1.5" on the driver baffle(s) is fine, along with .75" walls, assuming enough bracing is used. For a sub enclosure, tight matrix style bracing is overkill, but any unbraced surface longer than 1' long is insufficient IMO. So, for huge enclosures, a spaced out matrix brace may be necessary...but it really all depends on the how high you intend to cross them over.
Also, exterior scrap 2x4's can work good.
Another thing that can help is the use of push/pull or push/push style manifolds where the driver's vibrations cancel out.
Also, exterior scrap 2x4's can work good.
Another thing that can help is the use of push/pull or push/push style manifolds where the driver's vibrations cancel out.
