Interviewer: Naoki Nakabayashi   Editing: Phile-web Editorial Department
Nakabayashi : A major feature of the CKR series that draws our attention is the "world's first*" DUAL PHASE PUSH-PULL DRIVERS, that are featured in the high-end ATH-CKR9 and ATH-CKR10 models. To start, could you describe this mechanism in detail?
What are the "world's first*" DUAL PHASE PUSH-PULL DRIVERS?
The key characteristics are lower harmonic distortion and increased power handling.
Ozawa : First of all, moving two drivers in a push-pull fashion is technology that was originally developed for pure audiophile speakers, and in fact, there were speaker models in the past that feature this technology. However, these speakers didn't become popular because the magnetic circuits were exposed in the front and back of the units, which was not visually attractive. With earphones, on the other hand, because the entire driver fits in the housing, there is no need to worry about appearance and allows you to enjoy only the advantages of push-pull drivers.
The structure of the DUAL PHASE PUSH-PULL DRIVERS consists of two 13 mm dynamic driver units mounted facing each other. The most important point is that these two driver units move together.

Hirano : Can you explain in detail how they move together?

Ozawa : Driver 1 and Driver 2 move simultaneously but not in the same direction. One driver is fed with a signal that is out of phase with the other driver, making the two drivers move in opposite directions. For instance, when the diaphragm of Driver 1 pushes air and moves forward, the diaphragm of Driver 2 pulls in and moves backward. Thus the term is push-pull drivers, combining the two actions of push and pull.

Hirano : In other words, you are doubling the power by moving two driver units together.

Ozawa : Generally speaking, driver units are good at pushing air but not as good when it comes to a pulling motion, and this pulling motion tends to be slow. However, with DUAL PHASE PUSH-PULL DRIVERS, the sound pressure from the driver pushing air assists the pulling motion of the driver unit on the other side, achieving excellent linearity. Harmonic Distortion is also reduced through opposite phase motion.
The greatest reason for adopting this system is to increase the efficiency of the drivers. Because in-ear headphones are inserted in the ear canals, the drivers can be made only so big. You can achieve denser magnetic flux with a single driver by making the magnet bigger, but this makes the body larger and the headphones become uncomfortably heavy to wear.
On the other hand, DUAL PHASE PUSH-PULL DRIVERS ensure high magnetic flux and high driving force because there are two drivers. In terms of the sensitivity too, the ATH-CKR10 has 110 dB/mW as opposed to the regular range of 102 to 103 dB/mW. I don't think any other dynamic earphones have this level of sensitivity.
Hirano : The most striking thing you said in our previous conversation was that "headphones are not for feeling vibrations but for reproducting exact audio" My impression is that this is exactly what these new DUAL PHASE PUSH-PULL DRIVERS are for. To me, you focused on the natural power of drivers—high driving force without distortion.

Nakabayashi : The DUAL PHASE PUSH-PULL DRIVERS are dynamic drivers. When you were developing the ATH-CKR9 and ATH-CKR10, didn't you consider adopting BA drivers?

Kokubun : During the planning stages, there were in fact people who suggested using BA drivers. But as talks progressed, we couldn't move away from the appeal of the dynamic drivers and the richness of their expressive power. I think it was only natural that we chose dynamic drivers when we considered what we needed to create in-ear headphones that would allow customers to enjoy music even more.
BA drivers are considered to have some advantageous features such as the excellent attack and response, but when you listen to music through the ATH-CKR10 and ATH-CKR9, I think you will hear that those advantages are also present here. I also think the sound gives you an impression that there are additional advantages that only dynamic drivers can offer. Even during the production process, we were convinced that they would be great products.

Hirano : With the two driver units arranged so that they are precisely facing each other, was quality control to ensure consistent production extremely difficult?

Ozawa : Yes, it was. It's useless if driver units with a different sensitivity of more than 3dB are combined, so control during production is extremely strict.