I'm refurbishing a pair of 1968 Pioneer CS-33s and I want to make a whole new baffle with removable grilles, but this bass port has got me a bit flummoxed. Can anyone help me convert this into regular tube port dimensions and/or tuning please? It's 70 x 140 x 80 mm ...thanks!
If you know the port area you can input that to any cross-sectional area of a shape. For the tuning frequency you will need to figure out the internal volume of the box, Fb = (C/2pi)*sqrt(A/VL), where C = 344 m/s, A = area of port, V = volume of box excluding the port, and L = the length of the port.
It's not that complicated. As Hexaaa indicated you need the volume of the box and the diameter of the new port. From what I can tell the old port is tuned very high (around 100hz) If you want to duplicate you can use two 75mm ports 75mm in length. To tune to bottom of the frequency response use a single 75mm port 150mm in length.