Headphones Volume Booster and Bass Booster:Amazon.com:Appstore for Android
Headphone amplifier - Wikipedia
Improve your phone's sound: Headphone volume booster apps and more
headphone & EarPods Booster for Android - Free App Download
Amazon.com: eSynic Professional 16-300Ω Headphone Amplifier Portable Headphone Volume Amplifier Rechargeble Headphone Amp Desktop Amp With 3.5mm Jack & A Two-stage Gain Switch for MP3 MP4 Phones and Computers etc : Electronics