Short answer: the Harman Kardon Onyx Studio 9. It ranks #13 of 70 boombox speakers at $186.99; the Zealot ZE21 ranks #15 and costs $187.15, so there is not much of a tradeoff to weigh.
The case for the Harman Kardon Onyx Studio 9: Auracast multi-speaker connection alongside classic stereo pairing. The tradeoff: Slight recessed mids, boost in the upper mids, rolled off upper treble.
What the Zealot ZE21 gets right: Great value for the bass performance, play time and max volume in the boombox class, though the Zealot ZE41 now beats it out. The tradeoff: A little rolled off up top and not that balanced through the rest of the range.
Buy the Harman Kardon Onyx Studio 9 if the ranking matters more than the price. Buy the Zealot ZE21 if the price matters more than the ranking.
Specifications Side By Side
| Harman Kardon Onyx Studio 9 | Zealot ZE21 | |
|---|---|---|
| Price | $186.99 | $187.15 |
| Ranked | #13 of 70 in Boombox Size Portable Bluetooth Speakers | #15 of 70 in Boombox Size Portable Bluetooth Speakers |
| Bass Extension (-10dB) | 41Hz | 36Hz |
| Max Volume | 101dB | 116dB |
| IP Rating | None | IPX6 |
| Power Input | USB-C | USB-C |
| Stereo | Yes | Yes |
| TWS | Yes | Yes |
| Weight | 9.3 lbs / 4.2 kg | 20.4 lbs / 9.27 kg |
| App | Yes (Harman Kardon One app) | No |
| Bluetooth Codecs | SBC | SBC |
| EQ | Yes (App EQ) | Yes (multiple modes) |
| Party Mode | Yes (Auracast) | No |
| USB Playback | No | Yes |
| Bluetooth Version | 5.3 | - |
| Battery Life | 8 hours (Manufacturer specified) | 40 hours (Manufacturer specified) |
| Output Power | 50W RMS | 250W |
| Dimensions | 11.39" x 11.32" x 5.12" (289.2 x 287.5 x 130 mm) | 424mm x 262mm x 363mm |
| Drivers | 120mm woofer + 3x 20mm tweeters | 130W subwoofer + 2x 50mm woofers + passive radiators |
| Aux Input | - | Yes |
| MicroSD Playback | - | Yes |
| Power Bank | - | Yes |
| Built in Microphone | - | No |
The Two Speakers In Full
Harman Kardon Onyx Studio 9: $186.99 Amazon
Pros: Auracast multi-speaker connection alongside classic stereo pairing. Harman Kardon One app with EQ. USB-C charging, up from the previous generation’s AC power brick.
Cons: Slight recessed mids, boost in the upper mids, rolled off upper treble. Not as deep bass as previous Onyx Studio speakers.
| App | Yes (Harman Kardon One app) |
|---|---|
| Bass Extension (-10dB) | 41Hz |
| Battery Life | 8 hours (Manufacturer specified) |
| Bluetooth Codecs | SBC |
| Bluetooth Version | 5.3 |
| Dimensions | 11.39" x 11.32" x 5.12" (289.2 x 287.5 x 130 mm) |
| Drivers | 120mm woofer + 3x 20mm tweeters |
| EQ | Yes (App EQ) |
| IP Rating | None |
| Max Volume | 101dB |
| Output Power | 50W RMS |
| Party Mode | Yes (Auracast) |
| Power Input | USB-C |
| Stereo | Yes |
| TWS | Yes |
| USB Playback | No |
| Weight | 9.3 lbs / 4.2 kg |
- Reviews, Comparisons and Sound Samples
- Head-to-Head Comparisons
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- Harman Kardon Onyx Studio 9 vs Harman Kardon Onyx Studio 8
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- Harman Kardon Onyx Studio 9 vs Skullcandy Barrel
- Harman Kardon Onyx Studio 9 vs Tronsmart Halo 200
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- Harman Kardon Onyx Studio 9 vs Harman Kardon Onyx Studio 7
- Links
Zealot ZE21: $187.15 Aliexpress Amazon
Pros: Great value for the bass performance, play time and max volume in the boombox class, though the Zealot ZE41 now beats it out.
Cons: A little rolled off up top and not that balanced through the rest of the range. Clarity isn’t as good as better speakers. Bass EQ is bloated and muddy sounding
| App | No |
|---|---|
| Aux Input | Yes |
| Bass Extension (-10dB) | 36Hz |
| Battery Life | 40 hours (Manufacturer specified) |
| Bluetooth Codecs | SBC |
| Built in Microphone | No |
| Dimensions | 424mm x 262mm x 363mm |
| Drivers | 130W subwoofer + 2x 50mm woofers + passive radiators |
| EQ | Yes (multiple modes) |
| IP Rating | IPX6 |
| Max Volume | 116dB |
| MicroSD Playback | Yes |
| Output Power | 250W |
| Party Mode | No |
| Power Bank | Yes |
| Power Input | USB-C |
| Stereo | Yes |
| TWS | Yes |
| USB Playback | Yes |
| Weight | 20.4 lbs / 9.27 kg |
- Reviews, Comparisons and Sound Samples
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- Head-to-Head Comparisons
- Links
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Product prices and availability were last checked August 9, 2026 at 6:57 AM UTC 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.