Do you know a simple sound booster app for Mac?
Is there an app to amplify sound output on Mac OS X, I've put the volume to max and it's still quiet.
Boom is a simple program that does nothing except boost the system volume past its maximum. It can also increase the volume of audio files, although iTunes can also do this. It does cost money, but only $5.
VLC can boost the volume for stuff played through it by 400%. Your internal speakers might not like being pushed that hard though. You could also try the preamp on the iTunes equalizer. To use the equalizer, in iTunes, click Window > Equalizer and slide the preamp slider upwards. Also, for a system-wide solution there's Audio Hijack but you need to pay for the full product.