I have read so many different opinions on what to stuff inside the sub. Perhaps they are all good? or better depending on what the enclosure is like?
I am building a 2.6 cu ft slot ported box with a down-firing driver (on legs-end table style). What do I want to stuff into it? and how much??
Buying cheap pillows and ripping the guts out of them for stuffing sounds cheap and easy. But does that loose fill settle around the driver and cause problems?
I read a post about using craft batting from the fabric store and lining the walls with a layer (or several layers?). This sounds like what I see in factory made HT subs.
Or any better suggestions?
You can do like 4 lbs of polyfill, or 4 cheap walmart pillows for a 4 cu ft box. Less is fine, but more is not. The more you damp it the more it will change the charecteristics, think of it like stuffing a bass drum a little. It gets "thud" more and resonance less. I've not stuffed boxes and they sound ok, I've over stuffed boxes and they sounded poor, and removing half the stuffing improved. I'd error on the caution of stuffing a little less.
Overall, stuffing or damping the inside of a subwoofer’s enclosure is generally a good idea to prevent the internal reflections inside of the enclosure from bouncing around and coloring the response and sound. If you are looking for the utmost in uncolored and well-damped sound or if you intend to use the system extra high in frequency up into the lower midrange, it is recommended. If you are trying to be as absolutely loud and efficient as possible, then leave it out.
Parts Express sells an Acousta-Stuf Polyfill that is extremely expensive. They must make it with pulverized unicorn horns or something.
I would suggest at the low frequencies subwoofers produce, stuffing an enclosure is unnecessary. In a sealed enclosure, polyfill can make the woofer behave as though it were in a slightly larger enclosure, but that's about the only reason to use it.
In a full range speaker, there are different advantages to using it.
I am building a 2.6 cu ft slot ported box ... What do I want to stuff into it?
You don't stuff ported cabs. It should be lined with a couple of inches of damping to prevent internal reflections of above bandwidth harmonics back to the cone and/or out of the port. Any of the usual materials (polyester batts, open cell foam, Type 700 glass) will do.