Strewn across the fields of true technological and artistic credibility, the world of pro audio is littered with misinformation, overhyped irrelevance and useless complexities. Sorting through the debris to distill useful and accurate concepts can be quite challenging.
Whenever possible, I devise comparative test methods to prove or unravel various theories and assumptions. Rather than meticulously documenting the results, I opt for constructing and sharing simple repeatable test methods so that anyone who wishes to repeat the results can independently repeat them. My goal is to create a road map that allows me and others to make better audio decisions.
Over the years I’ve learned that no matter how simple or solid my tests and conclusions prove to be, there will always be counter opinions and beliefs. Or, in other words, other routes to reach similar or differing goals. I kind of like this, and it falls in line with the observation that there is often no true “right or wrong” in audio. Here are some observations and theories that have proven useful to me.
Our ears seek tonal balance. On the surface this concept is obvious and simple to demonstrate. Fire up a 15-inch, 2-way stage monitor at a relatively high volume level, and then mute the 15-inch woofer, leaving just the horn/driver on. Ouch! Without the low frequencies, the high frequencies hurt our ears - but when low frequencies are present and at a balanced volume level - the sound is no longer painful.
Expanding on this concept is the foundation behind equalizing sound systems utilizing pink noise to achieve a flat response. What may not be readily apparent is that the wider the bandwidth of the system, the louder it can be without being perceived as painful. Put into practical usage, this means that by extending the low-frequency response of a sound system, you can also turn it up a bit louder while it can still sound tonally balanced and enjoyable.
Perceived “flat response” is distance related. I believe this theory is extremely important. Not unlike perceptions of the flatness of the earth shift to a curvature, and then to a sphere as the viewing distance is increased, the sound we perceive as flat seems to change with distance as well. By “flat” I’m referring to “tonally balanced sounding.”
Many years ago, Harvey Fletcher and Wilden Munson came up with a curve showing that the tonal balance our ears perceive is volume dependant. Basically, the Fletcher-Munson curve indicates that sound is perceived as “brighter” at higher volumes. Or conversely, music that is tonally balanced at a higher volume level is perceived to lack both lower and higher frequencies when played at lower volumes.
It’s been my experience that a similar phenomenon occurs with distance. This is pretty easy to demonstrate, but I’m not sure as to the exact reasons why. In a recording studio control room, where the distance from loudspeakers to listener is relatively short, tonally balanced music that sounds smooth (and not harsh) to most people will show up relatively flat on a real time analyzer.
Conversely, with a large scale sound system measured at distances of hundreds of feet, if the music is EQ’d to flat, it will be painfully bright sounding. Knowing this is very useful for equalizing large-scale systems. Perhaps it’s that our ears expect a dulling of sound with distance, or maybe our ears act like a cardioid microphone, boosting low frequencies in closer proximities. Either way, I find that knowing to EQ “duller” for longer distances is valuable information.