Fostex Lab series 18" sub cabinets

Hello everyone, I'm new to the Free speaker plans family. Glad to be a member. I've owned and operated my sound co. for 17 years and have built my fair share of enclosures over the years. I am a Turbosound user and have a decent inventory but I recently ran across 4 Fostex Lab series 18s and I want to build some bass reflex double 18 cabs for them. I don't have any of the values for the speakers so I'm not sure about the port dimensions. I do know they are a double spider design like Gauss models but the cone resembles JBL 2245's. I was thinking of starting with the JBL plans and adjusting the port lengths if need be. Any suggestions? ideas?

There are ways of measuring the T/S parameters and at least one site on the web which has an online calculator. It basically involves doing an impedance vs frequency measurement in free air and in a known test enclosure.

If you just did the free air measurement you would at least be able to find out the driver resonance. Generally if you then tune the port to the same frequency as the driver fs then you'll be fairly close.