ermm... if i reduce the volt input gain further i cannot achieve any more bass.
it is perfect for most of the songs... but only a few songs that has really deep deep... and getting low and low... it will happen ... it doesn't has sound, but u'll see it blup blup... the lower i set my built in HU equalizer like +1db at 10-30range it is more severe!
well, i've try to overcome this uncontrolled vibration for days... changed to a thicker wood box (less than 1cm to 0.75inch) change the port length longer(3.5inches to 10inches). and i achieve a very good result. but still certain part of the songs will occur.