We've been offering these ports to our dealers for years, now you can purchase them direct!
 
These ports work great in small enclosures like OEM bags or speaker tourpacks, the size allows them to mount in a ton of locations. The size of the opening roughly equates to a 2.5" round port and they come 6" long. We've done some rough calculations to help you get started
 
@ 6" length
.45 cubic feet - 61hz
.50 cubic feet - 58hz
.55 cubic feet - 55hz
.60 cubic feet - 53hz
.65 cubic feet - 51hz
.70 cubic feet - 49hz
.75 cubic feet - 47hz