64 Audio at Audio46

64 Audio U4s Universal In-Ear Monitor




Product SKU: U4s


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Product Details

Audio46's Opinion

Although the exceptional level of precision and lack of significant coloration would suggest an almost clinical profile, the U4s is far from boring. The powerful lower-bass frequencies along with the spirited upper mids and high-treble give tracks a lively, yet controlled energy. Add to that a level of resolution that surpasses any other earbuds at this price point, and you’ve got one of the best performing IEMs on the market for under $1500.

Our Full Review

↓ Details provided by 64 Audio


A quad driver hybrid UIEM featuring ground-breaking patented technologies originally developed for our flagship products in order to bring a wider audience closer to their music. U4s explores a bold new color aesthetic for 64 Audio. The Slate Blue shell color was influenced by some of the world’s most beautiful bluedial timepieces while the unique faceplate pattern is inspired by Muonionalusta meteorite fragments. Both the faceplate and shell’s illuminant properties give it a unique tone in varying lighting conditions.

Its ergonomic anodized aluminum shell houses a single dynamic driver, two balanced-armature drivers, and one patented tia driver; all weaved together with our patented Tia, LID, and Apex technology. The four-way crossover is elevated with the use of our proprietary electronic low-pass filter; reducing lowfrequency distortion. The assortment of included apex modules and ear tips are an invitation to further shape the sound based on preference and source material while the ultra- low impedance premium silver-plated copper cable ensures unimpeded signal transmission.

The dissemination of tia technology within our product range brings that classic 64 Audio sound signature to a new price-point. U4s sounds light on its feet while effortlessly delivering physically engaging subbass without bleeding into the mid-bass. Balanced mid frequencies and a pleasant high-mid band respond well to a wide array of music and recording styles at every volume level; present but not fatiguing. The tia high-driver’s open airy quality couples with the extended sound-stage provided by apex for a lifelike sonic experience.


Wide Nozzle Silicone Tips/m15 Modules (Standard Configuration)

The frequency response of U4s follows proven targets for fidelity and preference. It’s powerful, enveloping, and deep while avoiding being muddy; this kind of bass can only be produced by a dynamic driver. U4s comes short of being classified as warm, rather it is like a tight and agile stand-mount speaker with a well implemented sub. The key to this is how the low-frequency rise starts low enough to keep out of the mid-bass.

Mids are revealing and present, contributing greatly to its wide stereo imaging and separation. U4s’ perfect balance of presence and body lends itself well to every type of music and volume preference.

High frequency response toes the line between neutral and detailed. Mixes that are typically “bright sounding” translate nicely without being harsh or fatiguing.



Tubeless In-Ear Audio is a patented IEM design methodology that aims to reduce unwanted resonance and distortion for a transparent and lifelike sound signature. The tia system consists of three major elements: open balanced armature tia drivers, the tia single-bore design, and tia acoustic chambers. U4s features two major elements of the tia system: the tia driver and the tia single-bore design.


Linear Impedance Design (LID) is a patented circuit that corrects the non-linear electrical resistance of the multiple driver-sets comprising this 4 driver IEM. Varying source amplifier output impedance in devices like smartphones, body packs, DAC/amps, and DAPs typically results in varying frequency response, depending on the increase in resistance. Restoring proper interaction with the source and preserving the desired sound signature enables a consistent reliable sound.


Air Pressure Exchange is a patented vent that releases air pressure in a sealed ear canal all while retaining standard IEM levels of isolation, enabling musicians and music enthusiasts to listen more comfortably for longer. This venting alleviates listener fatigue and allows for a much more realistic soundstage. Apex comes in four module variations for U4s: mX, m15 and m20.

Electrical Low-Pass Filter

Originally developed for U18s this crossover circuit replaces traditional acoustic dampers which can introduce unwanted distortion through vibration and air turbulence. Rather than using acoustic dampers to filter unwanted frequencies after the driver produces them the electrical low-pass filter lowers distortion by eliminating unwanted frequencies before they reach the driver

MX Modules

Widest imaging with a reduction in noise isolation. Sub-bass response is greatly diminished, giving you the ability to attenuate to your preferences based on music type and mix. It is ideally used for recordings that do not capture much sub-bass content while containing a lot of spatial information. Because of the reduction in sub-bass response, it creates a slight tilt towards the high-frequency band. (reduction by 1db-10db at 350hz-20hz).

M20 Modules

Greatly increased sub-bass response while keeping the mid-bass clean. Works great for overly bright mixes, as it tilts the response towards the low end. While this module shrinks the sound-stage width, it works great for synth-heavy or modern pop music that doesn’t contain much acoustic spatial information. The m20 module also unlocks some of the missing sub information in older rock recordings. (increase by 1db2db at 40hz-20hz).

Foam Tips

Narrows the mix and shifts HF resonant peak down. More secure fit.


Shifts HF resonant peak up. Best at handling microphonics and occlusion effects. The nozzle is decoupled well from the silicone touching the ear canal.

Wide Nozzle

Staging is less localized with better panning blend. Hits target frequency response curve with m15 module.


    2 balanced armature drivers, 1 tia driver, and 1 dynamic driver
    1 dynamic low, 1 BA low-mid, 1 BA high-mid, 1 tia high
  • SENSITIVITY 107 dB/mW @ 1kHz @ 1mW (94mV)
  • IMPEDANCE 11Ω @1kHz
  • CROSSOVER Integrated 4-way passive crossover
    -20dB w/ m20 module
    -15dB w/ m15 module
    -10dB w/ mX module
    0.23 Ohms total impedance
    7 x 7 x 4 Multi-twist Silver plated OCC copper wire
    26 AWG


  • U4s Universal In-Ear Monitors
  • 64 Audio Premium Leather Case
  • TrueFidelity Foam Ear Tips (S,M,L)
  • SpinFit Silicone Ear Tips (S,M,L)
  • Silicone Ear Tips (S,M,L)
  • 3.5mm Black Premium Cable
  • Apex Modules: m20, m15, mX
  • Cable Clip
  • Cleaning Tool
  • Round Sticker

Product Reviews


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Daniel K.
United States United States

Best Kilobuck IEM

The U4s is a fantastically colored, resolving IEM that handles all genres well. It has swappable APEX modules that can change the bass response, and sports a dynamic driver that handles the bass. The U4s is likely one of the best, if not *the* best IEM around a thousand dollars. Recommended.


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