check out a site called Funkaudio.com.Also look at the Seaton Submersive or from JTR the JTR Orbit shifter or the S1 or S2 to name a few.
Subwoofer to mate with Casta model C's.......
I have Casta Acoustic model C's with a 15" woofer, 17" custom horn midrange and 2" custom horn tweeter in each floorstanding speaker. The speakers are a sealed cabinet and are very efficient. My room now is 13 x 19 x 8 but soon will be 20 x 24 x 8 after renovations. I had previously owned an SVS PB13 ultra before purchasing the Castas but sold it knowing I wanted two in the larger room. The svs was a phenomenal performer. Can anyone give any recommendations on one or two subwoofers adequate to mate with the Castas and given room sizes. Budget is not an issue. THX in advance......