Koss KDE 250

Brief Review, Koss Wierdphones

This is a review of the Koss KDE 250, a rather different earphone that has been produced by Koss for about a decade. They are no longer listed on the current Koss website, but it is not clear that they are discontinued. I have no connection with Koss, nor with Massdrop, other than as a member. I bought these on a whim when Massdrop announced them, because of the great $59 price, and the fact that they incorporate a different design than other earphones. I was curious. (Now where is that man in the yellow hat?)

From the Internet Archive’s September 9th 2011 capture of www.koss.com, KDE 250 Specifications.

Koss developed the KDE/250 with a pair of dynamic transducers that mount at a perpendicular angle. The larger 20mm transducer is low frequency dominant and ported while the 13mm transducer focuses on mid and upper frequencies in a side firing angle. This combination of transducers allows greater efficiency and accuracy across the entire musical spectrum to levels that exceed audibility.

Each KDE/250 features a matching set of customized ear clips. These three clips can be adjusted for height with a special knurled knob on the element case assembly. Rotating the knurled knob dials in comfort for a perfect fit. Koss also developed a unique hinge mechanism to accommodate the intrinsic shape of the ear’s tragus. This hinge plate allows the listener to modify the attack angle of the transducer as it enters the ear canal improving comfort, isolation and enhancing transparency. The KDE/250 allows listeners to enjoy a custom fit while experiencing the full scale of the musical sound stage.
KDE250 SRP: $249.99
Frequency Response 40-20,000 Hz
Impedance 16 ohms
Sensitivity 95 dB SPL
Distortion <0.7%
Cord Straight, Dual Entry, 4ft

Initial impression and unboxing

The box is, well a box. Let’s take a look inside.
Everthing is nice and tidy here. That pleather case is about an inch and a quarter deep, and has a place to insert each unit for carrying and to wrap your wire so it doesn’t tangle. It’s too big to put in your pocket unless it’s a coat pocket or you are a nerd. No nerds here, right?
At last! A picture of the goods. The small round thing with the holes is the part that fits in your ear (see below). And the bigger black area has the woofer. In this shot, I have not yet started to adjust them. The metal hooks are threaded. These are the medium size. The knurled knob moves them up and down by their threads. The metal hooks are able to rotate, and there is an additional articulation visible where the hook holders attach to the drivers. This additional articulation is sort of rubbery, has a screw which can adjust it’s flexibility, and moves perhaps 25 degrees.

The first thing you notice about these is that they are an unusual design. In some ways, that can be a warning. If it were a GOOD design, wouldn’t more headphones use it? Koss seems to be prone to coming out with unusal designs, and these sort of amp up lessons learned with their various clip, porta-pro and stereophone designs. They are two separate unconnected units. This means that they won’t clamp your head in any way, and due to their size and weight, might come out or come loose.

The instructions tell you that you should take your time to make sure they fit right. Over the first week or so, I made a number of adjustments, and I will say that having patience and learning how they should feel helps them enormously. These come with 3 different length bars that when set properly help grip the headphones to the ear and rest against your head. I find the long ones work well for my ears, but maybe youngsters or people with less “Bernie Sanders” ears might use the medium ones, and if you are a pixie or have a shrunken head, the small might work for you.

There are two drivers, one of them, when properly inserted rests in your ear and fires forward. I’m not sure what the other driver does, as it is at a 90 degree angle to the one in your ears. Perhaps it provides nearfield. Once the headphones are set properly in your ear, a knurled tube allows you to adjust the height of the clip bar. It should be adjusted so that it can rest against your head putting enough pressure on the top of your ear to make the drivers fit firmly. It’s sort of a caliper, and while it sounds rather mad, when you get it right, it’s quite comfortable, and while I wouldn’t wear it while riding the zipper, it should be reasonably secure for ordinary activity.
The Zipper - Not recommended for use with the Koss KDE 250 Stereophones.

The sound of the headphones can be profoundly affected by how you have adjusted them physically. Because they are not inserted into the ear canal, nor do the seal and cut outside noise, having them improperly positioned will reduce bass. These are not bass-light phones.

I found that once you have found the proper adjustment, they can easily be inserted and removed by guiding the metal hook just above the ear and sort of twisting them on. Not that much harder than wearing glasses.

The actual sound is rather surprising. Unlike IEMs, I do not find them to be at all tiring, even if listening for an extended period, or with unassisted iPhone quality on Apple Music. Yet they have surprisingly nice sound, some actual bass, and very good soundstage. I do think that they suffer from a slight peak in the treble, probably about 2000 hz. However they are very clean and free from echo, so those who find fault with an echos in phones won’t find them here.

The build quality is very good, although the cables are perhaps a bit fragile looking. The Massdrop price on the headphones is much lower than list ($249) and they generally have the feeling of a product in the middle price ranges

2 When given the opportunity to use ROONs Parametric EQ with the KOSS KDE 250s, this shows the setting I preferred for critical listening.


Internet Radio – Radio Paradise

Spent about 3 hours solid listening to Radio Paradise on the FLAC setting. It’s not critical listening, but it’s good listening. This session included a few breaks and some fiddling around getting the KDEs adjusted. Each time I got closer to a good adjustment, there was not only more comfort and a less loose fit in the ear, but an improvement in sound. If there is one major fault with the KDE, it’s that you need to tolerate the fiddly period. Yes, you will be rewarded, but is it enough? While bass is the obvious change, dialing in the proper fit and direction of the front-firing drivers will also smooth the treble and improve soundstage. I did not use EQ listening to RP, and did not feel that it was needed.

Some Jazz and Classical

Two Worlds, Lee Ritenour and Dave Grusin, streamed on TIDAL 44.1k 16 bit FLAC. I’ve had this album on CD for years, but often listened to it on a high bit-rate MP3. 30 seconds in, I deleted the MP3, and downloaded Tidal’s FLAC.

BWV 1065- Concerto for 4 harpsichords, strings and continuo in A minor.

Surprisingly well balanced. Can hear the movement of the piano pedal mechanism clearly, especially at the start of the piece. This piece features a string bass doing a continuo, and it plays with authority. After my third or fourth go-though of this piece, I realized that I was not suffering ear fatigue as I frequently do with IEMs. Its true that I was using some of Roon’s EQ, adding +3db to the deep bass and dropping 2.5 db at 2200hz.

When the second piece came on, (Villalobos) Bachianas Brasileiras No.5, Renee Fleming’s Aria did sound just a trifle hot, but it was very clean and clear.

More telling for me was the third track, by Torroba. (Sonatina in A Major) I know this piece because its one my Mother played frequently, in a classical guitar arrangement. I believe it was something she did for a recital for her teachers at the Kansas City Conservatory. The guitar was spot on, but there was still a bit of spike in that upper treble. The resolution seems very upper mid-fi, not something I expected from this style of earphone. Despite the hot treble, finger sounds on the classical guitar strings were a bit muted, compared with what I expect live. Of course, that can also be very musician-dependent.

I’ll leave this album – which is good for evaluation – with a popular selection The Water is Wide/Shenandoah, familiar to most. I tweaked the EQ down to -4 db at 2400hz, and the sound improved. My general feeling is that I should not really have to play with EQ, but I know that’s a very arguable position. Renee Fleming’s rendition of this song will give you goosebumps, and the chamber orchestra takes me back to some of the Hallmark Great Performances straightforward arrangements I used to hear when TV tried to have some classy content.

Pop and Reggae

It’s not a secret that I’m a fan of The Easy Star All Stars, who do Reggae tribute albums, so I thought I’d do a bit of comparison. Listening through ROON, lossless quality, using the iFi xDSD with no bass or crossfeed enhancement, Michael Jackson’s Thriller 25 Super Deluxe Edition. The title track, THRILLER, is handled authoritatively at a low volume and no EQ. Turning the volume to a mid level, and you can’t believe that these headphones are a bizarre design and aren’t even sealed. The electronic bass is very clean. Drums are crisp. Add still more volume, and the percussion really comes into its own. Beat It is quite revealing, with Jackson’s voice well recorded at his best. There is a bit of bloom in the mid-bass, but it may be this recording and Jackson’s choice of electronica. I don’t hear the problem on Billie Jean. Brushes on cymbal are very good. Drums sound much less electronic. The occasional bass drum is well resolved. I can’t help just listening to peak Jackson genius here – all the care he devotes to production is gloriously evident on Billie Jean. Strings sound like strings, you can hear fingers on guitar strings, this is as good as it got for MJ.

So now we turn to the 2012 tribute, The Easy Star All Star’s “Thrillah”. General info: this is the same quality and audio chain. This is fun. The creaking of the door is even more overdone. There evil in the dark is voodoo-zombiefied. Now what’s startling about this track is that there is equally good production, but the instrument choice is even more revealing of the content. The KDEs are very happy with the triangle -like sounds. I suspect they may be electronic, but the sure sound like real percussion. There are more voices in this version, and they all are very clear and natural sounding. Of course bass sounds like the solid reggae bass you expect. Snare and cymbals don’t jump out at you, but are expertly blended in. While the spirit voices are creepy, I can’t help the feeling that you could save you skin by sharing a blunt with the zombies.

Beat It has some VERY deep bass. The limitation of the KDE is shown. You can hear the bass, but you can’t feel it. Aw heck, this is a $59 on sale stereophone, not HiFiman HD-560 and certainly not speakers. Cranking the volume lets you hear more bass, but at the expense of the treble being a bit shrill.

Billie Jean – what can you say? The MJ version is masterful, and the Easy Star All Star version is merely good. The vocal is excellent, and the strength of the material shows through. The slow, lazy, reggae rhythm works for the vocal, but all the rest of this song is musically thinner. If you didn’t know how MJ did it, this would be very good. The KDEs, and probably any headphone would tell you this is best left for some late-night dance, when the alcohol and smoke and sex have numbed critical sense.



Cracking write up. I enjoyed it greatly. As I’ve said before I like your writing style. They certainly are a very strange design. Especially with the metal around ear arms, for want of a better description. I would have thought that they’d be immensely uncomfortable, but it would seem not. They seem to have sold well over the years.


Thank you. Once you get them dialed in, they are not at all uncomfortable. Better than an IEM for me. Are they worth $250? maybe not, $59 heck yes!



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There is something vaguely disturbing about that ear. Perhaps the lack of hair extensions. Photoshop anyone?


Haha nice one. :grin:.

Grrreat review pennstac! I was about to hit the purchase button on massdrop but didn’t find any worthy review and that beat curiosity… yours is incredible! :+1:


Thank you. I got mine because of the good price and curiosity. Disclaimer: I did not actually TRY to wear the KDE’s while on the Zipper.

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Back live at Massdrop:


I’m liking these more and more when I happen to use them. They don’t have the isolation of an IEM, they are more comfortable, and they don’t have cavern echo or “help, I’m wearing seashells on my ears” sound of closed backs. Yet they still are pretty quiet for others in the room.

Yesterday, I tried them using the Schiit Loki, and was able to run them quietly with a loudness type contour, and louder with a slight reduction in treble. I was impressed at the sound compared to cheap IEMs.


Great Review! Very helpful (even before considering the classical guitar references where much of my listening is classical guitar).