It seemed to increase bass in all speakers. I turned mine all the way up, set the bass in the radio to +2 and turned loudness on. Mine seemed to have a lot of low bass (rattle your teeth bass) from the factory but no midbass (tight tump). The adjustment seemed to help with the midbass more. If you take the loudness off it takes away the low bass.
By the way, it took me about 10 minutes max start to finish. When taking the aft plastic out (the one that the net is mounted to) pull UP as it has snap fittings that will only release up. Someone may have said this but I missed it.