AF’s Weblog

December 21, 2009

The Thermodynamics of a Rock Show

Optimizing Live Sound

No matter what you test or measure, a considerable part of the sound of the show is controlled by environmental factors that are constantly changing. Knowing what they are is the first step toward being able to deal with them effectively.

Those of us who indulge in live sound spend countless hours paying attention to every detail in the audio signal chain – comparing, pondering opinionating and deciding every issue that crosses our path.  Does this mixing console sound better? Do I need to spend an extra $2,000 on a vocal compressor? Can you please move the guitar mic two millimeters to the left? Does phantom power really ruin ribbon mics?

One question persists, however: to what end is all this toiling done?


Blasting Perfection Into Chaos

Does it seem that a flown PA system sounds better than the exact same system ground stacked? How come it always sounds brighter when you stand on the mix riser?

Have you ever noticed that the same venue sounds different one night to the next, even when you do not change a thing? All of these things can be partially or completely explained by understanding the thermodynamics of a rock show.  Further, armed with this knowledge, you can make setup and mixing decisions that result in improvements that the people attending the show will actually notice – as opposed to things like fiddling with an expensive tube comp that the audience could not care less about.

This is not a scientific article peppered with equations; there are plenty of those out there already. My goal here is to present these complex factors as understandable concepts that will assist you as an engineer/system tech to optimize the sound in a venue.

In my mind, to keep things clear, I divide the relevant venue thermodynamics into three categories:

● Sonic absorption related issues

● Sonic direction related issues

● Sonic velocity related issues

So now let’s take a closer look…

The Bigger Picture

All in all, warmer and neutrally humid environments tend to be the way to go for a memorable adventure. Cold is drafty, sterile and often crisp and edgy sounding.  In my opinion, the hotter liquid atmosphere of a muggy rock show not only speeds up and tames the sound; it also seems to enhance that connection between the performers and those immersed in the performance.

Looking back at the three thermodynamic issues of absorption, direction and velocity, and combining those factors with practical experience, there are several useful concepts that can be distilled:

1) Humidity variations are sonically more tolerable in higher humidity environments.

2) Consistent temperature throughout the venue is sonically beneficial. Since the temperature of humans is fairly warm, and assuming humans will be attending the concert, having a reasonably warm venue temperature will assist in achieving that consistency.

3) A warmer indoor venue will tend raise in humidity levels more drastically than cooler venues due to human factors.

4) Sonic advantages are achieved by flying the loudspeakers.

5) Mixing a show while standing on a mix riser above the thermal/humidity provides the sound engineer an inaccurate representation of the sound the audience is hearing.

6) Venues with drastic variations in temperature and humidity tend to have complex and unpredictable responses.

7) No matter what you test or measure, a considerable part of the sound of the show is controlled by environmental factors that are constantly changing. Knowing what they are is the first step toward being able to deal with them effectively.

8) A thermometer and hygrometer can be useful tools for tracking and understanding more about how thermodynamics are affecting the sound of the show.

One of my favorite moments of mixing a show is the prediction and anticipation of that first note, the tones, the volume and the intensity of the unknown. The moment when the band first walks on stage is one of the biggest challenges any sound engineer faces.

Balancing all that knowledge with the tools at hand and formulating a mix to come up with a clear and accurate result is no easy task.  Each show presents a unique sonic landscape, and it is that uniqueness, that interaction between so many variables that we can and cannot control, that makes every live rock show a one-of-a-kind, potentially magical memorable experience.

To read the full detailed article see:  The Thermodynamics of a Rock Show

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