Short answer: the Sony ULT Field 1, if you are buying new. The EarFun Uboom Slim ranks higher than it (#43 vs #99 of 179 medium speakers, 3.7/5 vs 3.1/5) but is discontinued, so only consider it used; the Sony ULT Field 1 is still sold new at $138.
The EarFun Uboom Slim is the better-sounding, longer-running option. A slim, affordable waterproof stereo speaker with long battery life that doubles as a speakerphone. It is rated for 16 hours of battery against 12 for the Sony ULT Field 1. It keeps a wired aux input, which the Sony ULT Field 1 lacks. It plays in stereo from a single unit, unlike the Sony ULT Field 1. Watch for: Not as deep bass as others.
The case for the Sony ULT Field 1: A tough, waterproof small speaker that survives drops, with long real world battery life and stereo pairing. It supports AAC Bluetooth, which the EarFun Uboom Slim lacks. It has an adjustable EQ, which the EarFun Uboom Slim lacks. The tradeoff: Upper midrange peak, rolled off treble.
Buy the Sony ULT Field 1 if you want one new; the EarFun Uboom Slim is discontinued, so only look for it used.
Looking for alternatives? See the complete Portable Bluetooth rankings.
Prices on this page were last checked November 7, 2026 at 7:34 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.
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Specifications Side By Side
| EarFun Uboom Slim | Sony ULT Field 1 | |
|---|---|---|
| Price | $79 Discontinued | $138.00 |
| Ranked | #43 of 179 in Medium Size Portable Bluetooth Speakers | #99 of 179 in Medium Size Portable Bluetooth Speakers |
| Bass Extension (-10dB) | ~63Hz | - |
| Battery Life | 16 hours (Manufacturer specified) | 12 hours (Manufacturer specified) |
| Power Input | USB-C | USB-C |
| Stereo | Yes | No |
| Omnidirectional | No | No |
| Weight | 1.2 lbs (560 g) | 1.4 lbs (650 g) |
| Bluetooth | Yes | Yes |
| Bluetooth Codecs | SBC | AAC, SBC |
| Bluetooth Version | 5.2 | 5.3 |
| Built-in Microphone | Yes | Yes |
| Drivers | 45mm speaker drivers | 83mm x 42mm woofer, 16mm tweeter + passive radiator |
| Amplifier Power | 20W | - |
| IP Rating | IPX7 | IP67 |
| Digital Aux Input | No | No |
| Dimensions | 2.6”H x 7.1”W x 2.6”D (65 x 180 x 65 mm) | 8.1” x 3” x 3” (206 x 77 x 76 mm) |
| App | No | Yes |
| Aux Input | Yes | No |
| EQ | No | Yes |
| TWS | Yes | Yes |
| Party Mode | - | Yes (Party Connect up to 100 speakers) |
| Power Bank | - | No |
| Strap | - | Yes (detachable strap) |
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