Koss KDE250 Dual-Element Headphone (Playback 39)

Earphones and in-ear monitors
Koss KDE250
Koss KDE250 Dual-Element Headphone (Playback 39)

When I first saw Koss’ unorthodox-looking KDE250 headphones ($249.99), I was reminded of the punch line to a Saturday Night Live sketch where the actors peered at strange, inscrutable objects and then blurted out, “What the h*ll is that?”

In the case of the KDE250 quizzical looks arise for several reasons. First these ‘phones don’t look quite like anything else on the market, with a design that appears to be a cross between an ultra high-tech NASA-grade earbud and some sort of communication device from sci-fi film. Second, though you realize the KDE250 is surely a headphone of some kind (hey, the logo says “Koss” on it, doesn’t it?), it’s not at first clear whether you are supposed to wear the things on your ears or in them. And as it happens, the answer to that particular puzzler is “both.”


Koss’ KDE250 dual-element headphone provides separate, clip-on earpieces for your left and right ears and it is, as its name suggests, a dual-driver headphone of deceptively unusual configuration.

When you first look at the KDE250’s earpieces, two features catch your eyes. First, there is a moderately large, disc-shaped driver housing (for the 20mm low-frequency driver, as it happens), which is about the diameter of a quarter, but considerably thicker. Second, you’ll note that the earpiece housings incorporate futuristic-looking, satin-finished metal ear clips, fitted with cool, micrometer-type adjustment knobs that allow ultra-precise height adjustments for a comfortable fit. Finally, the earpiece frame is hinged in the middle so that you can adjust the angle of the driver assembly relative to you ears.

At this stage, one might be tempted to think, “Oh, I get it; the KDE250 is pretty much a typical on-ear headphone with a hinged frame, distinctive ear clips and cool adjustment knobs.” But while that assessment is partly true, it is also misleading, because the KDE250 offers design features that I, for one, have not seen on any other headphone. Allow me to explain.

If you turn the KDE250 earpiece over in your hand, you’ll make the startling discovery that its large disc-shaped driver housings are fully enclosed on both sides, meaning there are no apparent openings through which sound could be directed into your ears. Hunh? How could that be? Where does the sound come out?

We’re glad you asked. On the back of each main driver enclosure you’ll find an unusual appendage that protrudes at right angles from the main enclosure. Closer inspection reveals that the appendage is in fact a small, streamlined nacelle that houses the KDE250’s tiny 13mm tweeter/midrange driver, and that also provides vent ports through which the low-frequency driver delivers bass to your ears. But here’s the really unusual part. Those little driver nacelle/vent port assemblies are set up so that they fits sideways in the ear canal, radiating sound from the back toward the front of your ear canals. What is more, unlike typical in-ear headphones, the KDE250s make no attempt to form an airtight seal in your ears. On the contrary, the 250’s driver nacelle/vent port assembly fits comfortably within the ear canal yet without blocking it, so that wearers can still hear room sounds quite easily.

Why would Koss go to such lengths to create such an unconventional headphone? According to Koss President and CEO Michael J. Koss, the KDE250 is meant to provide “the ultimate in portable personal listening,” but I think the actual answer is subtler and more nuanced than that.

As near as I can tell, Koss had three objectives in mind with this product, all of which help to position it as a strong, viable alternative to traditional in-ear headphones (which, for the record, Koss also makes). First, the KDE250 strives to deliver an overall sound that is significantly different from, and in some respects superior to, the sound of typical competing in-ear ‘phones. Second, the KDE250 aims to provide a comfortable, customizable fit that deliberately overcomes the objections of listeners who dislike the tight, earplug-like feel of typical in-ear ‘phones (or who dislike the loose, imprecise fit of typical earbuds). Third, the KDE250 is targeted toward listeners who want to enjoy very high sound quality, but also need or want to hear potentially important sounds around them (e.g., phones ringing, office mates approaching to ask questions, etc.). As you’ll learn in this review, the KDE250 meets all three objectives quite successfully.


One consequence of the KDE250’s unusual design and shape is that newcomers invariably ask, “How do I put them on?”

True story: when I first saw these headphones at a trade show, I asked the Koss booth attendant the same question. And believe it or not, the answer was sufficiently non-intuitive that the attendant had to go find a photograph showing the 250’s being worn by a model before he could answer my question (no, I am not making this up).

In truth, though, the KDE250’s are actually extremely simple to insert and very comfortable to wear, though there are a few simple tricks that will help users come up to speed, as outlined below.

Orientation: start by examining the earpieces, noting that there are shallow “L” and “R” markings on the earpiece frames, which are found down near the signal cable attachment point.

Trial Fit: to get a sense for the how the KDE250’s are supposed to fit, trying swinging their ear clips aside (the clips are designed to allow this), and then gently inserting the 250’s in your ears for a “test fit.” Try moving the earpieces up/down and forward/backward until you find comfortable position.

Hint: the KDE250 earpieces should not put any undo pressure on your ear canals or outer ears. If you feel any excess pressure, reposition the earpieces and try again.

Hint: to dial in an optimal fit, try adjusting the hinged frames of the KDE250 earpieces until you find an “angle of attack” for that feels comfortable.

Adjust the Ear Clips: once you have a sense for the gentle, comfortable, low-pressure fit that the KDE250 is supposed to have, swing the ear clips back into position and hook them over the tops of your ears. Then, carefully dial- in the height adjustment knobs until you get a just-right fit.

Hint: the ear clips should support most of the weight of the earpieces, so that the frames/driver housings do not press downward too firmly on your ears.

Hint: the KDE250 comes with three sizes of ear clips (small, medium, and large), so that you may find it helpful to experiment to see if one size works better than the others.

As a welcome convenience touch, the KDE250’s come with a small, rectangular leather carrying pouch with a magnetic closure. The pouch includes an inner tray made of a firm foam material, which not only provide clever cutouts that fit the KDE250’s left and right earpiece frames, but that also serves as a cable winding spool (an idea we wish more manufacturers would implement).


As noted above, the KDE250’s sound quite different, in a qualitative sense, from other in-ear headphones (and also different from typical earbuds, for that matter). First, there is absolute no sense of the Koss drivers being “pressure coupled” to your ear drums, as would often be the case with in-ear ‘phones whose eartips seal tightly in your ear canal. Rather than sensing that there are tiny drivers positioned mere millimeters from your ear drums and that are “beaming” sound straight down your ear canal, you’ll find the KDE250’s instead create the illusion that sounds are originating from outside your ear canals and outside your head. In this sense, the KDE250 gives results similar to, but arguably even more dramatic in their impact than, those you might experience with Ultrasone headphones that use that firm’s S-Logic technology. As a consequence, the Koss ‘phones sound noticeably more open and transparent than most, and significantly less artificial, constricted, or “canned.”

Importantly, the Koss design let you hear music reproduced with genuine high fidelity, while at the same time being able to hear at least some ambient room sounds, which many will find a novel and pleasurable experience (kind of like having the proverbial “soundtrack for your life”). There is, of course, a tradeoff in that the KDE250 provides almost no noise isolation. But for those who want high-performance sound while still maintaining good “situational awareness,” the KDE250 is just the ticket.

I have three observations to offer regarding the KDE250’s tonal balance, starting from the top of the audio spectrum and working downward. First, treble is nicely extended and smooth (in terms of freedom from either large or small-scale response variations). To appreciate these qualities in action, listen to the high percussion in “Talking Wind” from Marilyn Mazur and Jan Garbarek’s Elixir [ECM]. On this track, the Koss 'phones effortlessly revealed the incredible high-frequency delicacy (and variety) of the instrumental timbres, without ever lapsing into edginess or brashness.

Second, the KDE250’s midrange is also quite smooth, but is pushed just slight forward relative to higher and lower frequencies. , giving these headphones a somewhat midrange-centric character overall. To hear this quality in action, put on “Seven Wonders” from Nickelcreek’s This Side [Sugar Hill, SACD], and pay close attention to the way the Koss 'phones handle the Sara Watkins’ violin, Chris Thile’s mandolin, and the upper register of Ms. Watkins’ voice. What I observed was that violin, mandolin, and voice sounded open and exhibited pristine clarity, but that they were also more penetrating and prominent than they would normally be with a more neutrally-voiced transducer in play. Still, I think most listeners would be so enthralled by the Koss’ terrific openness and transparency that they consider the KDE250’s midrange forwardness more a blessing than a drawback.

Third, upper-bass is well balanced, while mid-bass is somewhat more lightly balanced, and low bass is recessed further still. In truth, very low bass is not deeply extended—at least not down in the bottom octave where the deepest pipe organ notes live. In practice, this means the KDE250 can sound quite pleasing on records with solid upper and mid-bass content, but it is perhaps not the best choice for listening to music that requires a strong bass foundation down below about 40Hz. In fairness, however, let me point out that the KDE250’s bass has beautiful definition, detail and clarity, so that bass quality is consistently high—even if some might want for a bit more bass quantity.

The bass characteristics of the KDE250’s can easily be observed if you put on a track such as “Bass ‘N’ Drums” from John Paul Jones’ Zooma [Discipline US]. This track features the legendary Led Zeppelin bassist performing a syncopated, jazzy electric bass solo accompanied only by a drum kit. The Koss 'phones do a fine job with the upper register of the bass, capturing the “snap” and “bounce” of Jones’ inventive licks, while also making (most of) the drum kit sound very realistic, too. But, the lower Jones goes on his bass the more lightly balanced the instrument sounds and the drum kit’s kick drum seems lack both in appropriate punch and weight—almost as if it has gone AWOL in the mix, which is really not how this recording can or should sound.

Top-to-bottom clarity and definition are both very good—better, in my estimation, than is the norm for this price class. Part of this, I think, has to do with the KDE250 unique design, which consistently lets you enjoy qualities of openness or transparency, but without feeling like you are being “force fed” sonic minutia that doesn’t really contribute to the musical whole.


Consider this product if: you want a headphone that offers excellent openness and transparency, that is very light and comfortable, that can be dialed in for a precision fit, and that gets around the tight-fitting, “my-ears-feel-plugged-up” sensations that traditional in-ear headphones often entail. Finally, consider the KDE250 if you want to experience true hi-fi sound, while still being able to hear ambient sounds from nearby.

Look further if: you prize strict neutrality in tonal balance (the KDE250 sounds somewhat midrange-forward), or need a headphone that offers powerful, deeply extended low bass. Also look further if you need a headphone that offers high levels of noise isolation, as the KDE250 does not block out much noise.

Ratings (relative to comparably-priced competition):

⇒ Tonal Balance: 7.5
⇒ Frequency Extremes: 6 (bass)/9 (treble)
⇒ Clarity: 9.5
⇒ Dynamics: 8
⇒ Comfort/Fit: 10
⇒ Sensitivity: 7
⇒ Value: 8.5

Summing Up: Koss’ KDE250 offers what some listeners will regard as a compelling alternative to traditional in-ear headphones. The KDE250 is light, comfortable, and offers impressive openness and transparency, and it allows you to keep track of what’s going on in the room around you. Though not the last word in neutral voicing, the KDE250 offers a somewhat midrange-forward sound whose inherent clarity many will find irresistible.


Koss KDE250 Dual-Element Headphones
Accessories: 3 sizes of ear clips, carrying pouch with inner tray that serves as an earpiece holder and cable-winding spool
Frequency response: 40 Hz – 20kHz
Weight: Not specified?
Sensitivity: 95 dB (input levels not specified)
Impedance: 16 ohms
Warranty: Limited Lifetime Warranty
Price: $249.99

(800) USA-KOSS

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