Review: Thieaudio Legacy 4 – the Sound of Art and Art of Sound

Thieaudio Legacy 4 IEMs, name on faceplate display
Thieaudio Legacy 4 IEMs, name on faceplate display

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Is there a place in the Legacy family for another middle child?

First, a sincere thank you to Linsoul for allowing Headphonesty to review the Thieaudio Legacy 4. As is my standard, I did not read any reviews of the Legacy 4 before I evaluated them, and I have not experienced any other Thieaudio IEMs to date.

Thieaudio has gone to great lengths and investment to create a distinctly different set of IEMs in their Legacy line. Until the introduction of the Legacy 4, there were the 3, 5, and 9.

Fascinatingly, Thieaudio took the approach of designing the Legacy 4 and 5 concurrently to be a “middle ground” between the Legacy 3 and 5, both in terms of tuning and price. The Legacy 4 (USD$195) was introduced to the market following the others of the odd number nomenclature.

For USD$300, you can get a completely custom set. Upon selection from an astounding variety of 18 shell and 50 faceplate options, you will receive a custom earmold to shape and return to Thieaudio. After that, they will custom make your very own Legacy 4 IEMs.

Bottom Line

Thieaudio’s Legacy IEMs are clearly a notable achievement, technically and musically. Though I have not heard the others in the family, the Legacy 4 are an excellent high fidelity choice for those who will use them for critical listening. They are tuned to a discerning audience who enjoy natural, accurate sound reproduction and precision performance.

What We Like 😍
  • Works of art and engineering
  • Top-grade fit and finish
  • Light and comfortable
  • Secure fit with a decent array of silicone ear tips included
  • Abundant natural tones and textures
  • Treble extension, high detail, and clarity — bright!
  • No cable noise or interference
  • Two carrying/protective cases included
What We Don't Like 🤢
  • Benefits from extensive break-in/burn-in
  • Relatively flat, audiophile-friendly sound profile may not be loved by the masses
  • Bass, while natural, will be inadequate for heavy bass lovers
  • Compared to mass market IEMs, very bright and lively
  • No documentation for the hardware tuning switch functions
  • No included tool to adjust the switches (or magnifying glass to see them!)
  • No cable with microphone option
The faceplates have stunning depth when illuminated
The faceplates have stunning depth when illuminated

What’s most remarkable is Thieaudio’s willingness to create such a vast array of products aimed at highly specific, niche audiences. My Headphonesty colleague Trav Wilson conducted thorough reviews of both the Legacy 3 and Legacy 5, which I will reference several times ahead, as there is much useful information to compare and contrast should you choose to.

First Impressions

When opening the zippered case, you see the faceplates of the IEMs nestled into their place. My first impulse was to shine a light on the faceplates to reveal the depth of the artistry. The more I looked, the more I saw. It’s like being drawn into a micro cosmos — beautiful! They invite you to meditate on them and center yourself in the present before putting them into your ears for a blissful listening session.

Structurally, these Legacy 4 are just as captivating as the faceplate. Their flowing seamless shape is not something I’ve seen in other IEMs. Surprisingly, the shape made them easy to grasp and place properly in the ears and to adjust if necessary.

The Legacy 4's seamless resin and unique shape are exceptionally comfortable
The Legacy 4’s seamless resin and unique shape are exceptionally comfortable

They sat very well into my ears (I received a standard, non-custom pair) and proved to be secure and a good fit with the proper silicone ear tips.

Company Overview

Thieaudio was launched in 2019 as a creative endeavor of Linsoul Audio. The goal of Thieaudio was to serve as a creative platform for gathering the best teams of engineers to inspire revolutionary audio products for audiophiles and professionals alike.

“For each project, we hand select the most innovative and renowned engineers in his or her field to oversee the design, engineering, and manufacturing of the products.”

In a very brief period of time, Thieaudio has created a number of well-regarded products, including the Phantom planar magnetic headphones, as well as an extensive range of in-ear monitors (IEMs).

Technical Specifications

  • Transducer Driver: 1DD+3BA Hybrid Driver in-ear monitors — one proprietary 8mm poly-membrane dynamic driver, plus Knowles™ and Thieaudio customized balanced armatures (collaboration with Bellsing); 3-Way crossover network is integrated into a 2-switch tuning system
  • Impedance: 9.4 Ohms
  • Sensitivity: 108±0.5db
  • Frequency range: 20 Hz – 20 KHz
  • Noise isolation: 26dB
  • Style: In-ear, with earhook cable
  • Connector: 0.78mm 2 Pin
  • Plug Type: 3.5mm straight gold-plated plug
  • Cable length and type: 1.20m (120cm), OCC silver 4-core custom cable (option: upgrade EST cable — Litz 5N OCC Silver Plated Cable 100 wire x 4 core, 2.5mm balanced cable with included 3.5mm and 4.4mm adapter, plus USD$54)
The stately Legacy 4 box, encouraging you to discover the next case inside
The stately Legacy 4 box, encouraging you to discover the next case inside


The stately black box indicates the seriousness of what it contains.

The packaging reminds me of opening a Russian matryoshka doll. First, open the shipping package. Then remove the plastic wrap from the box inside. Upon opening the box, you will discover another box! This box protects a distinguished gray zippered clamshell-type carrying case. This gray case contains another miniature padded travel carrying case, large enough to comfortably hold and protect the IEMs and cable.

In the box

  • Large outer gray zippered textile storage case
  • Small travel sized gray zippered textile case
  • 2 Legacy 4 IEMs
  • 1 braided 0.78mm 2-pin OCC 4-core silver detachable cable
  • 7 pairs of black silicone ear tips
  • Minimal printed instructions, a quality certificate, and a guarantee/information card that you can fill out and keep
What's inside!
What’s inside!


The braided, 0.78mm, 2-pin OCC, (a specific manufacturing process — ohno continuous cast) 4-core, silver, detachable cable is itself an object of beauty and appears to be of excellent quality. All parts feel substantial, from the thickness of the cable to the connectors. It also performs well.

The bright glimmering white-silver cable is almost as beautiful as the IEM bodies. Interestingly, this color is very similar to my description of the sound! (More on that in a moment below).

The braiding is entirely consistent and transmits zero friction noise. The cable is supple and ear hooks have rigidity without a plastic cover sleeve. Magic! They shape well around the ear without exerting pressure, are secure, and comfortable — it’s easy to forget that they are there.

There is a single translucent plastic slider to adjust the cinch’s length below the chin. The wishbone protective splitter also feels sturdy. The cable has a straight earplug design and a 3.5mm gold-plated plug.

The beautiful silver Legacy 4 cable
The beautiful silver Legacy 4 cable


The Legacy 4 have a clear resin body, allowing you (with a magnifying glass or macro photography) a window into the internal drivers and wiring. They are fluid in appearance and feel, with no obvious seams. The nozzles and body are one continuous smooth shell.

According to Thieaudio, each Legacy 4 unit is handcrafted, from the medical-grade German resin, to the internal circuitry, to the painting of the faceplate, making each unit a one of a kind in design. If you choose custom options, they become even more uniquely yours.

Every Legacy 4 is uniquely made
Every Legacy 4 is uniquely made

The silicone ear tips easily apply and remove. The nozzle is long enough that I never feel the body of the IEM making any uncomfortable contact with my ear. When inserted properly, they look streamlined to the shape of the ear.


The smooth resin unibody construction results in a light and easy to handle package. Suspended into the right position by the ear hooks, the weight is not noticeable and is never an issue despite hours of use. Noise isolation is average with the right seal. Thieaudio claims 26 dB of noise isolation.

The cord’s comfort is excellent as well despite its substantial presence. The ear hooks hold well and conform around the ear without exerting any bothersome pressure.

Look closely and you'll see the drivers, internal wiring, and port hole
Look closely and you’ll see the drivers, internal wiring, and port hole


The Legacy 4 IEMs contain 4 drivers per IEM. They utilize a completely new in-house 8mm poly-membrane dynamic driver for the low end, designed for faster speed and enhanced texture. It is matched with the American Knowles ED29689 balanced armature (BA) and intuitive low-mid passive crossover design intended to emphasize a natural mid-frequency presentation. In partnership with Bellsing, Thieaudio developed a custom dual BA tweeter for the Legacy 4 that perfectly fits the mid BA driver.

Thieaudio: “You can trust that the Legacy 4 will provide one of the most natural, accurate, and enjoyable musical experiences among any IEM’s of its class.”

Brave and persistent reader, read on for the sound review!

Tuning switches

At some point, I noticed that the tiny switches (2 on each earphone) were inexplicably unmatched (in different positions).

The Legacy 4 IEMs have hardware tuning switches to customize the sound
The Legacy 4 IEMs have hardware tuning switches to customize the sound

As the switches are not easy to move, this must be how I received the Legacy 4 IEMs. After breaking my usual protocol of not looking too closely (or at all) at the manufacturer descriptions and marketing material, I found a paragraph on the switches on the product description at Linsoul.

Excellent, now I knew what they were, and were for — tuning!

According to Thieaudio, “the Legacy 4 crossover network is integrated into a 2-switch tuning system that allows the user to define the level of bass and mids. This tuning system means you can find the perfect sound signature no matter your musical preference!” I was most certainly curious to see if this was the case.

Wonderful! How do you do that?! No idea… what I did not discover from any of the documentation provided, or on the product website, was exactly how the switches worked. That meant more research.

Thanks to my uber-colleague Trav Wilson at Headphonesty for saving me even more aggravation, as he had already completed top-grade detective work when reviewing the Legacy 3. His research helped me adjust the switches settings to verify if they actually produced the results that Thieaudio suggested.

Here is a visual depiction of the switch settings:

Visual depiction of the Legacy 4 tuning switch settings
Visual depiction of the Legacy 4 tuning switch settings

To my ears, the adjustments are noticeable, though do not make for dramatic changes. I adjusted the setting to ‘Bass’ on both IEMs after some experimentation and left them there for the remainder of the evaluation.

Thieaudio Legacy 4 Sound

I received feedback from a number of our readers that they simply don’t trust any reviewers’ sound reviews, they only trust the objective data. To address this, let me be transparent about my biases and preferences.

First: I have highly sensitive hearing and tend to prefer smooth, warmer, darker sound profiles with a strong presence, adequate staging and imaging, and clean separation. I am not overly obsessed with micro-details and tend to focus on the full, holistic effect of my perception of the sound.

Second: dear data-based readers, please find a bevy of gorgeous graphs below for your technical analysis! I believe what’s most helpful is to verify if what you’re experiencing in sound seems to be validated by the frequency graphs. They may also be quite helpful in guiding you to decide on which listening apparatus to buy for your personal pleasure.

The nozzle and body are one seamless resin piece
The nozzle and body are one seamless resin piece

For evaluation, I listened to a great variety of music from numerous sources including:

With a very high sensitivity of 108db and a very low impedance of 9.4 ohms, these IEMs are easy to drive with virtually any source. That said, I found them to sound better with amplification via a quality AMP/DAC.

Below are the frequency graphs for the Legacy 3, 4, and 5 respectively for comparison:

Below: frequency graph for the Legacy 3.

Thieaudio Legacy 3 Frequency Graph - Headphonesty
Thieaudio Legacy 3 Frequency Graph – Headphonesty

Below: frequency graph for the Legacy 4 (provided by Thieaudio on the Legacy 4 box).

Thieaudio Legacy 4 frequency graph
Thieaudio Legacy 4 frequency graph

Below: frequency graph for the Legacy 5. (From Headphonesty)

Thieaudio Legacy 5 frequency graph
Thieaudio Legacy 5 frequency graph

Though I could not obtain the exact same graphs or an overlay of the three from Linsoul, please take notice of the shapes above, with particular note of the frequencies over 4K.

The differences in higher frequencies (8K and above) of the Legacy 3, 4, and 5 will significantly impact the listener experience.

The Legacy 4 IEMs are well suited for instrumental, acoustic recordings, performances with vocal emphasis, jazz, new age/world, opera, and orchestral/classical.

Before 30 hours of burn-in time (I let them play — I do a sample listening comparison every 10 hours or so), I found the sound harsh and overly bright. Thankfully, things improved with time.

The vast majority of buyers will be using these for dedicated critical listening, and I believe, will generally find these highly engaging and enjoyable.

These are IEMs that audiophiles will gravitate to — fairly flat, high dynamics, and accurate, clear sound with little to no obvious coloration. That is not to say that they are boring by any stretch! These earphones have a highly energetic quality — they demand your attention. I don’t believe they are for super casual background, easy listening.

Mid-range is the sweet spot, coupled with high treble extension. Channel separation is excellent and produces a fairly wide, above-average soundstage — spaciousness and imaging are excellent.

Using a FiiO A3 amplifier, the Legacy 4 seem to become smoother and a touch more relaxed. In combination with the physical EQ switches set to emphasize bass and the bass boost option on the FiiO turned on (with gain off), the sound signature sounds more balanced.

While I do not have a tube amp on hand, I would presume that the Legacy 4 might be even warmer with that sort of amplification.


Bass is natural and fast, which many may describe as accurate. The Legacy 4 can reproduce bass and sub-bass frequencies as expected, although without much punch. Bass is a bit thin for my tastes, and this is highly evident in music genres where low frequencies are prominent (EDM, techno, trap, club dance, hard rock, heavy metal, etc.)

Bass feels and sounds natural and appropriate when listening to a variety of jazz and vocal recordings. With acoustic, and especially classical and opera, I found my happy place with the Legacy 4. Texture is outstanding, and resonance feels exceptional from instruments like the cello and timpani. The sense of realism is notable.

These will satisfy listeners who appreciate natural tones; bass lovers may want to look elsewhere.

While the bass is tight and fast, it resolves so quickly that bass-heavy music seems thinner than it should be.


The Legacy 4 sound strongly midrange-treble forward, which is a definite strength for them. Mid to mid-upper frequencies can be highly prominent and forward depending on the source. I find the mids to be impressively differentiated, meaning that they are easy to distinguish between vocals, varied instrumentation, and nuances in emphasis or volume.

“With a less aggressive crossover design than the Legacy 5, the mids of the Legacy 4 presents a more musical experience that ever so slightly adds a dash of warmth to the overall signature.” – Thieaudio

Personally, I would prefer a few extra dashes of warmth in the recipe.

Natural sounds abound!
Natural sounds abound!


While treble smoothed slightly over time, the Legacy 4 treble emphasis results in very bright, clear, and crisp reproduction. “Shimmer”, as Thieaudio describes, resonates with my notes. I do not detect any sibilance, just a sharpness that at times can be exhausting to listen to. I generally find that listening to music at a lower volume than usual is advisable with the Legacy 4, which I have come to appreciate, as the detail is still there.

They can be tinny and hollow with certain sounds (for example, drum high hats and rim shots are very sharp sounding). The treble does not overshadow the midrange. I find transitions to be smooth between midrange and treble. The standard OCC silver cable may be adding just slightly to the perception of recessed bass and increased treble.

“Contrasted from the relaxed and smooth treble delivery of the Legacy 5, we have tuned the Legacy 4 to bring more upper treble presence, highlighting upper frequency overtones and details. This tuning and the extremely capable treble extension of our new tweeters brings an even greater level of airiness and shimmer to the mix, making the Legacy 4 an excellent IEM for both professional musicians and music enthusiasts alike.” – Thieaudio
Thieaudio - the stamp of quality
Thieaudio – the stamp of quality

Where to Buy

Thank you once again to Linsoul for providing the Legacy 4 for review. If you’d like to purchase a pair, you can buy them directly from Linsoul or AMAZON.


Thieaudio’s Legacy IEMs are clearly a notable achievement, technically and musically. Though I have not heard the others in the family, the Legacy 4 are an excellent high fidelity choice for those who will use them for critical listening. They are tuned to a discerning audience who enjoy natural, accurate sound reproduction and precision performance.

They are exquisitely designed and produced, with outstanding comfort and wearability. However, they are not designed for high-stress conditions (no IPX rating/water resistance, microphone, etc.).

The product descriptions seem quite accurate with the exception of the anticipated bass response, which I feel is somewhat lacking in certain genres of music. While tight, controlled, and musically accurate, I would not describe them as impactful.

Thieaudio suggests more warmth in the Legacy 4 vs. the Legacy 5. Though I cannot attest to the difference, I do not consider the Legacy 4 warm IEMs. Overall, I believe that Thieaudio has achieved their objective with the Legacy 4, a self-described “middle ground” and “unique twist” in the Legacy line.

In this middle price point Thieaudio will likely develop an appreciative fan base of audiophiles and music enthusiasts. The uniqueness of the Legacy 4 – design, shape, beauty, build quality, place in the Legacy lineup – plus an astounding array of customization options, means that you will have a pair that are truly yours to enjoy!

💬 Conversation: 6 comments

  1. Right now still reviewing and need time to burn in a bit. Love the Thie 3″s the gears,I think once I put 2.5 mm and upgraded cable as I did for the 3’s they will sound a whole lot better w/eq and bluetooth 5k dac/amp

  2. Hi Jack, apologies for not responding sooner. Have you decided and purchased anything recently? Or still weighing options?

  3. Hi. I just noticed that the “visual depiction of the switch settings” photo came from 1Custom JR from Jaben. It looked very familiar and when I saw the “specifications”, I was able to confirm that they are indeed from the 1Custom Jr. How do I know this? Because I have that excellent IEM of course. 🙂 My Legacy 4 will arrive this week too. I know, based on other reviews, they already have that small info about the tuning switches that was missing in yours. Kindly update that photo so that it will be legit. Hehe. Thanks. Nice review btw.

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