"Acoustic perception" is a complex psycho-physical process involving a multitude of (variable) parameters (e.g., air density, humidity, temperature, materials, etc.), which we will not elaborate on within this limited scope. However, we can draw upon existing observations, experiences, and knowledge and present them here in a simplified, practical manner.
The goal is to define and enable a listening position and speaker placement that makes listening to music enjoyable and emotionally engaging. This discovery process requires a willingness to experiment, curiosity, some technical knowledge—and time. The time and, if necessary, physical effort will be rewarded with listening pleasure.
A preliminary comment: Marketing strategists and copywriters are creative people. So, when we read that speaker X reproduces audio material exactly as the sound engineer / recording engineer mixed it in the studio, at first glance, that's not just a great thing, but a phenomenal stroke of genius. Factually, it is and remains wrong. Period.
And a note: Dare to explore unorthodox, undocumented, or unpopular paths. This means that measuring tools and aids make work easier, no question. They are, so to speak, the maps that help you get closer to your (listening) goal. Ultimately, however, it is your ears that, hopefully, take precedence over dogma and measurements.
Placement / Distance to Walls
Choose the distance of the speakers to all existing walls to be as large as possible so that reflections occur as late as possible and lose their influence on the localization of the audio signal. The empirical guideline, beyond which no further improvement usually occurs, depends on the listening distance and ranges between 70-150 cm.
If the distance is significantly below this value, there is the possibility to reduce the influence of reflection through damping or scattering. With damping, part of the energy is transformed by friction, e.g., by means of heavy fabrics hung a few centimeters from the wall or by means of furniture such as bookshelves, sideboards, etc., positioned along the wall. Optionally, the use of damping materials is recommended. Here, too, the choice of a heavy material is advisable. An area of 1 m height and 0.5 m width around the center of the reflection yields remarkable results. The goal is to make the sound reflect as unevenly as possible through scattering; e.g., by means of a shelf filled with books of different sizes. Optionally, so-called diffusers can be used.
Tip
Those who value depth staging particularly highly should choose a sufficiently large distance between the speaker and the rear wall. The wall distance influences the bass range. The closer the speakers or the listening position are to a wall, the more strongly the bass reproduction is amplified. It is advisable to choose different distances to the wall behind and next to the speaker; a ratio of at least 1:1.3 is recommended.
Stereo Triangle
Audio signals are usually best acoustically represented when the resulting triangle formed by the listener, the left speaker, and the right speaker is either equilateral or isosceles. The smaller the distance between the left and right speakers compared to the listening distance, the less the audio reproduction is influenced by the acoustics of the listening room, and the greater the impression of both center imaging and focus. A listening distance of at least 1.75 meters should be ensured so that the sound fields of the individual drivers have time and distance to sum up.
For large speakers not specifically designed for near-field placement, this minimum distance can also be greater. If you can only achieve significantly larger listening distances than two meters, particular care is recommended in furnishing the listening room. Every object dampens a portion of the sound waves reflected from it, with the degree of damping being frequency-dependent. Unfortunately, higher frequencies are damped by almost everything, especially curtains, carpets, armchairs, and sofas; low frequencies, on the other hand, are damped by large cabinets or windows.
The sound image is also influenced by the overall size of the stereo triangle: The smaller the side lengths, the more the listening room is acoustically blended out, the sound image becomes clearer, but also more present and less spatial. Here, too, the rule is: experiment. Use a mono sound source (speech, vocals). It should just barely be stably imaged in the center between the speakers.
Toe-in
Depending on how close or how far the speakers are placed to the (undamped) side walls, more or less strong early reflections can occur. This, in turn, can impair both localization sharpness and tonality. What was written above also applies here: Please experiment. Through a step-by-step approach, you determine at what degree of toe-in you perceive a coherent, homogeneous sound image.
If the sound is dark, muddy, heavy, it is advisable to direct the sound-emitting side of the speaker more directly towards the listener. If the sound is too bright, sharp, shrill, less toe-in and possibly even a parallel alignment is recommended. The latter option, however, can lead to a loss of center imaging – it may be useful to heavily toe-in the speakers (40-50 degrees) so that the radiation axes cross in front of the listening position. This approach can also enlarge the sweet spot.
Note
The most difficult topic to address in loudspeaker placement is standing waves. Standing waves are sound waves whose wavelength is an even multiple of half the wall distance. Standing waves amplify the bass and make it sound imprecise by unnaturally prolonging the decay of notes.
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