Uplifting Sound Quality For Crown

With sound quality in focus, Crown Equipment Corporation decided to explore how improving the sound of their forklift trucks could create a better product and, in turn, a more satisfying user experience. The result was better than they could have hoped for, with their newfound knowledge and skills leading to a more efficient and valuable development process – and the first of many new product designs.

Today, sound quality is being recognized more and more as an important parameter when defining product quality. 

Since our entry into the material handling industry in the 1960s, Crown has become known for exceptional product design, engineering, and manufacturing of an award-winning line of forklift trucks. However, in an industry facing product parity, we understand all too well how important it is for our products to have as many ‘quality defining’ features as possible in order to maintain our leading market position and support our sales processes.

Even though our trucks have always had a reputation for delivering market-leading functionality and performance, at Crown we have also focused on maintaining the highest quality when it comes to ergonomic features, such as comfort, style, and, naturally, noise – one particular area that we wanted to explore more deeply to augment our product development process.

Understanding the 'Crown sound'

Our central aim was to find new and more efficient ways to improve our development process. This represented a perfect opportunity to adopt the latest methods and state-of-the-art tools within NVH and sound quality.  

The decision was therefore made to examine sound quality in detail. On one hand, this valuable knowledge would help us to understand the factors that influence its perception; and on the other, it would also equip us with the right skills to engineer an even higher class of product. The big question was, how? 

Defining Goals For Sound Quality

In consultation with Brüel & Kjær, it quickly became clear that in order to create the ‘right’ forklift truck operating sound, we first needed to know what that sound actually was. To help clarify this, we brought on board Sound Answers, a sound and vibration consultancy company, who could help us advance our process and analysis abilities, and participate in design reviews based upon the analysis performed.

Sound Answers introduced the concept of a ‘Jury Study’ as one of the most effective ways of defining sound preference. This type of exercise involves a qualitative jury of end-users who rate the sound of a particular class of motorized vehicles in order of preference. These ratings are then correlated to highly specific sound quality metrics, such as sharpness, loudness, and modulation strength.

To collect the required data and generate the most conclusive results, Crown worked with Sound Answers to assemble two Jury Studies; one in the US and another in Germany. The juries consisted of managers and truck operators who were asked to rate a series of sounds from our own and our competitors’ equipment, which had been carefully recorded to eliminate any weighting or bias.

Jury selection and Sound Preference

The Jury Study proved to be very productive and enabled us to understand users’ sound preferences in more detail. In general, the results showed that people preferred forklift truck sounds to have a moderate level of low-frequency noise and be free of both high-pitched noises and excess modulation. The results also enabled us to pin down a specific combination that was the ‘preferred sound’. This could then be used as a benchmark for developing other products.

This led to several interesting conclusions. It enabled us to build an immediate ranking of how the recorded Crown products were judged against our competitors and to identify key opportunities, either for improvement or where we were already performing better. In addition to the recorded sounds, modified or synthesized sounds were included in the evaluation to help identify the dominant drive motor sounds that people preferred. Most interestingly – and usefully – these results enabled us to create a ‘Sound Quality Preference Equation’, a mathematical formula that could be used to accurately define the objective metrics of our ideal forklift truck sound (known as the Sound Target).

Virtual CAE Models

3D CAE models, like those created by Actran, enable engineers to validate and optimize designs using virtual prototypes. They are exceptionally valuable to reduce development time and cost by helping engineers to define and apply more precise results earlier in the design cycle.

This formula would help us to evaluate any of our trucks’ sound against our competitors’, reliably predict the impact of alternate designs, and communicate these clearly to our internal engineering teams.

In short, the equation would enable us to predict, measure, and make precise adjustments to the sound of all future product designs much earlier in the development phase and, crucially, based on actual user preference.

Putting Theory Into Reality

With this initial goal reached, we were then able to leverage what we had learned about defining, measuring, and analyzing sound quality and use it to support the development of a new sound quality model design; specifically, the exhaust system of our new line of LP Gas forklift trucks. 

At this stage, we were confident in our ability to put these new techniques into practice, with Brüel & Kjær and Sound Answers standing by to help us optimize the final design. Immediately, we were able to make full use of our new knowledge and tools; by running data through our Sound Quality Preference Equation, we could rank and analyze competitor products and set clear parameters for our own product’s sound quality target and design.

Then, in order to correlate, visualize and audition the test data, a 3D CAE model of the new exhaust system design was built using MSC Actran® acoustics software. In combination with Brüel & Kjær’s NVH post-processing software, Actran was able to simulate a working 3D model of our exhaust system that could display the mechanical, acoustic, and aeroacoustic characteristics of the system, along with its internal gas flow.

This enabled us to accurately predict and listen to how the final product would sound and behave under a wide variety of conditions.

Once we were satisfied with the CAE model design, we were able to move forward with a physical prototype. This allowed us to correlate the test results from the virtual and physical model and refine the design to bring the exhaust noise even closer to our Target Sound. As an important part of this, Brüel & Kjær’s Low-Frequency Sound Source tool was used to measure the transmission loss, which revealed how close our virtual model was to its physical counterpart. All this data could be correlated back to the Actran model to continue improving and optimizing the sound and, each time the model was updated, the results could be run through the Sound Quality Preference Equation to determine their impact.

Both indoors and out, sound can be an important customer consideration.

A final prototype was then built using the improved design from the updated Actran CAE model. Once it had been installed on a forklift truck, the entire project team, including those from Crown, Brüel & Kjær, Sound Answers, and MSC Software, each reviewed its performance in person for any final refinements. The unanimous decision was that the new exhaust system was a significant improvement over the previous design; an opinion that has since been widely affirmed across all our engineering teams.

The Value of Sound Quality: A Crowning Achievement

All of us at Crown have greatly valued Brüel & Kjær’s and Sound Answers’ roles in helping us to gain a firm understanding of how sound quality plays a vital part in product development – and how best to achieve it.

The entire exercise has had a major influence on how we conduct our development processes and now we are continuing to further develop our strong capabilities in acoustic modeling (along with other CAE tools). Previously, much of the important testing, evaluation, and refinement phases were weighted to the end of the project. Now, these can be conducted far more upstream, greatly shortening the development time, reducing the need for additional design-build-test iterations, and thereby significantly lowering development costs.

More importantly, this has enabled us to move from what was primarily a knowledge-based approach to one built on actual metrics. The data captured and results generated enable a far more efficient and effective development process where new learning can be transferred from one project to the next. As a result, we are now well on our way to a point where sound quality methods and acoustic modeling will be the principal means used to specify and validate noise requirements.

These methods and tools also have broad applications in many areas. We are conducting several projects aimed at reducing overall vehicle noise and vibration which will ultimately reduce operator exposure to noise and greatly enhance comfort and usability.

Crown’s vertically integrated processes provide a level of control and consistency that brings unsurpassed results for our customers. And today, with this invaluable new understanding, we are now equipped to lift those results even higher.