By Dave Rat • November 3, 2011 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. Read the rest of this post 1 2 About David Dave Rat President, Rat Sound Systems Dave Rat heads up Rat Sound Systems (www.ratsound.com), a leading sound reinforcement company based in Southern California, and has also been a mix engineer for more than 30 years. Comments Leave a Reply Cancel reply Your email address will not be published. Required fields are marked *Comment Name * Email * Website Whit says “Perceived “flat response” is distance related” YES! Though educated, I could never explain to anyone why this is true. Though I believe the “volume” or size of the room also contributes for more obvious reasons. Jonathan Johnson says I think the distance-related response is due to the directivity of higher frequency sounds. The inverse square law applies at all frequencies, but the apparent focal point of higher-frequencies emanating from a highly directional horn (unidirectional) is further behind the speaker than the apparent focal point of lower frequencies emanating from a large-diameter cone (omnidirectional). This means as you double the distance from the speaker, the amplitude of low frequencies appear be reduced to 1/4, but higher frequencies appear to be reduced to perhaps 1/2 (because the distance from the apparent focal point has not doubled). This makes the sound seem “brighter.” Ken Fingleton says In working at a plant, I found that a person playing a clock radio for the whole department to hear was an awful awful experience. Thankfully I was an electrician—there to get production going again—and I could leave the area when the machine was repaired. Years later the boom box entered the shop and it could play much louder and except for their choice of music, it was a really good sound. I always wondered why two, three and four inch radio speakers had the ability to wear you down so quickly. In just a few articles, Dave Rat has earned the term “pre-qualified”. For me that means, anything he writes is a must read! Joe Nickell says There are some interesting comments, but lack sufficeint detail to have a meaningful disscusion. The comment about comb filtering, is off. Comb filtering only occurs with sources providing the same source signal. I really respect Dave Rat’s experience and opinions, however some of these topics are non-starters or need qualification. Tagged with: Dave Rat Engineer Poll Techniques · all topics Subscribe to Live Sound International Live Sound International brings you information on a wide range of pro audio topics. Stay up-to-date, get expert tips, industry news, new products and technologies delivered. Discover how to make smart use of today’s sound technology, Subscribe Today!