I have written a piece of software called Driver Parameter Calculator, or just DPC. The development started while I was a student. It came into use at Dynaudio as a simple T/S tool for transducer development and later at Scan-Speak and SEAS. It is available here and at Brian Steeles web pages. It utilizes the simple Thiele-Small loudspeaker parameter model to calculate unknown parameters from a minimum of known parameters. Loudspeaker parameters is an advanced topic that I work with at Dynaudio as well. The simple DPC is nice for recalculating drivers, when certain parameters are changed. The list of parameters is very complete. Almost anybody, even hard core loudspeaker dudes, can learn something from the parameters build into this piece of software.
Besides the simple Thiele-Small parameters, it can also assist you (the DIY speaker builder) in measuring loudspeaker parameters, and you can pick between the normal two methods (added mass or closed box). With the closed box method it uses a slightly improved Thiele-Small model where leakage loss is included, baffle load can be included as well, so you should get some really nice and reliable data. In DPC everything is documented, formulas, theory, everything. A newbie in loudspeakers could learn a lot from the documentation. DPC supports any kind of units you would like to apply - and files for the UK and SI units are included. Take a look at this powerful little calculator, download DPC061.EXE, the version 0.6.1 installer package, compiled for Windows only (438 kb).
The software has not been maintained since 2004. It runs fine on Windows 7 and Windows 10 but beware that the files you save to disk gets stored in user\AppData\Local. I should mention that, as I later came to work for Scan-Speak, we also use the DPC software on a regular basis. I have introduced the software at SEAS as well. I have been informed that DPC is also used regularly at Audio Technology, as well as Wilson Audio (sometimes, for double-checking) and other places in the industry. Thank you for your kind feedback.
You can also download the version 0.5.0 archived as a ZIP file, DPC050.ZIP, with the installer package, compiled for Windows only (1 Mb). You can also download DPC049.EXE, the version 0.4.9 (for DOS) archived as an LHARC compressed, self extracting file (180 kb). Alternatively, check Brians DIYSUBWOOFERS page(s).
The manual for DPC release 0.6.1 is available online. Please check it out.
P.S. The section of the manual that deals with distortion in a loudspeaker cabinet was inspired by Kyle Lahnakoski. The link in the manual is out of date. You can find Kyles work here (on archive.org): Distortion. Check it out. There are other goodies in there.