Headphones take on many form factors, from tiny in-ear monitors to humongous electrostatic models that need dedicated amps and cost a small fortune. For many audio enthusiasts, a happy medium can be found in full-size, dynamic headphones. The KLH Ultimate One is an over-ear, open-back dynamic headphone that features Ebony earcups and drivers made with beryllium, while adding lambskin and leather to the luxury material list.They are a statement piece by the reborn KLH brand and with a $299 MSRP (real Ebony earcups) or $379 (real Zebra wood earcups, by special order). That makes the Ultimate Ones comparable in price with the Grado GH3 & AKG K701/702 premium dynamic headphones, as well as a number planar-magnetic models in that range.The moment I first saw the KLH Ultimate One headphones, my eyes opened wide and my ears perked up. When I heard the $299 price point (for the Ebony model I reviewed), and that you get beryllium drivers for that money, the anticipation went into overdrive. And when I picked up the pair for the first time and put them on my head, the feeling of the luxurious materials, plus the overall lightness, and a thoughtful minimalist design made a great first impression.KLH specifies the frequency response of the Ultimate Ones at 18 Hz to 22 kHz, which fully covers what you can hear. I’m not a headphones measurement guy—I have a miniDSP E.A.R.S. rig but it’s not “industry standard” so I only use it for personal insights, not to create charts for posting. Having said that, I’m always glad to check on the bass response claim since my results have tracked quite close to what dedicated headphones reviewers get with their rigs. Long story short, these headphones deliver that deep bass extension, as promised, despite being an open-back design.To be specific, and remembering that these are not “industry standard” measurements, as long as the earcup maintains a good seal, I measured the bass as being essentially flat; it’s only down by 2 dB at 20 Hz. Furthermore, THD at 20 Hz was under 2% and drops to under 1% at higher frequencies. I also measured response right up to my system’s 24 kHz limit. That’s inaudible to humans. It’s fair to say these headphones cover the entire audible range and do it cleanly without compromising dynamics.Ultimate one headphones ship in a leather-bound hard case that includes a soft carrying bag plus detachable cord, which connects to the left ear cup with a standard stereo 1/8 inch plug (1/4" adapter is provided). Kudos to KLH for not using some proprietary cable that’s hard to find and far too expensive; in a pinch you can pick up a replacement cord for these headphones just about anywhere where electronics is sold.These headphones are in the “Goldilocks Zone” in terms of performance, aesthetics, price, and even weight. The KLH Ultimate One design is timeless, there’s nothing of note to improve upon in terms of ergonomics or fit, no gimmick that’s going to replace the acoustic benefit of open-back headphones with beryllium drivers. At the $299 debut price, the build quality and performance of these KLH Ultimate Ones raise the bar at a very popular price point. And the 12-ounce weight adds to the appeal—these are headphones you can wear all day—every day—without any discomfort or fatigue.The signature sound of KLH is what I’d call “accurate yet punchy.” Whether it’s the company’s speakers (like these Kendall towers) or the Ultimate One headphones, listening sessions are defined by both the fascination of hearing many layers of detail revealed in a melody, mixed with the intrinsic joy of feeling the percussive elements in the rhythm, and actually falling into the groove. Yes, these are subjective notions, but I’m sure they are backed up by some sort of measurement. What’s key is that these qualities are readily apparent to the listener.I appreciate that these headphones are easy to drive with a mobile device. Having to carry around an extra amplifier just to get satisfying sound on the go is a hassle, but that’s the reality when it comes to planar-magnetic headphones. Here, thanks to the beryllium dynamic driver, you get dynamics and transient response that’s evocative of planar magnetics models (sold at similar or higher price points).I used a Creative Sound Blaster X G6 connected to a Windows laptop streaming Tidal HiFi for much of my at-home listening. On the road I relied on both a Galaxy Note 9’s built-in headphone jack, and an iPhone XS Max using the Apple lightning headphone adapter. Between the two, neither one had a clear advantage in terms of peak output and since open-back designs leak sound, I avoid playing them overly loud in public anyhow. Both phones drove the headphones at levels above what I need to be fully satisfied, including rock-solid ultra-clean bass.The Creative Sound BlasterX G6 is an affordable audio interface at $149 but it’s got enough oomph to push these headphones well past any listening level I’m comfortable with and goes well beyond my laptop’s built-in sound or what the phones can offer. I can’t say what an even pricier DAC/amp might offer in terms of sonic benefits but the main thing I wish to convey is you don’t need to spend time or money trying to make the Ultimate One headphones perform better than they already do. In that sense, these might not be “ideal” for fidgety hobbyists who insist only a pile of tweaked-out gear can deliver true audiophile listening experiences. Indeed, I’d recommend that sort of listener stay far away from the Ultimate Ones because it’s actually “too easy” to get a good sound out of them... you only have to plug them in and put them on your head and you are done with the “tweaks.”So here’s what I want to emphasize in this review: It’s not as much about how this or that album sounds, but a more basic notion: I’ve spent years setting up many systems and applying bass management plus room correction to get a good sound. It’s a sound that I recognize whenever I go into a studio, dedicated listening room, or dedicated home theater that is well-tuned. It’s balanced, with extension, it’s impactful, it gives you goosebumps when you hear something great. That’s the sound of these headphones.The open-back wood ear cups deliver an open sound that’s not “trapped inside your head.” You can feed these KLH classical music and hear the expansiveness of a concert hall. And when I played back a live jazz recording I made in New Orleans using a Zoom H1n recorder, I was surprised at how clearly the original listening experience came through in the recording.Snoop Dogg’s album Bush is a fantastic-sounding funk plus R&B excursion with Pharrell Williams handling production. It sounds straight-up sublime through the Ultimate Ones, with a thickness and weight to the bass line that few headphones can get right. Typically, to get this “much” bass you need to accept some muddiness but here it’s all gravy (to my taste anyhow). It’s CRAZY how a phone can make these headphones bump and give you a listening experience that—were this a stereo system—would cost thousands of dollars to emulate.Carl Orff’s O Fortuna from Carmina Burana has been performed countless times by the great orchestras and really “brings it” with its famous intensity. I went with the EMI Classics London Symphony version from 1988 and was rewarded with a rousing rendition of this 13th century poem that bemoans the role of luck in the fate of gods and men. It’s stunning to hear the buildup to the crescendo where the full chorus is joined by tympany and blaring horns. To unpack it all is a tall task for any transducer but these headphones—even powered directly by a phone—bring the necessary slam and a sense of grandeur to the proceedings. Captivating stuff.Coil’s album Love’s Secret Domain comes from the early 1990s when raves were exploding and house music ruled. The album is a true work of art, containing many samples but also build on a collage of contributions that add an eclecticism to the band’s already-trippy aesthetic. It’s an aural journey filled with thoughtful production touches that send the carefully crafted sounds flying all over the place. From the moment track 1 “Disco Hospital” starts playing, you know this is no ordinary album—it’s crafted to sound best through exceptional headphones and rewards deep listening (fully concentrating on the music, without distraction). The KLH Ultimate Ones are able to fully and properly translate Coil’s best album; that fact alone means I have to own a pair until something better comes along.Folks who have been reading my reviews for a while know that my standard issue torture test for handling bass—lots and lots of deeeeep bass—is the track “Disc Wars” from the Tron Legacy soundtrack. It’s Daft Punk plus London Symphony, with Disney paying for the production and the assumption being it’ll play in a top-tier home theater that can deliver the intense sounds contained within. I’ve used it to “tap out” subwoofer amps in the past because the almost-infrasonic rumble that forms the tracks foundation is continuous. Moreover, this is a bass sound that’s finely tuned and has to convey a sense of grit and “grip” not just “of there’s some bass” but rather a very specific flavor of bass. This is a test that the Ultimate One headphones absolutely aced. I heard the full spectrum of sound that comes through in a big system that’s perfectly tuned, and the soundfield was in no way constrained to my head—the presentation was shockingly natural and reminiscent of hearing a truly great 2-channel rig strut its stuff.My hunt for “perfect” headphones will never end because no one single design covers all uses. But, my hunt for the perfect pair of passive, open-back dynamic headphones could easily end with the KLH Ultimate One headphones and their exceptional sound that has to (at least partially) be credited to the used of beryllium for the driver.These are my “daily driver” headphones for use with phones and laptops—simple as that. My highest recommendation is “this is what I choose to use myself.” At $299, I consider the performance of these headphones to represent one of the best deals in audio. Therefore I’m giving the KLH Ultimate Ones a Top Choice award.