Audio-Technica engineers, Takao Kyotani and Yosuke Takubo, discuss the development of the A2DC.
Popularity of in-ear headphones with detachable cables
In-ear headphones with detachable cables have become extremely popular, and this popularity has given birth to something of a replacement cable culture. One of the most commonly adopted standards for connectors that attach cables to headphones is the MMCX (microminiature coaxial) connector. However, MMCX connectors are not perfect, and there have been certain issues with them since detachable headphone cables were first introduced.
Audio-Technica initially adopted the MMCX terminal, but since the release of the ATH-CKS1100iS headphones in 2015, the company has used the proprietary A2DC (Audio Designed Detachable Coaxial) connector that it developed in-house for all of its in-ear headphones (and select over-ear models) with detachable cables. The company has also produced A2DC-compatible replacement cables, and third parties have recently released A2DC-compatible cables as well.
Problems with the MMCX connector
The MMCX connector generally used in the in-ear headphone market was not originally designed as an audio connector, but as a standard primarily for wireless device connectors. But some in-ear headphone manufacturers discovered that a cable with an MMCX connector could provide an easy solution for replacing broken cables, so they started using MMCX connectors for their in-ear headphones. Later, third-party cable brands started selling replacement cables with MMCX connectors, and the connector became widespread in the industry.
MMCX connector (male side) generally used in cables.
However, with this increase in popularity, some problems became apparent. A well-known issue is that the connection is too loose and can easily become disconnected. Conversely, there are cables that fit too tightly and are difficult to disconnect. There are also issues with the connectors rotating, causing sound to drop out and generating unwanted noise. Cables with MMCX connectors may also get twisted easily.
“The initial concern with using MMCX connectors was that, structurally, there is an area where the male and female sides do not meet when the connector is moved. This can cause noise or a sound dropout,” Takubo explains.
“Since the part that does not connect is extremely small, even if the connector moves while you are listening, you usually won’t notice any difference. However, we wanted to eliminate the possibility of noise or of sound dropouts as much as possible.”
The problem of MMCX connectors not connecting properly with each other is also caused by their structure. Even if the MMCX connectors are in the range of tolerance (margin of error for the dimensions as allowed by the standard), if this value is large enough, there may be cases where the connectors do not fit together properly. Additionally, if they do connect but the tolerance is too large, the previously described issue of having areas of disconnection will become more severe, and it will be difficult to ensure connection stability.
Considering the fact that it was not an audio-dedicated connector in the first place, this is not the fault of the MMCX design. But for the listener it is a major problem. Takubo says that from the moment that MMCX connectors started to increase in popularity he “wanted to develop an in-ear headphone connector with the optimal specification for audio purposes.”
Reasons for developing the A2DC connector
The initial Audio-Technica in-ear headphone model with a detachable cable was the ATH-CK100PRO, which was launched in 2011. This device was a high-end model equipped with triple balanced armature drivers, and it used MMCX connectors.
Our first detachable-cable in-ear headphones, the ATH-CK100PRO, used MMCX connectors.
However, at that time, the company development team recognized the issues with MMCX connectors, and to make the size of the ATH-CK100PRO as small as possible and improve the fit, they went in the opposite direction of the industry standard by attaching a smaller male connector to the headphone and a larger female connector to the cable. Therefore, it was not possible to use general-purpose replacement cables manufactured by third parties that had the male connector on the cable side. From a manufacturer perspective, to build a product that was as “bulletproof” as possible, it was reasonable to develop an alternative connector to ensure a more reliable connection.
The IM series in-ear headphones, which were released in 2013, did not use the MMCX connector, but rather adopted a proprietary 2-pin connector. Whereas the connection stability of this 2-pin connector was superior to MMCX, there was still the issue of it connecting too tightly or too loosely. Additionally, as Audio-Technica anticipated extending its range of detachable cables to over-ear/on-ear headphones in the future, the company changed course and developed another proprietary connector, the A2DC.
A2DC structure resolves specific issues with the MMCX connector
The ATH-E70 uses the A2DC connector.
Typically with MMCX connectors there is a pin in the center of the male connector, surrounded by an outer ring. There is a pin receptor located in the center of the female side. Conductance occurs when the central pin (inner conductor) and surrounding ring (outer conductor/ground) of the male connector attach to their respective female connectors.
This is the general MMCX connector (male side).
The structure of the A2DC connector, however, is such that the male-side ring section (outer conductor/ground) is partitioned into tabs that face and press outward with spring-like action. In this way, the male-side ring section can be attached more reliably to the receptor on the female-side ring. This structure resolves the problem of the male and female sides not connecting completely.
Male side of A2DC connector. Slits partition the ring-shaped section into tabs.
The male side is equipped with a pin receptor surrounded by plastic.
This kind of structure remains strong even with repeated attaching and detaching. Takubo: “The shape of the A2DC connector ensures that it always connects securely. The fact that the male-side ring opens outward means that it bends like a spring. Therefore, it has an advantage in that, even if it is repeatedly attached and detached, it does not wear down easily. This means that it will continue to supply a stable connection for longer periods of time, even when it is repeatedly attached and detached.”
Kyotani: “As there is flexibility (yield) in the ring section, compared to the MMCX connector, it has an advantage, because connectivity can be maintained, even with a large tolerance.”
Cross-sectional image of A2DC connection.
Larger connector improves sound quality
The MMCX connector’s central pin is on the male side, but the A2DC connector places that pin on the female side, with the pin receptor in the center of the male side. Additionally, the area surrounding the pin receptor is reinforced with plastic, which prevents the pin receptor from spreading out and the pin from breaking.
The ATH-CK2000Ti A2DC connector (female side).
The A2DC connector is larger than the MMCX connector, and the ring section is longer and larger in diameter. This ensures a larger connection area, greater stability, lower impedance, and improved sound quality compared to the MMCX connector.
Female-side A2DC connector.
“The reason that the size of A2DC is large compared to the MMCX connector is because it is assumed that it will be used with over-ear/on-ear headphones,” explains Takubo. As a matter of fact, the A2DC connector has already been adopted for the company’s flagship open-back headphones, the ATH-ADX5000, as well as the closed-back ATH-MSR7b, for which portable use is assumed.
The ATH-CK100PRO MMCX connector (female side) is shown on the right-side of the picture. The center of the picture shows the A2DC connector (female side). Notice the difference in size between the two connectors.
A2DC connector does not easily rotate
One of the strengths of the A2DC connector is that the connecting part does not easily rotate. Typically, MMCX connectors have little rotation resistance, and tend to rotate if a turning pressure is put on the connecting part. This makes for a less stable connection and wears down the connector. Such wear can allow dirt to attach to the connector and cause noise. With the A2DC connector, the ring section spreads outward, increasing rotation resistance. Therefore, it is more difficult to unintentionally rotate the connector and cause wear.
No matter how good the conductance of the cable is, it will be meaningless if the connection is not stable. The secure A2DC connection eliminates sound dropouts and helps deliver the best sound quality possible.
Replacement cables using the MMCX connector continued to be released by a number of companies, which concealed the specific problems of MMCX connector tolerance, explains Kyotani.
Kyotani: “Even as replacement cables with MMCX connectors began to be released in force into the market, there continued to be a large margin of error in the size of these connectors, even if they were considered to be within tolerance. For this reason, depending on the replacement cables used, many issues concerning sound dropouts were seen in reviews of in-ear headphones. We hoped to improve in this area by using A2DC connectors.”
According to Kyotani, by using the A2DC connector, Audio-Technica saw a drastic reduction in the number of inquiries regarding defects and problems concerning the company’s in-ear headphone connectors.
HDC series replacement cables use A2DC connectors
In 2016, Audio-Technica released the HDC series replacement cables, which use A2DC connectors. This is a rich lineup of cables made for a variety of headphone types and equipped with different output connectors, from a standard 3.5 mm connector to 2.5 mm and 4.4 mm balanced connectors.
HDC series: Audio-Technica replacement cables that use A2DC connectors.
Kyotani: “All of our headphones that use detachable cables with A2DC connectors are designed to provide great sound quality when using the included cable. However, the number of users who enjoy using replacement cables has increased, as have the calls for cables with higher sound quality, which drove us to adopt the A2DC connector for our replacement cables.”
The Audio-Technica cables were designed from the standpoint of duplicating the high level of performance that existed with the company’s permanently attached cables. For this reason, A-T did not think of introducing a lineup that changed the character of the sound.
Audio-Technica wants this to become a widely used standard
To return the point of discussion to the A2DC connector, the process of developing a proprietary connector involves a lot of trial and error. From design to materials, Audio-Technica tried a wide variety of shapes and types, explains Takubo.
“At the prototype stage for the A2DC connector, a problem in selecting materials was that the spring connection was too strong and we could not get it loose (laughs). We had a similar problem with the shape. We prototyped a screw-type plug, for example, but the connector was too small and it was difficult to remove. We finally came upon the specification for the A2DC connector by experimenting with a wide variety of prototypes.”
Kyotani (left) and Takubo (right) both claim that they want to extend the use of A2DC connectors to a large number of in-ear headphones and cables.
The A2DC connector was developed based on issues found with the MMCX connector, but examples of applying this new connector to in-ear headphones are currently limited to Audio-Technica products. However, the company wants to make the A2DC connector a specification that’s available for other manufacturers to use too, so that its superiority can be experienced by a larger number of people. In terms of cables, Audio-Technica has started to see offerings from third parties that utilize the A2DC connectors.
Kyotani states that “if there are manufacturers who are interested in the A2DC connectors, we would welcome hearing from them so that we can meet their needs.” Indeed, Audio-Technica has already had inquiries from manufacturers who want to use the A2DC connectors.