Noise source identification
By tracing noise back to very specific components, engineers can target their mitigation efforts more precisely.
It is essential to reduce noise, and to understand and optimize noise that cannot be eliminated. With noise-source identification (NSI) equipment from Brüel & Kjær, acousticians can diagnose, visualize, understand and solve noise issues. By tracing noise back to very specific components, engineers can target their mitigation efforts more accurately.
Identification, mitigation and optimization
After locating noise sources, acoustical hotspots and leaks using a variety of tools ranging from hydrophones to outdoor arrays of up to 144 channels, it is possible to identify and characterize the most important sub-sources. Ranking these helps decide where mitigation strategies can most effectively reduce overall sound power radiation, or reduce certain noise components such as specific frequency content. Mitigating noise can be accomplished by reducing, damping, or decoupling noise sources from the overall structure.
Through the iterative use of NSI tools in the design and prototype phases of product development, the overall noise profile of the product can be optimized, thus ensuring proper compliance with given noise limits and regulations.
Colour-coded noise maps
Different stages of noise-source identification call for different capabilities. Early 'snapshot' measurements such as in aircraft cabins, demand equipment that is easy to deploy in order to obtain results as quickly as possible. Our software displays sound values as colour-contours in high-resolution noise maps that are easy to interpret. For fine, close-up detail such as on a hearing aid, acoustic holography delivers similar results in high resolution, while for noise source location on larger objects such as vehicles in a wind tunnel, or from a distance, beamforming can quickly identify noise contributions. Moving objects such as wind turbines and flying aircraft can be acoustically mapped using moving-source beamforming.
An easy, one-shot measurement process for mapping the relative sound pressure and sound intensity contribution from a source. The solution is well-suited for large objects such as vehicles in wind tunnels, where the array is placed relatively far from the source, outside the turbulent airflow. The number of microphones in the array can vary from 18 to 144. An integrated camera provides simple and intuitive documentation. The refined beamforming technique can be used to improve the spatial resolution.
Beamforming is valid for medium to high frequencies (500 Hz to 20 kHz). When used close to sources such as engines in a test cell, the patented wideband holography can be used to measure over a very wide frequency range. The addition of a transient option enables averaging in the domains of time, RPM and angle, making it ideal for powertrain analysis.
A basic PULSE beamforming system, including measurement and post-processing software, a planar sliced wheel array of 18 microphones and LAN-XI data acquisition hardware, is perfect for noise-source identification, troubleshooting investigations, Squeak and Rattle testing and industrial plant noise measurements. Based on one simple measurement, the system provides an acoustical map of noise sources by using the array of microphones to detect the direction of arrival of sound from the sources. The system can be expanded with holography.
> Beamforming measurements on a superkart (Video)
Sound intensity mapping is one of a number of noise identification techniques available to engineers working on noise, vibration and harshness problems. It is a versatile tool to measure the magnitude and direction of energy in a sound field for a variety of applications, such as determining sound power, sound absorption and sound transmission. Sound direction and noise ‘hot spots’ can be quickly determined regardless of background noise, with visual and aural feedback during measurements allowing convenient, on-the-spot results for sound sources in operation.
Colour-contour noise maps provide intuitive documentation and easy communication of results with others, and the selective sound intensity option can further identify the internal root sources and radiation mechanisms involved.
When measuring a large number of points, robotic systems can accurately automate microphone positioning; for use on-site or inside moving vehicles, we offer hand-held systems based on a sound level meter.
The recommended system for sound intensity mapping applications is based on a BK Connect data acquisition and analysis system with LAN-XI front-end with sound intensity front panel and noise source identification software. A sound intensity probe set with remote control and a sound intensity calibrator complete the system. The system can be expanded with a two-dimensional, automated positioning system for a sound intensity probe and a third input on the front-end is available for selective intensity measurements.
For measurements close to a source, acoustic holography provides fast and accurate acoustic maps of sound pressure, sound intensity and other sound field parameters at low to medium frequencies (100 Hz to 2 kHz). Our patented algorithms ‘SONAH’ and ‘ESM’ allow accurate measurement with relatively small arrays without encountering edge effects. Acoustic holography also allows results to be calculated closer to and further away from the source, and the capability of the system can be augmented with an automatic positioning system, transient and quasi-stationary calculations and sound quality metrics. Wideband holography extends the use of holography far beyond the usual frequency range limit.
A basic PULSE acoustic holography system comprises measurement and post-processing software, a planar sliced wheel array of 18 microphones and LAN-XI data acquisition hardware including the frame, modules and front panels. The system is ideal for mapping noise from engines, vehicle components, appliances, power tools, etc., and for sub-source sound power contribution analysis.
Ideal for in-cabin noise and leak detection, spherical beamforming is a quick way of mapping relative sound pressure and sound intensity arriving from all directions. The array consists of 36 or 50 microphones distributed across the surface of a solid sphere with 12 integrated cameras. The acoustical parameters measured over the surface of the sphere are then projected onto a 2D surface in the same way that information on a globe is represented on a flat map in an atlas. The algorithms used are ‘SHARP’ and our patented ‘Filter and Sum’, which increases the dynamic range of the array and suppresses virtual images caused by sidelobes.
A low-frequency extension means that the system can be used over a wide frequency range.
Spherical beamforming systems are supplied as customer‐specified projects. A typical system for vehicle interior noise measurements would consist of PULSE measurement and post-processing software for spherical beamforming, LAN‐XI data acquisition hardware including the frame, modules and front panels, a 36 or 50-channel spherical array, plus accessories (for example, a car seat fixture, pistonphone, splitter box, cables, etc.).
Designed primarily for use in the aerospace and automotive industries, BK Connect Acoustic Camera is a versatile and complete hand-held system for real-time noise source identification in almost any acoustic environment. It is capable of stationary and non‐stationary measurements over a wide range of frequencies using both beamforming and acoustic holography.
Equally suitable for noise source troubleshooting in aircraft cabins and cockpits, Buzz, Squeak and Rattle detection in vehicle cabins; and high-frequency leak detection, this portable system is up and running within 10 seconds of starting BK Connect Array Analysis, showing live maps on video.
Using an aim, shoot and measure procedure, the acoustic camera allows you to take, save and share screenshots using the functionality of your tablet; make, save and review video recordings of contour maps using BK Connect Array Analysis; and analyze recordings using BK Connect applications, according to your test requirements (available separately.)
BK Connect Acoustic Camera comprises software components BK Connect Array Analysis and BK Connect Data Viewer and BK Connect Hardware Setup (advanced). The hardware component includes a hand‐held array and LAN‐XI data acquisition hardware, which includes the frame, modules and front panels. The hardware is delivered in a waterproof case for easy transportation. The tablet is optional, and the PC and is not included.
The system also supports a range of other sliced-wheel arrays and all other planar, irregular arrays as well as a complete set of acoustic mapping and other sound and vibration tools available from Brüel & Kjær, including the patented Wideband Holography.
Finding the source of acoustic phenomena can be accomplished in many ways and often depends on the conditions in which the phenomena occur. For many vehicle manufacturers, investing in wind-tunnel measurements is often the only way to recreate real-world conditions for model and mule car testing. It is also a good method of validating simulated model data and of investigating the acoustic impact of noise-reduction treatments.
Aerodynamic noise is particularly important for passenger car driving comfort and high-speed train community comfort. At cruising and higher speeds, the aerodynamic noise is the dominant noise source in a car, so in relation to car interior aerodynamic noise, measurements are performed on full size vehicles in wind tunnels at different stages during development. To investigate exterior aerodynamic noise produced by high-speed trains, wind tunnel measurements are typically performed on scale models of train sections or on components such as pantographs.
Our PULSE Array-based Noise Source Identification Solutions can withstand the tough conditions of wind tunnels and still acquire reliable data. They include the two main methods for measurement on the exterior of vehicles in wind tunnels – near-field holography and beamforming. With beamforming, the array is placed relatively far from the source, outside the turbulent airflow. For near-field holography a scanning method can be used where an array of measurement microphones has to be placed close to the vehicle under test, usually within the airflow region.
Available hardware includes planar and half-wheel arrays and Surface Microphone Type 4949, designed for measurement of the true surface pressure, is exceptionally well-suited for mounting directly on the car surface during wind-tunnel tests.
Reduction of noise emissions is a critical technology for aircraft manufacturers and various analytical, empirical and numerical tools exist to help in the design of quieter aircraft. Given the complexity of the noise source mechanisms, wind tunnels are used for aeroacoustic measurements of aircraft noise sources and their directivities; both for validating prediction methods and for investigating the acoustic impact of noise-reduction treatments. Both open-circuit, anechoic wind tunnels, and closed-circuit wind tunnels are used for aerodynamic and aeroacoustic studies of various flow-induced noise phenomena. The choice of test facility is driven primarily by the type of application, the design speed, and the desired model scale.
Brüel & Kjær’s Wind Tunnel Acoustic Test System accurately performs all the tasks needed for aircraft acoustic scale-model testing. The system is based on our standard, commercial-off-the-shelf (COTS) products that are optimized for the specific issues faced with wind tunnel test applications. They cover the entire measurement chain of transducer, data acquisition, analysis and reporting.
A system typically consists of the necessary number of microphones, preamplifiers, LAN-XI data acquisition hardware, an acquisition workstation installed with relevant software, PTP (Precision Time Protocol) enabled LAN and one or more remote monitoring stations.
Ramp noise is a standardized acoustic on-ground measurement, detailing the noise print on a parked aircraft. Ramp noise testing evaluates and reduces the noise exposure of maintenance personnel and passengers boarding and disembarking the aircraft. The primary noise sources arise from Auxiliary Power Units (APUs), air cycle machines (packs) and brake fans.
For ramp noise measurements, the data acquisition system has to reach all around the airplane. A PULSE LAN-XI data-acquisition system provides data recording of hundreds of channels, and can be distributed throughout – or around – an aircraft and connected together with single LAN cables for synchronized results.
Together with real-time monitoring of test data, the system provides the capability of displaying a noise map showing noise levels around the aircraft, and sharing data throughout the test facility for post-analysis.
PULSE hardware and software solutions are approved for use by aircraft manufacturers in aircraft noise certification according to international standards.
As global air travel grows, so does the concern for noise around airports. This leads to increasingly strict legislation. Exterior noise is, therefore, a key priority for the aerospace industry and aircraft noise certification tests are required in order to establish certified aircraft Effective Perceived Noise Levels (EPNL) at each of the Approach, Flyover and Sideline certification flight conditions – in accordance with ICAO Annex 16, FAR 36 and IEC 61265 aircraft-noise certification standards.
The Brüel & Kjær Aircraft Noise Certification Test (ANCT) System accurately performs all measurement tasks needed for aircraft noise certification testing, and is based on our standard, commercial-off-the-shelf (COTS) products that cover the entire measurement chain.
PULSE hardware and software solutions from Brüel & Kjær have been approved for use by aircraft manufacturers in aircraft noise certification according to international standards. The PULSE-based ANCT system is a dedicated solution integrating and optimizing the different inherent features of our COTS products. These products encompass the whole measurement chain and provide you with a complete workflow-driven solution supporting all phases of the noise certification process.
To map noise sources on flying aircraft, Brüel & Kjær’s flyover beamforming software traces sound to individual engine or airframe sources. Large arrays of microphones are laid out according to geometries designed by our specialists and connected to a network of data acquisition modules distributed to keep analogue cables short.
The aircraft position during a flyover is measured with an onboard GPS system, and synchronization with array data is achieved through recording of an IRIG-B signal together with the array data and the GPS data on the aircraft. The Beamforming calculation is performed with a standard tracking time-domain Delay and Sum (DAS) algorithm with the capability of Diagonal Removal to suppress wind noise.
For each focus point in the moving system, FFT (fast Fourier transform) and averaging in short time intervals are performed to obtain spectral noise source maps representing the aircraft positions at the middle of the intervals.
PULSE Array Acoustics Flyover Moving Source Beamforming BZ-5940 provides a high-resolution acoustic map of sound sources using one simple measurement of an aeroplane as it flies over a ground-based array of microphones by differentiating sound levels based on the direction from which they originate.
In addition to BZ-5940, a typical system includes a horizontal wheel array, LAN-XI data acquisition hardware and PULSE array acoustics beamforming software.
Static aircraft engine noise ground tests are performed to define the engine ground static noise measurements. As static aircraft engine noise ground tests are usually less costly than flight tests and are less affected by atmospheric conditions, ground surface variations, flight paths, etc. and, therefore, more predictable, they are preferable to flight tests. After the initial aircraft noise certification, aircraft manufacturers do not need to do a full noise certification test on new engines or engines that have been modified. They can get the new (or modified) engines noise certified by the authorities via the Ground to Flight Equivalence (GTFE) procedure.
The Brüel & Kjær Static Engine Certification Test (SECT) system follows the measurement requirements and procedures set forth by the industry noise certification standards ICAO FAR 36 and Annex 16, and SAE ARP1846A and ARP866A – Standard Values of Atmospheric Absorption as a Function of Temperature and Humidity.
The SECT System accurately performs all the tasks needed for static engine noise certification and development testing and is based on our PULSE data acquisition and analysis platform and other standard commercial-off-the-shelf products that cover the entire measurement chain. It acquires all relevant noise and weather data needed to generate certificated noise levels, and corrects this data to standard reference conditions, for both measurement equipment and atmospheric absorption.
As SECT System is an open framework, additional research and development tasks (based upon individual customer requirements) can be added or incorporated within the workflow of the system.
Acoustic detection and identification techniques continuously become more advanced and sophisticated. As they evolve, so must acoustic stealth strategies. To maintain acoustic discretion, all of a vessel’s noise sources must be considered, including personnel, on-board equipment and cavitation, as well as the radiated noise signature of the vessel as a whole.
Static and dynamic acoustic ranging determines the underwater-radiated noise from a submarine or surface vessel, measured over an extended frequency range. Acoustic ranging covers the full operational envelope of the vessel, including the identification of the different sources that contribute to the ship’s acoustic signature.
The Brüel & Kjær Underwater Acoustic Ranging System (UARS) is an integrated solution for both static and dynamic ranging. Systems can be configured for specific needs, covering the complete measurement chain from sensor (hydrophone) to analysis (PULSE). A typical system could be a PULSE-based Remote Acquisition and Analysis Station – the main workstation running the UARS software – combined with hydrophones and LAN-XI data acquisition hardware. The number of data acquisition units and hydrophones depends upon specific requirements.
The Brüel & Kjær Self-noise Monitoring System (SNMS) is a permanently installed, integrated solution for vibration and noise monitoring of submarines and other vessels where management of the acoustic signature is vital.
Acoustic detection and identification techniques continuously become more advanced and sophisticated. As they evolve, so must acoustic stealth strategies. To maintain acoustic discretion, all noise sources of a vessel must be considered, including personnel, on-board equipment and cavitation, as well as the radiated noise signature of the vessel as a whole.
Brüel & Kjær has extensive experience in underwater acoustics and testing solutions that can be used in application-specific tasks, from investigating, analyzing and identifying noise sources to validating advanced designs.
Based on Brüel & Kjær’s Commercial-off-the-Shelf (COTS) PULSE platform, the SNMS integrates LAN-XI data acquisition hardware and PULSE software applications to provide a fully integrated solution for monitoring and analyzing noise sources.
The system comprises permanently installed transducers (hull-mounted accelerometers and external hydrophones), transducer power supply, data acquisition, data analysis, storage and display, and data interface. System enhancements include portable vibration meters and carry-on systems to perform time-limited tasks.