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The Carbon Footprint of Mall Music: Nitty-gritty

By Nik Sawe

Q: What is the carbon footprint of all the wretched, canned pop music played incessantly in the retail stores and malls of the world?

Asked by Gregory Wright, ’70, Sherman Oaks, Calif.

In the Essential Answer we gave you a ballpark of the carbon footprint created by piped music in U.S. malls, but we didn't explain how we got there. Now we'd like to go a little deeper into the numbers game behind audio power requirements and give you an idea of how it differs from continuously power-intensive devices like air conditioning and light bulbs. As you'll see, there are plenty of assumptions and a few uncertainties along the way, but our best estimate is pretty astounding: more than 7 million pounds of CO2 annually.

Crunching the Numbers: How does bad mall music translate into 40 billion pounds of CO2 emissions annually in the United States?

Soundsphere Loudspeakers, which makes speaker systems for retail spaces, has a handy System Configurator that determines the number of speakers you'll need for your space and the total power requirements of that system. What you get depends on several factors, principally the ceiling height, square footage of the complex and the amount of ambient noise you wish to overcome. Sound systems in public centers are generally set up to be audible against an ambient noise level of about 60-70 decibels (dB). For comparison, the gentle whisper of falling leaves is about 20 dB, and conversational speech runs about 60 dB. But what's a fair square footage? If you look at two of the shopping malls around Stanford, Westfield Valley Fair in Santa Clara and the Great Mall in Milpitas, they clock in at a whopping 1,478,000 and 1,357,000 square feet, respectively.

According to the International Council of Shopping Centers, the United States is home to more than 7 billion square feet of shopping center space. If we assume the average speaker is placed at 14 feet of height, and that these systems are designed to overcome an ambient noise level of 70 dB, Soundsphere's System Configurator ends up giving us a continuous power requirement for all those shopping centers of 3.9 megawatts. Let's assume these malls are open an average of 10 hours a day, 30 days a month. That's a collective 1.18 gigawatt-hours a month, and 14.15 gigawatt-hours annually. According to the utility company PG&E, one kilowatt-hour produces 0.524 pounds of CO2. If we extrapolate, we're putting out more than 618,000 pounds of carbon per month for music most of us aren't even paying attention to—that's more than seven million pounds of carbon per year.

Who thought this song was a good idea, anyway?

Charles Kettering, the head of research for General Motors, is famously quoted around the Depression era for saying, "The key to economic prosperity is the organized creation of dissatisfaction." This is a rather apt way for thinking about the presence of bland, persistent mall music: it may keep us vaguely dissatisfied with our predicament and subtly encourage us to buy our way out of it. And it was in Kettering's era, during the 1930s, that Muzak Holdings LLC first introduced the idea of background music in retail stores. From the beginning, Muzak's distributed tracks were bland by nature, with guidelines on song tempo and dynamics to help create a sedate and familiar atmosphere.

Ronald Radano, a music professor at the University of Wisconsin, wrote this paper in 1989 explaining the psychological and music theory behind Muzak. But for most of us, the reasons and history behind mall music are irrelevant. It's enough to know that we just plain don't like it. And it's worth noting that Muzak Holdings LLC went bankrupt in 2009. They're restructuring now. Hopefully, their new game plan will include music that's a bit more palatable.

Why bluegrass may be more eco-friendly than heavy metal

We mentioned that a 100-watt amp doesn't place the same power demands on the grid as a 100-watt lightbulb. The lightbulb is consuming the entire 100 watts whenever it's on, placing a constant electrical load on the system. The listed wattage in a speaker is the maximum it's capable of utilizing. Whether this will be fully employed depends on the strength of the music's signal and thus its varying decibel level, as shown below. This means that for a given song, at a given volume, we'll be using more or less power—for example, Soundsphere's typical mall/grocery store Q-8 speakers are rated at 100 watts RMS, but in fact typically draw less than 1 watt.

Figure from JBL Professional white paper, "Speaker Power Requirements"
Peak and average power requirements.

In this example, the amp needs to be capable of handling a least 300 watts of power, despite the fact that most of the sample audio signal clocks in at around a watt. Speaker systems are often "tapped" to a maximum wattage, setting the maximum amount of watts a particular speaker will draw in a system. For background music in retail venues, tapping the speaker at 1-2 W is common, and in our earlier computations, Soundsphere designed coverage so that each speaker only demanded about 0.9 W out of the system (the large number of speakers optimized coverage, but did not require each speaker to be especially loud, so the net power requirement was still quite reasonable). We can see that stronger signals, which have higher decibel levels, will raise the average power level required. This makes intuitive sense: louder music requires larger vibration and more energy. So a bluegrass or classical music track is likely going to have a less robust signal profile than a death metal opus, and demand less power from the system.

What does all this mean for malls and retail centers? The passive, canned elevator music they pipe through the halls has one saving grace: its relatively subdued role as background noise demands less power than if livelier, louder music was played. But as we've seen from mall music's heavy carbon footprint, everyone would be a lot happier and better off the world over if they just turned the music off.

NIK SAWE, '07, is a PhD student in the Emmett Interdisciplinary Program in Environment and Resources.

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