Volume Boosters and equalizers usually have little effect, on a stock phone there is little you can do to boost the volume and most newer phones have lower headphone volumes purposely for "safety" reasons, with the notable exception of many HTC devices.
To get significant improvements in volume you would need to root or install a custom ROM... there are multiple audio enhancements that can be done to improve volume at that point, such as Viper4Android, Xposed modules, or just ROMs custom build for improved sound quality and volume.