Is there a way to make the air purifier's maximum noise level lower?

It’s not a question I can answer with a simple yes or no. Before I answer it, I’d like to explain why air purifiers are often designed with a certain level of noise which is normally considered noisy—rather than being made as quiet as possible. 

First, the discussion above refers only to normal aerodynamic noise. Abnormal noises like bearing rattle should always be avoided in good design. 

The main source of noise in an air purifier comes from air being accelerated and colliding with itself. For a given fan, the higher the rotational speed, the greater the airflow, and the louder the noise.

Suppose Fan A:

• At 2,000 rpm, airflow is 100 m³/h and noise is 50 dB;
• At 3,000 rpm, airflow is 150 m³/h and noise is 58 dB.

Now suppose we replace it with a better fan, Fan B:

• At 2,000 rpm, airflow is 100 m³/h and noise is 48 dB;
• At 3,000 rpm, airflow is 150 m³/h and noise is 56 dB.

Under the same conditions and air flow output, Fan B is 2 dB quieter than Fan A. 

So if we put Fan B into an air purifier, will the maximum noise level be reduced? This sounds counterintuitive, but usually the answer is no.

To give users the greatest freedom of choice, designers typically push the fan’s maximum speed as high as possible, bringing the maximum noise level close to the regulatory limit—this allows the purifier to deliver the highest possible CADR (Clean Air Delivery Rate) when needed. 

So, if Fan B can achieve the same maximum airflow as Fan A with lower noise, the designer won’t simply lower the purifier’s maximum noise. Instead, they’ll raise the speed limit of Fan B until the noise once again approaches the regulatory limit. The end result: the maximum noise stays roughly the same, but the maximum airflow increases.

Thus, the key question isn’t whether the fan itself is quiet enough. Rather, it’s whether—it can be adjusted to a noise level that you find acceptable—and also the CADR and the price of the unit meet your expectations. 

From this perspective, the AirFanta 3Pro is one of the quietest air purifier in the world. If you spend the same amount of money to buy several 3Pro units and several units from other brands—keeping the total cost equal—and set both all to the same CADR, the 3Pro will have the lowest noise level. 

So, the answer to the question is:

AirFanta 5Pro and 3Pro can be adjusted to very quiet noise level and still can deliver a large amount of clean air.