The ThieAudio Monarch MK4 is a premium IEM that earns a spot in the S-tier for competitive gaming, offering a significant upgrade over its predecessor and A-tier competitors. It features a unique rumble mode switch that adds a satisfying low-end punch and weight without muddying the detailed, reference-grade tuning of the standard mode. While the CNC aluminum build feels exceptional, the design is a bit bulky and heavy, which can lead to some comfort issues during very long, multi-hour sessions.

For gaming, the technical performance is nothing short of phenomenal. The imaging is holographic and the depth perception is absolutely exceptional, providing a critical advantage in tactical shooters like VALORANT where tracking footsteps through walls becomes incredibly precise. The wide and deep soundstage pushes sounds off the player, creating an immersive experience. While rumble mode is preferred for titles like Call of Duty, the standard mode's clean and detailed signature shines in battle royales like Apex Legends, though the 2-4k range can make gunfire a bit shouty at higher volumes.

This is also an absolutely amazing set for music, delivering an elevated level of technicality and resolution. The standard mode offers a fast, clean, and neutral listen with great detail retrieval, while the rumble mode provides a weightier, more engaging bass profile for tracks that benefit from the extra warmth and punch. Ultimately, it's a very high-end IEM that delivers a top-tier experience for both competitive gaming and critical music listening.

ThieAudio Monarch MK4 comes in at $1,150 with a tribrid array—2 DD + 6 BA + 2 EST—a chunky stock cable with friction-fit swappable terminations, and a genuinely excellent, in-ear-operable “Rumble” bass switch. The new metal shells look tidy, but the fit is very large; on average ears it tends to sit a bit out of the concha and feel unstable (seal is doable, comfort is mediocre). Build details like the firm chin slider are nice, yet the cable bulk and loose termination retention detract from daily use.

Tonally, stock MK4 aims for a clean-neutral presentation with a meaty, sub-bass-focused lift, lively upper registers, and excellent extension. The flip side is a slightly dry / clinical character with a hint of treble hardness that can leave notes feeling a bit bodyless. Engaging Rumble mode thickens the curve from ~300 Hz down—more warmth and weight, bordering on “gigabass” territory—making the set fuller and more fun, though arguably too bassy for purists. Staging and imaging are solid, and resolution is high, but macro-dynamics land behind peers; compared side-by-side, sets like Dunu Glacier and 64 Audio U4S feel punchier, while Valhalla sounds warmer, smoother, and more effortlessly resolving.

Overall, MK4 is a technically capable tribrid with two distinct tunings on tap—clinical-clean stock and warmed-up Rumble—but it’s held back by fit size, cable quirks, and that slightly wooden bass texture. For listeners chasing a bright-leaning neutral with legit sub-bass reach (and who can accommodate a big shell), it’s a compelling try; in this lineup, though, it settles at a three-star recommendation next to more engaging or comfortable alternatives.

Priced between $1,150 and $1,300 depending on custom faceplate options like the butterfly design shown, the Thieaudio Monarch MK IV boasts exceptional build quality with a large but well-contoured titanium shell offering a secure and comfortable fit. Key features include the innovative rumble switch for adjustable bass levels on the fly, a durable two-pin connector, and a solid feel that inspires confidence in longevity. While the included accessories are considered fair but unexciting, the shell's customization potential and rugged construction are major highlights.

Sonically, the Monarch MK IV delivers a detailed, exciting, and clean sound signature that stands as the best in the Monarch lineage. The rumble switch provides two distinct profiles: the red switch (no rumble) offers a balanced, tactful bass presentation, while the gold switch (rumble) adds a satisfying sub-bass shelf ideal for genres like hip-hop. Treble performance is notably improved over the MK III, though a 10k peak requires careful ear tip selection for some listeners. It trades blows with flagships like the $3,000 Annihilator (better sub-bass focus) and the $1,800 Elysian Apostle (more vocal forward), often matching or exceeding their technicalities while offering its unique tuning flexibility.

Scoring a top-tier 9.8, the Monarch MK IV earns its place through a compelling combination of premium build, the highly functional rumble switch, and outstanding sound quality that feels both special and refined. While acknowledging the high price, it represents significant value against competitors like the $2,000 Thieaudio Valhalla or the fiddly Grand Maestro, offering a feature-rich, durable, and sonically excellent package that justifies its position as a current summit-fi favorite.

The Thieaudio Monarch MK IV presents two distinct tuning options, elevating its versatility. The balanced switch delivers a clean, smooth, and slightly airy presentation, offering a refined all-rounder sound that's very detailed, well-layered, and resolving – essentially a direct upgrade to predecessors like the Monarch MK3 and Top Pro, with slightly more treble detail and air. Conversely, the bass switch provides a significantly fuller, warmer low end with punchy, well-textured bass and a tamer upper midrange, addressing criticisms of thinness in earlier models and offering a specialized, engaging listen for bass-heavy genres.

Technically, the MK IV sits comfortably in the $1,000 tier, offering a slight bump in detail retrieval, refinement, and smoothness over the MK3 and MK2, comparable to the Dunu Glacier and Prestige LTD. While not a giant leap, the dual tuning options make it arguably a better all-rounder than single-tuning competitors; the balance switch excels with acoustic, classical, and cleaner genres, while the bass switch shines with rock, metal, R&B, and pop. Build quality is improved with an all-metal shell, though the flimsy cardboard case is a notable disappointment. Vocals are smooth, balanced, and enjoyable, though sets like the Monarch MK2, Mystic 8, RSV, or Arcanis offer more forwardness or unique character. Bass quality is excellent for most, though pure bass enthusiasts might prefer models like the Thieaudio Origin for its unique texture.

Ultimately, the Monarch MK IV is a highly compelling endgame option for the vast majority. It combines strong technical performance with exceptional versatility through its two excellent tunings, covering a wide genre spectrum effectively. While value-focused options like the Top Pro, Volare, or Mega5EST offer similar technicalities at lower prices, the MK IV's refinement, tuning flexibility, and slightly superior performance make it easy to recommend. It allows listeners to leave the hobby satisfied, provided they resonate with its sound – though chasing marginally better flagships involves steep diminishing returns. The king might be debatable, but the MK IV is undoubtedly a very solid $1,000 contender.