(Image credit: Astell & Kern)

Astell & Kern are one of the biggest names in portable hi-res audio, and 64 Audio – formerly 1964 Ears – are big in high-end IEMs. And now the two firms have collaborated to create the XIO in-ear monitors, made for audiophiles and featuring some very impressive engineering.

You can't accuse the firms of false modesty here. According to 64 Audio founder and CEO Vitaliy Belonozhko, the XIO "goes beyond simply reproducing sound – it embodies our philosophy of sculpting sound itself.”

There are multiple interesting things going on inside these IEMs, and the most obvious is that instead of one, two or three drivers the XIO have ten.

(Image credit: Astell & Kern)

Astell & Kern XIO: key features and price

The hybrid driver setup features two dual-dynamic bass drivers in an acoustically neutral chamber for deep bass, six balanced armature drivers for the mid-range, another balanced armature for the upper mids and a direct-radiating high-frequency driver. They're teamed up with a 4-way passive crossover and the frequency response is a wide 5Hz to 22kHz.

The XIO feature three of 64 Audio's key technologies – tubeless in-ear audio, which eschews typical sound tubes for a single-bore setup to reduce resonance and distortion; linear impedance design, which compensates for driver resistance quirks; and air pressure exchange, which reduces that weird clogged-up feeling you sometimes get with IEMs during longer listening sessions.

The main housing is machined from 904L stainless steel and coated in black diamond-like carbon, and the XIO ship with a custom silver-plated UP-OCC copper Litz cable that's four-core and cross-braided to shield against noise.

The new XIO earbuds will go on sale in August 2025 and so far only the US pricing has been announced. They'll retail for US$3,000, which is about £2,231 / €2,576 / AU$4,605 before tax.