Need help in choosing subwwofer for 50m^2 room

[bassbear]

Hello,
I have a set of KEF q950 + q650 + small teufel sorround speakers (4 pcs) powered by Marantz 5015 in ~ 50m² attic and i would like to extend it in music and HT with subwoofer as F3 of the speakers is 44Hz.
First idea was to just buy svs SB2000 which costs here in Poland about 700$ or klipsh R115sw for ~ 450$ (used one)). Maybe I can have something better if I make one by my own in similar budget. I have plan to use my amplifier T.AMP 1050 MK-X which goes 2x520W@4Ohm (lowest possible impedance accepted, does not work in bridge at 4 ohms).
I have found nice project from TLS guy
https://forums.audioholics.com/forums/threads/dayton-18-ho-ported-build-thread.93086/ with nice driver and f3 at 22,5Hz. Unfortunately in meantime new driver version appeared and after remodelling F3 goes to ~ 28Hz
My goal is to choose the best option for low good quality bass in similar budget. Would be nice to find european speaker if possible as e.g. RSS460HO-4 costs over 600$ in Poland in comparison to 429$ in US. This is still fine but possibly there is better option
Could any of you guys kindly help me to make proper decision in choosing best driver?
BR

 

[BoredSysAdmin]

I've found some raw subwoofer drivers from Poland:

Drivers - Professional audio

stx.pl

Not sure if there is anything decent in there.
There is also Spanish Beyma, which I think I've heard of before.

Products - Beyma - Professional Speaker Manufacturer since 1969

Find the speaker that suits better with your needs in an easy way, thanks to our powerful filters and the product comparator.

www.beyma.com

 

[lovinthehd]

B&C out of Italy?

 

[bassbear]

Actually STX was my first choice when it comes to budget and local - unfortunately none of woofers seems to have good parameters unless i will use more in one box (but of course I may be wrong).
In general I have heard warm words about beyma and B&C in PA/stage equipment. Possibly they are making also standard subwoofer drivers.
I have skimmed over B&C webpage - did not found any driver which can go lower that 29Hz.
Beyma webpage seems to have better search but not sure what other parameters are the most important here.
I assume you guys know better US speakers so i won't be stubborn on EU ones.

 

[BoredSysAdmin]

@TLS Guy waiting for your input here

 

[bassbear]

@BoredSysAdmin As we did not found any EU driver which fits reqs @TLS Guy shared box model for rss315hf-4
Unfortunately again driver parameters from the model are different than current driver parameters:

Dayton Audio - RSS315HF-4 12" Reference HF Subwoofer 4 Ohm

RSS315HF-4 12" Reference HF Subwoofer 4 Ohm

www.daytonaudio.com

@TLS Guy Could you please have a look if that driver is still ok?