Subtractive EQ
Let’s assume that you have five zones to equalize: left, right, front fill, underbalcony, and overbalcony.
We’ve already talked about front fill; generally speaking, it should be equalized to make the vocals—or other program content—sound natural and full.
But wait! There’s more. Always start by equalizing, listening, and generally making sure that you’ve achieved a balanced even sound quality from the largest and most powerful loudspeakers or clusters/arrays.
They almost always provide more bass than is necessary in most of the areas of the room, and therefore, those front fill loudspeakers, which are probably quite small, will not need to reproduce much LF because it’s already being delivered by the main system.
Consequently, the front fills can probably get much louder, whenever needed, if they’re high-passed so that they’re not being expected to provide much LF content. So EQ them while the main system is operating and use them to “fill-in” the portion of the audible spectrum (or program content) that’s not getting into the seating areas that they’re covering. This takes some time to master, and is aided greatly by using an accurate reliable measurement system.
By the way, I suggest never doing this by ear alone—very few ears are that good, if any. Our hearing just isn’t geared towards being refined enough to replace a high-resolution spectrum analyzer.
The same approach, that of subtraction equalization, can be used with great effectiveness for equalizing delayed loudspeakers, whether they’re under a balcony, over a balcony, on box booms, or anywhere else in the room. Before even bothering to listen to these loudspeakers (expect, of course to ascertain that they’re working properly), evaluate the energy that’s coming from the mains. You’ve already adjusted their spectral content in the seating areas that they’re intended to cover. (Right?)
Is the energy that’s arriving under and/or over the balcony the same? Or is it skewed rather badly? Chances are it’s the latter. The task is to use the loudspeakers in these regions to “fill in” the portions of the spectrum that aren’t arriving from the mains. And don’t forget the need to critically time them to support—rather than clash with—the main system, or the result will be all sorts of nasty comb-filtering.
Further, by equalizing the delay loudspeakers to provide the spectral energy that’s not being provided by the main loudspeakers, you will be greatly reducing the excitation of the reverberant field in the room. You can always add in reverb later; it’s a lot harder to take it out.
As noted at the outset, this is only a primer to get the thought process in motion. Many additional procedures exist that further your goal of going from “passable” to a beautiful sonic experience!
Over the course of more than four decades, Ken DeLoria has tuned hundreds of sound systems, and as the founder of Apogee Sound, he developed the TEC Award-winning AE-9 loudspeaker.
