ported box question

[Unkle Dave]

i recently built a ported box for two 10'' sundown subs. they were in separate chambers. with all my inputs winisd gave me a port length of 21in. that box came out great it sounds awesome. 

now my question is. if i build a ported box with a common space. and i get a port length of 21in. would both of my L's add up to 21inch or each L would be 21in?.

 

thanks

[Triticum Agricolam]

It needs to be 21" from the the outside mouth of the port to the inside mouth, measured down the centerline of the port.  If the port splits inside the box it still needs to be 21" end to end. 

[Unkle Dave]

okay thanks got it