? about box calculator / tune

Hey I ran across this www. Hometheatershack web site while searching for box calculators as I am trying to figure out what to build in my truck. Has anyone used this place by any chance. I am curious how accurate it is.

Also. This may be a noob question but after I figure up my box and port volume how do I determine what the box is tuned to per say. J ust because I have the correct overall volume in my box with the port does it mean it's to the correct specs. On the sa 8 it wants .5-.75 for ported witch of those would be more for sq - spl Is this .75 ported for spl and the .5 for sq

I have always been told to tune my box in the 30s but how is that number determined thanks for any help. I am trying to learn the correct ways on how to do the box building

Does this help at all?

Subwoofer Enclosure Calculators, Fraction to Decimal, Parallel, Series, Port Length and Volume Calculators

Ok after more searching I found on another site I select my speaker perameters and what not it tells me the length of my port to make a certain 35 hz - 40hz I enter
Box volume and hz i desire and what not

What do I do if i can not get the .75 the speaker diagram shows with the area I have to build my box can i go to a .9ft3 or would that be bad. Thanks for the site above I'm sure it will come in handy on my journey

Your sub manual tells you what to tune the enclosure to. If you use a different size box than what the manual states then your port length is going to change.

The manual say .5-.75 ported the smallest i can make tuning 35hz is like .9 I didn't know if that would be bad since they suggest .75