Different kinds of product: one is active with its amplifier built in, the other passive and needs one. Judge them on how you want to own the system, not just the specs.
| Area | Better | Why |
|---|
| Bass | A | Polk R700 digs deeper - 38Hz against 43Hz. A subwoofer would even that out. |
| What you buy | depends | ELAC Navis ARF-51 is a complete system - just add a source. Polk R700 also needs an amplifier: more money and another box, but you choose it. |
| Connections | depends | ELAC Navis ARF-51 has Bluetooth built in. With Polk R700 that all comes from the amplifier you pair it with. |
| Upgrade path | depends | Polk R700 can be re-amped later and outlive several amplifiers; ELAC Navis ARF-51 ages as one unit. |
| Size | depends | ELAC Navis ARF-51 is easier to place; Polk R700 is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | A | Polk R700: bi-amping. Polk R700 sits in a wider range (10 models), so a matched surround system is easier later. |
| Price | A | Polk R700 is cheaper - $2,198 against $3,798, about 42% less; arguably a different class. Speakers only - an amplifier narrows that gap. |
A Polk R700 B ELAC Navis ARF-51
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both speakers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
ELAC Navis ARF-51 suits you if you want one box, ready to play, with nothing else to buy. Polk R700 suits you if you already have an amplifier, want to choose the electronics, or expect to upgrade in stages. Neither is the better speaker in the abstract. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 43Hz anyway, so judge these on the other rows instead. In a large or open-plan room, Polk R700 has the cabinet volume to fill it more easily; in a small room, near a wall or at desk distance, ELAC Navis ARF-51 is the easier speaker to get right.
And remember what a spec sheet cannot show: how each looks in your room and whether the finish suits it, what dealer support and warranty are like where you live, and how they actually sound to you. If you can hear them first - ideally with your own music - that will tell you more than any number above.