I consider buying a subwoofer, but I'm not sure if it will do what I hope it will.
Let me try to explain what I'm looking for. Many years ago, I helped my parents buy speakers. Final choice was between their then current old square boxes from the early 70's (Radio Corp), and 2 others. The Radio Corp had about 11 inch woofer, and 2 maybe 3 inch tweeter. They lacked high frequency, were boomy, bad stereo image, but were pleasant to hear with an unconstrained feeling to the sound. A contender had great everything, punchy, but felt constrained, and was rejected. They finally bought B&W DM3000 speakers that had everything for themselves, apart from the price...
Fast forward today, I own B&W 683S2s. I'm quite happy with those, but when I visited my parents, I helped them with fixing a problem with their TV. I had my head close to the speaker and it struck me. Their speakers seem to sing effortlessly, (or breath easily or unconstrained), while mine don't!
Since I now have the old Radio Corp, and since the DM3000 are quite bigger than my 683, I tought: easy, that must be because they have better bass response! Let's add a sub to fix this!
I'm not sure after taking a look at the specs: -6dB at 30Hz for the 683 and -6dB at 35Hz optimized to give flat 3rd-octave response down to 20 Hz for the DM3000.
I know for sure the FR of the DM3000 is better. I had the measurement and it was roughly +/1 dB, while the 683 seems to have weird bumps in it, maybe a bit worst than +/- 3dB. THD are the same.
What does the optimized... means?
What can cause that constrained feeling, what measurement is linked to this?
There are too many variables to be able to explain simply why one speaker sounds good and another much older speaker sounds much worse. Yes, all the specs that affect speakers are known, but there are interactions. One is off-axis response that changes the frequency response at different angles. So the core spec is frequency response, but it varies with the angle, especially with tweeters. Distortion is another spec and it varies with both frequency and volume. If you're serious about learning this, and not just looking for a quick one-sentence answer (which doesn't exist anyway), my two AES videos explain most of this in detail: