The phrase "acceptable level" means something that is considered satisfactory or suitable to a certain standard or expectation. It implies that something meets the minimum requirement or criteria for being deemed acceptable. Full definition
The team will determine acceptable levels of risk, and coordinate risk management activities for the district. (nsba.org)
Around the back you've got a single speaker and a tiny hole through which it'll play sound at acceptable levels for an very small space. (slashgear.com)
Don't get me wrong, it is a huge improvement over plain HTML, but it is nowhere near for what is the minimal acceptable level for printed books. (safaribooksonline.com)