Spec
Driver: 9mm Dynamic
Impedance: 12 Ω
Sensitivity: 97dB±2 dB / mW @ 1kHz
Frequency Response: 15Hz~22kHz
Plug: Gold-plated L-shaped mini plug
Weight: 8g
Cable: 1.2m
Packaging, Accessories and Build Quality
PL21 comes in a similar style packaging as PL50, differentiating both from the older generation of SoundMAGIC's IEM. If anything, they do look more upscale than their price tags suggested. Inside, there are four pair of silicone single flange eartips (S, M, L, XL) and three pair of foam tips (S, M, L), warranty card, shirt clip, soft pouch and a pair of ear hook.
Build quality wise, PL21 is almost on par with PL50: the Y-splitter design is identical, but PL50 does have a slightly thicker cable and a similar but stronger mini plug. PL21's earpieces are similar to PL20, but smaller, prettier and have a slight angled nozzle.
Microphonics is about average on PL21, but the inclusion of shirt clip, ear hook and the angled nozzle make it easier to wear it over-the-ear which should ground any microphonics problem. Isolation is a tiny bit below average on the stock eartips, but better on the foam tips. I end up using Sony Hybrid clone (sourced from eBay) which gives a slightly better seal and isolation compared to the stock eartips. Overall, PL21 has one of the best build quality on all the $20-ish IEM I have seen.
Sound Quality
As usual, a minimum of 50 hours burn-in was carried out before the audition. As mentioned above, I used the Sony Hybrid clone eartips for the review. Though they are clone, the sonic signature is actually almost identical, which tend to absorb a tiny bit on the top end while gives a more solid bass, turning the sound slightly warmer and smoother. For PL21, it doesn't sound slightly less airy than the stock tips, but the gain on a more solid mid and bass performance due to a better seal is still an overall improvement IMO.
The overall sound signature is warm to slight dark, musical, smooth, and has a small emphasis on the mid. Bass extends very deep, does rumbling sub-bass better than any IEM of its class while retaining very good control. Quantitatively not a bass monster but it does show a good bass impact and body. Mid is full, a little forward and vocal is sweet, no sibilance to speak of. Treble has a decent extension but lacks sparkle to show fine detail. Soundstage is about average.
Conclusion
Well priced, well built, and a good sound - PL21 is one very solid IEM in the $20 range. As an overall package, perhaps it even rivals most of the sub-$40 options out there as one of the best all-arounder.
A quick sum up can be found here.