The sound is surprisingly open, almost as open as if you were listening to Grados. The problem with regular shaped earbuds don’t exist with this neckband, as you don’t have to shove the earbuds deep into your ears to get a good hold. Once placed on your ears, you can move it around a little to get the ideal position. The position of the earbuds will change the tonal balance a little, mostly the balance between treble and bass, so you can sort of tune the bass amount to fit your liking. I find that I personally like to have the fit a little loose, as it gives me the ideal bass/treble ratio for my music. And although the tiny drivers probably can’t make any bass-shattering bass, I do find it to have a good amount of punch to make most music lively and engaging. You can also add the supplied foam to the earbuds for a fuller bodied sound, although I like the treble better without the foams.
According to Headroom, the PMX680 is the best-built and best-sounding neckband headphones they’ve heard. And while I’m not going to go very deep to evaluate the the sound quality of the PMX680, I’m gonna say that the sound signature is incredibly easy to like and a fun all around headphone. Plenty of bass body and punch yet not bassy, engaging mids, good treble sparkle. To be honest, on most of the situations that I’ll be wearing the PMX680, I probably won’t be fully critical of the sound quality. And as it is, the PMX680 has a fairly fun and all rounder sound with just enough bass, mid, and treble quantity, and I really won’t fret over the other technicalities. While the soundstage performance falls really far behind my JH16Pro, the design of the earbuds make it far more open sounding than any of the IEMs I’ve heard, including the Pro. It’s quite a fun sound, and if you are not the type to worry over the technicalities, I think you’ll find the PMX680 to be a fun headphone.
I also had the chance to try out the OMX680, which is the ear-clips version, and the MX680, the earbuds+fins version. I really can’t get a good fit with the OMX680 clip on, perhaps due to ear shape factor. The MX680, on the other hand, has fins that work amazingly well to keep the earbuds placed firmly on the ear while you’re on the treadmill. There is also a CX680 model, which is an in-ear model with fins, although I didn’t get to try that one out. All these Sennheiser-Adidas sports series also come with microphone options on the “i” models. My personal favorite, however, is the PMX680 as I find the neckband design to be very practical in a day to day use.
I’ve been using the PMX680 more than the ultra-portables (even my long time favorite V-Jays) for almost every day now. The PMX680 is slightly inferior when compared to the sound quality of the ultra portables, but it’s the open design that gives a very open sound, and the convenience of the neckband design that keeps me coming back to the PMX680.