You will need
- Headphone amp
To make headphones louder, get an inexpensive headphone amplifier. Such a device is suitable for almost all standard models and is quite inexpensive.
Check the connection of your headphone's 1/8 or ? inch Jack. If your headphones connect via mini Jack, you will need to buy an adapter. Maybe he was even attached to your headphones, you should check their equipment.
Turn the volume knob on your amplifier to zero and connect it to the headphones. And to the amplifier connect the sound channel player or computer.
Turn on the music and gradually increase the volume on the amplifier until you reach the desired volume.