Short answer: the Onyx Studio 9 for sound, the Boom 2 Plus for everyday practicality. The Onyx Studio 9 ranks #14 of 75 boombox speakers against the Boom 2 Plus at #28, for $10 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.
Specifications Side By Side
| Harman Kardon Onyx Studio 9 | Soundcore Boom 2 Plus | |
|---|---|---|
| Price | $189.99 | $179.99 |
| Ranked | #14 of 75 in Boombox Size Portable Bluetooth Speakers | #28 of 75 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 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 |
| MicroSD Playback | - | No |
| Power Bank | - | Yes (USB-C, 5V/2A) |
| Built-in Microphone | - | Yes |
| Lights | - | Yes |
Related Speaker Comparisons
How Harman Kardon Onyx Studio 9 compares with other leading options:
- Earfun Uboom X vs Harman Kardon Onyx Studio 9
- Harman Kardon Onyx Studio 9 vs Tribit Stormbox Blast
- Harman Kardon Go + Play 3 vs Harman Kardon Onyx Studio 9
- JBL Partybox Encore 2 vs Harman Kardon Onyx Studio 9
- Harman Kardon Onyx Studio 9 vs JBL Partybox Encore Essential 2
Prices on this page were last checked September 22, 2026 at 5:11 AM UTC. Product prices and availability are accurate as of that date/time and are subject to change; the price and availability shown on Amazon at the time of purchase will apply to the purchase of this product.
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The Two Speakers In Full
Harman Kardon Onyx Studio 9: $189.99 Amazon eBay
Pros: An elegant 4.2kg living-room portable with a measured 41Hz -10dB bass point, 101dB maximum level, three tweeters, app EQ, stereo pairing and Auracast multi-speaker linking. Reviews praise its balanced, smooth presentation and non-fatiguing treble, making it a more music-focused choice than most party speakers. Measured bass extension of 41Hz (-10dB).
Cons: It has no water resistance, aux input or USB playback, and its eight-hour claimed battery life is short for an outdoor portable. Bass is less deep than some earlier Onyx Studio models, while the slightly recessed mids and rolled-off top end mean it is not the most open or detailed option; it still charges from an AC power cable rather than USB-C.
Full Harman Kardon Onyx Studio 9 review and specifications →
| Amplifier Power | 50W RMS |
|---|---|
| App | Yes (Harman Kardon One app) |
| Aux Input | No |
| Bass Extension (-10dB) | 41Hz |
| Battery Life | 8 hours (Manufacturer specified) |
| Bluetooth Codecs | SBC |
| Bluetooth Version | 5.3 |
| Digital Aux Input | No |
| Dimensions | 11.4" x 11.3" x 5.1" (289.2 x 287.5 x 130 mm) |
| Drivers | 120mm woofer + 3x 20mm tweeters |
| EQ | Yes (App EQ) |
| IP Rating | None |
| Maximum SPL | 101dB (measured by Alan Ross Reviews) |
| Omnidirectional | No |
| Party Mode | Yes (Auracast) |
| Power Input | AC Power Cable (2-Prong) |
| Stereo | Yes |
| TWS | Yes |
| USB Playback | No |
| Weight | 9.3 lbs (4.2 kg) |
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Soundcore Boom 2 Plus: $179.99 Amazon B&H Photo Video eBay
Pros: Quite a bit lighter than most of the other boombox size speakers. This speaker will likely move up as we get a good EQ tune that makes it a lot more neutral. Measured bass extension of 39Hz (-10dB).
Cons: Warm tuning meaning a rolled off treble and some upper bass boost. Reasonably deep bass, but not as good as the top ranked.
Full Soundcore Boom 2 Plus review and specifications →
| Amplifier Power | 140W |
|---|---|
| App | Yes |
| Aux Input | Yes |
| Bass Extension (-10dB) | 39Hz |
| Battery Life | 20 hours (Manufacturer specified) |
| Bluetooth Codecs | SBC, AAC |
| Bluetooth Version | 5.3 |
| Built-in Microphone | Yes |
| Digital Aux Input | No |
| Dimensions | 17.3" x 9.1" x 5.9" (440 x 230 x 150 mm) |
| Drivers | 2x 114mm (4.5") woofers + 2x 19mm (0.75") tweeters |
| EQ | Yes (Pro EQ + presets) |
| IP Rating | IPX7 |
| Lights | Yes |
| Maximum SPL | 111dB (measured by Alan Ross Reviews) |
| MicroSD Playback | No |
| Omnidirectional | No |
| Party Mode | Yes (PartyCast 2.0) |
| Power Bank | Yes (USB-C, 5V/2A) |
| Power Input | USB-C |
| Stereo | Yes |
| TWS | Yes |
| USB Playback | No |
| Weight | 8.4 lbs (3.8 kg) |
- Links
- Reviews, Comparisons and Sound Samples
- Alan Ross Reviews: This sounds totally different now! Soundcore Boom Plus 2 firmware 03.10 More from alanrossreviews →
- Alan Ross Reviews: Soundcore Boom 2 Plus Review - worst boombox speaker under $400?
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- GYMCADDY: Soundcore Boom 2 Plus Showcase - Lots Of Bass In A Small Package More from GYMCADDY →
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- Jagist reviews: Zealot S95 Vs Soundcore Boom 2 Plus!!! More from Jagistreviews →
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