The speaker is fine, it reminds me of the iphone speaker at the bottom. The way you hold the phone can also make it far more effective just as cupping your hands around your mouth to shout!
Nice knowing that setting the phone down on the table isn't going to muffle the sound!
I have experience in pro audio reinforcement/music production and sound is important but as previously mentioned it's ludicrous to expect a room filling sound from a transducer smaller than most tweeters on speaker systems!
If you want something to fill a room, check out the UE bluetooth speakers.
The mods will increase gain however the driver has absolute excursion limits as well as its driving amp and pushing the levels higher just results in compression and nasty distortion just like cranking your stereo amp into clipping. It won't damage your phone but sounds horrible!