UiiSii CM5 in-ear monitor


500+ Head-Fier
Pros: Unbelievable sound quality at this price point, comfortable, nice case, non-terrible earhooks
Cons: Stock tips do not isolate well, aesthetics of outer faceplate may not please everyone, issues with phone calls on Android
UiiSii CM5 Review


This review is based upon a commercial unit purchased by me for personal use. This review represents my honest and unfiltered opinion. I am not being compensated in any way for writing this review.

This review can also be read on my blog here.



I listen mostly to heavy metal, hip hop, and electronic music, as well as movie and video game soundtracks. I value detail, clarity, and soundstage above other acoustic qualities. I like V-shaped sound signatures, generally those with more of an emphasis on the treble. Other headphones I own or have owned in the past include the Campfire Audio Polaris, Meze 99 Neo, E-MU Teak, Mee Audio P1 Pinnacle, Mee Audio P2 Pinnacle, Yersen FEN-2000, Rose North Forest, Fostex TH-X00, V-Moda M-80, V-Moda LP2 Crossfade, Beyerdynamic DT-770 (250 ohm), KZ ATE, Mixcder X5, Mee Audio M6, Hifiman HE-400S, and (very briefly) Phillips Fidelio X2.



I have used the UiiSii CM5(L) with the following sources:

Xiaomi Redmi Note 4 Global > UiiSii CM5

Xiaomi Redmi Note 4 Global > Hidizs AP60II > UiiSii CM5

Windows 10 PC > JDS Labs The Element > UiiSii CM5

I have tested these headphones with Spotify Premium high-quality streaming and local FLAC.



The UiiSii CM5(L) comes in a squat rectangular semi-glossy box with a clear plastic front which showcases the IEM faceplates. The CM5 comes with a large rigid zippered carry case with UiiSii branding and five sets of silicone eartips of varying sizes. The case has a small elastic band on the axis it opens on for stowing the zipper when the case is closed, which is a nice touch and shows careful design and attention to detail on the part of the manufacturer.



Build quality of the IEMs is reasonable for the price ($12). The IEMs are wholly plastic with a hard crescent moon shaped faceplate with scalloping from tip to tip, and a dull, softer plastic with a rubbery texture on the ear-facing side. The hard plastic shell has a shiny luster and a fine grain pattern in the color. I don’t like the shape of the hard faceplate aesthetically. The nozzles are covered by fine metal mesh. The black rubbery cable is thin but sturdy. I prefer cables without memory wire, but the plastic tubing around the earhook section is one of the least irritating implementations I have used. I have not had any issues with cable microphonics. The cable has a small multi-function button on the right side above the Y-split above neck level. With my Android phone, the pause (1 press) and fast-forward (2 presses) functions work as advertised, but the rewind (3 presses) function skips 2 tracks forward instead.



I was unable to test the microphone or the call quality of the IEMs, as when I tried to make phone calls while the IEMs were connected to my Android phone, the IEMs produced a loud high-pitched tone until the call disconnected. I have not tested the IEMs with Apple products to try and reproduce this issue. The CM5 is advertised as having Android compatibility, so this is disappointing.



Despite the weird shape of the hard faceplate, the CM5 is very comfortable for long periods of wear thanks to the ergonomics of the rubbery undersides. UiiSii claims on the packaging that the CM5 shape has been designed for comfort based on extensive testing. However, the fit of the CM5 is shallow, especially with the included silicone tips. Isolation is poor with the stock tips. I highly recommend using third party foam or triple-flange silicone tips with these IEMs to improve both isolation and sound quality.


The sound signature of the CM5 is highly tip-dependent. With the included silicone tips, the sound signature is fairly neutral. However, when properly sealed using third party tips the CM5 have a warm V-shaped sound signature. I found the best seal with the triple flange eartips from the Mee Audio Pinnacle P1 and the foam tips from the Yersen FEN-2000. With the triple flanges bass is thick but not muddy, and sub bass extension is the best of any budget IEM I have used. Bass articulation is fast thanks to the graphene driver. Mids are slightly recessed. Treble is smooth but not incredibly detailed. Mids are slightly recessed. Soundstage is large and instrument separation is good. Resolution is far above average at this price point. With the foam tips from the Yersen FEN-2000 mid-bass is less pronounced and there is more treble sparkle.


My measurements were conducted with a Dayton iMM-6 microphone using a vinyl tubing coupler and a calibrated USB sound interface. The measurements are presented with 1/24th smoothing and without compensation. Measurements above 10k are not reliable.


UiiSii CM5 vs Mixcder X5
CM5 vs X5.jpg
The CM5 have very similar bass regions. CM5 has a more lifted upper midrange than the X5. Female vocals have slightly more presence on CM5. X5 is more sibilant but less detailed. Separation is better on CM5. Soundstage is bigger on CM5. Overall resolution is slightly better on CM5. CM5 is easier to drive. CM5 is more balanced and natural sounding overall.

UiiSii CM5 vs Yersen FEN-2000
CM5 vs FEN-2000.jpg
CM5 has less mid-bass. Midrange is less recessed on the CM5. CM5 seems clearer overall and makes the bass on the FEN-2000 seem bloated. FEN-2000 has a more detailed lower treble and is airier. FEN-2000 soundstage is larger. Imaging is better on CM5. Treble dynamics are better on FEN-2000. FEN-2000 has much better isolation. CM5 is more comfortable.



At an impedance of 32 ohms and a sensitivity of 104db, the CM5 can be driven from a smartphone but may benefit from additional headroom.



The UiiSii CM5 is patently inoffensive and shockingly competent. It does everything well and nothing badly. At $12 it is a superb place to start one’s hi-fi journey, and is worth picking up even if you already own more expensive IEMs.