10" self powered sub-woofers.....

https://www.parts-express.com/Dayton-Audio-HTS545HE-4-21-Kraken-High-Excursion-Subwoofer-with-5-Voic...

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Use 4 of these. Each one in a 12 CF box. A 1000 watt plate amp per box aught to do.

ADD 4 to the cart. :-)

Boom Boom in the Room Room and WAVES in the neighbors swimming pool. Bigger :-)

Regards

NHT is still producing and selling products online from their Stone Road location in Benicia, California within view of the Carquinez Straits. 

I've be able to have a legacy product repaired. 
https://www.nhthifi.com/pages/contact 

@ artemus_5  thanks for the response.  The 9i is listed at -6 db at 29 hz.  That's really not the direction I want to go and prefer a product more advanced on the phone control technology side.
@ oldhvymec   thanks for the response.  There is one in every crowd, isn't there?!
@ m-db  Thanks for the response.  I am aware they are alive and well and producing and selling new product.  What I don't see is any advances in phone app control tech.  The NHT C doesn't even have a damping setting (movie, music) so beyond the really nice NHT black piano lacquer finish I think I can do considerable better. . I made a conscious decision to upgrade both rooms low frequency response rather than try and get something repaired in Miami.  Boxing and shipping a 15 year old sub for repairs didn't seem to make much sense to me either and I have already given it to a friend who likes to try to do repairs like this would most likely entail..  It's already been picked up......I kept the screw in spikes and power cord.I like NHT gear.... I have a bedroom system which has their original video tower 5.1 set with their 12 sub which I bought after two Velodyne's failed right after their warranty expired. I think 3 NHT powered subs in one house may be enough.  :-)..

A smartphone to calibrate extra low frequency seems questionable but way better than no EQ and remote control. 

I've owned six Velodyne Acoustics subwoofer's beginning with the ULD and currently two DD Plus' for the past eleven years.
A failed remote receiver in my early DD was replaced for free well out of warranty but prior to the sale of the company.

I don't think there's anything out there that provides the convenience of the Velodyne Parametric Filter Frequency and Level drag and drop adjustment for eight individual frequency bands not to mention Velodyne's other features that I use often. 
By the way DD-10 Plus measures 13"W x 14.2"H x 16.5"D.

Good luck with your search. 
   

OP:
They are rather intimidating to look, but "brute force" isn't something I'm hearing (although they could be adjusted that way... like any other sub) while listening to them. The nice thing about having eight 10" woofers is they don't have to move much & as such, are very fast. I completely understand not wanting to wait however.