Koss TWS250i

True Wireless in-ears with neutral sound

In a nutshell

I summed up the TWS150i thus: “Good battery life, elegant design, neutral sound, great range, reasonable price – what else can one say, except to congratulate Koss that they have succeeded with the TWS150i, solid in-ears that make no mistakes sonically.” And I’d say exactly the same about the TWS250i. However, with two additions, because on the one hand I would like to praise the significantly better precision of the touch controls, and on the other hand, the extremely high wearing comfort, because the TWS250i are really almost imperceptible when in the ear. I would say that the rather discreet bass performance is a matter of taste because the lower frequency range is undoubtedly there and is reproduced precisely – just without that extra half decibel boost that makes up the fun factor. Fans of objective sound will appreciate this very much. Lovers of “sub-in-the-head” experiences, on the other hand, might find it too small (without equaliser intervention). I also sorely missed the option to use multi-pairing, because in modern life it’s pretty common to change players (mobile phone, tablet, laptop, etc.). Even if they don’t do everything right: All in all, these comfy and good-sounding in-ears from Koss score very highly on points, even when considering the recommended retail price of 89 euros.


In April of this year, Koss already earned an editorial recommendation for the smallest model in their Bluetooth in-ear series. Back then, it was the TWS150i that earned our recommendation thanks to their decent price-performance ratio. Now the next model up in the series reports to the command centre for testing, and naturally, and they want to leave at least as good an impression as their predecessor – if not a better one. And of course, we were happy to give these little earbuds the chance to take the stage (or the ears, as the case may be) to try to impress us.

The Koss TWS250i are True Wireless in-ears that connect to the playback medium via Bluetooth 5.0 (backwards compatible). The integrated rechargeable batteries provide up to six hours of listening or talking time, as the TWS250i also act as a headset when making phone calls. The charging process takes place in the supplied charging case; the integrated rechargeable battery has an additional charging capacity for around three charging cycles (approx. 20 hours). These in-ears are certified according to IPX5 and thus, according to the definition, resist “water jets (nozzle) from any angle” and “dust in harmful quantities”. So if you are listening to the TWS250i and get caught in a sandstorm combined with a downpour – which, in these climate change stricken times, is all not that unlikely – you can keep them in your ears without losing your warranty.


Although the TWS250i differs from the smaller model only by a single digit in its name, there are almost no visual similarities. While the TWS150i leans more towards Apple’s AirPods design with the antenna stem out at the bottom, the TWS250i’s housing looks more like a small fat bean. With a length of just 2.3 centimetres (height approx. 1.5 centimetres), these in-ears find enough space between the tragus (the fold in front of the ear canal) and the scapha (the back fold of the ear lobe) so that they do not protrude at any point. The charging case is correspondingly small. Its design reflects the oval look of the in-ears and is powered via a USB-C socket. The design of these earphones with their matt black surface is simple and unspectacular. An oval, slightly metallic shimmering ring around the back, emblazoned with discreet Koss lettering is the only decorative element.


The fact that the lid and base sit absolutely flush on top of each other proves to be a minor niggle when using the charging case. This looks nice, but if your fingers are just a little bit wet or greasy, it sometimes takes several attempts to open the lid successfully.


The backs of both of the in-ears act as conductive contact surfaces to trigger a whole range of functions. In various combinations of single and multiple taps and presses, the following can be triggered: on/off, volume +/-, play/pause, track forward/back, call answer/hang up and summoning voice control (depending on the device in use). I particularly liked the logical division: most commands can be triggered equally from both sides. Only the volume control is distributed between the left and right earpiece (press left = turn down, right = turn up), so that operation is very easy even when you’ve only been using them for a short time. In addition, the touch recognition responds very reliably.

Another big plus is the wearing comfort of the TWS250i. Once they have been placed in the ear with the right fitting (S, M, L), they literally disappear from your consciousness. They nestle so lightly and imperceptibly in the ear canal and against the outer ear that I went out a few times during the test and only noticed that I was still wearing them when the Bluetooth connection was broken in the hallway. In fact, you have to go through at least two walls and several metres away from the playback medium before the connection finally breaks down. In an open field, the signal range is up to ten metres, and I was able to confirm this in our test.


The speech intelligibility, on the other hand, was not as convincing when using the in-ears as a hands-free set. It is and remains a mystery to me why the manufacturers (in this case Samsung and Android/Google) do not manage to bring the excellent quality of audio reproduction that is possible with these (and other) in-ears to bear in phone mode. As before, Android seems to automatically reduce the data rate and frequency response here. Indeed, a comparison with a simple voice recording from an audio recorder shows that the sound quality delivered by the TWS250i is quite good.

Another, somewhat smaller minus point: Unfortunately, the TWS250i do not support multipoint, so that only one feed can be set up at a time. This is particularly inconvenient because resetting and reconnecting the Koss earpieces proves to be quite tricky and not always successful (put the earpieces in the case, press both earpieces for five seconds to switch off, then eight seconds to restart).


I begin my listening test with “Last Night the Moon Came Down” from the album of the same name by the recently deceased, visionary musical frontiersman Jon Hassell. A piece in which he spreads out a dense web of polyphonically harmonised trumpets and strings over percussion hidden deep in the dark reverberation space, from which sporadic solo interludes on violin and trumpet stand out. The TWS250i did a particularly good job of presenting the wind sounds and making the individual instruments audible. There is air in the highs and the necessary accuracy in the sound.

To assess the bass performance, I switched to an original production: the stoically marching, extremely delimited sub-bass on “Babe – Tape Redub” by “Sonimun” on the Telrae sampler “Slapback 1” is the integral factor that holds the whole number together. Here, too, the TWS250i did a good job, but in a direct comparison, they lagged behind my Bose Quiet Comfort, which delivered a good deal more thrust. Since I’d already noticed the rather discreet bass performance of the TWS150i, I assumed that this was a weighting intended by the manufacturer – which is completely legitimate. As a buyer, you’ll know in advance that the TWS series has a somewhat more discreet bass. Even though there are countless fans of a strong bass performance, there are still quite a few music lovers who feel disturbed by an especially pronounced bass range.

For an assessment of the transient representation and the stereo stage, I turn to Siriusmo’s grandiose 2017 album “Comic”. “Double Click” – a collaboration with “Mr. Oizo” – is one big fricassee of small percussion snippets with sharp transients, plus in the B part of the melody synth sequence, the reverb space changes dramatically from an intimate reverb to a big hall. The TWS250i reproduces this neatly as well as precisely so that the depth gradation and logical structure of the track are wonderfully spread out.

3 years ago by Numinos
  • Rating: 4.75
  • Sound
  • Handling
  • Price/Quality
  • Function

Technical specifications

  • Ear couplingIn-ear
  • Typeclosed
  • Transducer principledynamic
  • Frequency response (headphones)20 - 20.000 Hz
  • Sound pressure level (SPL)101 dB
  • Weight without cable10 g each, Case 44 g

What's in the box

  • 3 pairs of ear tips (S, M, L)
  • USB-C charging cable
  • Charging case

Special features

  • BT codecs: AAC, SBC
  • BT version: 5.0

2 Antworten auf “Koss TWS250i”

  1. Ward Oldham says:

    I find the review of the Koss TWS250i weird in one respect: You can’t find these anywhere to purchase, not even on the Koss web site. Could you offer a clue please?

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