Try using spikes instead of soft rubber feet, or worse, solid feet
For starters, never underestimate how much spikes can do for the sound. Most people think of them as a nice cosmetic touch. But they’re more than that. There are many oft-heard reasons behind this, but I don’t always agree on how the effect is explained. “Decoupling” (physically floating the speakers from any surface of the room) is impossible albeit ideal; you will always coupling your speakers to the floor, be it via elastic bands, rubber feet or hard metal spikes. The thing is, all methods do sound different.
In fact, with spikes, you’re hard-coupling your speakers more firmly to the floor. This has the tendency to tighten up the bass, make it faster and give more speed to the overall sound. Compared to no spikes, or rubber feet, spikes also make the sound more controlled and possibly more natural and honest-sounding.
Soft materials like rubber or elastonomers are approximately double in the effect they bring to the sound. When used under speakers their effect is arguably most clearly heard, better that is than under components. The plus side is that the high and middle frequencies get more natural, more honest-sounding. Sadly the downside is that the opposite goes for the bass: it tend to loses some of its pace and attack. Unless your system is too clinical for your taste, I don’t find it to be desirable. After all, you want your system to be as honest sounding as possible.
This is also an oft-underestimated aspect of speaker placement. The more accurate the speakers are, the more important this issue becomes. Whether you like them straight at your ears or more parallel is a matter of taste, but at all times, be sure to experiment and make sure that the speakers are aligned in an exact mirror-like fashion. So make sure that the left speaker has the same toe in and distance as the right speaker. Paying attention to this truly pays in the areas of focus, coherence and the size of the sonic sound-stage.
Distance from listening position
What happens if one speaker is further away from the listening position than the other, even if it’s only a centimeter, is that the bass becomes less controlled, less tight and more wobbly than when the speaker are totally aligned. 100% accurate alignment gives the tightest, most dynamic bass and attack. Do note: This does not necessarily give “most” bass, as inaccurate placement can make bass seem bigger and fuller when in fact it is slightly out of phase and therefore more boomy. This is because you are listening more to the bass harmonics instead of the fundamental frequencies. Sometimes a slight misplacement will actually give a more rewarding bass experience because it can be less dry than when the speakers are fully aligned — but this is a subjective thing. Objectively you want the sound to be as dry as possible. In that case, don’t worry and just enjoy the sound. Remember, separate from everything I wrote in these pages (which is very technical-based), regardless how accurate the sound is, if you don’t like it, it means absolutely nothing.
Relative speaker position
Relative placement of one speaker to the other also matters quite a lot. That this is true for panel-speakers such as electrostatics or line sources such as long ribbon tweeters is probably known, but that it also matters for regular dynamic speakers is less well known. But it can be very worthwhile for the focus and stability of the sound imaging, to carefully align the speakers such that the tweeters are at the same height and vertically at the same angle.
Tilt is the angle at which the speaker is relative to the floor. Some speakers are more sensitive to this than others. For example, electrostatic “panel” speakers’ sound can be easily customized to taste by adjusting the tilting. There are no definite rules on this, and the result can differ per listening room. In my client’s listening room, with Martin Logan Neolith speakers, the sound becomes more forward, more aggressive and subjectively more detailed when the speakers are tilted backward. When tilted forward, they sound more relaxed, get less aggressive and forward in the midrange and become more airy in the treble. The same was true for his previous Martin Logan CLX electrostatics, in a different room. But your results may vary. Just know that even small differences in tilt can make for large audible differences.
Fastening speaker units
This is something I first experienced with the Monitor Audio PL300. I installed them new and have tightened the back-screws as per Monitor Audio’s recommendation but over the course of a few months, the sound became too relaxed, and the bass is no longer tight. When I re-tightened the screws that fasten the units to the cabinets, the bass greatly benefited! It became tighter, faster and subjectively more dynamic. He had the Monitor Audio PL300 ever since and it turns out that their cabinets need some re-tightening every now and then. Depending on how your units are attached, it is important to be careful not to use too much force as this can damage the threading and actually cause a permanent looseness.
Swap left and right speaker
This might be surprising but just swapping the left and right speaker can make a difference. This is so as speakers are always slightly different from one another. It’s very difficult to make them exactly the same since you’re dealing with mechanical devices (well, even full-electronics items such as TVs have variance between units of the same model of the same manufacturing batch). Therefore, because rooms are most of the time also irregular, sometimes one speaker’s positive sides can work together with the room’s downsides and vice versa. That’s the reason you should experiment with this.
Never mind at this stage whether biwiring is better or not because opinions differ greatly on this subject. But it does really matter and there is a difference. If you have a biwire connection but are using single wire cable, just try a biwire cable. You’ll find that biwiring makes the soundstage larger, and gives more air to instruments within the stage. Some people find this unnatural and therefore vote for single wire but again, if you have the connections on your speakers, just try them and see for yourself!
Please note: it’s very important for the high-low coherence that you use the same cable on the low and on the high connections. Otherwise you might get disjointed, out of time bass and/or forward highs.
All the above essentially costs virtually nothing. So why don’t you try it yourself?