carnc1

Face veneers on most cabinet plywoods are extremely thin these days (as in <1/64" (looks like the new heritage veneers are even thinner), so you have to be real careful with them while sanding or cutting. A random-orbit pad sander (not disc-sander (too aggressive)) is ok to use (be very careful, or hand-sand near edges and corners). My standard way of finishing birch plywood with oil-based polyurethane (durable): sand with 220 if needed (plywoods are "sanded" to begin with), 320, 400 (optional) (I generally don't use steel-wool on unfinished wood, it easily snags in the grain, depending on the wood) apply a coat of minwax pre-stain "wood conditioner" (this is optional but tends to eliminate blotchiness), wipe off (this replaces the wiping the dust off with mineral spirits step) something as large as a speaker, I have an inexpensive gravity-fed spray gun (medium size cup on the top), and I take things outside, fill the cup with polyurethane and spray 2-3 light coats, sanding with wet/dry 320 grit and mineral spirits between coats. On a warm day, or room, these polyurethanes will dry in a couple hours enough for re-coating. The sraygun is easy to clean, pour in some mineral spirits, spray. The oil-based poly is not too obnoxious, like lacquers (having acetone, toluene etc), but wear a respirator. Oil finish (tung oils, Minwax "antique oil" etc), is easier to apply, but not as durable, also easy to repair. The main issue is with tops, where water or alcohol will easily stain oil finishes. Sand as above wipe off with mineral spirits dampened rag apply 2-3 coats by brushing and wiping off. Apply two coats of paste wood wax, buff. Agan, have to be very careful with the thin veneers used.

I just purchase a set of new Forte III's on sale (distressed oak, lambswool linen grills) (love-em so far!). Don't know if your grills are lambswool, but there's an instruction card that states "...remove the grills from the speaker and simply dampen the grill cloth with water from a spray bottle. This will restore the cloth to its original tension. The material may be more sensitive in dryer environments, requiring more maintenance". (I'd use a very fin mister bottle, those grille supports are not "waterproof"). How do those sheep keep from shrinking up out in the rain...