Hello

According to a test I saw, about 100db at full power. However, it can be operated in ECO mode, then it still reaches 70db.

Greetings

The Dyson V11 is SIGNIFICANTLY quieter than all Dyson cordless vacuums so far. It's not just the volume, but also the more pleasant sound (less shrill). The fact that you normally run the V11 in Auto mode makes it quieter (so it adjusts the power to the floor conditions and knows when to give more power and when to give less).
My "old" Dyson V6 was much louder and the battery lasted just enough for a quick round through the whole flat.
The V11 is quieter and vacuums better (also because of the wider floor brush) and the battery would probably last for 2-3 rounds through my flat! The display also informs you when you need to wash out the filter and gives instructions (remove filter, rinse with water, let dry, done etc).
The big disadvantage of the Dyson V11 is its much heavier weight - this is noticeable and for people with weak wrists, it is necessary to change hands frequently from left to right. I don't have a problem with that, because it is still much easier to handle than a "normal" hoover that is hooked up to electricity.
Despite the higher weight (and high price), I would buy a Dyson V11 again in a heartbeat!