64 Audio A12t

64 Audio is one of the market leaders for high-quality in-ear monitors for professional and audiophile use. The universal-fit models U6t, U12t and U18t have each earned top scores from us. So the question is obvious: is it worth investing in a custom version?

Custom Fit vs. Universal Fit

Unlike the U12t, the A12t’s impressive twelve balanced-armature drivers are housed in a custom enclosure that fits snugly in the owner’s ear. This requires paying for a visit to a hearing care professional and some time for manufacturing. However, there is no extra charge for the standard Universal Fit version. You only have to pay for some of the options offered for the model’s extraordinarily flexible visual design, which you can see on the manufacturer’s website before you buy (to the manufacturer’s website).

Package

The high-quality 64 Audio A12t is delivered in a decorative metal case that can be personalised with your name. The headphones feature twelve balanced-armature drivers on each side, divided into four drivers for the bass range, six for the midrange, one for the mid-highs and one for the treble range – all separated with a passive crossover. The latter driver is a TIA tweeter, which radiates directly at the edge of the structure towards the eardrum without any further sound conduction. Like the U12t, the A12t is designed entirely for high-quality music reproduction. The only difference is that the replaceable high-quality, low-impedance connection cable can be ordered with an integrated microphone for telephone calls if required. There is also a choice between two-pole and IPX connections. The standard cable ends with a gold-plated mini jack (3.5mm). However, there is also the option to purchase cables with symmetrical connections.

They are made of hard plastic and have a decorative bezel. Unlike universal-fit headphones, however, there are no fitting pieces. Rather, the A12t are placed directly in the ears. The output tip extends deep into the ear canal, while the back fully fills the pinna area of the external ear canal.

To allow the low frequencies and the ear to equalise pressure, manufacturer-specific Apex technology is used. For this process, small cylindrical modules have been placed in the housing, and this influence the bass range, the overall tuning but also the outer insulation. Modules with attenuation of 20, 15 and 10 dB are available – two of them are included in the package.

In practice

As mentioned, custom IEMs are generally larger than conventional universal fit models. They are, therefore, not quite as light. Instead, the fit is made optimal. The earpiece is turned into the ear cup and then fits securely, staying wobble- and slip-proof. The typical fitting problems experienced with other systems do not occur. At the same time, the wearing sensation takes some getting used to because the earpiece sits differently and more firmly in the ear. There may be an unaccustomed feeling of pressure, but that quickly subsides. In the end, the A12t hardly felt like a strange object to me. It was only when I took them out that a feeling of airiness occurred, as heat inevitably built up during longer listening sessions, especially at higher temperatures, for example, on stage.

The twisted cable is routed over the ear from behind. This is unusual, especially in these days of wireless solutions. However, it offered additional safety when using them on stage.

The passive noise insulation of the construction was good and better than with the corresponding Universal Fit counterpart. However, noisy fellow musicians were not entirely blocked out.

Sound

The A12t’s sound signature is the same as the Universal Fit variant. We used the DAP Shanling M3X and the RME ADI-2 Pro FS and SPL Phonitor 2 headphone amplifiers as feeds for our listening tests.

Sound-wise, the A12t performed at the highest level. They delivered a complete and balanced frequency spectrum, ranging from low bass to the airy highest frequencies. I didn’t notice any disturbing overemphasis. On the contrary, I was very surprised at the successful interplay of the numerous BA drivers that were active at the same time. After all, the individual drivers themselves offer little linear frequency response and work in a small housing whose construction primarily follows physiognomic rather than acoustic guidelines.

The relevant parameters such as frequency distribution, dynamics, tonality, transients and space were simply outstanding. The fine detail, transparency and the ability to produce precise, almost three-dimensional panning (Yello “Pan Blue”) was particularly remarkable. With these qualities, the A12t is undoubtedly suitable for professional stage use, but they are equally suitable for a professional assessment of mixes (with full frequency range) as well as for audiophile music enjoyment across genres.

Tasteful fine-tuning can be done via the aforementioned Apex modules. These mainly influence the bass reproduction but also have an effect on the other frequency ranges. They are cylindrical passive inserts that are placed over the back of the headphones. There they influence the sound conduction as well as the pneumatic ventilation of the construction and thus counteract ear fatigue. I used the “m15” module with two ventilation channels. If you switch to the “m20” type, the reproduction becomes slightly fuller and warmer, while the MX makes the sound even more defined and analytical.

In principle, the U12t can boast superlative sound, but for me, there was a significant distinction: in my case, the full sound experience occurred at significantly lower volumes, which of course, protects the hearing. None of my other headphones can provide me with such excellent detail resolution at such low levels. In terms of dynamics, I would even go a step further – the gradual level changes of a classical orchestra (Beethoven “Violin Concerto in D Major Op. 61”) from the delicate modulations of the soloist Anne-Sophie Mutter to the passages of the whole string sections were flawlessly reproduced even when riding on a high-speed train, listening at low levels.