Review: Sennheiser Adidas CX 680i Sports Headphones

I’m a runner, and after destroying 4 pairs of Apple’s headphones over the last few years by sweating too much on them, I decided it was time to pony up for a pair of sports headphones that are sweat (and water) proof. While in the Apple Store, I came across a new line of sports headphones by Sennheiser co-branded by Adidas. The line offered 3 different “i” models (i for compatibility with Apple products): the headphones I’m reviewing here: the Sennheiser Adidas CX 680i ($99), the PMX 680i, which wrap around your neck, and OMX 680i, which use earloops.

It should be noted that, even though we tested the CX 680i’s outdoors, noise-isolation headphones are generally not recommended for outdoor use due to safety concerns. If a car is coming at you, you’ll want to hear it. I personally run with only one earbud in my ear—the other tucked into my shirt—so I felt comfortable testing these in an outdoor setting.

There are three features of the CX 680i that make them “sports” headphones. First, they are waterproof. Second, the cord is reinforced with a durable material called Kevlar. Third, they have a feature called EarFins that help the earbuds stay stable in your ears while exercising.

The EarFins are, just as the name implies, shark fin–shaped, bendable pieces of rubber attached to the earbuds. To place the earphones and EarFins in your ear, you must first must press down on the EarFins, insert the earbuds, then let go of the fins, which expand and press up and under your earlobes. The EarFins do a great job of keeping the headphones stable during exercise. But I quickly discovered it was crucial to put them in your ears correctly at the right angle (for me, the cord had to be at a 4-5 o’clock angle), else the EarFins tend to slip out. The headphones were comfortable to wear, I generally did not notice them during exercise, even after a two-hour half marathon run.

For a pair of sports headphones, the CX 680i’s delivered excellent sound quality, even besting Apple’s default headphones (which we find to be good but not great). The 680i’s deliver an impressive amount of bass and also decent mid and highs, but they’re no match for “premium” headphones. We tested the 680i’s head-to-head with the similarly priced Klipsch S4i in-ears ($99, review), and found the CX 680i’s lacked the sonic clarity of the S4i’s. When listening to Big Boi’s “Hustle Blood,” the hip-hop bass dominated the mix with the CX 680i’s, where on the Klipsch S4i’s, the various other musical elements could be distinguished in the mix and sounded generally better equalized. With Bob Dylan’s classic “Like a Rolling Stone,” the background organ could be heard individually on the Klipsch S4i’s, but became lost in the mix with the CX 680i’s. Despite its flaws, we feel the CX 680i’s are above-average and could easily double as every-day earphones. And the fact that they are in-ear, noise-isolation headphones is always a big advantage, as in-ears generally outperform non-in-ear counterparts simply by delivering direct, focused sound.

The CX 680i’s are iPhone-compatible in that they come with a built-in remote dongle with microphone. The dongle gives you the ability to take and end phone calls and control your music—in short, it can do everything the default iPhone headphones can do. The dongle itself is a little bigger than we’d like, as we found that it flopped around a little too much until we either reeled in extra cord length or used the included shirt clip.

The microphone of the 680i’s performed well but not quite as good as the default iPhone headphone’s, as callers said they heard a bit more tin-can effect with the 680i’s. But overall, performance was good enough that callers could barely discern a difference.

The headphones have a long cord, almost 4-feet long, which is about a half foot longer than the default Apple headphones. Taller runners like me will appreciate the extra cordage, and if it’s too long, you can always reel in the extra.

In terms of durability, the CX 680i’s have a few impressive characteristics. First off, the waterproofing works, as we subjected it to several long sweat-drenching runs without any detrimental effects. Second, the headphones come with a two-year warranty, which is impressive for headphones and should remove any worry of being out $99 too soon from regular wear-and-tear. Third, the headphone cords are made out of Kevlar, the same stuff they make body armor out of. We will mention that headphones tend to have weak points, usually around the audio jack and where the cord meets the earbuds, and only time will tell how the CX 680i’s will ultimately hold up (we’ve been fooled before). But we’ve had no problems after a month of rough usage and several long runs, and as mentioned, there is that sweet two-year warranty.

In terms of looks, the headphones are dominated by the neon sport yellow of the cord, which helps increase your outdoor visibility. As a road runner myself, I appreciate all the visibility I can get. The rest of the headphones is a matte black color. Overall, the headphones have a modern sporty look. We’re not sure you’d want to make a fashion statement with them, but we found them attractive in a sport enviroment.

Included in the packaging are a nice collection of extras. There are 3 different sized sets of earbuds (S,M,L), 3 different sized sets of EarFins (S,M,L), 1 housing cover if you don’t want to use the EarFins (good for non-exercise use), 1 spare pair of diaphragm guards, 1 earwax cleaning tool, and an attractive nylon carrying pouch emblazoned with the Adidas logo.


The Sennheiser Adidas CX 680i sports in-ear headphones ($99) are sweatproof, durable, and stable in the ear during exercise. And they deliver above-average, bass-heavy sound that bests the default Apple headphones, but could not deliver the sonic clarity of premium headphones. The fact that they are in-ear, noise-isolation headphones makes them a safety hazard for the outdoor athlete unless you exercise in a controlled environment. Overall, we found the CX 680i’s to be well-designed and good performers in our real-word testing. We highly recommend them for athletes, assigning a rating of 9.1 out of 10.

Helpful links:

Official website for the Sennheiser Adidas CX 680i Sennheiser Adidas CX 680i $99


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2 Responses

  1. Bradford says:


    First off, great review. I love the details and detailed pictures. Secondly, thanks for touching base on all the key factors for these ear buds.

    I have been trying to find the best pair of running ear buds while not breaking the bank. My main issue is that I saw on the Apple site that a lot of people were saying the dongle will break or stops working after a while. Is this true? Have you had any issues with it since you bought them? Also, when was this review done?

    I do have to attest that the Sennheiser line of active headphones (in ear and band around the head) are SUPERB. My in ear buds finally broke after extensive use from running, work, and biking after about a year and half. I used them for gaming as well because they gave just enough bass and mids that I liked. The band around the head ones I am still rocking although the rubber grommet broke and peeled off while running one time, but they still are somewhat comfortable and still put out decent sound. They are on their last legs though after 2 years of use. Anyway, not to sound gimmicky or anything, but I’m hoping to get these headphones to replace my others. Let me know about the dongle as well, cause that seems to be an issue and I would hate to buy a product that will crap out on me in a few months. But I guess that’s what the 2yr warranty is for…


  2. Alan says:

    Hi Bradford, I did not have any issues with the dongle. These headphones lasted until Aug 2011 (the review was published in Sept, 2010) when I put them through the wash/dryer for the second time. They are water resistant but not waterproof. I ran probably 100-125 times with these headphones and they continued to work, but they weren’t indestructible—going through the rinse cycle twice over will destroy most electrical equipment.

    After using these headphones for two running seasons in Chicago, my only complaint really was the fit in the ear. Sometimes it was perfect, sometimes it was loose. Most of the time the stability fin kept it in my ear, but there was still a loose feeling to the earphone. I’ve had this problem with just about every in-ear headphone I’ve run with, and my theory is that my ear cavity can change shape/size depending on weather or something, making earbuds tight/loose depending on circumstances. I recommend going with the version of these headphones that come with an earloop, the OMX 680i, although note that earloops won’t keep the earbuds properly nestled into your ear while your run, just from falling off your ear entirely.

    Would I still recommend the Sennheiser line of earphones to runners? Yes. They will survive your sweat, just don’t think they are indestructible.

    By the way, what am I using now? I’m trying out wireless bluetooth “water-resistant” headphones. See my review of the Motorola SD-10’s, which were disappointing, and soon I’ll have a review up for the Jaybird Freedom 3s that, so far, I love.

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