Rated at 31mW @ 32Ω on the 3.5mm single-ended output, the output power is similar to that of many smartphones in the market. What this means is that, if you are using any earphones which are challenging to power on your smartphone, you are unlikely to gain any headway with the CM21.
The CM21 has a Signal to Noise Ratio (SNR) of 120dB, which explains why the CM21 exhibits a darker background with lower distortion.
At the low-end, the CM21 is energetic with plenty of punch, however, the energy was let down by the lack of resolution and details, ensuring a low-end experience that is lacking in clarity.
The CM21 exhibits a neutral mid-range, vocals, however, exhibit a lack of coherence. Attributable to the lack of in details and form, which has made the mid-range experience a rather grainy one.
Similar to the mid-range, the high-end exhibits a rather grainy experience. The lack of details and resolution ensures the absence of extensions and decay at the high-end.
The soundstage of the CM21 is one that is rather average, the lack of details and resolution across from low-end to high-end translate into poor sound imaging particularly instruments and vocals.