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When Eyes And Ears Don’t Agree: Perspective On The Role Of Measurement
Sound system design and implementation is first an engineering practice
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REALITY DISTORTION?

We work in an industry where a lot of money is made by distorting reality. You can drop a thousand dollars on a processor that essentially increases the harmonic distortion of your system or fills its response with deep notches, and feel like you have improved its sound quality.

Yet no one buys a processor for a television that makes the grass look blue or the sky look green. When the goal of a system is accurate sound reproduction (this isn’t always the goal) then accurate has no meaning unless a benchmark exists. This is where measurement comes in.

Consider the following scenarios:

1) You’re at an airport and you hear a perfectly awful announ-cement come over the sound system. Why did it sound bad? The initial reaction is usually to blame the loudspeaker, since it is where the bad sound came from.

But a good loudspeaker that is fed bad program material will still sound bad. Perhaps the problem is an overdriven amplifier, or poor micing technique on the part of the talker. How would one find out?

Once again, we return to measurement. If I feed the loudspeaker a known stimulus and it can reproduce it with good fidelity, then the problem lies elsewhere in the system. The process is repeated until the offending component is found, which could ultimately be a gate agent with a bad head cold. A sound system is only as good as its weakest link, and measurement is necessary to test the links.

2) A manufacturer may complete a run of loudspeakers, and find that two picked at random for a listening test sound dramatically different. Which one is the most “correct?” A measurement can provide the answer. Loudspeaker manufacturers measure each loudspeaker that comes off the line to assure that it falls within a set of tolerance values that were established during the model’s design.

Only measurements can verify that the replicas are identical to the original. No one wants to buy a loudspeaker whose only validation of performance was “Bill’s ears in Quality Control”. Bill may have been tired when my loudspeaker rolled off the line!

3) You’ve been called to tune a sound system which the client complains lacks “presence”. Most people would start boosting the high-frequency tone controls or the house equalizer to “restore” it.

But what if the system simply lacks the bandwidth to reproduce full-range music? A mixer with all of the high-frequency tone controls fully clockwise and a “smiley face” on the house EQ is probably deficient in bandwidth. Either that, or the sound guy just retired from 20 years on the road as “monitor engineer” for a heavy metal band. Some simple measurements can reveal whether the system is capable of what you are asking it to do.

4) The congregation at a local house of worship complains about poor intelligibility from the house system. Three different people have been consulted about the problem, and each of them suspects a different cause. Now how do we really get to the bottom of this?

The answer, of course, is measurement. It’s possible to spend a vast amount of time and money “fixing” the wrong problem. None of us would submit to surgery because our doctor suspects that we need it. We rely on X-Rays and CAT scans to reduce the risk of an incorrect diagnosis.

ORDER THE COMBO

Most sound system chores require a combination of listening and measurement. One without the other can yield completely unsatisfactory results. The two used together can quickly bring a system to its fullest potential, and also reveal the shortcomings of a sound system that might be addressed by equipment upgrades, changes to room acoustics, etc.

Those that don’t measure are operating in a world without references where “anything goes.” This approach is fine for purely artistic endeavors, but sound system design and implementation is first an engineering practice. Loudspeaker selection and placement is mostly science, while selecting what color to paint them is mostly art.

“Mostly” leaves room for the other, but points to the dominant process. Measurements assure that the science has been satisfied, paving the way for the artistic use of the sound system.

Pat and Brenda Brown own and operate SynAudCon, the leading independent professional audio education source, with training sessions held around the world and online. For more info go to www.synaudcon.com.


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