The importance of symmetry, in terms of equal distance of the loudspeakers from the side walls, derives from the fact that what we hear is not just the direct sound from the speakers but also the reflections from the room’s walls. The first wave reflections are especially important because they contribute to the spatial quality of the stereo image and its tonal richness.
Getting rid of the reflected sound waves by applying absorption is not the way to go, especially when it comes to side-wall reflections, because they have a positive impact on the perception of space. During audio post-production, a symmetrical speaker setup is used, therefore symmetry becomes a precondition for proper stereo imaging.
Having the audio system positioned closer to one of the side walls increases the level of the sound reflected from that wall and reduces the time it takes for the reflected wave to reach the listening position. This can result in a skewed and less realistic stereo image. Room limitations are something we cannot avoid completely, but we have to find ways to minimise their negative impact while preserving the room’s domestic functionality.
I am interested in this topic because my listening room situation is non-symmetrical, meaning that the left speaker is much closer to the side wall than the right one. Luckily, the situation is not as bad as one might expect because the nearest side wall has a diffusive character—it features alcove windows and radiators protruding from it. This unevenness of the wall surface helps break up the uniformity of the reflected waves. There are curtains as well, which, by reducing the acoustic energy, act as absorbers. By combining diffusion and absorption, the negative impact imposed by the lack of symmetry has been reduced.
While researching the topic, I stumbled upon an interesting article on Linkwitz Lab describing how to minimise the adverse effects of non-symmetrical audio system setups on stereo imaging. Linkwitz suggests that more toe-in is required for the speaker that is closer to the side wall. In short, the optimum amount of toe-in is a function of the loudspeaker’s distance from the side wall and its distance to the listener.
Currently, my speakers are pointed straight ahead with 0° of toe-in. This gives me a very nice tonal balance and widens the sweet spot so that a stable, centred image can be enjoyed from all three seats on my sofa. I tried the Linkwitz experiment by applying a slight toe-in angle to my left speaker, and I have to say that it worked. As usual, though, the devil is in the details, so getting the amount of toe-in right is crucial. Even a slight excess narrows the sweet spot that listeners can enjoy. With around 1.5–2 degrees of toe-in on the left speaker and 0 degrees on the right, I was able to detect an increase in the width of the soundstage, extending further beyond the nearest wall boundary.
Yesterday, while watching the latest episode of Tatort, a cult TV series here in Germany known for its outstanding sound engineering, I was struck by the three-dimensional rendering of the ambient sounds, which had gained a new level of palpability and realism. Ambient sounds seemed to emerge from behind and beyond the boundaries of the room. I had never noticed such a pronounced three-dimensional presentation before introducing the slight asymmetry in toe-in suggested by Linkwitz.
In short, what I learned in this case is that striving for symmetry in an asymmetrical setup does not necessarily lead to the best results.
Cheers!
Just found your article after spending a day being driven nuts attempting to set up speakers in an asymmetric room. I shall give that a try tomorrow. Thank you.