Short answer: the Onyx Studio 6, and skip the newer model. It ranks #13 of 113 boombox speakers at $130, while the Onyx Studio 9 ranks #15 and costs $184.99. Being newer did not make the 9 the better buy.
Warm, boosted bass is the Onyx Studio 6’s calling card. Reviewer Oluv rated it slightly ahead of the newer Onyx Studio 7 for sound, and its dual 75mm woofers pair with a -10dB bass extension of 37Hz against the 9’s single 120mm woofer at 41Hz. The 9’s tuning trades some of that low end for a brighter signature: notes on it call out recessed mids, a boost in the upper mids, and rolled off upper treble, with less deep bass than earlier Onyx Studio speakers.
The Onyx Studio 9 answers back with connectivity, not sound. It runs Bluetooth 5.3 against the 6’s 4.2, works with the Harman Kardon One app for EQ adjustment (the 6 has no app at all), and uses Auracast for multi-speaker pairing instead of the 6’s proprietary Wireless Dual Sound.
The water resistance gap is the real dealbreaker for the 9. The Onyx Studio 6 carries an IPX7 rating, meaning it can survive brief submersion, while the Onyx Studio 9 has no water resistance rating at all. For anything near a pool or the beach, that alone rules the 9 out.
Buy the Onyx Studio 6 for nearly every use case. It outranks the 9, costs less, sounds warmer by the site’s own notes, and is the only one of the two safe near water.
Buy the Onyx Studio 9 only if Auracast pairing or app based EQ control matters more to you than price, sound signature, or water resistance.
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Specifications Side By Side
| Harman Kardon Onyx Studio 6 | Harman Kardon Onyx Studio 9 | |
|---|---|---|
| Price | $130 Discontinued | $184.99 |
| Ranked | #13 of 113 in Boombox Size Portable Bluetooth Speakers | #15 of 113 in Boombox Size Portable Bluetooth Speakers |
| Aux Input | Yes | No |
| Bass Extension (-10dB) | 37Hz | 41Hz |
| Battery Life | 8 hours (Manufacturer specified) | 8 hours (Manufacturer specified) |
| Built-in Microphone | Yes | - |
| IP Rating | IPX7 | None |
| Bluetooth Latency | 180ms | - |
| Maximum SPL | 96dB (measured by Alan Ross Reviews) | 101dB (measured by Alan Ross Reviews) |
| Party Mode | Yes (Wireless Dual Sound) | Yes (Auracast) |
| Power Input | DC Barrel Connector (19V/2A) | AC Power Cable (2-Prong) |
| Stereo | No | Yes |
| Omnidirectional | No | No |
| TWS | Yes (see https://www.reddit.com/r/Bluetooth_Speakers/comments/w339x5/how_to_harman_kardon_onyx_studio_5_6_dual_sound/) | Yes |
| Weight | 6.5 lbs (2.94 kg) | 9.3 lbs (4.2 kg) |
| Bluetooth | Yes | Yes |
| Bluetooth Codecs | SBC | SBC |
| App | No | Yes (Harman Kardon One app) |
| EQ | No | Yes (App EQ) |
| Power Bank | No | - |
| USB Playback | No | No |
| Bluetooth Version | 4.2 | 5.3 |
| Amplifier Power | 50W RMS | 50W RMS |
| Dimensions | 5” x 11.5” x 11.2” (128 x 291 x 284 mm) | 11.4” x 11.3” x 5.1” (289.2 x 287.5 x 130 mm) |
| Drivers | 1x 120mm (4.7”) woofer + 1x 25mm (1”) tweeter + 1x passive radiator | 120mm woofer + 3x 20mm tweeters |
| Digital Aux Input | No | No |
| Strap | No | No |
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