The frequency balance of the B4s is well chosen. By that I mean first that they sound quite flat overall, and then that there aren’t obvious dips or peaks within their frequency range. In addition, I found the B4s to have a very pleasant degree of lower midrange warmth. As a result, the B4s let you hear excellent detail in string bass or cello, as well as more natural balance in vocals. In contrast, far too many small speakers offer weak lower midrange response and as a result sound small (and thin)
I also thought the smoothness and overall level of the B4’s treble was close to accurate, though perhaps a touch less extended than I’ve heard in vastly more expensive speakers. The blend between the midrange and treble is fine in terms of the relative balance of the midrange region to the treble region, but there is s sharpness on transients in the upper midrange that made me think the blend isn’t perfect. This sound can be quite impressive (e.g., on rim shots and the like) and makes the B4s sound really dynamic, but it is on the strong side of neutral. I should note that our earlier testing of the B4 showed that the transient performance of the speaker is somewhat amplifier dependent.
In a way it is great that PSB offers a truly affordable speaker that can reveal what many people regard as subtle differences between electronics components. Fortunately this doesn’t mean that, “the B4s reveal that you should get out your checkbook and buy expensive amps.” Instead, it simply means the differences between, say, a class AB integrated amp, a class AB receiver and a class D integrated amp—all around the same price—could be heard distinctly.
Despite the general sense of slight warmth, you should know that the bass of the B4s (when used without the SubSeries 1) is neither weighty nor deeply extended. A 4” woofer simply isn’t going to deliver 30Hz in useful amounts because physics prevent it. PSB says the B4s are flat to about 70hz, and I’d say it was more like 120 Hz in our room with a slow roll-off below that (we place the B4s for smoothest bass, not for maximum extension). If you want punch or slam in the bass, you’ll have to add a sub or use another speaker.
Enter the PSB SubSeries 1 subwoofer. My experience here was quite different from what usually has happened when mating a sub to mini-monitors. Usually, getting a satisfactory blend is almost impossible and when you do, somehow the magic of the main speakers is diminished. But with the SubSeries 1, I found within minutes that I had meaningful bass extension but without killing the midrange smoothness and clarity of the B4s.
I spent another hour on and off tweaking level and filter frequency settings, and then adjusting the sub’s room position. My end result at that point gave good output in the 40-70 Hz range, but with response that was perhaps a little down in level in the mid-to-upper bass region, with a dip from 80 Hz up to the transition point (about 110Hz). That arrangement played to my preference for avoiding upper bass levels that are set too high, which could potentially cause the sub to call attention to itself.
Note several things. First, it wasn’t hard to set up the SubSeries 1 in a way that improved the overall sound without detracting from the core sound of the B4’s at all. Second, I was able to tweak the sound to fit my particular listening requirements (to avoid what I call “realism inhibitors” while fostering “realism triggers”); you might do the set-up differently to fit your own specific requirements, but the point is that the SubSeries 1 is flexible and easy to adjust. Third, be aware that the results you will achieve with any sub can be quite dependent on the room at hand, so be careful about generalizing from my specific results.
What I do think is true about the SubSeries 1, and which you might miss, is that PSB has designed a real woofer here. Which is to say the SubSeries 1 does quite well in the real bass range (the range between 40-80 Hz contains most of the bass action in typical recordings). The sub can’t completely compensate for the upper bass reticence of the B4’s, or a least it couldn’t in my set up with a modest effort to dial things in. The upside to this, in my experience, is that part of the seduction of mini-monitors is built precisely around this deliberate touch of upper bass reticence (which helps you avoid the sort of upper bass boominess that can ruin imaging and soundstaging). Thankfully, the core strengths of the B4’s were preserved when I added the sub, meaning that with the SubSeries 1 you can have your cake and eat some of it too.
You can go a step beyond this level of integration, though, if you use a receiver that is equipped with a good automated speaker/room correction system. The beauty of this approach is that you can place the sub to generate more output (though before correction is applied it’s response will be less smooth) and then leave it to the speaker/room correction system to smooth out the bass response and nail the phase settings (the SubSeries 1 only has a two-position, 0-180 degree phase control, which is helpful but not ideal). Given the low cost of receivers with room correction I would recommend this as a starting point for most people who are buying electronics components at the same time they buy their speakers.