Four Driver Hybrid In-Ear
64 Audio’s U4s is a universal fitting counterpart to the custom fitting A4s released in 2021. This four driver Universal In-Ear Monitor (UIEM) features a Dynamic low-frequency driver, two balanced-armature drivers, and one patented tia™ driver; making it our fifth “hybrid” UIEM. U4s is designed with the ground-breaking patented technologies originally developed for our flagship products in order to bring a wider audience closer to their music.
Tia, LID™, and apex™ are all housed in an ergonomic anodized aluminum shell along with an assortment of apex modules, ear tips, and an ultra-low impedance premium silver-plated copper cable.
U4s’ Striking New Look
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 blue-dial 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.
The democratization 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 sub-bass 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.
U4s Apex Module Variations
m20 apex modules
Using the m20 apex modules with U4s increases sub-bass response while keeping the mid-bass clean. Works great for overly bright mixes, as it tilts the response slightly towards the low end. While this module slightly 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 1db- 2db at 40hz-20hz).
mX apex 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).
The New m12 Apex Module
Originally released exclusively with U4s (included in all units up to August 1st 2023) is our new m12 apex modules. They are now available for purchase as an accessory on the website and will be included with select models in the future.
The m12 modules were developed for those who felt that the bass drop between m15 and mX was too drastic. Perfect for tracks where the bass is just slightly overpowering the rest of the spectrum. Increases mid-range punch. (reduction by 1db-4db at 130hz-20hz).
Wide nozzle silicone
Staging is less localized with better panning blend. Hits target frequency response curve with m15 module.
TrueFidelity foam tips
Narrows the mix slightly and shifts high-frequency resonant peak down. The foam tips also offer a more secure fit.
Shifts HF resonant peak up. Best at handling microphonic and occlusion effects because the nozzle is decoupled well from the silicone touching the ear canal.
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, m12, m15 and m20.
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.
The Reviews Are In
Headphone Show | 64 Audio U4s Review – Carving Out a New Sweet Spot
Headfonics | 64 Audio U4s Review