he agreed.

The two of us then started to study the concept and research on how to make balanced armature drivers that are smaller than dynamic drivers. We then made the first Sony handmade balanced armature prototype units after studying the concept, we got the parts and made some special arrangement for the terminals to be fixed on the board to complete the prototype in 2010. The first prototype was very small and has high sensitivity, however, the sound quality was not ideal and that was the start of Sony’s balanced armature development.

The balanced armature drivers were then further developed and introduced in 2011 to power a new series of in-ear under the XBA sub-brand, which stands for “Experience Balanced Armature”, with 11 models in total, namely the XBA-1, XBA-2, XBA-3,XBA-4, XBA-1iP, XBA-2iP, XBA-3iP, XBA-4iP, XBA-NC85D, XBA-BT75 and XBA-S65.

The biggest challenge is to create balanced armature drivers that are smaller than the current dynamic drivers. During the introduction of the XBA series, we were able to showcase balanced armature drivers that sport the same sensitivity as a 13.5mm dynamic drive but at a quarter the size. The most memorable moment has to be hearing the first handmade balanced armature prototype unit for the very first time, it was better than expected.

[BY] Kuwahara-san, from your role in the team, would you be able to share with us your biggest challenge alongside Nageno-san?

[EK] I joined Sony shortly after the introduction of XBA-1, my role in the team revolves around product development using the acoustic technology available, to decide the sound direction and eventually the sound quality.

When I came across the balanced armature drivers, I requested many units of the driver from Nageno-san, because I wanted to make a new pair of headphones using the balanced armature drivers.

The XBA-C10 was my first product based on the balanced armature drivers, released in 2013. Biggest challenge alongside Nageno-san is always creating something smaller while improving sound quality. I often discuss with Nageno whom I look up to as a Professor as he is the walking “encyclopedia” of MDR category.

[BY] Nageno-san and Kuwahara-san, tuning a multi-driver IEM is always challenging, especially when it comes to tuning a hybrid configuration such as the 2DD + 1BA on the IER-Z1R. Would you be able to share with us how the team go about tuning the reference signature series in-ear headphones? What are the methods used? How different is it from tuning the MDR-Z1R?

[EK] Yes, it’s very difficult and challenging. We wanted to provide customers with the best listening experience of being at the best seat in a concert hall. So, I designed it closer to a more realistic world by the expansion of the frequency band and dynamic range with new HD Hybrid driver system. At the same time, the phase characteristics and frequency characteristics were finely adjusted by Refined-phase structure and Sound space control to improve the reproducibility of the tone of the instrument.

IER-Z1R is similar to MDR-Z1R in terms of the sound concept. Both are based on the concept of the expression of the sound stage allowing the listener to feel the air. Although the technology used is partially similar, most are different.

IER-Z1R provides listeners with a sensory experience beyond music you can hear, something which cannot be felt in conventional in-ear headphones. Our ideal sound signature which we hope would be a reference to many.

[BY] Tomoaki Sato-san, in a report in the Nikkei Asian Review on the 13th of April, 2018 titled “How Sony saved itself, as seen from the trenches”, you were quoted saying you “never imagined such a device would actually reach the market.” The device is the NW-WM1Z. Are you able to share with us what was going through your mind and thought process during prototyping and what made you “decided to try some oxygen-free copper on a whim”? and your reactions when management decided to commercialise it?

[TS] Before the starting phase of the NW-WM1 series, we have made an oxygen-free copper prototype during the development of NW-ZX2. Copper as a material is soft and is difficult to shape, at that time we did not have the solution for mass production using copper, therefore we released the NW-ZX2 in aluminium.

The oxygen-free copper prototype has a very different sound quality from the original NW-ZX2, so we wanted to release this product. However, the management says our design is not for a hobby, our design is for business. The oxygen-free copper prototype was originally Hiroaki Sato-san from the mechanical design, but we didn’t release it at this phase, he wanted to release it next time.

Ichiro Takagi-san, Senior Executive Vice President and Officer in charge of Consumer AV Sales & Marketing shared with the team that for the next product, he wanted it to be smaller and lighter however that was not what we wanted to propose. After proposing the oxygen-free copper prototype on numerous occasions to the management, finally, Takagi-san listened to the prototype and discovered that it truly delivers amazing sound, however it was also super heavy. He said, he will go to Hirai-san now and wants to borrow the prototype and that was when Hirai-san got to listen to the prototype. That night, Takagi-san wrote an email to me, informing me that Hirai-san is very happy, and we have received the green light for the product. This prototype eventually evolved and became the NW-WM1Z today.

[BY] Hiroaki Sato-san and Tomoaki Sato-san, last year, the team introduced DMP-Z1, a product which previously didn’t exist in the market. Following your experience in 2016 with the NW-WM1Z/1A, did you imagine that the DMP-Z1 would be commercialised? What was the motivation behind creating the DMP-Z1?

[TS] During the development process, we did not believe it can be commercialised. However, management was aggressive to commercialise it, and we were encouraged by their willingness to put the DMP-Z1 on the market.

After the introduction of NW-WM1 series, we just felt we need more amplification power to satisfy all the hi-end customers. While the D.A. hybrid amplifier built into the TA-ZH1ES headphone amplifier achieves a high output, producing a high-quality sound even from high-impedance headphones, it relies on a large (AC) mains power supply which often carries considerable noise as its drawback. On the other end, we have our flagship Walkman NW-WM1Z running on clean battery power, meaning the audio quality is very high. However, it is limited by its size and can’t ensure the large output required for high-impedance headphones.

The motivation behind creating the DMP-Z1 was to create a product that would allow our customers to easily get the full potential out of their headphones like the TA-ZH1ES and run on clean battery power with no external elements, like the NW-WM1Z.

During the initial design phase of the DMP-Z1, the size was intended to be half of what you see today but Hiroaki Sato-san wanted more power to bring out the best from high-impedance headphones and that meant using large-capacity, high-output batteries to operate it.

[HS] We had been using the S-Master HX digital amplifier in the Walkman for a long time, since it became compatible with High-Resolution Audio, is an excellent amp that’s power-saving, space-saving, and achieves high audio quality, but it wasn’t designed with high output in mind. However, we have been researching a way to combine an analogue amplifier and a DAC from another manufacturer for more than five years now.

[TS] The research began in 2013 around the same time NWZ-ZX1 went on sale.

[BY] Hiroaki Sato-san and Tomoaki Sato-san, there is a question from readers about the naming convention of the DMP-Z1, is it missing an “R”? i.e. DMP-Z1R?

[TS] The naming convention of the DMP-Z1 is correct. There is no missing R.

[BY] Hiroaki Sato-san and Tomoaki Sato-san, the use of the large analogue volume control on the DMP-Z1 have left many of my readers using the NW-WM1Z or NW-WM1A wishing for a rotary volume knob for future Sony Walkman replacement models, is this possible? Technologically will it enhance the sound like it did to the DMP-Z1?

[TS] The analogue volume control on the DMP-Z1 is designed based on the same concept as models that already incorporate the S-Master HX digital amplifier used in the Walkman. However, our design philosophy is to deliver great audio to the users by keeping volume attenuation to a minimum in the digital processing stage and attenuating it directly before it becomes an analogue signal, ensuring no loss of information.

The use of a digital volume control will require a lot of power to ensure low-noise performance for headphone audio, this aspect, however, is not aligned with the high-quality, battery-driven audio concept which the DMP-Z1 is based on.

[HS] Audio signals travel directly through volume control; it, therefore, plays an essential role. After testing many different analogue volume controls, we chose the Alps Electric RK501 as its sound quality was hugely impressive amongst tested.

[TS] We then contacted Alps Electric to work together on a customized version of the RK501 for the DMP-Z1. The first customisation that we did was to swap the brass casing to aluminium with the objective of reducing the weight of the device. Unfortunately, while the knob was very light, the sound quality too was very light.

In order to create a customised volume control that surpassed the original RK501 in terms of sound quality, the team continues to try out different variations to try and improve the sound quality and eventually changed the base metal used in the casing back to brass and after applying the copper plating and gold plating to achieve the customised RK501 for the DMP-Z1.

[HS] With the customised RK501, the DMP-Z1 is able to reproduce a clearer and more transparent high end than the original RK501, coupled with incredibly deep and powerful bass in the low end. Improvement to the sound quality is why we implemented a rotary volume knob on the DMP-Z1.

For the team to consider implementing a rotary volume knob for future Sony Walkman replacement models, its implementation must improve the sound quality.

[BY] JEITA introduced the Hi-Res Audio Wireless logo on Nov. 28, 2018, with LDAC currently being the sole Certified Audio Codec. Will the new Hi-Res Audio Wireless certification play a significant role in the future signature series offering? What is the team’s outlook and view of Wireless Audio and will we see a Signature series wireless product soon?

[TS] Bluetooth is very popular in the market, which is why we implemented the BT receiver function on the NW-ZX300, NW-WM1A and NW-WM1Z. Future products will be determined by demand.

[KN] Basically we cannot comment about the future product plan. We will try to make good products with Wireless High Resolution, maybe if we can develop one to meet the standard of a Signature series product. We will try.

[BY] Our readers would like to know from each of you, throughout your career in Sony. Which is your favourite product which you are part of the design team and why?

[EK] My favourite product must be Sony IER-Z1R Signature Series. The product is a Flagship and is my most challenging project at Sony so far. Being the acoustic designer and development leader of the product, I have many challenges during the development, and I believe this product is successful in entirety particularly in the area of design and sound quality. Overall, the product has exceeded my expectations and is a product I am proud of.

[TS] My favourite is the Sony Walkman NWZ-Z1000. This is Sony’s first Android Walkman and the first Walkman product I designed. Before this, I was in charge of car entertainment system design in Sony from 1993 to 2011. My technical specialisation is in system design, so when the Walkman team needed a system designer for their Android model, so I moved from the car entertainment team to the Walkman team. There were significant challenges when I first moved over to the Walkman team, the design requirement is different at the Walkman team requires better responsiveness from the system. At the same time, the audio team doesn’t have GPS and Wi-Fi solutions, so we had to introduce not only digital but also the wireless solution. The key challenge here is integrating so many technologies into a small device. In 2011, Android was not as popular as an operating system for the Smartphone, unlike today. We have since moved from Android to Linux following feedback from customers, however, recent feedback has requested that we relook at Android. I think there are two different groups of customers now, one group Android and another Linux.

[HS] In 1990, we made the Sony CFD-K10 Portable CD Radio Cassette Recorder, this is a mobile audio product with high-quality sound. This is my favourite product, without the development of the CFD-K10, I will not be able to do NW-ZX1. The Portable CD Radio Cassette Recorder design features many high-quality capacitors and a very expensive CD module.

[TS] During the design phase of the NW-F880, Sony’s first high-resolution Walkman, I invited Hiro into our team to collaborate and he oversees sound quality while I handle the rest.

[KN] I have been involved with too many products in the 28 years with Sony. I am sorry, I cannot choose one favourite.

[BY] Nageno-san, Tomoaki Sato-san, Hiroaki Sato-San and Kuwahara-san, on behalf of our readers at Porta-Fi, I would like to thank all of you for taking the time to accept our interview over breakfast.

[KN, TS, HS, EK] Thank you.

[BY] I would also like to take this opportunity to thank Sony Electronics Asia Pacific Pte. Ltd. and Sony Singapore for facilitating and arranging the interview.


  • Goh Beng Yeow, the Founder / Editor at Porta-Fi™, is a recipient of the IT Youth Award in Singapore. Twice nominated for EY Entrepreneur of the Year Awards, Beng Yeow has previously founded startups such as PDALive.com, Coded Pixels Consultants and was a Tech writer for TODAY, a national daily newspaper under MediaCorp. Since 2017, he has been writing, editing and producing commentaries, interviews, news and reviews on Porta-Fi™. In 2019, Beng Yeow was appointed Advisor to LHDC™, the industry's latest low latency and high-definition Bluetooth audio codec.

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