Foam Core Board Speaker Enclosures?

I have plenty of both, but working on the dining table the bottles were definitely closer!

(Most of the enclosures are all hot glue, but I ran out on the very last panel for that centre speaker and had to switch to PVA - and I had a bad panel gap from a sloppy cut, thus the clamp on the corner. Fortunately foam will bend to conform!)
 
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Thanks Jim,
Good to know - I can imagine that it is slow since it is not porous. Liquid Nails (non VOC) works well too. The box I made for my 10F/RS225 speaker is still standing and solid. I used a 3/16in thick subfloor plywood on the baffle face to allow the wood screws to hang the heavy 8in woofer. That was also bonded to the XPS with Liquid Nails (non VOC). The XPS box measures better (slightly lower THD) than the same box made out of 3/4in BB plywood. Important to use non VOC glued since solvents and their vapors will melt the foam.

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And, I'd like to try using XPS for something larger, say floorstanding single-fold tapered TL/horn 60L internal 20x116x26 (2cm boards) -- which size I had stayed away from due to mass/cost/difficulty. I assume it would have to be well-braced and weighed down with (removable) bricks, and the upper baffle "composited" with 1cm plywood for attaching (relatively light) drivers. Does this make any sense?

p.s. reading the FH3-inspired-mini-build-HOWTO...
 
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I was contemplating "facing" the XPS with Cu or Al self-adhesive foil/tape to increase stiffness but then thought of a problem: very different coefficients of expansion. Use thin plywood instead, but that is susceptible to moisture/humidity-induced instability unless very well coated. I think vinyl veneer will likely creep or bubble up as well (25C and 100% humidity summer-winter differentials here). Hmm.

Ordered enough 1cm and 2cm white boards for a few experimental pairs.
 
@xrk971 - I was thinking of building two sets of speakers, the 24x24" Cornu designs for the FaitalPRO 3FE25.

However, for one of the applications I don't think i have enough wall real-estate for a Cornu of that size. What would you recommend as an alternative? The wall-mounted MLTL looks promising, taking the approach that you'd mention where you split the cabinet in two so that you have a single-driver stereo pair.

Unfortunately I noticed that the new DIYAudio forum appears to put twice as many messages per page, so the links in the first post are a little broken. The solution I've found (for anyone reading) is to halve the page number after going to the link, and it'll get you close to the intended message :)
 
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I'm not sure it has been mentioned in 172 pages of posts, but I have found that Titebond PVA glue works well with XPS "Foamular" boards, but it takes a LLoonngg time to dry, about 4x longer than using it on wood.


For a couple more data points, I tried:
LIQUID NAILSĀ® Paneling & Molding Adhesive (LN-710) - LN-710 is the important bit at the bottom in front of the size in oz.
LOCTITEĀ® PLĀ® PREMIUM CONSTRUCTION ADHESIVE - with the 3X, not Premium MAX, not with the 8X Fast-Grab.
GORILLA HEAVY DUTY CONSTRUCTION ADHESIVE - not Ultimate and not Clear.
All used on Pink XPS Foamular foam from Home Depot (I haven't tried it with the green foam from Lowe's yet).

Note: Liquid Nails is confusing, there are a lot of products with only slight differences in the packaging and available at different stores, so the "LN-xxx" is important because they are apparently different formulas, not just packaging for stores.


I tried all three with a block glued end to side (like a T) for a test.

This Liquid Nails was the weakest, it popped off with little effort. After testing I saw the application note on the side that said not recommended for use between two non-porous surfaces. The other similar but different LIQUID NAILSĀ® Paneling Wood & Foam Molding Adhesive (LN-606) may be more suitable for XPS foam.

The Loctite PL Premium and Gorilla adhesives both held (although I wasn't as heavy handed after the first one popped off, I was trying to gently get one to fail before the other).

The Gorilla adhesive seemed to remain more tacky, more like caulking.

So, with both holding, the Loctite PL Premium was the one I used first in application. Gluing up the doubled front and back panels of a large speaker.

However what I found: when I cut a 12" speaker cutout, the platter had a visible gap/split. Just a light touch separated the two, leaving a flexible rubber/gasket disc that pulled the writing off the foam board. Kind of like a big floppy thing used to help open jars.
-- Can't say this wasn't operator head-space and timing, I did not wash the foam down with any cleaner but I did remove the plastic film. I did use flat exercise bench weights, however the glue line ended up about one mm thick.
-- I did later happily cut this and used it as gasket materiel for mounting the speaker though.

So, I switched to the Gorilla adhesive. It remains caulk like. I haven't replicated the panel bonding test to see if it works better or not.
 
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There is also the square pizza box MLTL I used for the Alpair A7.

https://www.diyaudio.com/community/threads/full-range-on-wall-for-home-theater.260758/

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Probably make it 2in deep and it should work well.

Use the AMLTL technique to size the vent. That is, use the box volume and set frequency to say, 70Hz and use bass reflex calculator to set the vent diameter and length.

https://www.diyaudio.com/community/threads/accidental-mltl-technique.231951/

Thanks @xrk971 ! Just to clarify, is the 2 inch depth (instead of 2.5) for the FaitalPRO driver?
 
Yes, maybe even thinner if you like. Play with volume and bass reflex calculator to optimize volume for the tuning frequency.
I had a quick go with an online port calculator (http://www.mh-audio.nl/Calculators/WVC.html):

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@xrk971 - I assumed the same Schedule 40 PVC pipe that you'd used in your original design, and so with the 2.5 inch thick enclosure it looks like we have a 5.55cm long port. Given the box is thinner than the original, a longer port makes sense to me, but am I correct in that thinking?