MEElectronics' new SP51 headphones are a novel thing. At first glance, they're rather inconspicuous, with their flat, one-piece housings and conventional dynamic drivers. But this set of in-ear headphones has a party piece that I haven't come across anywhere else: it has adjustable resonance chambers. These serve to tune the headphones' bass level. Because of this, the SP51s can serve triple duty, delivering great sound that's adjustable for all genres.
The SP51s enclosures are smooth, black metal cylinders; they've got a very solid feel and the one-piece construction makes them seem pretty abuse-ready. The cord is virtually identical to that of MEE's slightly-lower-end M21, consisting of a braided cable inside a transparent plastic sheath. Notably, the clip on the SP51 is not removable, which is a bit annoying if—like me—you never use it. All four sets of silicone rubber tips sit comfortably in the ear, although the bi-flanged tips make the headphones cumbersomely long. The SP51s have straight housings rather than the forward-canted ergonomic style I prefer, most likely because of the resonance ports' limitations.
The advertised "bass tuning" is accomplished by three sets of metal "screw-in" endcaps that have differing acoustic properties. It's hard to tell the difference visually because of the size, but a few characteristics are notable: namely, that the "extreme-bass" (black) caps have an unobstructed hole drilled through them, while this hole is baffled in the "balanced bass" (silver) and "enhanced bass" (gunmetal) caps. I'm assuming, therefore, that the tuning ports operate in a similar fashion to loudspeakers' reflex ports, allowing for increased efficiency and minimizing distortion in the 10mm dynamic drivers' lowest frequencies. At the same time, this method of bass enhancement—acoustic adjustment, rather than pumping the signal through an equalizer—promises a clearer, more lifelike sound. So, in theory, these three stages should offer peak performance in a multitude of genres, accurately reproducing everything from country (silver) to dubstep (black).
I'm happy to say that the SP51s do exactly that. Initially, I was afraid that the silver caps might sound throttled or restricted and that the black ones would ring uncontrollably, but MEElectronics' crack team of engineers has ensured that the caps don't change the color or character of the sound, just the balance. The "balanced bass" setting offers a clear, very neutral sound. The middle-of-the-road "enhanced bass" caps offer some increased volume at the low end, but by my testing the range isn't extended below the silver caps' 80Hz lower limit. The black "extreme bass" ports, however, do extend the usable range—the volume drop-off now occurs at 50Hz—and they bump up the response even more. It's not quite as punchy or hard as the name implies, however; the SP51s' bass is warm, round, and rumbly. I found it soothing. When compared to the same level of bass-volume increase through equalizer adjustment, there is much more resonance and much less high-volume, low-frequency distortion. In all three cases, treble is largely unchanged in terms of volume, although you do sacrifice the slightest bit of clarity in with the black caps in. But if you're using those, you're probably not too worried about the treble anyway.
So it's all great so far. But before you rush off and order a pair for yourself, your significant other, your parents, or your cat, note that there are a few limitations to this novel sound-changing system.
First of all, if you listen to many different types of music in rapid succession, it's not feasible to change the end caps every time your playlist jumps from Tupac to Tchaikovksy. The things are just too small and slippery—you will drop them (I have, many times) and lose them (I nearly have). That could mean listening to the Les Miserables soundtrack with heavy, booming bass, for example. You'll end up stressing over which caps to install before you leave the house each day.
Secondly, the bass ports in the black caps are open. The hole is small enough that you generally shouldn't have to worry about dirt finding its way in and clogging it, but I came home one particularly rainy night to find that water had actually gotten inside.
These minor issues aside, however, the SP51s are great for day-to-day use. They can be adjusted to suit your personal needs, and the sound they deliver is very strong. MEE could easily have made the tuning port system a harmless (but ultimately useless) gimmick, but they took the time and effort to ensure that it was implemented properly. Well done.
- Driver: 10.0 mm dynamic drivers
- Housing: Metal housing with swappable rear tuning ports
- Frequency Response: 15Hz – 20KHz
- Sensitivity: 100 dB
- Impedance: 16 ohms
- Maximum Power Input: 40 mW
- Connector: 3 pin stereo 3.5mm gold plated 90° plug
- Cable: Designer black 130 cm cable (51 in) with attached shirt clip
- Accessories: 4 sets of silicone ear tips (small/medium/large; bi-flange), clamshell zipper case