There are some ways by which you can prevent sound leakage. These are:  1. Using a smaller driver size: The reason why earbuds aren’t prone to sound leaking is because of their smaller driver size. To ensure every single note is heard, try using closed-back headphones. 2. Transducers have a considerable bearing on sound leaking. It would be recommended to not use Planar Magnetic Transducer as these dissipate a lot of sound energy.  3.You can make use of foam or gel in the headphone to reduce the loss of sound.