I don't care so long as you guys try to make your arguments informative. Here are a couple of articles on the subject:
Loudspeaker Cabinet Bracing and
Myths and Facts about Loudspeaker Cabinets. For subwoofers, I would say so long as the cabinet is strong enough and doesn't have any audible resonances, it doesn't matter what you use. That can be achieved with any of these substances. My understanding is that panel resonances tend to be more problematic at higher frequencies than what subwoofers normally do, and there may be a slightly stronger case for MDF in tower speakers. I think any of these materials are just fine for subwoofers, and the audio performance differences between them is an academic matter that doesn't have any real-world consequences. HDF and Birch may be more preferable if you want a subwoofer or loudspeaker with a more robust cabinet. Personally, I want a subwoofer with a carbon-fiber enclosure- that would be pretty cool.
