What is Acoustics and what is acoustic testing used for?
Acoustics is the study of sound, noise, and vibration. Understanding the acoustical performance of your product is important because different types of devices have different thresholds for acceptable amounts of acoustic noise. Acoustic testing services assess how your product will perform in real-world conditions, and whether or not further revisions should be made to reduce noise. Acoustical testing helps product manufacturers from various industries determine these values.
Acoustic quality and acoustic design are key aspects of product performance. Sounds play a critical role in conveying the right message about a product’s features and functionality, and reinforcing brand image attributes. At the same time, regulations and competitive pressure are forcing manufacturers to limit noise levels and meet stringent noise-making or noise-limiting standards. Engineers need productive tools to design, refine and validate prototypes throughout the development cycle.
Covering the broadest range of industry applications and engineering tasks while conforming to the latest international standards, our acoustic testing solutions adjust to your project’s requirements.
Design innovative products with a compelling acoustic signature, relying on the expertise nested in our intuitive solutions.
Acoustic noise testing is the measurement of sound emissions radiating from the equipment under test. In other words, how loud is the equipment?
Many markets and industries require acoustic noise testing to protect the hearing of technicians and users of equipment, for example:
Consumer electronics: Equipment that generates annoying or loud tones and buzzes can easily be heard throughout a home and office environment.
Military: Military and defense products are required to undergo acoustic noise testing to prevent hearing loss, permit acceptable speech communication and minimize aural detection by the enemy.
Regulatory: international regulatory bodies require that acoustic noise emissions values of many different types of equipment be declared in order for the equipment to be legally sold.
Telecommunications: require acoustic noise testing to be performed on products being deployed in central offices, data centers, customer premises and outside plant environments.
What is the difference between sound and vibration and what is the relationship between them?
Sound is created through the vibration of air. When something produces vibrations, it creates sound waves. The movement of the vibration through the air is what we hear when we hear sound.
Vibrations are the way that sound is made. For example, imagine a drum being hit with a mallet. The drum vibrates, creating a sound wave. The reason the drumhead creates sound waves is because it moves outward and inward, which pushes and moves the air around it. The air gets pushed by the drumhead, so it moves faster than the surrounding air. As the faster-moving air travels, it collides with the air around it and transfers the extra energy. The movement or vibration of the air molecules continues to get transferred farther and farther away until the energy dissipates.
There are many factors that can have a direct effect on vibrations and thus sound. For example, a louder sound is produced when the vibrations are increased in intensity, and a higher-pitched sound is heard when the vibration frequency is increased. In fact, the frequency of the vibrations is what allows an organism to hear. There are many frequencies humans are unable to hear, but other animals, such as dogs, can.
Source of sound
When you think about measuring sound, what usually comes to mind is measuring sound pressure with a microphone. But is this the best way to qualify an acoustic source? When a metal plate vibrates, it moves the air particles around it. When the sound wave acts upon a particle, it is temporarily disturbed from its resting position. The excited particles transfer momentum from one particle to another. What we measure with a microphone is the disturbance of the air particles. Depending on where we hold the microphone or if we are inside or outside a building, the measured sound pressure will vary. In order to objectively qualify the source of the sound, we have to measure sound power; the acoustical energy emitted by that vibrating metal plate expressed in watts [W]. It is independent of the environment, distance or direction; sound power is the cause and sound pressure is the easily measurable effect.
An example of a similar phenomenon would be a heating system. For instance, a regular household radiator releases heat, but to measure the effect, we use thermometers, which display the temperature (in degrees Celsius or Fahrenheit). Depending on where we put the radiator, in the middle of a desert or in an igloo, the measured temperature will differ, but the radiated heat will remain unchanged. Sound power is measured to make objective comparisons but also because legislation requires it. To release a new product, it is often compulsory to certify it according to International Organization for Standardization (ISO) standards as well as local and regional regulations. Apart from certification, sound power testing helps to develop better products in compliance with industry and ISO standards. In fact, it can enable firms to meet or even exceed expectations, thus improving their competitive advantage and supporting their branding strategy.
Sound power levels may be used for:
Certifying noise emitted by machines or equipment
Verifying declared values
Comparing noise emitted coming from different machines (in type and size)
Engineering work to reduce noise emitted by machinery
Predicting noise levels
Characterizing the noise source
Measuring sound power
Measuring sound power is not a straightforward process. Sound power can be determined either through the measurement of sound pressure [Pa] or sound intensity: the rate of energy flow through a unit area, expressed in watts per unit area [W/m2].
Additional methods, such as acoustic holography, are also available but are not ISO compliant. The added value of quantitative array techniques is the localization information, but the results obtained with acoustic cameras cannot be used for legislative purposes.
Sound pressure-based sound power measurements can only be performed in very specific environmental conditions, usually only met in acoustic rooms (anechoic or reverberant chambers). The sound pressure-based approach is most commonly used when performing certification measurements. A set of ISO standards governs these requirements and indicates measurement procedures that are necessary to obtain quality results.
Sound intensity-based sound power can be measured in any sound field, but certain requirements with regard to the type of sound must be met. The measurements can be performed on individual machines or sound sources in the presence of other components radiating noise, because steady background noise does not contribute to the measured sound intensity. However, this approach has a limited usable frequency bandwidth, time demanding measurement procedures and limitations on the characteristics of the noise source. ISO standards govern sound intensity-based measurements and describe the procedures that are required to obtain quality results.
Selecting one of the above methods depends on the purpose of the test as well as the available equipment, desired grade of accuracy, background noise level or the test environment.
Precision method:
This is a grade 1 method that gives the most accurate results. Measurements have to be performed in laboratory conditions with the most precise equipment available. Precision methods ensure the lowest uncertainty values but require the most effort during measurement.
Engineering method:
This is a grade 2 method that gives very accurate results. The influence of the acoustic environment as well as the source type is taken into account. This is the preferred grade of accuracy when performing engineering actions such as preventive or reactive sound design campaigns.
Survey method:
This is a grade 3 method that requires the least amount of time and equipment. The results are meant to compare sources with similar characteristics, but have limited value in evaluating noise.
Equipment used to determine sound power
To obtain results that comply with the ISO standards and can be used for noise marking and noise limiting, good quality measuring equipment should be used. Each of the standards from the ISO 3740 and ISO 9614 families specify requirements on the equipment used to determine the sound-power levels based on the chosen method and desired grade of accuracy.
General equipment used for sound power determination: microphones, intensity probes, cables, filters, calibrators.
Our broad range of acoustic testing solutions combine intuitiveness, efficiency and expertise. See some of our solutions below:
Active Sound Design
The electrification of the powertrain brings active sound design to the next level. Although artificial sound served mainly the sound quality and emotional considerations in ICE vehicles, sound design becomes functional and an integral aspect of the driving experience in the electrified vehicles. In hybrid vehicles, this technology can acoustically cancel out disturbing interior acoustic events (for example, the moment between the engine switches). For electrical vehicles this solution offers options to create consistent acoustic feedback for the driver, reflecting the engine orders and driving conditions (acceleration, braking, etc.), which is per default absent in electrified engines.
Active sound design also represents a solution for the recent legal requirement of AVAS in electrified vehicles to achieve minimal noise levels. The same system can emit exterior sounds to alert other road users. This sound signature should be brand-bounded and easily identifiable.
The expectations for new vehicle sound, either technical or emotional, carry new challenges for the acoustic development teams. We offer a comprehensive toolset to address them in an integrated manner.
Aero-acoustic Wind Tunnel Testing
In the automotive industry, vehicle wind tunnel testing represents an effective solution to measure and optimize the wind noise after applying thorough CFD and 3D vibro-acoustic simulation in the earlier development stages. However, with the rising electrification trend, the wind tunnels are in great demand. As the combustion engine no longer masks wind noise, it becomes a top priority to refine. Because of the high cost related to vehicle wind tunnel testing, testing facilities need improved procedures to cope with demand versus cost. For this reason, it is essential to capture as much information as possible during each test run. As a result, there is a shift from more basic testing systems towards more advanced, high channel-count systems.
Engineers are challenged to get the maximum out of test campaigns and need to understand which methods and technologies are the right mix for the job. By combining all different technologies into one integrated platform, new insights for improving vehicle aero-acoustic performance can be obtained. Our solutions offer state-of-the-art technologies, maximum productivity, and reliability and are a safe choice for current and future needs.
Pass-by Noise Engineering
In urban areas, traffic noise can be a prominent source of discomfort, affecting the daily lives of millions of people and potentially diminishing their health and well-being. To create a more harmonious living environment and reduce the risks of noise exposure, legislators are working on establishing acceptable emission levels and imposing limits on pass-by noise (PBN) levels. ISO certification standards are used to make sure vehicle comply with established legislation. This type of certification is required for all types of road vehicles, including trucks, buses, motorcycles, passenger cars and recreational vehicles. For hybrid and electric vehicles, new standards are in place for measuring minimum noise emission. For these vehicles an acoustic vehicle alert system (AVAS) adds exterior noise to ensure pedestrian safety. We offer a complete portfolio of modular hardware for reliable data acquisition combined with comprehensive pass-by noise engineering software. The combination of both results in enhanced accuracy and efficiency, but also delivers engineering insight well beyond the certification procedures as such, for instance by pinpointing root causes of dominant noise contributors.
Sound Quality Engineering
One of the trends in product design and development is the increasing number of design variants that are offered to consumers. This trend puts pressure on the noise, vibration and harshness (NVH) engineers in many development and validation teams, who must deliver test results faster and in a more efficient way. Regardless of their level of expertise, engineers need tools that help them achieve better results faster, while enabling them to maintain the same level of quality and confidence in their analyses and methods. The NVH and sound quality engineering capabilities embedded in our solutions are specifically designed to meet all these requirements. They will enable you to troubleshoot sound-quality issues, benchmark against competition, increase productivity in NVH testing and last but not least gain a true insight into how customers perceive your product’s sound. The greater productivity, better customer understanding and accelerated decision-making will support you to deliver great-sounding products to the market faster.
Operational NVH Testing
Efficiently assess the acoustic signature of products, in real operating conditions and in the shortest delays. Our intuitive and scalable operational NVH testing solution helps you perform fast and reliable measurements. Occasional and expert users can equally combine recordings of analog sensors inputs with data from a binaural headset, the vehicle bus, and the GPS antenna. They effortlessly validate data on the spot using embedded data processing and audio replay functionalities.
Sound Intensity Testing
Simplify the processes of intensity-based sound power testing while ensuring compliance with ISO measurement standards for both scanning and point-by-point methods. Our solution integrates a fully automated procedure, with robotized movements of the probe. It delivers adequate results for certification processes and additionally permits sound localization on a 3D geometry as well as the ranking of sound sources.
Sound Power Testing
Quantifying the sound power generated by a product is critical to many industries. Sound power values are required for certification, but also for engineering and benchmarking purposes. Our certified sound power testing solutions guide operators to comply with international standards and regulatory directives while offering the flexibility to incorporate custom, in-depth acoustic engineering workflows.
Sound Source Localization
Accurately, intuitively, and quickly visualize sound sources with our sound source localization (SSL) solutions. SSL helps you immediately confirm that you focus on the dominant noise issue. Our modular digital and analog microphone arrays support a wide range of applications from acoustic troubleshooting to sound power ranking, and aero-acoustic wind tunnel testing.
Sound and vibration quality affects all of us in our daily lives - from the smart phones we use, the cars we drive, the machines we operate, to the environment in which we all live.
Leading companies are challenged to deliver smart, efficient and customized products with a unique sound and vibration quality experience in a timely manner.
Our wide range of EMC or anechoic chambers and comprehensive range of solutions and services assists test engineers with competitive benchmarking, detailed engineering, troubleshooting and certification. Based on a systematic approach, sound and vibration measurements are combined with root-cause analysis and clear reporting to tackle the most challenging testing tasks. Our measurement hardware ranges from pocket-size, handheld analyzers up to portable, multi-channel systems. Our task-driven software is straightforward to use and provides flexible access to the latest sound and vibration testing technology.
ETS Solutions Asia and Simcenter testing helps sound and vibration engineers to take smarter decisions, to increase testing productivity, to ensure compliance to industry standards and ultimately to deliver a unique sound and vibration quality experience.
Webinars available on demand
Introduction to the fundamentals of acoustic engineering
ON-DEMAND WEBINAR | 18 MINUTES
Master sound perception before a prototype is available using the vehicle sound simulator technology
ON-DEMAND WEBINAR | 47 MINUTES
