soundcore Sleep A10 does not support active noise cancelling (ANC). If the passive noise reduction is not working as expected, there are several ways to improve the passive noise isolation effect.

1. Choose the right size ear tips and wings.

The ear tips that come with Sleep A10 are available in different sizes. It is important to choose the right size that fits your ear canal snugly. This will help to create a better seal and improve the passive noise reduction effect. 

2. Enable the Smart Volume Control.

After Sleep A10 detects that you have fallen asleep, your phone will automatically adjust the sleep sound's volume according to the level of external noise. If the Smart Volume Control effect isn't up to scratch, try a different size of ear wings and ear tips. 

3. Make sure you are wearing them correctly.  

By following these tips, you can improve the passive noise reduction effect of Sleep A10 and enjoy a more peaceful sleep.