Sound and vibration quality and target development

Engineering services for establishing objective sound and vibration quality metrics and targets that correlate with end-user subjective preferences.

The sound quality of a product plays a big part in how end users perceive the overall product quality. Some product noise is inevitable, but it can often be transformed into something less objectionable or even a pleasant sound, like the roar of an engine. However, sound quality perception is subjective. To work with it in a structured manner, it is necessary to establish objective sound and vibration quality targets which correlate to end-user subjective preferences. This can also assist in the development of more representative pass/fail criteria that can be incorporated into the manufacturing process taking the guesswork out of subjective sound quality specifications.

We have worked with a number of customers on projects such as jury studies to capture users’ subjective preferences and correlating them to objective data, development of sound quality metrics and targets for a variety of products, and turning these into recommendations on how to improve the SQ performance.  

Here are some of the projects we have worked on with customers to optimize product sound and vibration quality:

Subaru wanted to identify the sources of vibroacoustic emissions that drivers both hear and feel, understand their sound and vibration strengths and weaknesses and thereby ensure it was continuing to deliver what customers want from their current and future vehicles in terms of NVH performance and character.

We worked together with Subaru at the Application Research Centre and conducted numerous in-depth subjective and objective studies of sound and vibration of both their own and competitors’ vehicles. A test-based SPC model was built to predict the noise contributions from different sources and to identify the dominant sources and paths affecting these contributions. And to ensure that customers’ expectations were met, another project was developed to create sound quality targets and a subjective jury evaluation using the Brüel & Kjær NVH Simulator. We were able to help the Subaru fine-tune their existing sounds – identifying sounds that customers found desirable in some vehicles but not others – and create virtual prototypes for developing the characteristics of future vehicles.

> Read the full case study

Acoustic brand management allows for better brand differentiation, higher brand recognition, stronger emotional reaction from consumers and therefore an improved experience of the brand. An automotive OEM wished to develop a brand sound identity for one of its vehicle lines. The vehicle OEM also needed to develop powertrain Sound Quality (SQ) metrics correlated to the Brand Image. To this end, binaural acoustic data was collected at the driver and passenger’s positions while driving both OEM and competitive vehicles on the road in normal driving conditions. We developed a software application specifically for the subjective evaluation of the recorded sounds on the Powerful/Refined plane. Sounds were grouped by vehicle segment and compared to the SQ Metrics to show what features of sound correlated best to each of those descriptions. The OEM was able to use this information to define sound quality design targets.

An automotive OEM wanted to investigate the mechanisms affecting the perception of impact harshness and develop objective metrics for both acoustic and tactile cues. Operating acoustic and vibration measurements at the human-vehicle interfaces were conducted on-road during the subjective assessment. Operating deflection shapes (ODS), wavelet spectrograms, time domain (envelope), frequency domain (energy spectral density), sound quality, and vibration quality metrics were all measured/calculated to identifying the relative importance (contribution) to overall perceived impact harshness of the different vehicle interfaces. A preliminary model of impact harshness perception was developed along with a recommended roadmap for further refinement by leveraging in-lab simulation tools in place of actual road tests.
A North American vehicle OEM wanted to establish acceptability/annoyance thresholds for the sounds generated by the exhaust system after the engine is shut off. These are transient, ping/pop type of sounds. They are caused by the metal reacting to the temperature gradient as the exhaust cools down. The vehicle OEM recorded all data following their test procedure, and supplied the data to us for analysis. A formal jury test was designed and used to determine customer reaction to these sounds. The results of the jury test were used to develop a preference equation that predicts the customer annoyance from key objective attributes of measured data. In addition, a formal test procedure was published by the OEM for their exhaust suppliers  whom we have helped meet these new targets.
Wind noise sound quality measured with microphone and HATSAn automotive glass supplier wished to understand the impact of acoustic laminated glass with respect to wind noise for different vehicles and segments. We collected various acoustic binaural recordings in-vehicle at the driver’s and passenger’s positions during normal driving conditions, with windshields of different glass composition. Some of the recordings were used to synthesize virtual sounds representing different characteristics. Recorded and synthesized signals were then used to design a formal Sound Quality jury test where jurors were asked to indicate their preference. The results of the subjective tests were correlated to wind noise sound quality metrics to develop a predictive model that can be used in product development and evaluation.

A manufacturer of premium home refrigeration appliances had already worked with us on a jury study to audit their products during normal operation and to drive Sound Quality performance during their product development. A follow-on project was undertaken to include similar analysis for start-up and shut-down events. Acoustic measurements of transient refrigerator events were collected and used to assemble a formal jury test. The results from the jury test were used to develop a preference equation that could be used in conjunction with the existing “running sounds” model. The consumer products manufacturer is now able to more effectively use Sound Quality models to project customer preference from measured objective data.

Investigation of a High Frequency Sound Quality Concern in a Refrigerator and Resulting Compressor Design Study (Conference paper)

Alarm sounds in the medical industry must be easily detectable and recognizable so that an immediate and appropriate course of action may be taken by caregivers in the event of an alarm sounding. A medical technology supplier approached us for help to perform a study of existing medical alarm sounds so that they could develop an alarm sound for a new product. Our engineers measured alarms sounds on-site at three hospital locations using both a Binaural Head and Torso Simulator and a hand-held sound-level meter.

Medical alarm sound data acquisition and analysis

These sounds were collectively analyzed to gain an understanding of their time and frequency domain contents, and to determine what opportunities exist for new alarm sounds.

A medical equipment manufacturer requested help in estimating the how the sound of a dialysis machine disturbs sleeping patients. Acoustic binaural recordings were measured to mimic what the patient would hear in the course of normal operation of the device. We developed a method of analysis using sound quality metrics to best understand what impact the machine would have on sleep disturbance. These results can be used by the manufacturer to set target levels and metrics for product development.

Product sound quality and sleep disturbance (Conference paper)

A medical corporation that provides research and development for major corporate clients outsourced measurement of sound quality performance and definition of a sound quality test procedure on a home dialysis system to us. Operating acoustic measurements were collected within a hemi-anechoic chamber. To analyze time domain, narrow band spectra, and sound quality metrics, binaural measurements were used. A preference equation was derived based on key attributes of the sounds from the analysis techniques discussed and a formal jury study. This testing allowed the customer to improve its customer’s perception of quality for their dialysis system by moving from subjectively capturing customer preferences to using objective measures. The results will also enable the customer to use objective data to drive development work in the future.

A forklift truck manufacturer asked that we work alongside their engineers as a technical consultant on a sound quality project. Acoustic measurements were made to construct a matrix of sounds for a formal jury test.

Fork lift sound quality

We used the jury test results to create a preference equation using key metrics from the measured sounds, which in turn was used to derive preliminary sound quality targets for product development. The manufacturer was able to use the derived targets to drive the development of vehicle components to achieve the desired overall vehicle image in terms of sound quality. Throughout the course of the project, the manufacturer’s engineers received technical training and direction in the processes as well as methodology in developing a formal sound quality jury test.

> Read the full case study

A manufacturer of small engines used in lawn care products wanted to establish sound quality targets for product development and to drive marketing efforts to establish a new, best-in-class acoustic image for their products. Jury evaluation and Source Path Contribution (SPC) analyses were conducted in USA, Europe and Australia. The results were used to identify the dominant characteristics of mower sound, and then determine which components contribute most to the creation of those characteristics. Analysis of the results in various global markets showed fundamental agreement of Sound Quality preference. However, this study helped to identify subtle differences in each market based on real customer expectations. The jury results were used in conjunction with the SPC results to aid the manufacturer in setting targets for future product development and provided a firm justification for their sales and marketing direction.

development of car door closure sound quality

An automotive OEM wanted to identify objective metrics for the perceived quality of door closure sound. Acoustic binaural data were recorded from door closure events of multiple vehicles. A formal jury test was designed and conducted and the results were used to develop a functional relationship between perceived sound quality and objective signal parameters. This allowed the vehicle OEM to develop objective sound quality targets to be used during vehicle development.

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