What app make a iPhone 4 louder?

What app make a iPhone 4 louder?

The loudness is decided by the hardware. Software cannot increase it.

The best thing for you to do is to set the EQ in the settings app to Loudness. That doesn't help overly much and makes audio not as clear. If you were to jailbreak your iPhone, the Cydia app store should have a couple of tweaks that you can install. Some tips when just normally using an iPhone: cup your hand around the speaker.

Just set your EQ to max.