Short answer: the Onyx Studio 9 for sound, the Boom 2 Plus for everyday practicality. The Onyx Studio 9 ranks #15 of 113 boombox speakers against the Boom 2 Plus at #39, for $15 more.
The Onyx Studio 9’s tuning is close but not flawless. Our notes describe slightly recessed mids, a boost in the upper mids, and rolled off upper treble, along with less deep bass than previous Onyx Studio generations. In exchange it offers Auracast multi-speaker connection alongside classic stereo pairing, plus the Harman Kardon One app with EQ control.
The Boom 2 Plus leans warm rather than bright. Our notes call out a warm tuning with rolled off treble and some upper bass boost, along with reasonably deep bass that falls short of the category’s top performers. It is also noted as quite a bit lighter than most other boombox-size speakers.
Two practical gaps favor the Boom 2 Plus outright:
- Battery life: 20 hours against the Onyx Studio 9’s 8 hours.
- Water resistance: IPX7 rated for brief submersion, versus no water resistance at all on the Onyx Studio 9.
- Output power: 140W against 50W RMS, with a max volume of 111dB versus 101dB.
Everything else lines up closely: both offer stereo pairing, TWS, an app with EQ, and Bluetooth party mode, though under different names (Auracast on the Onyx Studio 9, PartyCast 2.0 on the Boom 2 Plus).
Buy the Onyx Studio 9 if sound quality is your priority and you don’t need it away from an outlet or near water.
Buy the Boom 2 Plus if you want longer battery life, actual water resistance, and more raw volume for less money.
Want more options? Browse the full Portable Bluetooth rankings.
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Specifications Side By Side
| Harman Kardon Onyx Studio 9 | Soundcore Boom 2 Plus | |
|---|---|---|
| Price | $184.99 | $169.99 |
| Ranked | #15 of 113 in Boombox Size Portable Bluetooth Speakers | #39 of 113 in Boombox Size Portable Bluetooth Speakers |
| Bass Extension (-10dB) | 41Hz | 39Hz |
| Maximum SPL | 101dB (measured by Alan Ross Reviews) | 111dB (measured by Alan Ross Reviews) |
| IP Rating | None | IPX7 |
| Power Input | AC Power Cable (2-Prong) | USB-C |
| Stereo | Yes | Yes |
| Omnidirectional | No | No |
| TWS | Yes | Yes |
| Weight | 9.3 lbs (4.2 kg) | 8.4 lbs (3.8 kg) |
| App | Yes (Harman Kardon One app) | Yes |
| Bluetooth | Yes | Yes |
| Bluetooth Codecs | SBC | SBC, AAC |
| EQ | Yes (App EQ) | Yes (Pro EQ + presets) |
| Party Mode | Yes (Auracast) | Yes (PartyCast 2.0) |
| USB Playback | No | No |
| Bluetooth Version | 5.3 | 5.3 |
| Battery Life | 8 hours (Manufacturer specified) | 20 hours (Manufacturer specified) |
| Amplifier Power | 50W RMS | 140W |
| Dimensions | 11.4” x 11.3” x 5.1” (289.2 x 287.5 x 130 mm) | 17.3” x 9.1” x 5.9” (440 x 230 x 150 mm) |
| Drivers | 120mm woofer + 3x 20mm tweeters | 2x 114mm (4.5”) woofers + 2x 19mm (0.75”) tweeters |
| Digital Aux Input | No | No |
| Aux Input | No | Yes |
| Strap | No | Yes (detachable strap) |
| MicroSD Playback | - | No |
| Power Bank | - | Yes (USB-C, 5V/2A) |
| Built-in Microphone | - | Yes |
| Lights | - | Yes |
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