The following description comes from the
Google Play Store
description of the app:
Simple, small, free app to boost your speaker or headphone sound volume. Useful for movies, audio books and music.
USE AT YOUR OWN RISK. Playing audio at high volumes, especially for a prolonged amount of time, can destroy speakers and/or damage hearing. Some users HAVE reported destroyed speakers and earphones. IF YOU HEAR DISTORTED AUDIO, LOWER THE VOLUME (but it may be too late).
By installing this application you agree that you will not hold its developer responsible for any damage to hardware or hearing, and you are using it AT YOUR OWN RISK. Consider this to be EXPERIMENTAL software.
Not all devices support this software. Try it AT YOUR OWN RISK and see if yours works.
There is also an identical Donate version if you want to support the developer.
NOTE 1: This app does not work on most Android 4.2.1-4.3 devices. It should work on Android 4.4 and higher, as well as on devices below 4.2.1.
NOTE 2: This is NOT for adjusting the speakerphone volume in phone calls (that has its own boost, I think), but for adjusting the volume of music, movies and apps.
NOTE 3: When you set the boost to zero, Speaker Boost will be off. The notification icon is just for ease of launching. If you don't like seeing the notification icon when Speaker Boost is off, just go to Speaker Boost's Settings and set it to appear only when Speaker Boost is running.
NOTE 4: Source code is at github.com/arpruss/speakerboost