I'd like to build a small, reasonably light and reasonably portable sub that I could use to test various environments for low frequency response and appropriate sub location and acoustic treatment. Ideally, I'd like flat output down to around 10~15Hz at a reasonable level, say 75~80dB. I'm thinking small sealed cube with Linkwitz-Transform and modest plate amp, and possible a purpose built active EQ circuit after near-field measurements if the response isn't flat enough. In other words, I'm looking to put together a portable "reference" sub for room setup and calibration. It doesn't seem like a PR design is appropriate, but I'd appreciate any thoughts in case I'm heading down the wrong path.