Short answer: both are discontinued, so this only matters if you are buying used. Used, the Harman Kardon Onyx Studio 6 is the better pick: it ranks #13 of 112 boombox speakers by sound quality (rated 4.1/5), against #76 (rated 2.8/5) for the Diamondboxx M3. If you want one new, the Harman Kardon Onyx Studio 9 replaces the Harman Kardon Onyx Studio 6 and is rated 4.1/5 at $184.99.
The Harman Kardon Onyx Studio 6 is the better-sounding, lighter pick. A waterproof carry speaker with warm sound, deep bass for its size, and pairing with a second unit. At 6.5 lbs (2.94 kg) it weighs much less than the Diamondboxx M3 at 11 lbs (5 kg). It is rated IPX7, while the Diamondboxx M3 has no water resistance. It links with other speakers (Wireless Dual Sound), which the Diamondboxx M3 cannot. Watch for: Warm tuning with boosted bass, and not as loud as others.
The Diamondboxx M3 is the longer-running option. A compact, very loud boombox with a powerful amplifier and a choice of large battery packs. It is rated for 40 hours of battery against 8 for the Harman Kardon Onyx Studio 6. It plays in stereo from a single unit, unlike the Harman Kardon Onyx Studio 6. The tradeoff: Despite its output, bass does not reach as deep as the best large portables and can distort when pushed hard.
Buy the Harman Kardon Onyx Studio 6 only if you find one used in good condition; both are discontinued, and it is the better rated of the two. For a new speaker, buy the Harman Kardon Onyx Studio 9, which replaces the Harman Kardon Onyx Studio 6.
Still deciding? The full Portable Bluetooth rankings cover every ranked option.
A waterproof carry speaker with warm sound, deep bass for its size, and pairing with a second unit.
A compact, very loud boombox with a powerful amplifier and a choice of large battery packs.
Prices on this page were last checked October 31, 2026 at 7:11 PM 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.
As an eBay Partner, we may be compensated if you make a purchase.
Specifications Side By Side
| Harman Kardon Onyx Studio 6 | Diamondboxx M3 | |
|---|---|---|
| Price | $130 Discontinued | $700 Discontinued |
| Ranked | #13 of 112 in Boombox Size Portable Bluetooth Speakers | #76 of 112 in Boombox Size Portable Bluetooth Speakers |
| Aux Input | Yes | Yes |
| Bass Extension (-10dB) | 37Hz | - |
| Battery Life | 8 hours (Manufacturer specified) | 40 hours (Manufacturer specified) |
| Built-in Microphone | Yes | No |
| IP Rating | IPX7 | None |
| Bluetooth Latency | 180ms | - |
| Maximum SPL | 96dB (measured by Alan Ross Reviews) | - |
| Party Mode | Yes (Wireless Dual Sound) | No |
| Power Input | DC Barrel Connector (19V/2A) | USB-C |
| 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) | 11 lbs (5 kg) |
| Bluetooth | Yes | Yes |
| Bluetooth Codecs | SBC | SBC |
| App | No | No |
| EQ | No | No |
| Power Bank | No | No |
| USB Playback | No | No |
| Bluetooth Version | 4.2 | 5.0 |
| Amplifier Power | 50W RMS | 200W RMS / 400W peak |
| Dimensions | 5” x 11.5” x 11.2” (128 x 291 x 284 mm) | 14.7” x 9” x 8” (373.4 x 228.6 x 203.2 mm) |
| Drivers | 1x 120mm (4.7”) woofer + 1x 25mm (1”) tweeter + 1x passive radiator | 3” woofer + tweeter array |
| Digital Aux Input | No | No |
| Strap | No | - |
| FM Tuner | - | No |
Related Speaker Comparisons
How Harman Kardon Onyx Studio 6 compares with other leading options: