Help understanding this page of a JBL enclosure guide

[d123]

Hi,

I want to build a cabinet for a single JBL2245. This page from a JBL enclosure guide is confusing to me. Could someone tell me how to read the duct info for #11 (a single 2245 cab)? I don't understand the Equivalent duct tube and ID column. I understand that ID is the inside diameter of a tube, but what is the number in parentheses?

Thanks, Dan

Here is the page:

67625

[Flaesh]

Hi,

what is the number in parentheses?

Six tubes 4" ID = 75+ sq. inches vent area

[d123]

Thanks much.