I Have two sa12's on saz-1200d in a ported box @38hz its a hammer to the chest loud .. only problem its lacking low end.. box is 4 cubes total.. I don't want to give up much of that ear drum pounding that it has now but pick up low end would going to 35hz be a good change.. an would the box size need to go up or down ?

EQ down the peak (to simulate a lower tuning) and see if the overall frequency response is more to your liking. If it is, than just keep the setting or build a new box. you can find the recommended enclosure size on sundowns website probably. if you keep the same NET volume and tune lower the port will be longer and the overall size of the enclosure will have to increase. 

How would I go about downing the eq peak ?

The eq on my head unit only goes down to 40hz

if you have an android phone download funcgen and play test tones at 30, 40, 50, 60, 70 hz and compare the relative loudness at each of those points. you can download these tone somewhere else or if you have an iphone there is probably another app. so if you see that 40hz, for example, is louder than lower and high frequencies (or a peak in the subwoofer's frequency response), eq it down. 

Edited March 3, 201411 yr by lithium