My first subwoofer was a B&W PV1d for my main system with Quad 2805 electrostats, bought about a decade ago. The sound quality was dispointingly woolly and a bit booming. I then discovered about room modes, and bought a DSpeaker Antimode 8033 cinema dsp room eq box, which cured the sound quality, although primarily for the main listening position. It can also do a wider area equalization, but that is not as effective. A bit later I decided to add a passive high pass filter at 80 Hz and also raise the low pass filter frequency on the sub. One day I decided to experiment and use the P3ESRs from my study instead of the big Quad electrostats (and with the Antimode). The result was stunningly convincing with massive and refined full range sound seemingly coming out of tiny boxes. It could not quite fill the large listening room, but that was just about the only limitation.
With Covid I started to spend more time in my 18 sq study at home, so I decided to treat myself to a small subwoofer for the system in my study. I decided an 8 inch sub was enough in something as small as an 18 sqm study, and I bought a Kef Kube8b for just 359 euros. These KEF Kubes looked stylish, and proved to be easy to integrate. Sadly my PV1d died, so I moved the litle KEF to the main system while the PV1d was being repaired (which took a while). Not surprisingly the little KEF was not as convincing as the more powerful PV1d in this large open plan listening space, although it still managed pretty decent output at 25 Hz. In the end I decided that a subwoofer was not really worth it in my small study, so once the PV1d had been repaired I kept the KEF as a second sub in the main system. Here I discovered that the KEF produced an incurable switching thud into the PV1d. When I connected the subs directly to my RME ADI-2 this did not happen, but somehow the Antimode passed on the thud. So I decided to get a miniDSP 2x4HD instead of the Antimode, and this does indeed not pass on the thud. The bad news is, of course, that I now had to roll up my sleeves and do a lot of manual measurements for Multi Sub Optimizer. Once I had to do this, I decided I might as well do it properly and get myself a third (bigger) sub in Earl Geddes style. So I bought an SVS SB2000. I bought the older model without the fancy app and filters because the miniDSP already gives me the filters, and the SVS non-pro model is currently an awful lot cheaper than the Pro (I paid 600 euros). The idea was to simply get one sub that is clearly more powerful than the others, use it in the front corner for an extra boost to do the heavy lifting, let MSO do the equalizing of the high output from the corner position, and leave the two smaller uncorrelated subs to further smoothen the response over a wider area.
I have currently come as far as disabling the tone controls and filters on my ADI-2 in preparation for the REW measurements, and installing the latest version of REW. Making proper measurements is now the next step. However, with the three subs in uncorrelated positions the sound is already quite a lot smoother than last week when they were sitting close together while I was waiting for longer cables to arrive.
So what have I learned? First and foremost that the room is far more important than the actual quality of the sub. Second, that even in a large room dsp room eq is necessary, and third that multiple uncorrelated subs are necessary if you want that smoothly equalized sound quality over a wider listening area. And as you can see, my subs are not at all identical. The SB2000 is the biggest one, and it is also the least good looking one, but that does not matter because it sits out of sight behind one of the huge Quad speakers. The position in the back of the room went to the PV1d for the simple reason that it is more powerful than the KEF, and because the location is in front of a window, in bright sunlight (it is an aluminium sphere). And it looks good, which matters in such a prominent position. The little KEF is located along a side wall next to a modern sofa in what counts as near field, and also close to a modern chair where I sit most of the time. The KEF's location is in the shade, and that is probably a good idea because it has a cloth wraparound finish. I like the look, but it may not survive that long in bright sunlight. So as you can see, my recent decisions were mostly very practical, using what I already had for whatever reason, and with a view to what suited the intended location, and without spending too much.