Much like new speakers or a new car, some headphones need a break-in period. That is to say that before delivering maximum performance, they require time to adapt. The best way to do this is to leave the headphones plugged in on their own, with music playing in a loop and/or pink noise. There is no "standard" duration, but you can assume that at least during the first 20-50 hours of listening, it will not be at its maximum quality level. Do not hesitate to do this break-in in successive volume steps, rather than subjecting it from the start to high volumes, which could have a negative effect.