Sennheiser CX 400BT True Wireless review: New premium earbuds sound great but are a bit chunky
The excellent sounding CX 400BT True Wireless earbuds are a more affordable alternative to the Momentum True Wireless II.
Updated Sept. 2, 2020 4:00 a.m. PT
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David CarnoyExecutive Editor / Reviews
Executive Editor David Carnoy has been a leading member of CNET's Reviews team since 2000. He covers the gamut of gadgets and is a notable reviewer of mobile accessories and portable audio products, including headphones and speakers. He's also an e-reader and e-publishing expert as well as the author of the novels Knife Music, The Big Exit and Lucidity. All the titles are available as Kindle, iBooks, Nook e-books and audiobooks.
ExpertiseMobile accessories and portable audio, including headphones, earbuds and speakersCredentials
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Sennheiser has a new pair of premium true wireless earbuds and -- surprisingly -- they're not called Momentums. The CX 400BT is kind of a value play for the company although the earbuds are still fairly pricey at $200 (£170, AU$300). The idea is to sacrifice a bit on the design side but little on the sound side in exchange for a $100 lower list price compared to the Momentum True Wireless II, which earned a CNET Editors' Choice award. While I'm not sure the trade-off is really worth it, the quick skinny on the CX 400BT is that they're excellent sounding but bulbous and arguably not quite as comfortable to wear as the Momentum True Wireless II. They ship in mid-September.
Available in white or black, the earbuds have a clean, elegant design. While they don't look or feel as premium as the Momentum True Wireless II, they clearly rise above the level of a budget model. For instance, the case is pretty basic looking -- it's overall more compact than the Momentum True Wireless II's case -- but the hinge feels solid and the top of the case snaps shut with authority (an integrated magnet secures the lid) in place.
Sennheiser CX 400BT True Wireless features a simple, clean design
The original Momentum True Wireless certainly stuck out from your ears noticeably, and the buds were a bit chunky. Sennheiser didn't reduce the size of the second-generation Momentum True Wireless II by a lot, but it was just enough for the buds to fit more comfortably.
In-ear, the CX 400BTs feel more like the original Momentum True Wireless, and over longer listening sessions I found myself adjusting them to take the pressure off certain parts of my ears. They would seem less than ideal for folks who have smaller ears, but their comfort level will depend on the shape of your ear.
The earbuds come with four different size ear tips. I usually go with a large or XL tip, but with the CX 400BT I got the most comfortable and secure fit (and tightest seal) using medium-size tips. You can do light workouts in these, but unlike the Momentum True Wireless II, they don't offer any water or sweat-resistance rating; I wouldn't trust them to stay in my ears for running. In that sense, they are similar to the Sony WF-1000XM3, which aren't sweat- or water-resistant and aren't intended for sports use (but I have used them for light workouts).
A tight seal is crucial for optimizing sound, and Sennheiser recommends twisting these into your ears with a counterclockwise turn, which I did. And with a tight seal, these sound great, though not quite as great as the Momentum True Wireless II, which feature the same dynamic 7mm drivers but seem to have a little more bass (it could be that the fit had impact but I just thought the Momentum True Wireless II had a tad bigger, richer sound).
The CX 400BT's sound is nicely balanced with a respectably wide soundstage, good detail and punchy, well-defined bass along with natural-sounding mids. They have that refined quality that brings out the nuance in your music, allowing you to hear each instrument separately. I had no problem listening to these for over an hour straight, only pausing, as I said, to make slight adjustments to the fit.
Along with the SBC and AAC audio codecs, the buds also support aptX streaming from devices like Samsung Galaxy phones that support it (some people swear the aptX codec sounds better, but AAC, which iPhones use, is plenty good).
Battery life is rated at 7 hours on a single charge (the case charges via USB-C), with close to two extra charges from the case (total battery life is listed at 20 hours).
These have touch controls, and they're responsive and generally work well. You can adjust the volume by tapping and holding (the left bud is volume down while the right is volume up). A single tap on the right bud gives you access to your voice assistant. You can use Sennheiser's companion Smart Control app for iOS and Android to customize the controls as well as the sound. The app also allows you to update the earbuds' firmware as updates become available.
In my tests on the streets of New York, the wireless connection was pretty much rock solid -- the buds are equipped with Bluetooth 5.1 -- and they did a decent job muffling background noise when I was making calls (these have noise reduction but not active noise canceling like the Momentum True Wireless II). Whenever you speak a little, ambient sound creeps in while you're making calls, according to those I spoke with; these aren't quite on the level of the top earbuds for making calls. Overall they're solid in that department, just not stellar. The Momentum True Wireless II seem a little better for making calls.
In the end, the CX 400BT is a very good set of true wireless earbuds that delivers excellent sound but may just be too big for some people. Other models like the Jabra Elite 75t and Elite 75t Active may not deliver quite as good sound, but they cost a little less and fit better. I do think that in time you'll see the CX 400BT selling for closer to $150, particularly as we see the Momentum True Wireless II discounted to $250 or less.
Like some of Sony's new true wireless earbuds, it appears from the CX 400BT's build quality that Sennheiser may have a little room to play with pricing. We'll see how it plays out this holiday season, but these are definitely worth keeping an eye on if superior sound is what you're after and can't quite afford the Momentum True Wireless II.