Originally published in the May 1999 issue of:

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System Measurement and the Contractor

by Barry McKinnon

of Mc2Systems Design Group

If you ask many contractors why they make measurements, they'll tell you it's because they have to, it's in the specification.

Luckily test equipment hasn't increased in cost the way the original 427 Shelby Cobras increased in value.

Over the past 20 years measurement systems and equipment have dropped significantly in cost, while improving in precision and accuracy. We've also had entirely new methods of measurement introduced in that time such as TDS (Time Delay Spectrometry) measurement that has led to new insights into how sound systems operate in the real world. As an industry we've been presented with literally dozens of new and cost-effective tools to measure the daylights out of everything we assemble, build and install. What hasn't changed is the reason we measure systems, but the reason we measure things is seldom addressed when we talk about measurement equipment, because there's an assumption made that everyone knows why we measure things.

If you ask many contractors why they make measurements, they'll tell you it's because they have to, it's in the specification. At the most superficial level that is true, it is in the specification, and the reason it has ended up written into the specification is that the knowledge of the bigger reason for making measurements seems to have been lost or ignored in the evolution of systems contracting market.

Set the Wayback Machine for 30 years ago Sherman, let's see how the industry got here. Historically, the system specification was written by the consultant, and the instructions for assembling and installing the system were passed down to the workman in the field, and after a time the consultant was called upon to view and pass judgement on the work to see if it was found wanting. The consultant would arrive, adjust, equalize, deliberate and measure the work against the specification and days later would emerge and present the deficiency list. This was known as the Golden Age of Consulting, and appears to be the source of the consultant imagery that persists to this day of a large entourage, the minions waving giant ostrich feather fans, childish imps sprinkling rose petals before the consultant etc. Well, nice image but, back in those days the reality was a full set of audio and video test equipment cost as much as three or four 427 Shelby Cobras, and the only people that would ever own that much test equipment was a consulting firm that made use of it on a regular basis. Much of it was so specialized (like the first Hewlett Packard 1/3 octave Real Time Analyzers developed for Don Davis at Altec Lansing) that it was out of reach of all but the largest sound contractors. Luckily test equipment hasn't increased in cost the way the original 427 Shelby Cobras increased in value.

Because the consultants owned that vast array of test equipment, consultants also reaped the biggest available benefit from making measurements, they learned a vast amount about the way the systems worked in the real world. And they learned the same way we all learn, by being surprised that things didn't always work the way they were expected to work. Because they owned the test equipment, they were able to invest the time and effort to see why things measured differently than they expected, and they learned the exceptions to the rules, and the reason behind the surprises and as a result those issues were no longer surprises, they anticipated those problems, and instead found new and different surprises and learned from correcting those difficulties as well.

When Richard Heyser's TDS system was presented to the world in a commercial form it arrived as a very expensive table full of Bruel & Kjaer measurement equipment, but some consultants immediately recognized the learning potential that this equipment presented, and purchased the system. Most contractors could only dream of investing $50,000+ in measurement equipment, even if they knew the potential. I remember attending the introductory sales tour of B&K's TDS system while I worked for a sound contractor and was amazed at the concept of being able to measure a speaker in a room while having the option of ignoring the room. It was several years later that I lobbied the owner of that sound contracting firm to purchase a TEF12 analyzer for less than 1/3 the cost of the original TDS equipment stack, and I made that sales pitch based on the value of the TEF as a tool to learn more about the systems we were building and installing. And as a result the TEF analyzer paid for itself in three years in outside billing alone... who says learning doesn't pay.

A close look at system measurement

...the contractor should not view measurement as a necessary and expensive evil that they are bound to by a contract.

The measurement process should make you question your assumptions about how things work.

Enough subtlety, a contractor should make measurements to learn more about the systems they build. And that's the reason to make measurements, to own measurement systems and to measure virtually everything that they assemble, build, or install. Now this statement makes another assumption, and that assumption is that they're in the contracting business because they are interested in being a systems integrator, and not just a box sales house, or a box sales house or music store with a wireman working for them. If the contractor is serious about the quality of work that they do, and about learning and understanding more about the systems that they install, and not just about meeting the terms of the specification document, or about having the fastest project turnaround possible, then they are in a position to reap the benefit of learning from the process of measurement. This means that the contractor should not view measurement as a necessary and expensive evil that they are bound to by a contract.

The process of measurement includes another inherent assumption. To measure a system, the technician must first understand in advance what it is that they expect to see when the measurements are made. One can only measure for what one expects to find. Which means that the technician needs to have some fundamental understanding of the system under test, and the type of variations from "normal" that they will encounter. This means that they will recognize valid results, and also recognize the exceptions and anomalies that will lead them to new understandings of the systems they install. This means that the contractor has to be prepared to spend the time to learn the fundamentals of the industry. There is no shortcut, there is no easy way to learn more about what you do as an industry. You can't hope to gain any real benefit from making measurements if you are not interested in delving below the most superficial layer (also known as the Marketing Layer) of the systems contracting industry.

Fast forward... so we are now past the Golden Age of Consulting, in a kind of Putty Beige Plastic Age of Consulting, and now the consultant is just like everyone else in the world, just as harried and as busy as they can possibly be, the rose petals and ostrich feather fans have been eliminated in the interest of economic efficiency, and time is a precious commodity. Because test instrumentation is no longer worth as much as an apartment in downtown Tokyo, the consultant is now expecting more from the systems contractor or integrator. In the Golden Age, the consultant was the only one who could truly tell when the terms of the specification was being met (indulge my hyperbole), now the consultant has a reasonable expectation that the contractor will own, or have access to, enough test equipment that basic measurements and setup should be done by the contractor as part of the process of determining when it's time for a substantial completion inspection. I don't think any consultant is amused by the idea of travelling to a site only to find that only half the system passes signal, or that the system gain structure or routing is incorrect.

By requiring the contractor to make those initial measurements and system adjustments, the consultant is also transferring to the contractor the opportunity to learn from mistakes, and quantifying the mistakes through measurement. In an ideal situation the contractor will find most of the measurable signal path deficiencies, and fix them, long before the consultant arrives on site. This greatly speeds the system commissioning process, and reduces costs for the client/owner of the facility, as it is almost always less expensive (per hour) to have the contractor find problems than the consultant. From the consultant's perspective this also means that the contractor should have a much more thorough grasp of the system operation and function which improves the after sales support that they can provide to the client.

For the systems contractors that also do their own design/build work, the measurement process provides an auto-didactic (self taught) process for thoroughly understanding systems design and operation issues such as gain structure, equalization, signal to noise ratio, and how those issues are interrelated to each other. More complex issues like compressor and limiter operation can be examined to understand how those devices operate on the signal path at a depth that will reveal far more than you can glean from listening tests alone.

On the electroacoustic side, making detailed loudspeaker system measurements with a time domain measurement system can reveal all the complexities of loudspeaker interaction and why some loudspeaker configurations work and some don't. Measuring is no substitute for listening, but can be a valuable adjunct to listening, and can train the motivated contractors to be more critical listeners. If you can hear it, you should be able to measure it, and if you understand the systems you're building, and the measurement systems you can use to measure them, then you can track down anything you hear or see.

The measurement process should make you question your assumptions about how things work. For the contractors that really have an interest in understanding how things work, rather than simply trying hard to prove their existing assumptions no matter what evidence is presented to the contrary, the process of measuring systems can be an amazing eye opener. Testing and measurement have to be approached with full scientific method, you start with an assumption, measure and test for it, if the evidence supports your assumption, fine, if not, rethink the assumption and test again until your assumptions match reality. The world (and the laws of physics that control our systems operation) is what it is, and we have to find the method of measuring it that reveals the reality that it operates under.

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