THAM15 and SS15 are bigger boxes - 187 litres and 260 litres respectively
They both have a lot of output above 50hz, and drop off considerably any lower than that
Lots of noise from relatively compact boxes, but you'll have to determine if that suits your needs,
@bitSmasher wonderful so i can probably expect up to a 6db difference in loudness then with the tham or close to 9db with the ss15 
Your "loudness" expectations seem to be quite inflated compared to reality
.Actual results would depend on the drivers used, cabinet volume and box tuning (Fb).
if you raised the Fb on your 82 liter boxes to match the Tham's frequency response, there would be little difference, even with the cabinet volume disparity.
Stoneeh's tests using the same driver (15LB075) in a 140L net bass reflex box with the same Fb (43Hz) as the Tham show the BR sensitivity almost +4dB @ 43Hz, the Tham only+2dB at 100Hz.
The larger JBell SS15 is the same sensitivity as the BR at 43Hz, and about +5dB at 100Hz.
10% distortion limited output for the BR, Tham and SS15 are similar, the SS15 ahead by +3-4dB other than 50-66Hz range:
The 15LB075 driver Xmax is only 4mm, so one could expect more output from a driver with more linear excursion, but that would apply to all the different cabinet types.
https://www.diyaudio.com/community/threads/tham15-a-compact-15-tapped-horn.175658/page-35
https://www.diyaudio.com/community/threads/pa-sub-shootout-2021.378295/
Art
Without the TS parameters of your "HP Audio PA400", can't say if the SS15, or any other cabinet will get the most out of them.
At 36Hz Fb, likely you have them tuned below their FS.
In your small box you could probably get ~6dB more out of them just by raising the Fb to ~45Hz.
Community Light and Sound's (and my own) cabinets in the 1970s were built using the same fiberglass principles used in boat building.
Showco and dB sound (both acquired by Clair Brothers sound) covered plywood cabinets in fiberglass, as were my cabinets from 1980-1992.
Clair Brothers, now Clair Global, the largest sound company in the world, used foam core as used in boat and surfboard construction to save weight in their S4 cabinets. Replacing the plywood back with the foam core knocked off 40 pounds of weight, about 10%.
Sound Image joined the Clair Global Group last summer.
In the 1980s, Sound Image built entire sound systems using foam core, surfer culture..
Fiberglass, epoxy or polyester resin, foam core material and intensive labor construction costs are why there are few examples now, but from a stiffness to weight ratio the construction beats plywood by a huge margin.
Art
Thats my point, we are in 2024
The 80's was 40 years ago.
La400 plywood
Sb1000 plywood
Ks28 plywood
Srx700 plywood
Srx800 plywood
Srx900 plywood
And I can go on and on
Manufacturers only did those techniques to not financial success.
Money matters and you can have the lowest weight cabinet but if it cost more than plywood, guess what the market will buy?
Yes S4 series use those weight saving techniques and save 10% weight but the price is not 10% of the other manufacturers and that's why only some of the largest production companies use them not all, small and medium operators do not use Claire Global.
My question to Randy was for him to show the plans of 8mm PA subwoofer cabinet, that him failed to show, only to state that he built fiber boats?
There is people that like to get In to an argument just for the fun of trolling around.
Don't recall ever seeing any remotely like those.
You can pull the parameters of your driver with one of this
https://www.parts-express.com/Dayto...er-Based-Audio-Component-Test-System-390-807?
https://www.parts-express.com/Dayto...er-Based-Audio-Component-Test-System-390-807?
I had a quick look, and found this trail of breadcrumbs...
Product catalogue excerpt, that references hpaudio.biz: https://literature.puertoricosupplier.com/039/PC39057.pdf
Using the Wayback machine that shows the site was last maintained in 2008 - later entries are just the domain listed for sale: https://web.archive.org/web/20211101000000*/www.hpaudio.biz
Doesn't look like there's much info out there...
Coincidentally I was playing in HornResp last night, modelling the THAM15 and larger variants (pushing dimensions to 50w x 60d x 75h to better suit my needs), and thought it'd be an idea to do some "due diligence" and model a reflex box of similar to sense check my ideas. This is all anecdotal since I didn't save the files or capture screenshots.
The THAM15 and resized variants were very sensitive to driver inputs, as expected the design wants a specific range of T/S specs to perform optimally.
I'd selected an "ideal" 15" driver to reference in the resized THAM, and compared a fairly affordable 18" driver in the reflex of same volume, and found there wasn't much difference in the plotted outputs for the same power input, with both of them tracking low frequency response within a few dB - very surprising!
Of course it's not quite like-for-like given the larger driver in reflex, but also note the 18" driver is cheaper and lighter than the "ideal" 15" driver to suit THAM and reflex is a simpler build with more tolerance for variance in T/S specs.
Something to consider, that follows what weltersys was suggesting - perhaps a redesigned reflex box will give you more output from your current drivers.
It'll be a safer bet than putting an unknown quantity in a tapped horn design that wants a driver of a specific spec.
Product catalogue excerpt, that references hpaudio.biz: https://literature.puertoricosupplier.com/039/PC39057.pdf
Using the Wayback machine that shows the site was last maintained in 2008 - later entries are just the domain listed for sale: https://web.archive.org/web/20211101000000*/www.hpaudio.biz
Doesn't look like there's much info out there...
Coincidentally I was playing in HornResp last night, modelling the THAM15 and larger variants (pushing dimensions to 50w x 60d x 75h to better suit my needs), and thought it'd be an idea to do some "due diligence" and model a reflex box of similar to sense check my ideas. This is all anecdotal since I didn't save the files or capture screenshots.
The THAM15 and resized variants were very sensitive to driver inputs, as expected the design wants a specific range of T/S specs to perform optimally.
I'd selected an "ideal" 15" driver to reference in the resized THAM, and compared a fairly affordable 18" driver in the reflex of same volume, and found there wasn't much difference in the plotted outputs for the same power input, with both of them tracking low frequency response within a few dB - very surprising!
Of course it's not quite like-for-like given the larger driver in reflex, but also note the 18" driver is cheaper and lighter than the "ideal" 15" driver to suit THAM and reflex is a simpler build with more tolerance for variance in T/S specs.
Something to consider, that follows what weltersys was suggesting - perhaps a redesigned reflex box will give you more output from your current drivers.
It'll be a safer bet than putting an unknown quantity in a tapped horn design that wants a driver of a specific spec.
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@bitSmasher Yeah I was thinking it may be best to just build a larger reflex for my drivers seeing that I cant find the specs for em, they seem to really like reflex boxes tho. They have good xmax too, measured it today and it was 12mm. Thanks for looking into tho
Not really, box size sets low corner limit.
