Because of their tiny size, balanced-armature (BA) drivers can go where other drivers can't, making them ideal as in-ear monitoring systems for studio mixing and concerts.
If you have gone to a live gig or music concert before, you probably have noticed an earpiece in the ears of the artist or musician. That earpiece that they wear in their ears is actually a single balanced armature in ear monitor that they use to hear themselves on noisy stages.
Most in-ear monitors are the hybrid type using a mixture of dynamic drivers and a single balanced armature driver to deliver the high frequencies.
With that said, you can also get standalone, single balanced armature in-ear monitors like the FiiO FA1 which uses customized Knowles ED-33357 balanced-armature drivers with a 20Hz~20kHz frequency response.
From the transparent resin body to the eye-catching wavy texture design, the FiiO FA1 are a rather unique pair of single balanced armature IEMs.
Instead of using the traditional injection molding process using plastic filament, the FiiO FA1 body is made with liquid resin cured under light using a Digital Light Processing (DLP) 3D printer.
Each earpiece weighs 4.6 grams so the total weight of the FiiO FA1 earpieces, excluding the cable, is a little over 9 grams which is extremely lightweight.
To deliver the sound, the FiiO FA1 makes use of a 3.5mm unbalanced headphone cable with copper-plated oxygen free (OFC) silver wiring and MMCX (micro-miniature coaxial) connectors which are a smaller version of MCX coaxial RF connectors used to connect external antennas to GPS receivers.
Balanced headphone cables do improve the overall sound quality delivering clearer, stronger sound with less noise, louder volume (+5dB more volume ) and wider sound-stage. At first glance it looks like the FA1 IEMs use a balanced cable but actually they don't.

Balanced cables tend to use a 2.5mm connector but you can also get IEMs with balanced cables with 3.5mm connector (i.e. HiFiMan RE-600). Usually, if the connector has 3 black rings (TRRS) it is a balanced cable and unbalanced if it has 2 black rings (TRS). The addition of a balanced cable would have definitely made the FiiO FA1 much more appealing though having a 3.5mm plug means you can use the FA1 IEMs with the M3K digital audio player as well as the BTR3 and BTR1K Bluetooth headphone amplifiers
The FA1 earphones have a high sensitivity(111dB) to low impedance (15 Ohms) ratio, making them very easy to drive very loud (more sensitive than the F3 IEMs and FB1 IEMs) and without distortion.
The FiiO FA1 unbalanced MMCX cable has top notch construction with MMCX connectors shrouded in gold-plated metal, thick rubber strain reliefs and thick protective cable sleeve reinforcements that can withstand the onslaught of daily use.
The copper-plated oxygen free (OFC) silver wires make up each of the four separate cables in the FiiO FA1, which are all braided into one audio cable with separate wires for the left and right channels. The length of the cable is 1.2 meters long.
Aside from the beautiful resin shell 3D printing design and MMCX unbalanced cable, the FiiO FA1 features a rather unique nozzle design too reminiscent of a science lab test tube.
The tube nozzles have no mesh filters and are customized with a smooth and natural sound signature that delivers fast bass, rich mids, and detailed treble. The FiiO FA1 IEMs use standard silicone or foam eartips to create a proper seal in the ear canal.
There no foam tips included but you get s selection of soft silicone eartips which make wearing the FiiO FA1 earphones inside the ears comfortable.
The FiiO FA1 fit is secure thanks to the loop design that allows the cable to be worn around-the-ears rather than straight down.
Around the ears or over the ears IEMs are nice because it minimizes accidental yanking out, as well as the annoying rustling "microphonics" sound you can sometimes get with straight-down IEMs when the earphone cable rubs against something.
The carry case that is included with the FiiO FA1 single BA in-ear monitors is not the standard EVA (Ethylene Vinyl Acetate) case or drawstring carrying pouch you get with most IEMs.
Instead, with the FiiO FA1 you get a transparent hardshell plastic case that does a superb job at protecting the contents while complimenting beautifully the FA1 transparent/ripple theme. A thoughtful touch indeed! See the review of the FiiO M3 Pro DAP and the review of the new FiiO FH1S dual driver iems