Custom IEM Model Overview 

64 Audio makes nine custom in-ear monitor (CIEM) models ranging from 2-18 drivers per side which cost between $499-$2,999. Our goal with the whole product range is to offer the best possible sounding monitor at each price point. Regardless of driver-count we aim to get the most out of components for balanced, accurate and musical IEMs. All of our models reflect that signature sound, and with the increase of drivers and cost you get increased fidelity/resolution.

For more IEM info take a look at our Educational Series.

64 Audio A18s custom in-ears on desk

A18s Story

The A18s Custom In-Ear Monitor is one of our 18-driver custom fit IEMs, the other being A18t. 64 Audio revolutionized the IEM industry in 2016 with the worlds first 18-driver IEM (A18t/U18t). A18s is built on the heritage of that 18-driver platform and further pushes the envelope. A18s combines 36 proprietary drivers, LID technology and a new electronic crossover network to deliver a uniquely exceptional listening experience.

While A18t/U18t was designed for mastering engineers and audiophiles, and later adopted by live performers, A18s was designed for the most demanding live performers in the world and now being adopted by engineers and audiophiles as well.

It all started with a special artist request. A long time A18t user was hoping to implement a thinner/lower-profile cable which had a higher resistance. Because A18t does not have LID technology, plugging into a wireless pack with that cable would potentially change the frequency response (while monitoring). Adding LID turned into experimenting with different drivers and crossover techniques, eventually coming together as A18s. The three main additions that set it apart from A18t is higher maximum output, warmer tonality, and LID technology.


A18s outperforms all of our IEMs (and most competitors) when it comes to maximum output, or max SPL. This refers to how loud the IEM can operate before audible driver distortion. While the two are often confused Max SPL is different than sensitivity.

Sensitivity refers to an IEM’s efficiency, or how loud it will play with a certain level of amplification compared to another IEM at the same level of amplification. While one IEM can have a higher sensitivity (like A18t compared to A18s) it is not correlated to max SPL.

A real world example: while using a wireless body-pack, going between two IEM models. With your volume knob at a certain position switch to a different IEM model. Without changing the position of your volume knob, if that new IEM is louder it has a higher sensitivity than the previous IEM, if it is quieter is has a lower sensitivity. The way to properly correct that is usually adjusting the gain staging upstream of your pack, so rather than just turning the knob up you either adjust the transmitter volume or boost the signal going into the transmitter.

Understanding that 99% of people don’t come close to distorting IEM drivers in normal operation, why make something that has such a high max SPL? Simply put, it increases clarity and transient response at all volume levels. Building something with vast headroom allows for the whole system to be less stressed and perform in a much more agile state.

LID (Linear Impedance Design)

One of A18s’ main features that sets it apart from A18t is the addition of our patented LID technology. A18t will most likely never see the inclusion of LID because it would result in drastic changes to its frequency response, phase, sensitivity, and total impedance; you could say that A18s was born because we wanted to add LID to our 18-driver IEM. While A18t will remain in the product lineup as one of our flagship IEMs, because of it’s uniquely flat tonality it is very picky when it comes to power; you really want to make sure you’re driving it with an ultra low noise and low impedance (<.5ohms) headphone amplifier to get the intended frequency response.

Understanding that professional musicians are often using devices that have higher noise and higher output impedance, and often go between devices that have varying impedance between one another, we wanted A18s to offer the security of LID. LID flattens the IEM’s impedance curve which ensures that the voltage from the headphone amp is distributed evenly across all of the driver sets. So if you use a Shure pack one day and listen to a mix on your laptop the next, you will be hearing the same intended frequency response.

Low-Pass Filter

One of the “industry-first” technological developments used in A18s (and has trickled down to some of our other new products as a result) is the implementation of an electronic low-pass filter for the low frequency balanced armature (BA) driver pack, consisting of 8 BAs. A low pass filter is used as a crossover, ensuring that only low-frequencies are driven to the low drivers, and every frequency above a certain point is diverted to the low-mid drivers and above.

This new filter addresses multiple potential problem areas that have plagued IEM design. First it replaces some of the previous acoustic methods of low-pass filters. Typically you’d see some version of air volume restricting devices called “peak tube filters” used in the tubes of low drivers. These would eliminate high frequencies by restricting air flow in the tube, but could result in turbulence and distortion. Second it unburdens the low-driver pack of all unnecessary work. By only sending the relevant frequency band the driver pack is unencumbered by the other frequencies that would otherwise unnecessarily stress the drivers. These unnecessary frequencies are diverted from the drivers in the circuitry before it hits the drivers, rather than after the drivers.

Solving both of these problem areas contributes to the high max SPL of A18s and makes it a more effective monitoring tool.

64 Audio A18s custom in-ears on red keyboard

A18s Sound

Because it is built on our 18-driver platform, A18s is capable of extraordinary detail and separation. It takes the the extreme flat tonality of A18t and slightly increases amplitude in the mid-bass region for a warmer sound. As is true with our other “reference monitor” models, like A12t and A18t, A18s is a flavor of that trustworthy reference sound that studio professionals are after. You can mix and master a record on any one of those three models confidently, the choice is really up to personal preference on the small differences between the three; similar to choosing between large scale studio monitor brands/models.

64 Audio A18s custom in-ears on desk

It displays the additional driver headroom that will accommodate less dynamically processed inputs and mixes without saturation and distortion. Thanks indeed for working to lift the product offering to a better level than what is already in my opinion the best suite of product available to the market.

Brad Law (Monitor Engineer: Hillsong UNITED)

64 Audio A18s custom in-ears on table

A18s is my new go to IEM. It sounds big and powerful like a full blown line array with subs, yet has the clarity and resolution of a studio monitor.

James Berry (Monitor Engineer: Beyonce, Kings of Leon, Lionel Richie, Fantasia & Maxwell)

Custom-Fit, Custom-Look, & Custom-Made

Each 64 Audio CIEM is hand built in Vancouver Washington by highly specialized technicians.

Ear impressions are first trimmed and scanned into our 3D detailing software. Our patented 3Dfit technology is used to perfectly recreate the intricacies of your ear shape. We virtually accommodate for all of the internal components before 3D printing with hypoallergenic acrylic material.

Once the shell is printed our assemblers insert the pre-soldered driver packs associated with the model of the IEM.

hands assembling 64 Audio custom in-ears under microscope

The assembled CIEMs are later completed with a faceplate. Along with the 5 shell options, there are dozens of faceplate colors and materials which translates to hundreds of variations. On top of all of those options we’re also able to use custom artwork to make your IEMs truly one-of-a-kind.

earphones aligned on a white background to form a 64 Audio logo

A18s Specs

  • Transducer Type/Count: 18 BA
  • Transducer Configuration: 1 tia high, 1 high-mid, 8 mid, 8 low
  • Bore Configuration: Single
  • Freq. Response: 10Hz – 20kHz
  • Sensitivity: 106 dB/mW @ 1kHz @ 1mW (84mV)
  • Impedance: 8Ω Nominal
  • Crossover: Integrated 4-way passive crossover
  • Isolation: -20dB w/ m20 module, -15dB w/ m15 module

A18s Technology

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Air Pressure Exchange (Apex) is a patented vent that releases air pressure in a sealed ear canal. In addition to relieving air pressure, it also maintains standard IEM levels of noise isolation. The attenuation of ambient noise and pressure relief enables 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 three module variations available for A18s: mX, m15 and m20.

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Tubeless In-Ear Audio (tia) is a patented IEM design methodology that aims to reduce unwanted resonance and distortion for a transparent and lifelike sound signature. The tia system is comprised of three major elements: open balanced armature tia drivers, the tia single-bore design, and tia acoustic chambers. A18s features two major elements of the tia system: the tia driver and the tia single-bore design.

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3D-Fit preserves the detail of your ear impressions using a new process of digital rendering and 3D-printing. The patented process of incorporating acoustical tuning features within an IEM’s shell allows for designs that would otherwise be impossible to build using traditional methods. We incorporate these advanced and uniquely complex features into the shell in order to manipulate the audio produced by the IEM. This process also reduces distortion in the impression for the most precise and comfortable custom in-ear monitors available.

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Linear Impedance Design (LID) is a patented circuit that corrects the non-linear electrical resistance of the multiple driver-sets comprising this 18 driver IEM. Varying source amplifier output impedance in devices like smartphones, body packs, DAC/amps, and DAPs typically results in varying frequency response across them, depending on the increase in resistance. Restoring proper interaction with the source and preserving the desired sound signature enables a consistent reliable sound.