Hello, thank you for your review. The most common cause of sound degradation is a dirty headphone filter. This defect may not be visible at first glance, but you can easily find it by removing the filter from the headphones and listening to the headphones. They will play as loud as new.
You can replace the spare filters that are included in the package yourself without losing the warranty. Changing the filters is also suitable for hygienic reasons. therefore, we recommend changing the filters every six months.
If you need advice on anything, write directly to the manufacturer at
[email protected], they will be happy to advise you on everything. Thank you and have a nice day, Ondřej - Alza expert