Found these calculators on line & they seem to be accurate.
I worked backwards from what I want to achieve....so, I determined that the 620 cabinet box tuning is 40Hz by entering the slot dimensions & changing the tuning frequency until I got a slot length of 3/4".
Then I changed the slot dimensions until I got a slot length of 1&1/2".
From my calculations, with a front baffle 1&1/2" thick, I should need a slot of 11" x 3" to maintain the original 40Hz tuning.
The second attachment shows the results when using a round port.
For this you need 2 x 7.9cm ports 1.4" long......or 1 x 6.5" port 1.4" long.
I prefer to use the rectangular port option to maintain the original look of the cabinets.
Cheers.
Bookmarks