18 inch subwoofer vs multiple 12 inch subwoofers with bookshelf speakers

@thxbest. 3x KEF LS50 Metas with 5.25-inch midrange drivers, 2x KEF Q150

Correct me if I’m wrong, your Musuc/HT system isn’t design for more than 4-6 people in a medium size room. These speakers will have a hard time with anything larger anyway.

Here in Las Vegas, I see how they setup 2k+ seat show rooms. They use horn loaded speakers above 60-70Hz hidden above the stage and place a 12”-15” subs hidden behind/below every 2 to 4 seats. The sound tech will go into sections across the show room and EQ/balance each zone against main speakers. One more device they use is multiple delay lines to sync the whole room. Yes this is an oversimplification but you get the idea.

I’m a humble advocate of placing subs behind your listening seats. Using digital delays to retire bass signal to sync arrival times gives me perfect base every time.

Best Regards 

Mosler666

PS: I choke every time when I see someone say bass overtone with subwoofers. Proper sub at proper xover feq will not produce any such nonsense.

I too generally have preferred multiple subs, especially when crossing to small (bookshelf type) mains.

Driver Xmax and surface area will not be the same. Depending on how you plan to integrate the subs, that may not be a negligible difference. An 18” driver will offer ~10-12% greater surface area than 2x 12” drivers.

In your case, without knowing the specs for either model, I’d still be inclined to use two smaller subs vs. one bigger sub (again, especially with small mains and with music being a strong use case).

I have been using two B&W AWS600 Series 8” subs paired with Harbeth SHL5+ Bookshelf monitors and found them more than adequate. 200W x2 offers more than enough power without overfilling the room with a super boom boom bass punch that can move your furniture. In short, too much can be way worse than not enough. The size of the area you need to support coupled with the crossover frequency and how hard you can drive the monitors is what drives the formula, not just the bottom end.

Not to 'X' foils with Erik, but...imho 'smaller' is faster, but I've played about with trying to pace with the large Heil AMTs'...but I goof about with various combinations to fill the hours.

Currently, the low-mids X out from a pair of 6.5s' into a pair of 10s' for most of their range.  The 'bottom' Xs' down to an 8" self powered sub...

An odd coupling, perhaps...but my space 'x v. y' is similar to our OPs'....except for ceiling 'z', which is 13~14 ft.  And there's other issues that drive me to 'ignore the room' per Linkwitz...

(...still trying to convince our cats to act as bass traps, but they ain't buying it...messes with their sleep patterns....🤷‍♂️🤦‍♂️...)

I've got 2 - 18s', a 12 that's better suited to a 'street boomer', a pair of JBL 10s' that could be pressing into service.... But, have 4 - 8" that I'm considering for a 'swarm' arrangement for my walsh drivers....*s*

Got the means and the methodology    just have to give up that annoyance called 'sleep'....😏👍

Another vote for multiple 12 inch subs. We have 4 REL S510s in our home theatre and it is fantastic