Hidizs' new MD4 IEM is also a quad driver like its predecessor - the Mermaid MS4 - but the MD4 is an all BA (balanced armature) IEM with four balanced armature drivers per earphone and on-board EQ via a nifty 2-switch tuning filter mechanism!
Despite the lack of dynamic drivers, the Hidizs MD4 balanced armature drivers have been tuned to handle all the frequencies, including bass. Two of those balanced armature drivers handle bass, and the other two balanced armature drivers handle the midrange and treble respectively. To accomplish this, the Hidizs MD4 uses a 3-way audio cross over (just like most multi-driver IEMs and stereo speakers) to split and send the right frequency to the correct BA driver. A 3 way cross over is basically a filter circuitry with three filters (low-pass filter, band-pass filter and high-pass filter).
The Hidizs MD4 earphones have very low impedance (8 ohms) and high sensitivity (102 dB), which means you can get plenty of volume without the need of an external DAC Amp. As far as sound/audio quality, it is an interesting one because of the tuning modes.
Despite the name, the "Warm" tuning mode is actually more balanced than the "Balanced" mode and the best all-rounder out of all 4 tuning modes. The bass is clean (not dynamic) and midbass focused; hence very little sub-bass thump/slam. The sound stage is very wide and frequency layering very good naturally separating vocals, instruments and treble, letting you retrieve details very easily.
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