Although I agree multipul subs is better, splitting the budget into 3 or even 2 may mean purchasing a set of subs that don't go deep enough. I'm a solid believer that if the sub cannot maintain 20hz at at least 80hz then a single better sub would be a better choice than buying two or three that don't cut it. You can always add another later.
I'm still using a single PB13u and placement was key to making it sound decent throughout the room. (Yes a second sub is going to happen some day but prioritys in other areas of the system took over)
Hey Tony, that is a common argument against Geddes idea. I think this is a tough area for suggestions because the research is sparse. The research that was done didn't go and test cheap subwoofers against good ones, it tested pretty competent subs and found more was better, and by a long shot. Theory, which in this case has good real world research to back it up, tells us that bass in a small space is dominated by room effects, that what we hear is the bass only after the room has fully molested (This word has two definitions!)it. What that means in practice is that all subwoofers sound the same in a given room, they sound like your room. The differences are in peak output and extension (which you mention). As is often noted, technically any subwoofer can produce any frequency, it just may not do so at a reasonable level. That then leaves us with what subwoofers are capable of meeting your needs in peak output and extension, and can multiples better achieve that than a single.
I would thus argue that there are in fact large inexpensive subwoofers that can reach down below 25hz, which I think is good enough for most people) that are inexpensive. Their problem would be in peak output, it would be too low, and packaging (they would be larger). Multiples of these subs would allow for a big increase in peak output.
https://www.parts-express.com/dayton-audio-sub-1500-15-150-watt-powered-subwoofer--300-634
That is a good example. It's large size allows it to be fairly efficient at reproducing low frequencies since the large 15" cone won't need to move as much to produce the low tones as compared to a typical 10" or 12" driver. That means the 150 watt amp is going a lot farther. Still, this thing probably can't do more than about 95db's at 20hz and 105-110db's above that point (which is still very loud). Now if you use 4 of these you have spent $800. You have also added 12db's of headroom/peak output to the equation though. Now the question becomes if a single $800 subwoofer could produce 105db's at 20hz in room and more than 120db's say above 50hz. In the DIY world there are options, in the manufactured sub world, I do not believe there are. That isn't even accounting for the improvement in overall response. Not only do you get a smoother response across a range of seats, typically it helps get rid of nulls in any single seat that are often difficult to get rid of with a single sub.
In the DIY realm you have drivers like this:
https://www.parts-express.com/dayton-audio-dcs385-4-15-classic-subwoofer-4-ohm--295-206
Which at just $100 gives a lot of performance for the dollar. It's also quite efficient. A flat response with about a 90db efficiency at 1 watt is possible in a 10-12 cubic foot box tuned to 20hz. It's max in room output would be about 115db's all the way down to 20hz. Distortion would rise or it would be down a bit between 25hz and 40hz, but it would still do 110db's cleanly. Again, now do 4 of these and that's a lot of clean low distortion output.
So then I think the common counter-argument becomes 2 fold: 1) what is the value in expensive subwoofers then, and 2) What do people hear such big differences when they upgrade to better subs. I think there is an easy answer to both of these. The value of more expensive subwoofers is more output per box volume. How many people are willing to put four of those Dayton 15" subs or the 12 cubic foot DIY option? Great that they can do 110-115db's max output, but they do it in a large box most people won't live with. Getting similar performance in a package that is much smaller simply costs a lot more money. The SVS PB13 Ultra would outperform two to three of those Dayton 15" subs in a package slightly larger than one of them. The value of expensive subs is thus allowing someone to get the extension and output needs in a package people can manage. The sound difference people here is the same thing, just because four 15" Daytons could rival a single more serious and much more expensive subwoofer doesn't mean people make that kind of comparison. They typically go from one regular sub to one uber sub and the output and extension differences are extreme.
I'd really like to see a comparison of 4 inexpensive subs like the Dayton I linked here against 1 uber sub to see what are the benefits and drawbacks of each approach. Geddes will argue that the 4 subs will always win, but like I said, nobody ever tested this directly that I'm aware of. I'm certain he is right from the standpoint of bass smoothness, but if the 4 subs are not capable of meeting your output or extension needs and make bad noises from overloading during your normal listening, certainly you wouldn't prefer that to a single uber sub that doesn't do that. Now having used and heard the 12" and 15" Dayton sub I know they don't do that until pretty loud levels, but I also know they absolutely have their limits before the port chuffing and amp clipping becomes audible.
