General Information



Model: Sound Linear Fitz 4E

Total Driver Units: 2 BA + 2 Electrostatic Drivers per-side

Crossover: 2-way Passive Crossover

Frequency Response: 8-22,000 Hz

Sensitivity: 107 dB/mW

Impedance: 60 ohm

IEM Connector: Detachable MMCX

Cable: 3.5mm Jack, 1.3 meter

Warranty: 1 Year

Latest reviews


New Head-Fier
Pros: Excellent treble extension without being harsh.
Mids are clean and natural.
Emotional bass quality, powerful yet controlled.
The build is beautiful and solid.
Cons: Quite challenging to drive with low-powered devices.
The soundstage is limited.
Before the review, I would like to thank Mr. Chua from Sound Linear loaning me this product free of charge in exchange for my honest opinion.


Sound Linear is an emerging Malaysian manufacturer that produces high-quality custom in-ear monitors (ciem). They offer a variety of ciem models (the Fitz-10 Flat, Fitz-4X, and Fitz-4B) for sound engineers, musicians, and audiophiles. The new (will be on sale soon) product which I'm going to review is their latest 2 balanced armature and 2 electrostatic driver hybrid ciem, the Sound Linear Fitz-4E. The selling price is still undecided by the manufacturer, I will update once they announce it.


Here are some technical details for the Fitz-4E. It consists of 2 balanced armature drivers and 2 electrostatic drivers linked by a 2-way passive crossover making it achieve a frequency response of 8-22kHz. With a sensitivity rating of 107dB/mW and impedance rating of 60ohm, the Fitz-4E is clearly not easy to drive.

The Fitz-4E comes with a silver cable as the stock cable. I'll share some pictures below for you guys to have a look at the iem.


This unit which I review is the demo unit, thus it is in universal form. Despite that, the build quality is very good as the shell and faceplate is bubble-free and nicely done. The internal driver placement, wiring, and soldering are also professionally done. Thumbs up to Sound Linear for this one.


The Fitz-4E features 2 balanced armature drivers for the lows and mids, and it has 2 electrostatic drivers for producing that very nice treble which I will mention in the sound analysis section. One thing worth mention is the mmcx connection on the Fitz-4E, unlike conventional mmcx port on some Shure and Sony products which gets slightly shaky after some period of usage, the one on the Fitz-4E it is very sturdy. There is a very nice click when attaching mmcx cables, and judging from the picture below the mmcx female port is not your usual gold-plated port..... I suspect it to be rhodium material which is a good thing. Rodium material has low electrical resistance, good corrosion and oxidation resistance to perform a more stable contact for transmitting audio signals.


Sound Analysis

The first time I tried the Fitz-4E was in an audio gathering event in StarsPicker Audio Cafe, I remember pairing it to the Sony WM1A and my impression that time was the Fitz-4E is a power-hungry ciem. In single-ended high-gain mode, I cranked the WM1A to the maximum volume just to get a slightly higher than average listening volume (the WM1A is not powerful by the way). Before I give it a serious listen, I put the Fitz-4E through about 144 hours of burn-in with pink noise and a bunch of tracks. With burn-in, I think the internal electrostatic energizer and crossover components will get conditioned and perform at their best. For this review, I paired the Fitz-4E to my Chord Hugo, a very powerful portable dac/amp which has a reference sound signature.


As an owner of the Noble Kaiser 10U aluminum, my sound impression for the Fitz-4E will be made with the K10U as reference. With that, I find the Fitz-4E to have an organic and warm sound signature. Typically when people heard the word 'warm', they tend to have the impression of emphasized bass, lush mids and rolled off highs. But not this time! Despite having a warm signature, the Fitz-4E reveals a good amount of details from the music in a non-analytical and organic way. The most astonishing part is how realistic and natural the Fitz-4E sounds. I personally owned and tried many high-end iems, they might have better detail retrieval or soundstage or whatsoever. But when it comes to tonality naturalness, the Fitz-4E is a step ahead out of everything I tried before.


I would describe the low-end with the word "muscular", it is big in quantity and high in quality, just like a bodybuilder with a good physique. The sub-bass has a great extension with good definition. Mid-bass is punchy yet controlled without bleeding into the mids. Traditional and rock music lovers will like this a lot as the drums sounded so natural as I was listening to it at live. Although the bass of the Fitz-4E might not satisfy the extreme bass heads, it still provides enough "boom" for those people who like EDM. In short, the bass has a natural texture. It is detailed and full-bodied, but not overly emphasized.


The Fitz-4E has detailed, sweet, and slightly lush mids, that results in producing natural vocals. Whether or not you are listening to shouty rock songs or Rebecca Pidgeon's beautiful voice, the mids is always so well pronounced that I can hear great details from the singer. The Fitz-4E does not only brings out the sound of guitar strings and acoustic music, but also the emotion. The mids have respectable separation too, instruments and vocals can be heard and differentiated clearly when listening to classical musics.


The treble region is what makes the Fitz-4E special. The quality of the treble feels like nothing I experienced in an iem before, and I am pretty sure the 2 electrostatic drivers are really doing their magic here. The treble has a unique characteristic which is well extended, sparkly, detailed, and transparent. Typically, iems that have the same treble characteristic like the Kaiser10U sounded a bit splashy, but the Fitz-4E's treble adds in the wow factor of being natural, slightly smooth, and zero sibilance. With that, I actually use it to listen to my Japanese song collection (heavily mixed and brightly recorded) without hurting my ear, and I can listen to it for a longer period of time. But the Fitz-4E does not make classical music or other music genre sound blunt either. In fact, it preserved the sparkle that brings music to come alive, cymbals are crystal clear and well defined.


My only critic is the soundstage. The soundstage is very limited, it has that "in your head" kind of sound. The Noble K10U trumps in its even 3-dimensional soundstage here. I think it is a good all-rounder for all kinds of music with the exception of classical and orchestral music. They sounded clear and nice, but with that closed "in your head" kind of sound reproduction, it just sounds a little bit weird to me. Maybe I'm too used to wide sounding kind of stuffs.


This is my first time listening to a pair of iem which adopts electrostatic technology. It is not easy to drive, but if you power it right, the Fitz-4E does reward you with soulful and natural music playback. Bass is appropriately emphasized without being overpowered. Mids are crystal clear and well pronounced with a touch of softness. Treble is detailed, extended without being harsh (or sharp). So guys, if you love rock, EDM, or more into acoustic music, please give the Fitz-4E a try. I'm pretty confident you will appreciate it. Cheers!
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A full review but not once is the price mentioned. Shouldn't that be part of any review?
@iBo0m Hi! this is just a universal demo unit for me to try, the actual product will be made based on the shape of your ear for a perfect fit.
Hi, @Carlsan this a new product which hasn't been launch to the market yet, thus the price is unknown. But I will update once it is published.


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