I'm doing this mostly to absolve myself of all the people who are asking if I can build/sell them a measurement rig. I believe this project is the cheapest and easiest way to get reliable and precise measurements out of a headphone. BTW I reserve all rights to turn this into a commercial project and sell it for $199. What you need for this project: Digital interface (or mic pre) with 48V phantom power Single block of foam Square of creatology foam (optional) Square of felt (optional) Electronic parts Panasonic WM61 (or replacement) = $3.75 2N5551 BJT = $0.20 5V Zener diode - $0.19 ~100p ceramic cap = $0.20 10k resistor = $0.20 Small piece of protoboard 3 pin male XLR connector Misc. wiring Assembly: Start with the soldering. You should put together the circuit based on this schematic. Example layout This is basically the same cascode circuit used in John Conover's writeup (Figure XXXVIII) on the WM61. Advantages are: Stupid simple Low part count No coupling caps to limit LF response Extra gain takes load off the preamp Low distortion Disadvantages mainly include single-ended wiring, so don't run long cables to your input. I've never had a problem with a ~1m cable run into my pre FWIW. I place our transistor near the end so I can bend it off the board and our whole profile remains relatively flat. Securing the board can be easily done with tape. I do some crossbracing to keep it tight. The pre-soldered mic leads should be just about perfect to reach from the edge through the foam. If your foam is solid, just make a small slice with a thin blade in the center and slide the mic on through. Should look like this from the front: Here's what it'll look like in action with a creatology square: During usage you can lie it flat on a desk, or stack in sideways with some books or foam. Feel free to use different square materials for coupling, you'll get varying results therein. You can also use certain techniques to break the seal. It's still all a matter of looking at the results and interpreting based on what looks most indicative of actual performance.