The Soundplane 8x8 is a force-sensing surface you can build yourself. It's made from wood, rubber, copper and plastic. It's entirely passive, meaning that there are no electronics inside that require power. Instead, an eight-in, eight-out audio interface along with DSP software is used for sensing and calibration.
Please see the NIME 2009 paper, written by Randy Jones and colleagues at the Univeristy of Victoria, for more information and construction tips. If you have questions, feel free to get in touch via our forums.
The software requires Max/MSP/Jitter to run. The Max/MSP/Jitter SDK is needed to compile it. All of this software is Mac only, but should be easy to port to Windows. I'm releasing it under the MIT License, which basically says: reprinting or use of the software must be attributed, and the software comes with no warranty.
There is a lot of tolerance in various parts of the design, including thickness of materials. If you can find something close to what is specified, try it!
If you are excited about making any kind of multi-sensor controller, starting by making a single-sensor version is always a good idea. This will allow you to get a feel for the materials and techniques and the work that will be involved in creating your 64 by 64 point dream surface. And, if you decide to go no further, a single-point pressure sensor is actually a useful thing to have.
For more history, theory and ideas about how to connect a sensitive surface to physical modeling synthesis, you can also read Randy’s M.Sc. thesis Intimate Control for Physical Modeling Synthesis.