Originally Posted by tsloms
After having designed and built several horn subs including BF's THT, Tuba 30, and Autotuba I am definitely a firm believer in using good quality 1/2" ply and brace it properly. The end result is an enclosure that is vibration free and still built as light as possible. Using the 3/4" ply will create a larger enclosure due to the thicker wood which eats up volume and also vibrate more especially with the unsupported wide panels.
I've built and tested several of the BFLD cabinets, as well as a bunch of my designs. I have no problem using thinner ply for cabinets not designed to play low, or cabinets that are not designed to use a large driver. The F-20 uses a large driver, and plays low.
I used 1/2" plywood with the Anarchy/Insubnia, the Example Tapped Horn, the Shopsub, and the upcoming T-6, as well as nearly all of my prototype builds and a PA sub design I did. I don't disagree that a braced 1/2" cabinet is an adequate solution in most cases, provided you use good ply. Braced cabinets are, in my opinion, an absolute pain to build, so I avoid bracing in cases where it is not necessary.
I have built far more horns out of 1/2" material than 3/4" material. In my opinion (based on my experience), when hanging a driver the size of the MFW (or the Shiva X2 or Tempest X2 for that matter) off of a baffle panel, the added strength of 3/4" thick ply is more than worth the additional weight/cabinet volume. Weight is a secondary concern. These cabinets are not PA cabinets that need to get moved twice a night, they are home theater cabinets that are typically set in place until the next upgrade.
I personally draw the line at 12" drivers. I will not use 1/2" ply with 12s anymore unless it is true Baltic Birch, and won't consider it at all for a proper sub. Even with full bracing throughout, I've had some 15" PA subwoofer cabinets move around under their own power when constructed with good 1/2" ply. There is a reason that most manufactured sub cabinets use 3/4" ply.
In this case, I wanted to keep things as easy to build as possible, so I decided to try an unbraced cabinet. Based on my measurements, I'm of the opinion that with good ply, I got away with it. With cheap ply, it might make a difference, but only at really high levels. Moral of the story? Use good ply.
For me, this effort was about designing and sharing the simplest to build bass horn that would provide reference levels at 20 Hz, and be no more than +/- 3 dB for at least two octaves above the low corner without requiring corner placement. I chose to work with the MFW-15 driver because it is arguably the best "bang for the buck" 15" driver right now, and it happens to be a pretty good fit in a horn.
I want to be clear, this effort was not at all about designing the best ever 20 Hz bass horn, I wanted to share something that anyone with a circular saw, router, and a screwgun could make in their own garage. This is not a complicated build. I chose this path for a reason.
If someone wants to add bracing, LTD02 offered some good suggestions, and I added to them. I'll be completely honest though - I do not feel it is worth the additional effort and frustration with this build, just use good plywood.
Would I brace 3/4" material when spanning widths over 18"? Absolutely.
Will I ever use 1/2" ply (braced or otherwise) for another large-driver sub cabinet design? Absolutely not.