Bluetooth speakers don't have to be or sound small. They can be large and full-sounding, like the Harman Kardon Onyx Studio. This $399.99 (exclusive from Sprint) Bluetooth speaker is powerful and offers plenty of bass, and users who want a good amount of rumble without a subwoofer will be satisfied. Its status as a portable speaker is held back by a large profile compared to the Editors' Choice Bose SoundLink III, though, and it doesn't sound quite as crisp as it should. It's a good choice if you want tons of power, though the same-price Editors' Choice Marshall Stanmore offers a slightly more robust sound with better (and optional, thanks to its bass and treble controls) emphasis on the high end at the cost of losing all portability.

Design

The Onyx Studio is a black disc that measures 11 inches in diameter and is shaped like a convex lens approximately five inches thick at its widest point. It stands on two metal legs built into its body that let it sit at a slight angle. It features a black cloth grille bearing the Harman Kardon logo on the front and a rubber passive radiator with a metal disc (also with the Harman Kardon logo) on the back. Above the radiator, a large grip makes the 4.6-pound speaker easy to carry when moving it around. The speaker ships with a transparent plastic cover on the metal plate covering the bass radiator. It's easy to miss, but must be removed for the speaker to work (and not produce a very strange-sounding low end).

The controls on the Onyx Studio are minimalist to a fault. Around the edge of the speaker sit Power, Volume Up/Down, and Bluetooth pairing buttons, and that's it. The inputs are even more scant; besides a power port and a micro USB port, the Onyx Studio offers no physical connections. The power port is proprietary, and connects to a laptop charger-like power brick with a separate power cable for plugging into the wall. The micro USB port is just for firmware upgrades, so the speaker has no options for wired auido playback. This is surprising, since nearly every other Bluetooth speaker across all ranges of sizes, prices, and feature sets offers at least one auxiliary input.

The Onyx Studio is technically portable, but it's not a speaker you can casually take anywhere. It's bulkier and feels less rugged than other, smaller Bluetooth speakers like the Bose SoundLink III, and Harman Kardon rates its battery at a scant five hours compared to the Bose's 14. The battery and handle make it easy to move between rooms and take out to your backyard, but it's not a speaker you can just toss in your bag and take anywhere.

Performance

For a one-piece Bluetooth speaker, the Onyx Studio puts out some impressive sound. It sports two 3-inch woofers, two 3/4-inch tweeters, and two passive radiators, with 15 watts going to each active driver for a total power level of 60 watts. Harman Kardon claims the speaker boasts a frequency response of 60Hz to 20kHz, and the bass response seems to confirm that. The speaker reaches deep enough into the low end to offer an appreciable sense of rumble, and handled the sub-bass synth hits in The Knife's "Silent Shout" at full volume with plenty of force and no distortion.

The Onyx Studio emphasizes the low end slightly, and some audiophiles might be disappointed with that focus. Lows and low-mids get plenty of presence and warmth, as I heard from the robust-sounding upright bass in Miles Davis' "So What." The piano and horns were still the highlight of the presentation, but the higher notes lacked some of the brightness other speakers offer with brass that allow it to cut through the mix. It's still a very satisfying sound that doesn't boost the bass too much, but it won't appeal to purists who want the most accurate, flat response.

The Rolling Stones' "Gimme Shelter" benefits from the focus on low end and the slight softening of treble. The opening plinky guitar notes, which often sound quite bright on most speakers, sat back slightly to share the stage with the bass in the intro. It wasn't the most energetic reproduction of the song I've heard, but the strong bass and rounded lead gave it a pleasant sense of sculpted balance.

Monster Magnet's "Negasonic Teenage Wasteland" also benefited from this effect. Dave Wyndorf's vocals are usually just deep enough for the higher, sharper guitar riffs to overwhelm them with a flat-response speaker, but the boosted lows and pulled-back high end kept them anchored in the center of the track.

Conclusion
The Harman Kardon Onyx Studio is a solid one-piece Bluetooth speaker that will satisfy fans of bass who don't want to deal with a really bulky and constantly powered system. It's larger, less rugged, and more expensive than most portable Bluetooth speakers, but it can put out enough sound, particularly in the low end, to justify its size and price. It's a bit more focused on bass and offers less crisp high end than the adjustable-bass-and-treble, always-plugged-in Editors' Choice Marshall Stanmore or the much more portable (but less powerful) Bose SoundLink, but it remains a very appealing speaker. If you don't need portability and don't want to spend $400, take a look at the $150 Editors' Choice Boston Acoustics MC100 Blue, which is less than half the price of the Onyx Studio or the Stanmore.