Year of the System 2010: PA Anatomy – The Main Event
Now that Drive is over and we’re starting to settle in on the tuning of the system, I’m going to try to get this going again. So here it is at last, the Mains.
The heart of our system is comprised of two arrays of Meyer Sound MICA’s with 7 boxes per side. The choice of MICA’s dates back to 2005 when they were demoed for the 2005 Drive Conference. The experiences of the staff at the conference have become legend over the last four years, and now that I have heard the system in our room I understand why. I was in all honesty genuinely surprised by how great the boxes sounded, again, simply with an iPod daisy-chained to each box in the array. Through the optimization process, the coverage smoothed out even more. It is a huge win for me to be able to stand in the back corner of the room as far away from the stage as you can get and to still hear things clear as day. Now even if you arrive late and end up standing against the wall, you can listen to clean and clear spoken word that makes up the bulk of our services.
So why line arrays? Line arrays give us wide coverage for our very wide room along with very consistent coverage to the back of the room. One of the greatest challenges of our previous system was definitely room coverage; as you moved to the far outside sections of the room, the coverage dropped off. I think our previous system did very good for its time, but it was 12 years old and did not meet the programming intentions or performance expectations of a modern PA.
Part of the coverage challenge in our room related simply to distance. Since the room gets wide, the far outside corners needed the main loudspeakers to throw much farther to reach them than the center area. The Inverse Square Law dictates that whenever you double your distance you lose 6 dB. So if the PA measures 96 dB at 50 feet from the speaker, it will measure 90 dB at 100 feet. This creates a couple of interesting issues. For starters, we’re losing about 1/3 of our loudness with every doubling of distance. While this might not be an issue for the folks that don’t like the rock music, they probably have a different opinion when it comes to spoken word. Another issue relates to our friend, the Equal Loudness Contours.
The Equal Loudness Contours demonstrate that we do not perceive all frequencies the same as loudness increases or decreases. It’s almost as if there is an internal EQ in our head that adjusts as the volume changes. If we mix at one level or within a consistent dynamic range, the contours don’t really matter to our perception. However, if we mix at one level and our mix is listened to at varying levels, the tonal perception of the mix will be perceived differently as the listeners move farther away from the mix position and their listening level changes. A mix position in the middle of the room might be the best of both worlds in a situation like this, however, think about how many times mix position is put in the farthest possible location. As loudness increases so does our sensitivity to higher frequencies especially in the hurt range around 4k. In this type of situation an even mix in the back of the room might have the same spectral balance up front, however it could be perceived as much brighter where the loudspeakers are closer and louderto the listeners. Conversely, the farther seats–such as our far corners–could sound duller as the level drops.
Line array loudspeakers are bound to the same Inverse Square Law just like any other loudspeaker, however, the way the boxes interact within the array counters some of this and manipulates physics for fun and profit. Basically, the array uses destructive interference to reduce SPL in the nearfield. As distance from the array increases, the array trades destructive interference for constructive interference creating a more consistent SPL level front to back than we can achieve with a traditional loudspeaker system. As the listener moves beyond the point of maximum constructive interference, the line array begins to act like a single loudspeaker and Inverse Square Law returns. However, the bottom line is in our room our new MICA arrays give us much more consistent front to back coverage than we previously had.
And then there’s quite simply the sound. The MICA’s have a sound that we like that I would compare to hi-fi studio reference monitors; you can really hear every nuance, for better or worse, in your sound sources. While this is somewhat characteristic of just about every Meyer Sound loudspeaker I’ve heard, by utilizing line arrays we get a very even response throughout the coverage of the speakers. We also get a nearfield effect throughout the coverage; basically you can stand in the back corner of the room and it sounds like the person talking on stage is right in front of you which is great for the more conversational style of teaching we tend to feature on our stages.
There is still one installment left in PA Anatomy, and I’ll try and get to that sooner than this one.