Step 1 – Placement
This involves establishing the optimum distance between the speakers and the rear and side walls and between each other. Although my process involves constant and precise measurement, this allows me repeatable rather than symmetrical adjustment. Once I have achieved the most linear and powerful low-frequency response I then ensure that the speakers are perfectly upright and level with each other. This then becomes our Zero Point, or point of departure for Step 2. Such precise alignment requires laser levels with digital readouts of angular error and targets to assess relative position. Those tools will be fundamental to the process of optimization – by allowing me to adjust each speaker precisely, relative to that Zero Point, rather than maintaining symmetry.
The Concept Of Noise
I’ve already spoken about the concept of assessing audio performance in terms of intrusive or additive noise – and improving system performance by eliminating that noise. It is an especially useful concept when it comes to speaker placement. Bass hump in your room? That’s noise. Slap echo or early reflections? Noise. But how does that help us position loudspeakers?
The acoustic pattern within a room is defined by a grid of pressure peaks and troughs that vary in height/depth – and those peaks and troughs are surprisingly close together. That’s why the bass output of a speaker changes when we move it; we are balancing it against a peak or trough in the room’s acoustic grid in order to minimize excess noise. It’s also why there is often more than one place that a speaker will work – and why we can often achieve remarkable performance even from an unpromising starting point.
Step 2 – Optimizatization
But it’s not just the room’s acoustics that operate on a grid principle. As well, the sound dispersion characteristics of each loudspeaker can be put into a three-dimensional grid extending from each of its drivers. Visualizing this grid is enormously helpful in understanding how and why a speaker sounds the way it does and what you need to do to correct it. Try to imagine the three dimensional grid as the sound suddenly freezing, becoming solid and visible. Each speaker driver would have a differently sized and shaped grid, depending on the frequencies being reproduced. A tweeter would have a tightly spaced grid, made up with very small cubes that represent the short wavelength high frequencies. The midrange driver’s grid would be made from somewhat larger cubes, and the grid generated by the woofer would of course be composed of large cubes that represent the long wavelength low frequencies. Each grid would be shaped by its driver’s dispersion. Using this visual model, a designer’s goal should be to have those grids coincide perfectly at the listening position, the perfectly superimposed boundaries representing a perfectly neutral and phase coherent speaker.
Of course, things are never, ever that simple. Those driver grids will never be perfectly matched or regular. They might be distorted by non-linearities in the drivers or suffer interference from room acoustics. Nor will the drivers and crossovers in a “pair” of speakers be perfectly matched. But my job is to align those grids as carefully and accurately as possible, by moving the speakers forwards and backwards, raising them and tilting them, sideways or forwards and backwards. This works because the different drivers are at different heights on the baffle, so adjusting the speaker angle at its base affects each driver slightly differently. With practice you get to recognize the sonic symptoms (congestion, thinning, holes in the soundstage etc.) and how to move the speaker to compensate. And because the tools I use map those shifts precisely, they are always repeatable.
I’ve described a classic three-way dynamic speaker, but the basic principle and approach will work for any kind of speaker. Di-poles might drive the room very differently, but visualizing that process is immensely useful in positioning them for optimum performance. The same is true of sub-woofers – or any other kind of loudspeaker. Conceptualizing the problem is what makes solving it possible: that and a lot of tools and a heap of experience.
It is a long and exacting process, but the results really are quite remarkable. Your speakers might not end up placed exactly symmetrical or stood at the same exact angle – but they’ll never have sounded so good.