Making of a Hand-Held Analyzer, The

Weir, Jim

My first experience with a sound level meter was as a young avionics engineer at tho Loarjet Company, I was asked to evaluate some cockpit noise levels. My visit to tho tool crib brought me face to face with a pale green instrument that was a bit intimidating, if only by its size. It barely fit in my large hands, and definitely two hands were required. The sturdy instrument offered a tapered ‘top’ to minimize reflections that may disturb the accuracy, and had only two knobs, making it easy to figure out. The top ‘Range’ knob was a clever double attenuator that allowed me to set the measured level to easily fall within the instrument’s massive 20 dB display range.

History. The instrument I used was the first generation sound level meter/analyzer by Brüel & Kjær, the Type 2203. In 1965, the Type 2203 changed the way sound level meters looked, and in many ways how we used them. Massive gray boxes with gooseneck microphones, usually from General Radio, were its predecessors.

I joined Brüel & Kjær in 1983, when we were introducing our second generation of hand-held analyzers, and the first microprocessor-controlled model on the market, the Type 2230. just a few years later, the programmable Type 2231 followed. The shape of the analyzers was similar to the older instruments, though now they fitted easily in one hand. That let you use your other hand to set the controls to display the many parameters stored in the analyzer’s memory. Start a measurement and you could switch between maximum, minimum, and L^sub eq^ – the average level.

Technology Never Sleeps. Along with technology, the needs of acousticians and other users started to creep into standards, and the requirement for sound measurements grew in scope and scale. By the mid ’90s, statistical parameters like L^sub dn^, L^sub 10^ and L^sub 90^ became common measurement requirements and no longer was it sufficient to measure values over a fixed time period. At Brüel & Kjær, Multi-D(TM) measurements of level vs. time vs. frequency was introduced with the 2260 Investigator Platform almost a decade ago. Now a digital signal processor and a microprocessor collaborated to fill up megabytes of information the users could vise for diagnostics and analysis.

Interestingly, Brüel & Kjær used this third generation product to introduce the first new shape in hand-held analyzers. The display section was moved to the more practical user end of the instrument. The controls were moved toward the middle of the unit so it could be gripped and operated by one hand. And, the sleek distinctive shape minimized disturbing reflections from the measurement end of the instrument.

Brüel & Kjær used the latest technologies available when introducing the Type 2260 Investigator. This, coupled with the Investigator’s flexibility of applicationbased measurement technology, has enabled the instrument to persevere in a competitive market, with sales increases in each successive year. In 2003, the Type 2260 platform sales in North America and worldwide wore the best ever.

Planning Ahead. As innovative as a company can be, it is useful now and then to get a reality check on the direction you are moving. Sometimes, the reality check comes from a now competitor introducing new technology. The reality check may also come from an unexpected drop in sales when customers’ needs drift away from the products and services you provide.

A few years ago, the environmental marketing group at Brüel & Kjær began a project to initiate a reality check of our own. We called it the Handyman project. New technologies such as laptop computers and Palm PCs were now capable of serving the portable sound measurement market. We asked ourselves, “What do our customers want to have to perform their jobs?”

More important actually, is that we went to the customers and asked them that question. We enlisted sixty customers considered to be expert users of hand-held sound level meters/analyzers and interviewed them about their job function and work processes. We mediated discussions in small groups about such things as platform type, workflows, integration, and reporting . . . “Do you want to bring your laptop into the field?” for example.

We then engaged in ‘brainstorming’ sessions with these users, letting them come up with ideas, characteristics and features. We made a feature puzzle, with each expert using a stack of tiles, each one representing a feasible instrument feature or characteristic (like “color screen”) and a playing area. They then had to fill the playing area with tiles. Easy enough, except that there were more tiles than space on the playing area, so a choice had to be made. The result was a set of desirable features. The playing area was then halved, and the process repeated (using the same set of liles). The playing area was halved once more and the tiles placed again. The result for each member was therefore a description of three instruments representing the nice to have, should have and must have features.

Time to Start. About the time we were wrapping up the Handyman research project, we were getting one of those unexpected reality checks. The sales of our mid-range sound level meters, Type 2236 and 2238 had fallen off 30 to 40% from peak levels in the late ‘9Qs. We discovered that while the measurements these instruments made were sufficient for most customers, some of our customers were looking for additional features like real-time frequency analysis and a 100 dB dynamic range. Now was the time to place the Handyman research into practice.

During this project, a reoccurring set of descriptors continued to show up in our discussions. We would hear, “It has to be easy to … (hold, use, set up, calibrate, etc.) or “Our (data, measurement, use) has to bo safe.” And, “It would sure be clover if it could . . . (record sound, use standard memory cards, accept sound and vibration transducers, etc.) The words ‘easy,’ ‘safe’ and ‘clever’ became the mantra for the development of the new instrument.

When designing the Type 2250, every idea and feature was tested against “Is it easy, safe and clever?” If the answer was no, then either the idea was modified until a yes was achieved, or the idea was scrapped.

The feature set chosen by the experts in the Handyman project allowed us to rapidly accelerate the design and development of the new instrument. We knew what features we had to include, and we had a guideline to define the technologies customers were expecting for the next mid-range platform hand-held analyzer.

An Instrument Takes Shape. For example, the panels of experts said the Type 2250 should be safe to hold, so an instrument with a pre-formed handle like on a power-tool would be ideal. Unfortunately, this was unacceptable from an acoustical standpoint. There was obviously a conflict here. Instead, a streamlined model of the proposed instrument was made in soft clay, and then given to a large number of people to hold.

Over time, the combined grips of big and small hands, with long, short, wide or narrow fingers, made indents in the model (see Figure 2). This gave us an average grip shape. This shape was then modeled in a computer-aided design system that could also perform acoustical calculations. They showed where the grip shape caused the frequency response to fall out of tolerance. By iteration, the shape was modified to make the frequency response acceptable. When finished, a solid model was made from a polyethylene block, and tested on the same people. This revealed that the grip was good, but still suffered from small aberrations. So the whole process was repeated, the final result being the shape used for the Type 2250 today.

Sandy McDonnell, of McDonnell-Douglas Aircraft Company, once said of the dovelopment of a new aircraft, “When the weight of the paper matches the weight of the airplane, it will fly.” Well, a handheld analyzer isn’t a DC-10, but we had a ton of features to fit into our little instrument to be. And it had to be Easy, Safe and Clever. From the experts’ input it was obvious that a dedicated hand-held platform was preferred over hybrid Palm-PC or laptop data acquisition formats. Because we could make it environmentally rugged, we could control the way the user operates the device.

It was decided early that a color touch screen is a convenient user interface. But it is clever to include screen formats with high contrast for daytime measurements and a low contrast night vision mode for measurements in the dark. Also, you may need one-handed control of the instrument so buttons can be used to navigate the functions of the touch screen. It was also clever to allow the buttons to be back lighted for easy nighttime operation.

Technology developments allowed us do some things nobody has done before. We can now measure from a standard microphone’s noise floor to 140 dB for broadband measurements (weighting networks A, C and Z) and also maintain the same dynamic range for octave and 1/3-octave measurements. Now, you are unlikely to overload or under-range a measurement by mistake. Technology also brought us the latest low power consumption DSP and microprocessors to provide extended battery life, while the latest battery technology allows one to get thousands of recharge cycles from a single battery.

One unique feature that came from the Handyman project is the Type 2250 user log-in that lets one customize and save individual setups and measurement templates, while a colleague can use their own personalized configurations. And, as the experts requested, the instrument is easily setup and synchronized with a PC using included software, making it even easier to download and upload measurements and settings.

Perhaps the most daunting task was that of the hardware designers to fit all this stuff into the marketing teams’ easy to hold compact hand-held analyzer package. USB, compact flash interlace, SD memory slot, signal input (with accelerometer power supply), trigger connector and a standard headphone mini-jack all had to fit on the rear face alone. The Type 2250 has to be water resistant, retain its look and feel over a wide temperature range, and meet the demanding standards of a next generation Brüel & Kjær sound level meter. Turn the meter on, touch a log-in ID, and press [black right triangle]/|| . Thats it! You are measuring the way you want – Easy, Safe, Clever.

Acknowledgments. We are grateful to julian Simpson and the rest of the 35 + member Briiel & Kjasr Denmark Marketing and Development team for their information, support and pictures.

Jim Weir, Brüel & Kjær North America, Norcross, Georgia

Jim Weir, jim.wuir@bksv.uuni, is a product manager with Bruel & Kjeer, Norcross, GA. You can take a tour of the new Type 2250 at;

Copyright Acoustical Publications, Inc. Jul 2004

Provided by ProQuest Information and Learning Company. All rights Reserved

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