Perfecting Sound in the Wrong Environment

Ideas are magnetic and once a concept takes hold, minds and innovations seem to congregate, refine and push the limits, often to the point of absurdity. Or at least way past the point of diminishing returns. Meanwhile there are seemingly gaping holes between the popular concepts and those in dire need of resolution.

Take a moment and picture the scenario of setting up a table layout for a grand formal dinner with perfectly folded napkins, crystal champagne flutes, fine china and pristine cutlery placement. Confident with the presentation as guests begin to arrive you realize that mysteriously the table, upon which the masterpiece is set, begins to morph into something similar to a slightly undulating water bed. The exquisite meal now sits precariously balanced upon a liquid filled membrane as the stream of  guests obliviously lean against and push waves into rolling motion. Glasses toppling,  food sloshing and culinary chaos ensues. With a flurry of panic,  the staff reaches in all directions to regain control, sop up spills and replenish the losses. Just when it seems the entire meal will be hopelessly lost to calamity, the intensity begins to ebb, all that will spill or break, has already The messes become familiar, you’ve the replaced champagne flutes with more stable coffee cups on saucers. All excess frivolity has been carted away. A balance has been reached, tensions relax with a new and different result than the original intent but the wonderful food and smiles ramp up into a meal to remember with a rough start. The following day we begin our task again, we set this table carefully attending to each detail and once again the arriving guests are subjected to a chaotic start to an evening meal mess perched atop a rippling unstable surface. Over and over again each night the mystery repeats with us scrambling to resolve the issues as they arise. Until one day it dawns upon us and we realize the table has always been made of melting ice turning to various levels of slushy water each night sometime between preparation and meal time.

In this equation, we as sound engineers and system techs are the waiters setting the table, the band is the chef in the kitchen and the show audience is the dinner guests. Not unlike the sloshy water table party, we too as sound engineers, face the challenges of a changing and interactive environment. The venues we setup in may well be the same physical dimensions throughout the night but come showtime, the world we mix in often has significantly differing acoustic properties. My questions are: With so much precise analysis and prediction, why do we still enter showtime with so many loose ends unresolved? and Why do we not have an advanced set of tools to solve it?

I find tuning sound systems to be a real world example of what I wrote in the first paragraph regarding people clustering efforts in one direction while turning a blind eye to other critically important issues that dramatically effect the quality of the outcome. For example; it is not uncommon to spend surprising amount of time fine adjusting every single detail of time alignment, phase alignment and loudspeaker positioning resulting with complex EQ curves and extremely precisely calculated alignments. Then, after all of that time and energy spent on tuning, it is naturally tempting to have a  a vested interest in the correctness of those settings and to embrace an “I have this perfectly dialed in, don’t touch anything” mentality.

Meanwhile, many if not most situations wherein a sound system is setup, tested and tuned for sound check we find that the tonal balance and coverage of the sound system has significantly changed by show time. Perhaps we knowingly already made some predictive adjustments, perhaps we kept our settings from the previous night, to fall back on or maybe we just avoid soundcheck tuning altogether and use a previous gig file with some modifications for system configurations changes. Regardless, there is the clear and persistent disconnect between what we measure in an empty room and what we experience at show time.

Why? Why does the status quo of system tuning seem so relentlessly shortsighted? Is it ok to be repeating the same plan over and over again when nearly every time the results are flawed? Is the change in sound just some odd mystery that no one truly understands or is it just so unsolvable that we just ignore it and do a blind approximation after spending hours avoiding approximations?

Ah yes, its been repeated so many times it has actually become humorous. “Yeah yeah, it will sound better once the room is full” mocks the band back at me when I used to offer that as an explanation. Somehow as if we have the sound now and then we will have a different sound later and since we have no way of knowing what the other sound will be except different and most likely better but usually worse at first before we fix it.

Is it possible to bridge the gap? Is it possible to predict and compensate the difference between an empty and full room? Cold and warm room? Sunshine versus nightfall? I realize it may be a complex endeavor to predict the way an audience and environmental factors will alter the sound of a venue, but how complex? More complex that predicting the weather week in advance or designing a digital processor? We know where the people will be. It can not be that complex to calculate the approximate sound absorption of typical clothing and the sonic diffusive nature of a cluster of  human bodies. We know the average skin temperature and it would not be a stretch to calculate a thermal range for the amount of heat generated by dancing versus sitting. In most indoor venues we can have control over the room temperature and for outdoor venues, it is pretty easy to find out approximately what the air temperature will be. Is it truly out of our realm to continue the meticulous system tuning and carry it forward into the probable influences of the known factors?

One common issue I encounter involves flown clusters at outdoor festivals. Here are three scenarios:

  • The coverage area that the predictions software indicates based on the temperature used in the calculations
  • The actual coverage that occurs during the warm day wherein that heat from the ground refracts the sound upward and extends the coverage area, sometime hundreds of feet.
  • The coverage where the ground is colder than the air and shortens the coverage until the audience brings in their warm bodies creating a warm layer and extending the coverage.
As the coverage area is increased or decreased, there are also noticeable tonal changes that occur. The refractive changes caused by temperature are more prominent in high frequencies which means that as the coverage area is reduced, the sound in the coverage area gets brighter.
Ok so out of all of this, here are a few things:
  • The sound of a venue over time is dynamic and constantly changing due to numerous factors, I covered mainly thermal but wind, diffusion and absorption by humans as well as attenuation of frequencies over longer distances due to temperature/humidity.
  • Prediction software will not give you correct results if the real world environment is vastly different than the prediction environment. If the prediction is for 70F and the venue has 85F degree humans packed tight on a 60F degree night, the actual coverage will be way off.
  • It is important to properly tune and align a system, it is also important to be prepared for the inevitable changes that will occur when the people arrive and environment changes. Take note of the changes that occur and build a strategy for dealing with them into your system tuning plan.
Here are a few things that I do:

First of all, knowing that the venue sound is constantly changing I follow a “what EQ’s what” strategy. I use the channel EQ’s to make the mic/instrument combo sound correct.  I use the system processor  to fix any issues with the sound of the loudspeaker system design and array configuration issues. And I use a house EQ as a hands on control to deal with the constantly changing room sound.

For over a decade now I have been carrying an infrared thermometer which I use to measure room temperatures and work with the production manager and venue to try and create a consistent thermal environment.

I started using a Fluke Thermal Imaging Camera so I will be able to take more accurate readings.

I wrote an article called Thermodynamics of a Rock Show for Live Sound Magazine a while back which was nice to see recently re-released.

I posted  youtube video showing how a heatgun can demonstrate the refraction of sound away from the heat.

In the Youtube video I used a highly directional Parametric Speaker by SoundLazer which functioned well for the demonstration but I I felt the demo would be even more credible if I used a conventional sound source. So I did a short instagram video showing the heat from a stove burner altering the sound from a Jambox speaker.

Here is an article called Thermodynamics of a Rock Show for Live Sound Magazine a while back which was nice to see recently re-released.

Here a great article by Dennis A. Bohn from Rane Corporation:

Cool cool, as you can tell I am dwelling further into the heat aspects of sound for awhile.  Hopefully to find some ways to make things a bit more predictable.



Author: Dave Rat

Sound consultant, sound system designer, curious human