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various other items
DuraTex is the best durable enclosure texture coating around. Roller-grade DuraTex and the 4" texture rollers are the way to go if you want to do a cab or two with little trouble and easy cleanup. It's also superior later on, for touch-ups that blend right in with the original application coating. If you desire a custom color it can be had from its maker, AcryTech. Or you can get it in custom tinted from them, after selecting the shade you want from sample chips or color codes available there. Consult with AcryTech and say greenboy sent you.
DuraTex gives more protection with fewer coatings and less weight without having to deal with solvents and long-term toxic out-gassing. It also looks great even if you are a novice at this and bonds incredibly well to any decently prepared surface. Many commercial enclosure companies use DuraTex, as have many DIY builders. One gallon can typically do three full coats on a 15/6 and leave enough extra paint in the bucket for another 2 to 3 cabs and some touch-up work when/if bad scratches or gashes offend. Some people do a primer undercoat with cheaper flat latex to use less Duratex, and many use flat or satin interior/exterior latex for the port interior and baffle in place of Duratex.
PL Premium glue
There's no stronger glue for woodwork. This stuff is also great because it will fill gaps without running and can provide airtight seals where needed without additional caulking. Thus it simplifies the cutting and build process for those with less-than-perfect tools and skills. No toxic solvents involved, sands easily, can be built up in beads/fillets along joins on the interior - multiple times if desired - to get additional glue surface and seal. Because of this and its incredible bond strength, butt joints on 1/2" (12mm) panels can be used everywhere without any fEAR for structural integrity or long-term durability. Image below exaggerates amount of glue needed just to illustrate how joins can be built up and sealed.
For clean-up or for working it, it's nice to have some latex or cotton-yinyl gloves, and a putty knife or three around, and/or a wide screwdriver, or some disposable plastic knives. Also helps to keep some rags handy to smooth beads and clean up any drips. PL Premium can be worked into shape for a short amount of time before it begins to harden, and dragging one of the above-named implements along an inner join edge at an angle makes it easy to do this like caulking after doing the initial flat-run gluing on the two surfaces that will be joined.
It's also available at many home improvement and building stores locally. Here's the technical data & instructions pdf.
Bondo or Plastic Wood
If using a brad nailer or screws to suck in surface-glued joins for tight bonding, you may later want to fill in and sand over the heads after everything is dried, and go over any exterior panel joins as well. Bondo is probably the best for this.
DAMPING: lining for ported enclosures
Lining most of the interior of a ported enclosure with damping material is desirable because it minimizes midrange reflections coming back at the cone and combining destructively with the cone's output. That causes causes nasty peaks and scoop-out valleys in the response and makes a signal seem not so time-aligned. Don't want that. Lining the inner surfaces makes the lower frequencies seem more even too, by focusing what one hears of the midrange frequencies, and the general effect is to make the speaker cabinet respond more accurately and pleasingly.
Materials? Acoustic fiberglass has often been used, or even less dense but thicker home insulation. But after decades of using acoustic fiberglass to line enclosures I finally decided it too unpleasant to work with. Now I use either a dense 1"-thick polyester batting that can usually be found in fabric stores, or "egg crate" open-cell foam of acoustic density. I've even lined enclosures with alternating patterns of poly batting and open-cell foam simply because I had some of each around but not enough to finish out a box in just one type.
At the minimum, a single layer of 1"-deep batting is generally sufficient on the top of the shelf, the back and sides of the midrange chamber, and the top panel, with a double layer on the back wall and perhaps also doubling up on the side panels. Make sure you leave some free space behind the shelf area so as to not obstruct port functioning, though. With egg-crate foam I'd be happier using the 2.5" thick product, but some people might think the 1.5" depth is enough, perhaps.
To damp more effectively with batting I might overlap in more areas, to get the average thickness up to 2.5" or even 3" or beyond. Conversely, with the 2.5" egg crate foam, you also add some non-eggcrate foam behind it on the back joining them with light application of spray glue, or by using a thicker Auralex product... I've sometimes listened to cabs and then went back inside to add damping in some spots. One can also finishing out any open areas on the interior of the baffle to knock back reflectivity more.
Too much or too little? Let some experimentation and critical listening help you decide. I have found though, that some of the "mattress topper" stuff found in big box stores isn't the best choice. Something about its makeup or density seems wrong. I do hope to give a try to some of the non-fiberglass batting in the near future, presumably made of reclaimed, treated denim. It seems to have a very good absorption coefficient.
Also note that the 1212/6 and 1515/66 dual-woofer enlosures can benefit from batting or foam on that cross-bracing running from front to back and side to side between the two woofers. Here's how. Cut two shape-fit mats. Then spray a moderate amount glue on the top and bottom of the cross-bracing, and lightly on the damping mats. Next press one mat onto the cross-bracing and then press the second mat in from underneath using the lower woofer hole for access. Compress each mat into the other. This will affix the the two mats to the cross-bracing and hold them together while still allowing free air passage - provided the glue on the mats themselves isn't sprayed too thick and too wide. You don't want to clot the porosity.
I do favor using aerosol glue to affix batting or foam, over other methods I've tried. Locally available at fabric or upholstery shops or home improvement centers, products such as 3M Super 77 or other cheaper spray adhesives are a nice alternative to staples - which often end up tearing through the batting or rattling around inside the enclosure until stuck to driver magnets. That said, brushed-on contact cement will also work well, though to me it's not as quick and convenient. Other glue products probably will work too, though some are not going to be so easy to deal with.
The spray glue method also makes it easier to layer damping materials, and it's easy to remove and re-use damping should you wish to move crossover boards or add some more bracing cross-members. Inside the enclosure itself, with some protective cardboard or newspapers down on the floor if you are not so graceful with your spray positioning, spray lightly on both surfaces and let it tack up a bit before firmly pressing the damping to the panel so that it sets positively. You don't need to go crazy. The damping products don't weigh much; as long as you've pressed tacky glue surfaces to each other and let them "set" they tend to stay in place.
DAMPING: fill for closed chambers
The Midrange Chamber of any fEARful also needs to have damping. The correct method in this case is not to just line its interior walls, but to also stuff the chamber liberally with polyester fill right up to the driver sides and back so that waveform reflection is minimized yet the driver's cone is not obstructed. One can apply a little spray adhesive strategically so that it conforms well yet doesn't leave much free air space. It can press against the driver motor as long as it is not heavily compressed to the point where it would be densely "fighting back". You want enough to really fill the area without any trying to go back into the backside of the driver's cone.
One could purchase polyester "pillow" fill... but I just tear/shred some poly batting I already have and wad it in until I have a good moderately dense but fluffy. Alternately, one can line the mid chamber first with open cell foam as I've done sometimes, and then complete the fill/stuffing process with the polyester product. Or, if you have sufficiently deep acoustic foam, you can even cover all internal surfaces and then bring additional foam right up to the back and sides of the driver.
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