Sealed Box: poly fill, egg crate foam or both? And Finishing Question

[greg77543]

I'm building a pair of kit sealed box LS3/5a clone speakers. The kit is supplied with egg crate foam for interior walls. I thought sealed box speakers all needed loose poly fill of some sort. Should I use egg crate foam, loose poly fill, or both? And if poly fill is needed, what type/brand do you recommend, and what amount?

Another question: these will be built with a traditional birch ply cabinet. What do you recommend for finishing the birch ply as far as stain, sealant, etc.? I'd like to keep it in its natural color or slightly darker at worst

[Bear]

I'm building a pair of kit sealed box LS3/5a clone speakers. The kit is supplied with egg crate foam for interior walls. I thought sealed box speakers all needed loose poly fill of some sort. Should I use egg crate foam, loose poly fill, or both? And if poly fill is needed, what type/brand do you recommend, and what amount?

Another question: these will be built with a traditional birch ply cabinet. What do you recommend for finishing the birch ply as far as stain, sealant, etc.? I'd like to keep it in its natural color or slightly darker at worst

I don't know about the efficacy of egg crate foam. Polyfill (and variants) are what is generally used as the standard when looking at fill for sealed cabinets. Wool is supposed to be even better, but expensive. Likewise, real wool felt is likely better than foam for lining the walls.

[Steve Manning]

As far as finish goes, if you use a waterborne lacquer you will not have much of an issue with the color of the wood changing. Something like this https://www.mlcampbell.com/product/a...te-plus-clear/

[JonMarsh]

Cabinet stuffing ideally varies in density with proximity to the enclosure walls. You could still use the egg crate foam, but for a small speaker like that, I'd recommend medium density felt liner, (say, 1/2" to 5/8"), and stuff with AcoustaStuff or long fiber wool. Fiberglass if you're on a budget.

And if you're not on a tight budget, then use weighted auto body sheet damper material on the wall first. Why? When you have the boxes built, tap the walls lightly. For a stiff cabinet, you'll hear a "ring" of sort well up into the midrange. You'd prefer to have the completely damped out as fast as possible. These days I wouldn't recommend lead sheet, BUT that works very well. These days they use damping sheet usually made of butyl and aluminum, such as Sonic Barrier (available from Parts Express and other resellers)

https://www.parts-express.com/sonic-barrier-ut-4-ultra-sound-vibration-damping-sheets-with-foil-155-sq-ft-315-x-181-4-p--268-040?gclid=EAIaIQobChMIxoO3kNT05gIVhK_sCh0TTQe5EAQYAyABEgJAsvD_BwE

[TEK]

For finish you could also evaluate Shellac. That will keep the woods natrual finish and darken it a little bit - depending on the color of the Shellac you get. It is very easy to work with if you just do a regular. You may also look into french polish if you want to get more advanced ;-)

Different variants of oils may also be an option if you are looking for a natrual look.

https://youtu.be/EDiN9TCZkHk

Many combines both oils and shellac with beeswax - probably for a more repellent finish.
The advantages of oil is that the are easy to fix if you get a chip, dent or scratch and has a very natrual look and feel. While paint/laqure make a
layer on top of the wood, the oil penetrates deeper into the wood.