" Do big subwoofers just automatically mean someone is a bass head and the bass they are getting is of poor quality? Many people here said that a well designed large subwoofer is not inferior or slower than a small subwoofer. Do you disagree with that sentiment?"
No, I don't think using big subwoofers automatically means someone is a bass-head and they're relegated to poor quality bass. I believe there's a variety of viable options using 2 or more subs to incorporate better bass performance in the lowest 2 octave range, about 16-32 Hz in frequency, into one's system and room.
Unfortunately, I just understand I lack the knowledge and personal experience of the various possible options, including the use of various sub sizes, to confidently and reliably state how well large subs perform on music and HT as compared to multiple smaller subs.
I can tell you with complete confidence and certainty that the AK Swarm or Debra DBA , utilizing 4 rather small subs and priced at a complete kit price of about $3K, will provide near sota bass response for music and HT.
I suspect that 4 larger subs in a similar DBA configuration, however, would perform at least as well or likely even better than either AK system. The best suggestion I can offer you is to select 4 larger subs, from a vendor with a liberal return policy, and give it a try. The main drawbacks would be the time, effort and the required optimum setting of the volume, crossover frequency and phase controls on each sub individually.
" Besides, I don't think there's much if any available music or HT source material that has content below about 20 Hz."Another statement I see often. Pipe organs can go below 20 hz and I find frequencies below 20 hz provide an incredible sense of space, scale, growl of the organ that I really love. Also lots of my EDM/techno/ambient goes below 20 hz. So I think there is value there."
I formerly believed commercially available music and HT content had bass extension below 20 Hz, too. But then someone asked me to identify a single commercially available music or HT recording as an example. I searched for a while but couldn't find a single example, not even one. Of course, you're more than welcome to try and find an example if you'd like.
The closest I could find was a group of guys that discovered an arcane method for retrieving any sub 20 Hz content from some discs if any trace of the original master recording with deeper bass extension was still accessible. They maintained a list of such discs that did on some online site I've forgotten. Talk about bass-heads.
Best wishes,
Tim