Measurement Troubleshooting and analysis

In order to effectively control noise levels at the operator position in a vehicle, it is important to have a good understanding of what elements of the vehicle contribute to the operator position levels. We performed source path contribution (SPC) analysis on a skid steer loader to help understand the dominant contributors to the operator position sound pressure levels. The SPC analysis requires acoustic (P/F) and vibration (A/F) transfer functions from the source locations to the receiver location in addition to operational source characterization (radiated acoustic and vibration) measurements, so that the contribution from each source and path may be calculated.

We augmented this analysis with what-if studies, in which the data was analyzed to show what reductions in source strength would be required to reduce the operator levels to a desired target level. From this testing and analysis, the vehicle manufacturer was able to gain a better understanding of how best to control the noise at the operator position. They also got an insight into and understanding of the SPC process and capabilities.

> BOBCAT reduces operation vibrations with whole-vehicle analysis (Case study)

A medical devices company needed assistance in evaluating the NVH performance of a wound therapy device and identifying best guidelines  for reducing noise and vibration. Operational noise and vibration measurements were conducted within a full-anechoic chamber. We used the source-path-receiver approach, concentrating on FFT and order analysis to identify the root causes of noise and vibration introduced by the device. 

From the test results, we were able to suggest effective countermeasures to reduce noise and vibration both at the source and along the path to the receiver. However, as the device was already well into development, the customer decided to implement only path-related countermeasures.

A manufacturer of agricultural, environmental, and construction equipment elected to outsource the measurement of sound power on their tub grinder. They also wanted to learn the techniques to troubleshoot their sound power issues on their own. Standardized sound power measurements were conducted and used to quantify sources with a focus on assessing which bands contributed the most to the overall level. Once focus was narrowed, both acoustical and structural resonances were calculated/measured to determine whether the root cause was a forced response or natural frequency. A root cause was identified and recommendations were accepted that significantly reduced the sound power results of the tub grinder. The customer learned the techniques used for this project so that they can solve similar issues in the future.

A Korean transplant  needed a buzz, squeak and rattle (BSR) validation of a facelift  of its production vehicle for the North American market. Areas of concern were the instrument panel, the centre console and the headliner. To conduct this test, we placed the vehicle on a 4-post shaker, with various drive files used to excite different BSR events.

To facilitate the communication with the Korean team, we used a spherical beamforming array system to take acoustic pictures of transient BSR events before and after the adjustments to the vehicle. 

A North American automotive OEM asked us to investigate the mechanisms that affect the sound quality (SQ) of a door closure event. Measurements were made on the customer’s vehicle and on a target vehicle with good door closure SQ. The vehicles were instrumented with seal pressure measuring systems, accelerometers to extract operating deflection shapes and strain sensors to estimate forces at the latch/striker position during controlled speed door closure events. Near-field acoustic holography measurements were also conducted to visualize the noise radiated from the door surface as a function of time and frequency. The collected data were analysed and compared to those from the other vehicles to draw conclusions regarding physical differences and to formulate hypotheses of dominant controlling mechanisms.

A tier 1 supplier of vehicle roof systems needed engineering support for: integrating their PULSE NVH production test systems into their production line; developing/setting product acceptance targets; and troubleshooting noise and vibration issues in the screened samples. Operational vibration measurements were made on a number of end-of-line systems in the US and abroad. Different analysis techniques were applied for each identified failure mode, such as frequency spectra, envelope analysis, and time-domain statistics. The source-path-receiver approach was used for troubleshooting NVH-related issues. Subsequently, the product acceptance criteria correlated to subjective preference and was implemented in the end-of-line production system.

An OEM that builds commercial truck power trains asked us to troubleshoot a vibration-related durability issue with its fuel lines. Vibration and strain measurements were taken on a dynamometer and at an off-site facility. These were compared to static modal component test results. The root cause of the high vibration was traced to modal alignment of the fuel system components. In the project, we devised and tested several countermeasures that significantly reduced fuel line vibration and strain on its mounting components.

A global provider of information technology services and equipment requested assistance in identifying sources of noise in their pay cheque sorter unit and providing countermeasure proposals for overall noise reduction. Both operational and stationary measurements were made in an anechoic chamber. Near-field acoustic holography measurements were made in conjunction with narrow-band, 1/3-octave band, and frequency response function (FRF) analysis to troubleshoot all relevant noise sources. Countermeasures to address resonance issues and lower overall levels were accepted by the customer. In addition, sound quality design recommendations were made which the customer decided to take into consideration during  future design processes.

A leader in the development, manufacture and worldwide distribution of electronic and electro-mechanical components and systems requested our help to understand and to identify the root cause of a noise issue that had delayed the release of one of their product lines. Operational acoustic and vibration, static FRF testing, and sound quality measurements were made to determine objective parameters to discriminate between good and bad. The source-path-receiver model was applied focusing on frequency domain analysis to identify the key noise characteristics of the objectionable noise. This resulted in the implementation of countermeasures to reduce the specific noise issue at points located both at the source and along the path to the receiver. The recommendations from the project helped the customer direct their efforts at launching this product line with an improved motor design.

A vacuum cleaner and floor care product manufacturer needed help to understand the main sources of noise that contribute most significantly to the overall sound pressure level and annoyance of the operator of an industrial vacuum cleaner. Operating noise measurements were taken in a hemi-anechoic chamber and a quiet room to better simulate a typical operating environment. Multiple microphones, a binaural head, and sound intensity mapping were analysed in both narrow-band and 1/3-octave bands to determine key noise sources. The outcome was a number of design recommendations that were incorporated into this product line and used as design guidelines in all future platforms.

Wind turbines are fitted with alarms to make sure any imbalances in the system are identified and corrected before a turbine develops critical faults. A maker of custom wind turbine blades and ventilation equipment asked us to investigate an imbalance issue in a blade at a customer site in Mexico, as the imbalance alarm kept sounding. To understand the issue, we conducted operational vibration measurements on-site. We used FFT, order analysis, and balancing techniques to characterize the imbalance associated with the blades. The measurements showed that it was not imbalances in the blades setting off the alarm. An issue elsewhere in the installation was the source of the vibration issues experienced by the blade manufacturer’s customer. 

A large vehicle chassis dynamometer exhibited excessive background noise in the 200 and 250 Hz band. We performed operational and artificial excitation testing and established that the noise was structure-borne and due to a bending and a torsional mode of the reaction mass of the dynamometer motor, coupled to a bending mode of the motor driveshaft. The animation of the modes at these two frequencies was confirmed from both modal testing and from operating deflection shapes extracted from operational data. Tuned mass dampers were designed and successfully installed to solve the problem.

A manufacturer of access equipment and specialty trucks for defence, fire and emergency, as well as commercial use, needed to identify key noise sources and paths and provide design recommendations for reducing acoustic levels of a fire suppression system. Impulsive acoustic and vibration measurements were conducted according to customer specifications at the customer’s facility. Both time-domain and frequency-domain analysis were applied to quantify source and to assess if there were reduction opportunities through the path of the system. Design recommendations to reduce the impulsive noise were made and countermeasures to further reduce noise levels in discrete frequency ranges were introduced.

A manufacturer of heavy duty axles and axle components for military vehicles and off-highway machines needed assistance in identifying the source of an objectionable rattle in a gear assembly and requested countermeasures and recommendations to help reduce or eliminate the noise. Operational noise and vibration measurements were made at an independent off-road vehicle testing facility. We used time- and frequency-domain analysis, order analysis, envelope analysis and modal FRF measurements to identify the source of the noise. Design recommendations were made focusing on lowering forcing functions and understanding/moving  resonances. It was also recommended to increase isolation to help reduce the rattle noise further.

We worked with a manufacturer of lawnmowers to help them understand the vibration performance of one of their products. To identify the frequency ranges of interest, we acquired artificial excitation data. We then measured during operation to understand the mower's vibration levels under normal use. Modal analysis was used to understand how best to improve vibration at the operator (receiver) location. The results were delivered to the customer for integration into future development of vibration quality in their products.

An agricultural equipment manufacturer approached us to troubleshoot an acoustic boom  in a tractor and to identify possible countermeasures. We measured static and operational noise and vibration at the customer’s facility applying the source-path-receiver model. Spectral, order, and modal analysis were used to understand key components of the acoustic boom.

The boom consisted of high source levels coupled with a modal alignment issue that appeared after a design change. We recommended reducing the source level and shifting the coupled resonances. In addition to recommended changes, we also helped the customer develop a mode alignment chart to use as a reference during future tractor development processes.