Sennheiser CX 400BT – superior earphone sound for the masses

Sennheiser CX 400BT

The Sennheiser CX 400BT in-ear buds focus on sound above all but at an attractive price. That focus is both its strength and weakness.

Sennheiser is 75 years old founded post-WW2 in Germany by Dr.-Ing. Fritz Sennheiser (originally known as Laboratorium Wennebostel (Lab W). Its first products were microphones.

Let me tell you that when I owned an AV/Theatrical staging company in the 80-90s, the sound technicians staff would not use anything but Sennheiser mics. I bought my first pair of Sennheiser cabled ‘cans’ (much to my ex-wife’s disdain of anything that pleased me) at the eye-watering cost of over $700.

And that is the strength and weakness. If you want audiophile quality, Sennheiser is way up there. Its IE 80 S BT earphones are $799 – for buds!

If you want cheap Sennheiser is also way up there (literally). Sorry, the brand is for people that value sound quality.

But times change, and Sennheiser had to introduce a ‘very good’, ‘extremely good’ and ‘off the planet good’ ranges to appeal to the masses.

In the ‘extremely good’ range is its $499.95 Momentum True Wireless 2 buds (review here 4.7/5). For sound, battery, and quality it is a 10/10 but for ANC – well you can get higher levels in other brands.

But that brings me to the question posed by our AV expert Thomas Bartlett to Christian Ern, Portfolio Manager for Consumer Headphones at Sennheiser, Germany.

In essence, Thomas said that while Sennheiser’s ANC (noise cancelling) was good, it was not as good as other brands like Bose. Christian was not exactly apoplectic, but his Germanic response was “Yes, and it ruins sound’.

Christian made several interesting points – not just about the new Sennheiser CX 400BT. (paraphrased)

Sennheiser has one of the oldest sound pedigrees. Its focus is on sound. For example, anyone can make True Wireless earphones or headphones (the term is for the Qualcomm’s True Wireless chip range). They look at the price they must meet, subtract from that the cheapest chip they can get away with, and the rest is for the battery, DSP, speaker, housing and case.

That is why you can get absolute junk under about A$150 and why the Sennheiser CX 400BT is $299.95. We start with the speaker (transducer) – no compromises. We make it, and it is like the original 7mm in the original Momentum. In fact, the whole device is like the Momentum (review here 4.6/5), and we updated the tech. Its how we can produce the CX for almost half the price.

Then we look at how to use BT to connect without altering the sound signature – to be neutral to the sound. That means a lot of work on the digital signal processor and using three codecs – SBC, AAC (Apple) and aptX (Android).

ANC, especially heavy ANC, destroys the sound quality. The stronger ANC, the weaker the sound. That us why Momentum 2 costs so much more and why we try to be light-handed with ANC.

The CX 400BT uses noise isolation via the right size silicone tip into the in-ear canal section. It does not go very far in – it’s all about a good fit.

Finally, we have quite an amazing Sennheiser Smart Control app that has a ‘finger’ drag to make the music you want.

Mini-Review – Sennheiser CX 400BT

  • Website here
  • Price: $299.95 for White or Black
  • Warranty: 2-years International ACL compliant warranty if purchased from an authorised retailer
  • Country of Manufacture: China
  • Sennheiser (Est, 1945) is a German audio company
  • In the box: XS/S/M/L silicone ear adapters, 25cm USB-A to USB-C charge cable, charge case (no charger)
Sennheiser CX 400BT

The buds are held magnetically in the charge case. A LED displays the charge status.

Note that we use FAIL, PASS or EXCEED against the various paradigms suited for this type of device.

Basic stats

  • 7mm transducers capable of an amazing 5Hz to 21kHz and up to 107dB SPL with <.08% THD
  • Dual microphones 100Hz to 10kHz
  • BT 5.1 LE with SBC, AAC and aptX. Pair up to eight devices but only use one at a time. HSP, HFP, AVRCP, A2DP
  • Weight: Buds are 6g each and case is 37g – light
  • Touch controls – split over both buds to lessen confusion
  • Slightly vented to reduce eardrum pressure
  • Voice prompt and voice assistant

Setup – EXCEED

After charging they pair using standard BT on your PC, Mac, iPhone, Android etc. No app or account required for use. Once paired, you can download the Sennheiser Smart Control app for Android or iOS to add EQ and easy connect functionality. These device stores these settings.

Ear fit – PASS

A lot has been written recently about the ‘ins and outs’ of in-ear canal buds. For example, Samsung’s new Jelly Bean shaped buds extol the virtues of not going in the ear canal. These are not ANC and have limited noise isolation. Or put it positively they ‘let the outside in’.

The CX400BT do not sit in as far as some and rely on a decent tip fit for noise isolation. After four hours of use, they are still comfortable.

With the proper fit, there is no reason they should fall out.

PS – you can use the right bud separately.

Volume – EXCEED

There is a little trick here. While your device controls BT volume, these also have, and amp and touch volume controls. Right touch/hold increases volume and left decreases it. They can be quite loud without any hint of distortion (.08% THD).

Voice assistant – PASS

A single right tap can summon Siri, Google or other assistants. I kept getting Bixby – I will work out how to get Google Assistant soon. The dual mics have beamforming and some noise cancellation. They do not feed your voice back through the buds.

 Voice dialling is dependent on having a person’s name in contacts.

Battery Life: PASS+

  • Buds: 50% volume seven hours for 55mAh batteries
  • Charge case: 14 hours (total 20+ hours) for 420mAh batteries
  • Charge time with buds and case from 0%-100%: 1.5 hours. The case can charge independently of buds
  • Quick charge: 15 minutes for one-hour play
  • Charger: Anything from 5V/1A or any USB-C PD

How do the CX 400BT headphones sound? EXCEED

We can only be subjective as we cannot measure frequency response in a bud. All tests are neutral EQ.

  • Sound stage: wider than you head, so you feel stereo separation
  • Bass: Its good and not overbearing
  • Mids: Nice and flat offering clear vocals
  • Treble: There but recessed to avoid harshness
  • Noise isolation: Fine for everyday use and to let just enough surroundings in. If you want ANC, the Momentum 2 is the choice

Overall, its fairly natural and you can get ‘warm and sweet’ – the nirvana for most music – with just a touch from the EQ.

GadgetGuy’s take – Sennheiser CX 400BT – superior earphone sound for the masses

It is a hard choice between the current ‘good’ crop of True Wireless (noise isolation) buds – Google Pixel Buds+, Samsung Galaxy Buds+, Plantronics BackBeat Pro 5100, Jabra Elite 75t, Jaybird Vista, JBL Live 300TWS… (Note we are waiting for Sony’s 2020 range)

I don’t think there is much difference between them all except that I really like the Sennheiser Sound Signature.

Value for money
Ease of Use
Sennheiser's fabulous sound signature is hard to beat
Great battery life
Comfortable fit
Easy to use app that stores settings on the buds
Dont confuse noise isolation with noise cancellation