Short answer: the Soundlink Flex 2nd gen for better sound quality, the ULT Field 1 for the lower price. These rank #37 and #99 of 179 medium speakers, and $21 separates them.
The two have very different sonic problems. The Flex 2nd gen’s notes describe it as pretty much identical sounding to the original Flex, which is a known quantity: warm, with overly boosted bass that drowns out midrange detail. The ULT Field 1 instead has an upper midrange peak with rolled off treble, a different kind of imbalance. Neither is neutral, but the Flex’s issue sits in the bass and midrange while the Field 1’s sits higher up, so which bothers you more depends on what you listen to.
Battery behavior is where the real gap opens up. The ULT Field 1’s notes put its real-world battery life around 28 or more hours with the ULT bass boost mode off, well past its 12 hour spec rating. The Flex 2nd gen carries a real downside here instead: it self-drains about 10% of its battery a week even when not in use, so a speaker left in a drawer for a month can show up dead.
What both share: neither is stereo on its own, both stereo pair with a matching second unit, both carry an IP67 rating, and both include a built-in microphone for calls.
Buy the Soundlink Flex 2nd gen if bass-forward, warm sound is what you want and you are willing to charge it before storage.
Buy the ULT Field 1 if you want longer real-world runtime and a lower price, and can live with a brighter upper-midrange tuning instead of boosted bass.
Looking for alternatives? See the complete Portable Bluetooth rankings.
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Specifications Side By Side
| Bose Soundlink Flex 2nd gen | Sony ULT Field 1 | |
|---|---|---|
| Price | $159.00 | $138.00 |
| Ranked | #37 of 179 in Medium Size Portable Bluetooth Speakers | #99 of 179 in Medium Size Portable Bluetooth Speakers |
| App | Yes | Yes |
| Battery Life | 12 hours (Manufacturer specified) | 12 hours (Manufacturer specified) |
| Built-in Microphone | Yes | Yes |
| EQ | Yes (3 band) | Yes |
| IP Rating | IP67 | IP67 |
| Party Mode | Yes (Bose Party mode) | Yes (Party Connect up to 100 speakers) |
| Power Input | USB-C | USB-C |
| Stereo | No | No |
| Omnidirectional | No | No |
| TWS | Yes | Yes |
| Weight | 1.3 lbs (586 g) | 1.4 lbs (650 g) |
| Bluetooth | Yes | Yes |
| Bluetooth Version | 5.3 | 5.3 |
| Dimensions | 7.9” x 3.5” x 2” (201 x 90 x 52 mm) | 8.1” x 3” x 3” (206 x 77 x 76 mm) |
| Aux Input | No | No |
| Drivers | 60mm full-range driver with passive radiators | 83mm x 42mm woofer, 16mm tweeter + passive radiator |
| Bluetooth Codecs | SBC, AAC, aptX Adaptive | AAC, SBC |
| Digital Aux Input | No | No |
| Strap | Yes (built-in loop) | Yes (detachable strap) |
| Power Bank | - | No |
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