Short answer: the Zealot S89 for value, the Onyx Studio 9 for connectivity. The S89 is a great value for bass performance, play time and max volume in the boombox class, though it is on the heavy side. The Onyx Studio 9 adds Auracast multi-speaker connection alongside classic stereo pairing, but has slightly recessed mids, a boost in the upper mids and rolled off upper treble.
Buy the Harman Kardon Onyx Studio 9. It is rated higher for sound quality than the Zealot S89 and costs less, so it is the default pick unless a specific strength of the other one matters more to you.
If battery life is a priority, the Zealot S89 is rated for 40 hours versus 8 hours for the Harman Kardon Onyx Studio 9.
Water resistance is not close: the Zealot S89 is rated at IPX6 (powerful water jets), well ahead of the Harman Kardon Onyx Studio 9 at no water resistance.
Still deciding? The full Portable Bluetooth rankings cover every ranked option.
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Specifications Side By Side
| Harman Kardon Onyx Studio 9 | Zealot S89 | |
|---|---|---|
| Price | $184.99 | $193.58 |
| Ranked | #15 of 113 in Boombox Size Portable Bluetooth Speakers | #19 of 113 in Boombox Size Portable Bluetooth Speakers |
| Bass Extension (-10dB) | 41Hz | 36Hz |
| Maximum SPL | 101dB (measured by Alan Ross Reviews) | - |
| IP Rating | None | IPX6 |
| 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) | 16.1 lbs (7.3 kg) |
| App | Yes (Harman Kardon One app) | No |
| Bluetooth | Yes | Yes |
| Bluetooth Codecs | SBC | SBC |
| EQ | Yes (App EQ) | Yes (multiple modes) |
| Party Mode | Yes (Auracast) | Yes (PartyAdd up to 100 speakers) |
| USB Playback | No | Yes |
| Bluetooth Version | 5.3 | 5.3 |
| Battery Life | 8 hours (Manufacturer specified) | 40 hours (Manufacturer specified) |
| Amplifier Power | 50W RMS | 250W |
| Dimensions | 11.4” x 11.3” x 5.1” (289.2 x 287.5 x 130 mm) | 21.2” x 10.4” x 9.4” (538 x 265 x 240 mm) |
| Drivers | 120mm woofer + 3x 20mm tweeters | 130W subwoofer + 2x 40mm drivers + 2x tweeters |
| Digital Aux Input | No | No |
| Aux Input | No | Yes |
| Strap | No | No |
| MicroSD Playback | - | Yes |
| Power Bank | - | Yes (USB-A + USB-C) |
| Built-in Microphone | - | No |
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