10 Knowles BA design | Custom Knowles · enhanced bass BA

drivers |  Rubycon audiophile-grade film capacitor crossover

DLP 3D printed shell  |  Monitor/HiFi” mode switch

8 strands of 224 wires pure silver cable | Hi-Res Audio certified

*Pictures are for reference only. The actual product may vary.

10 Knowles BA IEMs 

What's the core

Rubycon audiophile-grade crossover capacitors

Mid-frequency notch filter

Negative feedback bass enhancement system

With tolerance errors below 0.1%, these capacitors separate frequency band extremely accurately for true flagship-level exquisite sound.

Custom Knowles bass balanced armature units are arranged in a scientifically designed structure to guide low-frequency sound waves to the rear cavity for deep, rich bass.

10 Knowles BA design

Inside the FA19 are 10 Knowles balanced armature drivers per ear, a monumental achievement for multi-driver IEMs.

Ensures a smooth transition from mid to high frequencies to allow the drivers to work to their maximum potential.

Trailblazing into a new world, Moving BAs into a new realm

Our goal was to create a truly monumental multi-BA driver IEM. We aimed to shake up the current market of flagship multi-BA driver IEMs, and spent three years on refining it to do so. For the ten balanced armature drivers FA19, we collaborated deeply with Knowles. Together, we built a custom enhanced bass balanced armature driver specifically for the FA19 to provide the listener with a deep low-frequency experience uncommon in multi-BA driver IEMs. Additionally, FiiO also worked closely with Knowles to optimize the mid and high-frequency drivers so that they not only sound highly detailed, but also pleasantly smooth. With the FA19 we carefully tuned all parts of the frequency response curve for a truly coherent and resolving sound. Welcome to a new world for multi-BA IEMs, and the FiiO FA19 will be your guide.

Swift as the wind, with a thunderous impact 10 Knowles BA design

The FIIO FA19 is designed based on both science and actual listening tests. For the FA19 we settled on using these drivers per ear: 4 custom Knowles bass BA drivers, 2 Knowles ED mid BA drivers, and 4 Knowles SWFK treble BA drivers.


Having more drivers in an IEM does provide certain advantages. It significantly increases the energy density within a given frequency range, resulting in more detail reproduced. This is especially apparent during dynamic audio passages, where more drivers are better able to handle the nuances present, ensuring that the resulting sound is not compressed. And thus, the IEM is better able to faithfully reproduce the original sound.


When tuning IEMs, it is important that there are ample energy reserves from the drivers so that the engineers have enough to work with to achieve their sound goals. This may simply not be possible with fewer drivers. Thus the FA19 employs ten outstanding BA drivers. And the physical + electronic three-way crossover accurately segments different drivers working on different frequency ranges, resulting in a clear, reference monitor-like sound quality.


The FA19 is an IEM that reaches the heights of sound quality with a thunderous impact, being able to faithfully reproduce every last single audio detail.

Rediscovering the essence of bass,

Custom Knowles · enhanced bass BA drivers


FIIO collaborated closely with Knowles to create a custom bass BA driver. By improving the airflow throughput of this driver, we enhance its overall energy. Additionally, the FA19 uses four of these custom drivers per channel, further ensuring there are enough drivers to produce detailed and powerful bass. The result is truly robust, impactful bass.

Clean coherent transition· Scientific HiFi Mid-frequency notch filter

A smooth mid-frequency curve not only stems from the core unit’s quality but also results from meticulous tuning by professional acousticians. The FA19 employs two classic Knowles ED mid BA drivers, known for their high resolution and favored by demanding listeners. However, if not implemented properly they can sometimes exhibit sibilance which negatively affects the overall listening experience. To address this, engineers have specially designed a mid-frequency notch filter at the bottom of these two mid BA drivers.

Enhanced mids

Sibilance eliminated

Refined treble

Measurements show that the mid-frequency notch filter increases  the sound pressure level between 1kHz and 3kHz in the FA19, avoiding a “hole” in the mids. This ensures not only that the highly detailed nature of a BA driver continues to come through, but also that the mids sound lusher a nd more realitic, as if the singer really was in front of you.

The mid-frequency notch filter effectively filters out the 8kHz peak of the mid-frequency BA driver.  Doing so  reduces  the overlap in frequency response  range between the  mid   and treble BAs, eliminating sibilance and enhancing overall clarity.

Additionally, the mid-frequency notch filter shifts the crossover point between multiple drivers to 3.5kHz. By establishing a clean separation between the mid and treble drivers, both sets of drivers properly work to their maximum potential within their designated frequency ranges without any interference.

Working principle of the FA19’s mid-frequency notch filter

When the frequency of sound waves approaches the inherent frequency of the resonant cavity, frictional vibrations occur between the cavity walls and the air, converting specific frequency bands of sound energy into mechanical and thermal energy, thereby dissipating sound energy and absorbing the sound. Conversely, when the frequency of sound waves deviates from the resonant cavity, the  resonance effect inside the cavity weakens, resulting in less sound absorption. Based on this principle, the mid-frequency notch filter is designed for the FA19 to weaken the high-frequency signals of the mids unit, thus achieving bandpass physical crossover.

Approaching frequencies with surgical precision Rubycon audiophile-grade crossover capacitors

Truly be immersed with each striking musical note thanks to a precise crossover. The FA19 employs audiophile grade film capacitors as its electronic crossover components, which boast exceptional precision. While typical resistor used for crossovers have an error tolerance of around 1%, the FA19’s resistors have an impressively low error tolerance of 0.1%. Thus, compared to ordinary ceramic capacitors, the FA19 not only attains more accurate crossover points but also features enhanced high-frequency resolution without sacrificing tonal finesse.

One button, two worlds

“Monitor/HiFi” mode switch

Choose between two carefully crafted listening modes,  by easily flipping a switch on the fly on the back of the IEMs. Use the FA19 as an audio production tool anytime, anywhere.

· —: “Monitor” mode, delivers clean detailed sound, especially in the treble, making the FA19 an excellent tool for audio production.

· On :“HiFi” mode, which adds energy to the mids and bass, with a special attention to the bass to give it more impact and quantity. It is the ideal way to experience pleasant HiFi sound.

-Monitor mode

ON HiFi mode

First-class experience DLP 3D printed shell

To successfully implement the negative feedback bass enhancement system and for high overall sound quality on the FA19. The FiiO FA19 is made with advanced DLP-3D printing technology with a precision of up to 0.0375mm, ensuring that the shell can be precisely crafted to meet our ambitious sound quality goals. The shell is made of photosensitive resin, which is highly durable and is able to offer robust protection for precision components such as the multiple BA drivers.

Pure black magic

S.Turbo patented acoustic design

The FA19 incorporates FIIO’s patented S.Turbo acoustic turbine-shaped design. By extending the tube that guides low frequencies, it serves as a filtering device that effectively eliminates high-frequency sound waves emanating from the bass BA drivers. This ensures a smooth transition between low and mid frequencies. This also leads to a cleaner split between the low and mid frequencies, resulting in purer sound that better reflects the original sound of the music.

Patent number:ZL2018211416279

The FA19 comes standard with a high-purity pure silver cable, consisting 8 strands of 28 wires each for a total of 224 wires. Each individual wire is independently insulated, and the cable is twisted using a Litz structure. The cable sheath is made from imported transparent eco-friendly TPU, enhancing the cable’s appearance with a bright and clear appearance. Additionally, this TPU material effectively prevents yellowing due to prolonged use  and stiffening of the cable due to use in low-temperature environments.

High-end cable, for stunning sound Included 8-strand 224 wires pure silver cable

*This cable is the same as LC-RD Pro 2022

 8 strands of 224 wires pure silver cable 

Expanded MMCX connector Stable, quick and convenient

Litz braided

Straight twist-lock swappable audio plug Supports 3.5/4.4mm plugs

*Swappable audio plug patent licensed from FABRILOUS

Overseen by acoustic experts Carefully tuned Hi-End frequency response curve

FA19 has been certified by the JAS (Japan Audio Society) and CEA (Consumer Electronics Association) to be hi-res audio capable. It is a testament to the product’s ability to bring you accurate high-fidelity audio, as close to the artist’s original intended sound as possible.

Flagship sound, golden quality Hi-Res Audio certified

Abundant accessories

1-------------------------------------------------------------------------------FA19 box*1

2---------------------------------------------------------------------Quick start guide*1

3-------------------------------------------------------------------------------HB5 case*1

4----------------Magnetic cord clip*1, Swappable plug sterling silver cable*1

5-------------------------Foam eartips*2 pairs (M), bass eartips*3 pairs (S/M/L),  

                                    balanced eartips*3 pairs (S/M/L) (M pre-installed),

6--------------------------------------------------------------------Magnetic cord clip*1

7-------------------------------------------------------------------------Cleaning brush*1

8-----------------------------------------------------------MMCX quick release tool*1

9--------------------------3.5/4.4mm swappable plugs*1(4.4mm pre-installed)

10----------------------------------------------------------------------FA19 earphones*1

11-------------------------------------------------------SpinFit eartips*3 pairs (S/M/L)

12----------------------------------------------------- -- HS18 eartips*3 pairs (S/M/L)

Basic specifications

Earphone type: 10 balanced armature earphones

Wearing style:in-ear and around-the-ear

Drivers: Custom Knowles bass BA*2, totaling 4               

                Knowles ED mid BA*2                  

                Knowles SWFK treble BA*2, totaling 4

Frequency response:20Hz-40kHz



Cable:8 strands totaling 224 high purity pure silver wires

Cable length:about 1.2m

Single unit weight:about 7g (excluding cable)

Earphone connector:expanded MMCX

Audio plugs:straight twist-lock swappable plugs

With four custom enhanced bass balanced armature drivers per channel developed by FIIO in collaboration with Knowles, the FA19 boasts ample bass. Engineers creatively made use of the precise DLP 3D printing technology to create a shell that helps to guide this low-frequency energy into the earphone’s rear cavity, effectively lowering the resonant frequency there – essentially a negative feedback bass enhancement system. The result is a bass that reaches extremely deep, uncommon among IEMs of its class.  

Furthermore, this ensures that the front cavity of the earphone is adequately vented, effectively preventing wearing discomfort caused by excessive pressure in the earphone’s front cavity. Thus this negative feedback system also  improves both wearing comfort and soundstage size, so that the wearing experience is not sacrificed in the pursuit of high-fidelity sound.

Don’t follow the crowd, stand out from it Negative feedback bass enhancement system