At home, you have another much larger speaker enclosure for your music. It's the listening room. The resonant frequency between parallel walls is a half of the wavelength and its multiples. Depending on the positions of the speaker and the listener, additional sound reflections and their interference occur. Imagine a jagged line oscillating up and down – this is the graph of how your room's sound changes.

You don't need to imagine this alone. The free audio measurement software REW - Room Acoustics Software (https://www.roomeqwizard.com) has a separate menu button called Room Sim. Initially, there is quite a daunting graph of a standard 4x5m room. To model your listening room, you need to input the room dimensions, speaker positions, listening position, and select the appropriate speaker configuration. Then, it's very easy to drag the speakers with your mouse and see if one location is better than another. In any case, this is easier than moving speakers and cables around.

In addition to this, there are some firm recommendations and some questionable ones. Let's start with the firm ones.

The best sound is usually achieved when the listener's distance from the speaker is about the same as the distance between the speakers. This creates a proper stereo image but doesn't yet separate the speakers into two distinct sound sources. Depending on the room, this distance can be slightly wider or narrower. Besides the speakers, the sound comes from room reflections, and not every location can be physically occupied by speakers, so there can be some variation here.

The tweeter and midrange driver of the speaker should be at the same distance from the listener's ears. Exceptions are speakers with shifted or rotated drivers. In such cases, follow the manufacturer's instructions. Otherwise, it's important to ensure that there is no phase shift in the higher frequency ranges and resultant interference (lobing). In some cases, this might require tilting the speaker backward if the legs and center of gravity allow or using a speaker stand. More expensive speakers often have this tilt already designed into their asymmetric shape, but you should check whether this tilt is meant for addressing the listening position or for driver alignment. You can check this by looking at the direction of the tweeter. If it's pointing at the listener, then the listening height is as the manufacturer intended.

The third solid recommendation is that the speaker should slightly toe-in. The background of this recommendation is also straightforward. When you move slightly to one side in the listening area, the speaker on the opposite side becomes more straight, and sound from there becomes stronger. This way, even when moving away from the listening center, the sound from both speakers remains equally strong. This ultimately provides a wider and more uniform listening area. Different manufacturers have different recommendations for this, but generally, an angle of 5-15 degrees incline should work. This angle depends on the speaker's horizontal sound profile and distance. A narrower sound profile and greater distance will result in a smaller angle. The angle of toeing-in the speakers with a wide listening area and speakers close to each other can be greater. Like everywhere else, exceptions can also be found here, and some speakers sound better when they are looking past the listener. If there are no recommendations, simply experiment with the horizontal angle.

Fourth, a less common recommendation is the distance of the speaker from the listener. If room reflections and resonances are strong, having the speakers closer to the listener can help. This strengthens the direct sound and weakens reflections. The human ear is relatively adept at distinguishing direct sound and ignoring reflections. The later and weaker the reflections, the more the direct sound becomes important. Thus, in a bedroom, the best speaker position might be near the foot of the bed along the side walls instead of being against the opposite wall. However, bringing the speakers too close to the ears should be checked against the recommendations for tweeter and midrange driver distances and whether the central focus point is still there, or you have two separate sound sources. When the speakers are very close and narrow, it might also reduce the perceived stereo width, diminishing the listening experience.

Some of the questionable recommendations can actually be tested using the REW software. Some are less measurable and thus require experimentation. For each questionable recommendation, you can also find opposing suggestions. This allows you to explore and experiment on your own. All these questionable recommendations pertain to the optimization of sound resonances within the room and the management of reflections in relation to the positions of the listener and the speakers. Below approximately 300 Hz, the primary goal is to control resonances, while above that frequency, the main task is to address reflections.

When the path of the sound, whether direct or reflected, differs by half, one and a half, two, etc., wavelengths, the sounds cancel each other out. If the distance of the sound differs by the wavelength or its multiples, the sound that has traveled toward the wall joins the sound that has traveled directly. As reflected sound arrives later due to its longer path, strong reflections also reduce sound clarity. This might sound a bit discouraging, but humans have grown up in and learned to listen in rooms. Thus, the characteristic change in sound due to the room is already built into our perception, and it's not advisable to try to eliminate it. However, dealing with extreme cases and finding the best position for the speaker can be the missing "golden speaker wire" that perfects the listening experience.

Let's start with the simpler rule for dealing with sound reflections – don't amplify reflections multiple times. This means avoiding symmetrical placement to walls in corners, so that the speaker is equidistant from both the back and side walls. Additionally, when considering walls, remember that sound also reflects from the floor and ceiling. Here, symmetry should not be created. You might come across recommendations to change the listening axis, such as making it diagonal to the room, but there are usually opposing suggestions as well. Still, since most optimization is for controlling bass and bass is relatively non-directional in terms of listening, you may better control bass with the asymmetry of the speakers in the room. While doing this, don't forget that the speakers should still be symmetrical to the listener.

Another simple rule is that the closer the speaker is to a reflective surface, the stronger the resulting reflected sound will be. This brings us to the next piece of advice. For achieving spatial sound, it is recommended to position the speakers away from the back wall and closer to the side walls instead. Early reflections from the side walls can improve the auditory experience by adding a sense of spaciousness and enhancing the perception of a three-dimensional soundstage. When the speakers are placed close to the wall behind them, reflections from the central part of the wall strengthen, resulting the soundstage with more central focus.

If you optimize the placement of the speakers in the room, then achieving the desired spatial distribution of sound becomes the primary objective. Side wall reflections can be employed to expand the room's acoustical space, while rear wall reflections can be harnessed to establish a central sound image. As it is all related to reflected sound timing, then different distances from different walls should be tested to find the best position for the room.

Subwoofer placement is a separate topic, as it needs to ensure that the phase of the sound doesn't reverse when transitioning from the speakers to the subwoofer (otherwise, they might cancel each other out within a certain crossover range). As a rule of thumb, the subwoofer's driver is late, so it should be slightly closer to the listener than the main speakers to ensure that the sound arrives simultaneously. This also depends on the frequency filter (and if the corresponding switch exists, the phase switch of the subwoofer). With certain filter types, the phase can be shifted, and a different position might be necessary. Since the wavelength of sound at the subwoofer's crossover frequency is typically two meters or more, you can confidently move the subwoofer around to find the optimal position. Often, it's easier to find a location where the sound is attenuated at the crossover frequency and there's a dip in the frequency response. By moving away from there, you can find the position that fills the dip most effectively.

When the main loudspeakers or subwoofer amplifies the bass resonance in the room, there is a simple rule for suppressing some of these resonances. Room length resonances are suppressed when the speakers are placed along the center of the room, meaning the distance from the front and back walls is the same. Room width resonances are suppressed when your two speakers are positioned 25% away from the room's walls, with 50% room width distance between them. Room height resonances are suppressed when the bass is played at half height of the room. If these speaker placement locations are not feasible, you can look for the next best location. Playing the bass near a wall amplifies the resonance between that wall and the opposite wall. If your speaker system includes a subwoofer, you may also consider using two to four subwoofers, positioning them to minimize the feeding of room resonances with energy and/or suppressing resonances.

Of course, the listening room is never empty of furniture. Thus, the arrangement of furniture can be used for diffusing and absorbing sound reflections. For instance, bookshelves, armchairs, beds, and sofas all to some extent reduce reflections and slightly improve the room's soundstage (or sometimes worsen it). You can find the points of sound reflection by replacing them in your mind with light sources. If you can see the speaker in a mirror on the wall, that's a point of reflection. Here, remember the acoustic solutions used in modern concert halls. You often see slanted wall panels of varying lengths and angles, which diffuse reflections. Thus, at home, you can use a wardrobe or a bookshelf for the same purpose if desired.

There are also mobile applications for setting up the placement, but some of them cause more confusion than clarity. Usually, a smartphone's microphone has a unique sensitivity profile, so these apps can't measure the final profile accurately. However, they can be used for comparing positions. After trying out most of these apps, my choice comes down to the two simplest tools. Spectroid (https://play.google.com/store/apps/details?id=org.intoorbit.spectrum) is a straightforward app that displays the current sound profile and can record the maximum line. With the maximum line, you can also measure a sweep, but it's easier to use a web page such as https://29a.ch/noise-generator/, choose Pink Noise, and direct it to the speakers. By adjusting the subwoofer using this method, you can find the best integration point for the sound fairly easily, while also seeing the effect of room reflections on the speaker's sound. To confirm that it's a room effect, look at the profile directly in front of the speaker's driver in the frequency range of interest. This will show whether the problem comes from the speaker or the location and the room.

For the final verification of placement, the best approach is to swap positions and listen to the sound. Even a small shift can affect the sound. The best positions for the speakers and the listener are those where your favorite music sounds most expansive and authentic, and the soundstage is the most spatial. In the ideal position, the speaker becomes "invisible" and it seems like the sound is coming between the two speakers, from each sound source's unique position.

Footnotes:

The listening room and speaker placement are among the most influential factors in the listening experience. Spending an hour trying out the REW software, another hour shifting or adding furniture, and a third hour doing listening tests can provide you with an upgrade worth several thousand euros, rather than buying new audio equipment. Also, even with better and more expensive speakers, having them in the wrong position remains the wrong position, and while the initial sound quality might improve, the listening experience might not. When designing speakers, the opposite holds true as well – when room issues are resolved, speaker issues become more apparent. But now, upgrading your speakers makes more sense.

I don't recommend active room correction software. They are all still a bit crude and unfortunately, poorly specified. Also, it's not advisable to adjust the parameters of an active signal filter's parametric equalizer according to the room. It's best to listen to the sound that has the original and correct profile. The brain can manage the necessary adjustments. If the room's resonance is severe, it's better to deal with it by changing the speaker's position. If nothing else works, adding frequencies should be avoided. If you need to bring down a frequency peak by half, this is the maximum allowable correction that won't completely disrupt the soundstage. However, this change needs to be remembered, and each subsequent time you move the speaker, your chair, etc., you should re-evaluate whether the adjusted setting is still appropriate. In most cases, it's not, and you need to start over...