Search For Meaning
But what does it all mean? Do these irregularities relate to some characteristic of the sound, or are they just another academic exercise?
And if there is a relationship, how close is it? How much irregularity is noticeable and how much is unacceptable? What is the actual significance?
As with many sound characteristics, these questions have never been studied. This doesn’t mean they’re insignificant!
A system with measured characteristics like these will not sound as good as it should, and the cause of the characteristics is probably destructive interference between multiple sound sources.
Improving the loudspeaker configuration should improve the sound quality. (Another likely conclusion is that the measurements are at least as sensitive as our ears are at identifying the problem and indicating its severity.)
In this case, like many others, there was no opportunity to reconfigure the loudspeakers other than the slight re-aiming. The only realistic thing left to do was correcting the overall frequency response/timbre/tonal balance as much as possible.
But: exactly what was this overall characteristic? In an attempt to define it, I carefully drew an average of the various traces, as shown by the heavy line.
This technique is admittedly questionable, but it does reveal some interesting information. (again, Figure 2)
First, it indicates that the overall response is neither flat nor smooth. Most prominently, there is a dip centered around 720 Hz and a peak centered at 4700 Hz. These do not look too severe on this stretched-out graph, but note that the difference in level between these two points is 15 dB. Quite significant!
Incidentally, the loudspeaker manufacturer’s data sheet indicates a similar curve, so this is believable.
There are also numerous smaller response irregularities that may also be significant. Again, this has never been thoroughly studied, but limited studies have shown that a third-octave response bump which is 2 dB or 3 dB high can be clearly audible, as can a hump an octave wide which is only 1 dB high.
Most certainly, there should be concern with irregularities of these magnitudes if they’re consistent over much of the seating area.
For example, the irregularities in the 400 Hz to 500 Hz region are clearly in this category.
Our ears are most sensitive to response irregularities in the region of a few kHz, and become less so as we move away from this region.
The response below 100 Hz is probably acceptable, but the region between 125 Hz and 250 Hz could benefit from a little correction.