this may be old new but i figured i would share it anyway. i did some test using a sound pressure level meter. the meter was placed one inch directly in-front of the iphone speaker. i tested music, speech and multiple frequency levels both before and after i installed audio amp.The music was the first two minutes of Blue October's "You Make Me Smile" and the speech was a Disney Cinderella story. the measurements are the max spl level, dBA weight with a slow response. here are the results:

before i installed audio amp.

500 Hz...90.5 dBA
800 Hz...95.5 dBA
1250 Hz...100.5 dBA
2500 Hz...103 dBA
4000 Hz...102 dBA
8000 Hz...95.5 dBA
Music...95 dBA
Speech...94.5

after i installed audio amp.

500 Hz...90.5 dBA
800 Hz...95.5 dBA
1250 Hz...101.5 dBA
2500 Hz...103 dBA
4000 Hz...102 dBA
8000 Hz...95 dBA
Music...95 dBA
Speech...94.5 dBA

As you can see the only difference is a 1.5 dB difference at 1250 Hz. Otherwise there was no difference at all.

Like I said, it's old news but I figured you may like some proof...and yes, I do have too much time on my hands

I think there may be another tweak out there and I will try to do the same test(s) to see if that really makes a difference...that is if anyone cares.