Thieaudio's Monarch MKIV represents the latest evolution in the brand's flagship IEM series, building on the success of the MKIII with significant upgrades. Priced at $1,149 from Linsoul, these IEMs feature a sophisticated driver configuration with two dynamic drivers, six Sonion balanced armature drivers, and two Sonion EST drivers per shell. The standout feature is the new tuning switch that allows users to toggle between reference neutral mode and Rumble mode, which adds a 3dB sub-bass boost.

The build quality sees a substantial improvement with a metal chassis replacing the previous resin design, available in Stellashot or Kaleidoglow finishes. Custom shell options remain available for an additional $100-$150 with extended wait times. Despite larger shells, the angled sound nozzle design maintains comfort for extended listening sessions. The modular cable includes both 3.5mm and 4.4mm connectors, though the brown color may not appeal to all users.

After three months of testing with various sources including the Fiio K19 DAC and M23 player, the Monarch MKIV delivers exceptional sound quality in both tuning modes. The standard mode offers neutral presentation with controlled bass and detailed treble, while Rumble mode provides warmer tonality for those preferring enhanced bass response. The soundstage remains engaging across both modes, with excellent layering and instrument separation making these IEMs worthy contenders in the premium audio market.