Denon 110 Anniversary Interview Series Vol. 4 With Yoshinari Fukushima, Headphone Engineer

Denon Staff

59-Year History of Headphone Manufacturing

Mr. Fukushima has been a big help to us in our headphone engineer interviews for the Denon blog. As we celebrate the 110th anniversary of Denon, we asked him about the history of Denon headphones and some of the memorable models. Mr. Fukushima is currently in Germany, and joined our interview via the internet.

Fukushima：I am looking forward to sharing stories with you.

First of all, can you tell us about the history of Denon headphones?

Fukushima: Apart from earphones as accessories, I think Denon’s first model of audio headphones was the SH-31, which was released in 1966.

Denon has been making headphones for 54 years, is that right?

Fukushima: Correct. People may think Denon is a strong Hi-Fi audio brand that started making headphones relatively recently. In fact, the brand has a history of more than half a century in the development of high-end headphones.

I see there is a picture of audio equipment in the background of the SH-31 document photo.

Fukushima: I think the picture helps bring to light the fact that they were high quality headphones that can be primarily used for audio. In those times headphones and earphones were positioned as accessories, and there was not much emphasis on sound quality. I think that's why Denon dared to show that the level of quality could be used for critical listening.

What kind of headphones has Denon released since then?

Fukushima: There is a driver technology that recently became a hot topic in the headphone industry called a "flat driver.” The entire diaphragm moves more evenly by making it flat, which has the advantage of reducing sound distortion and improving response. You may think that this method is new or novel, but Denon released a flat driver in 1976, the SH-90. I believe this signifies how Denon is a technology-driven brand and has innovated in the challenging field of headphones for decades now.

Fukushima: In 1980 we developed a series called the “Pro moni” series, which stood for Promonitor. The idea was to provide audiophiles with sound quality similar to a producer’s level, which had improved dramatically with PCM recording and other technologies at that time. It was during this period Denon began to use the "AH" as a model number for its headphones.

So "AH" is still the current nomenclature of Denon headphones? What does it mean?

Fukushima: Some people call them Audio Headphones and others call them Accessory Headphones. To be honest no one knows anymore, and there is no way to find out (laughs). We also introduced wireless (cordless back then) headphones in 1991, which became very popular in the last few years.

So in 1991 Denon introduced Wireless headphones? Did that market even really exist yet?

Fukushima: There was no Bluetooth back then, and you had to connect an infrared transmitter to the headphones jack of an audio device or TV.

Wireless headphones have been around for 30 years then?

Fukushima: Denon is usually too quick to release new products (laughs). The technology is a bit ahead of its time, and it seems like the boom comes a few years after Denon released a product. Nowadays, Bluetooth and wireless have become common, but Denon has been focusing on wireless technology since 1991. That is how we got to where we are today.

The Legendary Ah-d7000 Created the Domestic High-end Headphone Boom

Which model did you first work on in the development of headphones?

Fukushima: I have been involved in the development of headphones since the period of AH-D7000.

The AH-D7000 is a legendary model, not just for Denon, but in the history of the headphones market in Japan, isn't it?

Fukushima: Yes the AH-D7000 certainly did make waves when it was introduced, and I think it was a precursor to the current boom in high-end headphones. It became a huge hit not because of the result of our advertisement, but rather by being highly evaluated for its sound quality by professionals. A number of recording engineers at various studios used it, consequently word of mouth spread to the general public.

What do you think contributed to the AH-D7000's success?

Fukushima: The AH-D7000 was released in 2008, when there were not many domestic manufacturers who sold headphones this expensive (priced at 126,000 Japanese yen including tax). The sound was also extraordinary, and the amount of data they translated was far greater than the standard of headphones at that time. Personally, I believe these headphones not only provide a great deal of information, but also deliver the emotions of music to the listener. For these reasons, I believe the AH-D7000 ushered in an era of high-end domestic headphones.

The AH-D7000 has a unique wood housing. Was it new for Denon?

Fukushima: The AH-D7000 was the first model to use a wood housing. Until then, we had used plastic and metal.

What are the advantages of using wood? Are there significant differences?

Fukushima: Real wood does offer acoustic advantages. There was a model called the AH-D2000, which was almost identical to the AH-D7000 around the same period. They are almost exactly the same shape as the AH-D7000, but with a plastic housing. The amount of information transfer is not much different between the two, but the wood housing sounded superior in terms of warmth and emotion.

What advantages does wood have as a housing material?

Fukushima: Engineers use the term "high internal loss," which basically means there shouldn’t be any unwanted vibrations. Wood does not have any inherent resonance, so there is less of a phenomenon we call "squealing.”

Each Model Uses Different Types of Natural Wood in Current Real Wood Series

Does the wood housing expertise of the AH-D7000 translate into the current Denon "Real-wood" series of headphones?

Fukushima: The usage of natural wood is indeed a continuation of the AH-D7000. From a marketing standpoint, it is a direct descendant of the legendary AH-D7000. But the AH-D7200, the first model released in the current Real-wood series, was not initially developed with wood housing.

As I mentioned before, Denon is a technology-oriented brand and we don’t typically rely on lots of marketing to sell our products. If there was a better material that sounded great, regardless of the marketing disadvantage, I think we would use it. But right now the AH-D7000 sets a very high bar and we’re continuing to strive to improve upon that.

When the AH-D7200 was announced, there were a lot of arguments about whether it could surpass the legendary AH-D7000 or not.

Fukushima: After researching the housing material, we were willing to do anything to improve the sound, and we concluded that a wood housing was the best choice.

The main reasons for choosing a wood housing were the richness of the information, solid low frequencies, and high resolution. Secondly, the ability to achieve the new Denon sound philosophy "Vivid and Spacious," which is promoted by Denon's current Sound Master, Mr. Yamauchi. Recently, the amount of information on high-resolution sound sources has increased, and the material has to be able to express these sound sources sufficiently. I chose it for these reasons.

In the Real-wood series, each model uses a different material: Moso bamboo from Kochi prefecture for the AH-D9200, American walnut for the AH-D7200, and zebra wood for the AH-D5200. How were these materials selected?

Fukushima: We spent a lot of time on choosing a material. We chose mahogany for the AH-D7000. It was also important to us that the wood is not incredibly challenging to process. We made various prototypes with several wood materials, but most of them turned out to be not suitable for mass production.

What kind of wood was too hard to process?

Fukushima: For example, a quince tree. Quince wood is very hard. There were a lot of things to consider in addition to processing, as we produce products on global scale. We must ensure we can secure a stable supply of wood and be sure the wood we do select won't bend over after many years’ use. We must also critically focus on whether the product keeps the sound quality after five or ten years. Choosing the right material was difficult in these respects. We chose three types of wood in the Real-wood series to meet these requirements.

For the AH-D5200, we chose zebra wood in the aim of getting monitor-like sound. The zebra wood has a characteristic of rather dry, tight sound. The AH-D7200 is made of American walnut, which delivers a warmer sound and a wider sound stage. The AH-D9200 is made of Moso bamboo from Kochi prefecture, a material that provides a much greater information and spatial expression (see here for a video explaining the manufacturing). However, these sound characteristics are not just derived from the differences in the wood housing but are the result of tweaking various aspects, including the drivers.

What kind of difficulties did you face in the development of the Real-wood series, Mr. Fukushima?

Fukushima: Going back to what we talked about earlier, since the AH-D7000 was one of the best models in the Denon headphone line up. I kept it literally next to me and used it as a point of reference when developing the AH-D7200. I remember feeling the pressure of our own products.

Another challenge was the material cost of magnets, steel, and other components has increased since we introduced the AH-D7000 10 years ago. This made it impossible in certain instances to use the same grade of material while maintaining a price point we thought people would be comfortable with. Rare metals and copper are now three or four times more expensive than they were. It was really hard to cover these costs while exceeding the performance of the AH-D7000.

Yet there are also improvements from 10 years ago. We've made advances in measurement technology. Now we can accurately measure lateral pressure and other factors we couldn’t, so we are able to design the ear pads with careful consideration of where pressure is applied, which has been a big help in this process.

Finding Optimal Balance Between Sound, Comfort, and Durability is the Goal of Headphone Engineering

Denon headphones have been around for more than half a century, but what are the features of their sound?

Fukushima: Denon sound is described as "subtle and powerful," "precise and stable," and "Vivid and Spacious," and our headphones are engineered to achieve those qualities.

To be specific, the first thing to note is well-balanced sound. In particular, we enrich the vocals and bass to achieve this balance. This also contributes to the real-ness of the sound. On top of that, our sound character has a tight, neat treble, and a good representation of the information that the music source has to offer.

Next is "linearity," or the quality of soundstage expression. We emphasize the dynamics of linear sound from small sounds to large ones. It also creates a sense of speed by responding quickly to the music on the time axis. The sound is engineered so that the sound stage feels like it’s in front of you instead of localizing it in your head, which is common of headphones. Most of what we’re able to execute is because of Denon's 100-plus years of accumulated technologies. For example, the “Free Edge” driver and Denon's patented nano-fiber diaphragm used in the Real-wood series have been in use since the previous generation, but a continuous improvement of these technologies is the key to achieve richer dynamics and more linear reproduction.

What do you find the most challenging about engineering headphones?

Fukushima: Engineers look at three factors when it comes to headphones: (1) great sound, (2) comfort, and (3) durability. If you do not satisfy these three elements you cannot make a pair of good headphones. No matter how good they sound, they will fail if they can be broken after a year of usage, or they cause pain to your ears after a long period of time of usage. Finding the best balance of these three factors is both the most challenging and most fun part of building headphones.

You do not need to worry about the comfort or weight to make a good sound if you are designing component audio. For example, there was a power amplifier called the POA-S1 made by Denon in the past, and it weighed 79 kg (~175 lbs.). It tends to be heavier if you want to improve the sound in an audio equipment, but when it comes to headphones the heavier they are, the less comfortable they are. Finding that balance between sound, comfort, and durability is what ultimately leads to successful products.

Denon’s headphones, including the Real-wood series, are very well-received in Japan. You are currently based in Germany, what is the reputation of Denon’s headphones overseas?

Fukushima: Sales are steadily increasing in Europe as well. Most headphones in Europe are open-back headphones, but Denon's Real-wood series are really well-received by many people here even though they are closed-back. I think this is because our headphones provide a wider soundstage despite their closed design, enhanced midrange sound expression which is distinct from the open-back, and a high level of craftsmanship.

Product manager Mr. Fukushima has done an excellent job, and the AH-D9200 has been fine-tuned with great success. Crystal clear highs and a powerful midrange. Nothing over the top, the bassline reaches to the very bottom and remains dry without any gimmicks to fool you. This is, without a doubt, the best Denon I have ever had the pleasure of using. And it is worth this Euro (price).

Fukushima: By the way, this is a German review magazine, and recently, the AH-D9200 has received very high ratings. A German magazine gave the Denon headphones even a better rating than to a local German manufacturer.

It has been a tough journey, but I am pleased they are beginning to garner clout here.

That is fantastic!

Next time, please let us talk about Denon perception in Europe.

Thank you for your time today.