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Why Measure A Sound System? A Detailed Look At Where It Matters

It’s not at all clear that we’re correctly interpreting or understanding measurement results

By Bob Thurmond September 15, 2016

There exists a long list of important sound system characteristics that we have no meaningful way to measure or evaluate.

Besides, the really important skill is to be able to listen, identify problems by ear and correct them on the spot, right? But is this realistic or just an elusive dream?

Even if problems can be identified subjectively, they still need to be solved physically. Therefore, we must know exactly what, where and how much. These parameters can be learned with a lot of “cut and try”—or by measuring.

True, there are cases where measurement did not lead to a good solution, but this doesn’t mean that it’s useless. Rather it’s more likely that the measurements taken were inadequate, or weren’t the right ones, or that the results were misinterpreted.

Meaningful, useful system performance measurements have been taken and used beneficially for decades. The techniques involved are widely available and not difficult, but still little known.

Perhaps looking at a specific example to see exactly what was done, what was learned and what was gained can be instructive.

Wayback Machine
It’s 1984, and I’m working at the Aquacade, part of the New Orleans World’s Fair. The test equipment is a standard GenRad (now Teradyne) unit.

Why look at a 20-year-old project done with 50-year-old test gear rather than something more current? Stay with me…

The project requires me to assist in the design and execution of systems at several venues, and nearly all of the sound system equipment has been supplied by a MI manufacturer. The design challenge: figuring out how best to use the given system items.

Program material for the Aquacade is pre-recorded stereo music tracks and live announcements via a wireless microphone system. The loudspeaker allotment is just six two-way cabinets (compression drivers on 90-degree horns plus 15-inch woofers).

Figure 1.  The Aquacade, with loudspeakers located in the dark sheds atop the structures behind the corners of the pool. (click to enlarge)

The seating area to be covered are fairly high bleachers gently arced around the pool. (Figure 1)

I succeed in getting the loudspeakers located high enough to attain decent front-to-rear coverage, but they are required to be housed inside weather-resistant enclosures behind two “corners “of the pool. (Talk about interesting resonances!)

Each enclosure includes three loudspeakers, placed side-by-side and aiming straight out. Horizontal coverage stinks, and overall sound quality isn’t much better.

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