Acoustics involves the study of sound, noise, and vibration. Understanding the acoustic performance of a product is crucial, as different devices have varying acceptable noise levels. Acoustic testing evaluates how a product will perform in real-world environments and identifies whether adjustments are needed to minimize noise. Manufacturers across many industries rely on acoustic testing to establish these performance benchmarks.
Acoustic quality and design are essential components of product performance. Sounds significantly influence how a product’s features and functionality are perceived, while also supporting its brand identity. At the same time, manufacturers face increasing regulatory demands and competitive pressure to reduce noise levels and comply with strict noise-making or noise-limiting standards. Engineers require efficient tools to design, refine, and validate prototypes throughout the development process.
Therefore, acoustic testing solutions must be versatile, adapting to a wide range of industry applications and engineering tasks, all while adhering to the latest international standards.
Leverage the expertise embedded in our solutions to design innovative products with a distinctive acoustic signature
Acoustic noise testing measures the sound emissions produced by equipment under test—essentially, how loud the equipment is. Many industries require this testing to protect the hearing of both technicians and end-users. Some key examples include:
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Consumer Electronics: Devices that produce disruptive tones or buzzing can be noticeable in home and office environments. With rising demand for exceptional sound quality in products like headphones, smartphones, speakers, laptops, and other household appliances, this challenge is ever-present for manufacturers.
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Aerospace & Defense: Acoustic noise testing is critical for aerospace and defense products to prevent hearing loss, allow for clear communication, reduce aural detection, and ensure mission-critical performance in demanding conditions.
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Automotive: The rise of electric and hybrid vehicles introduces new challenges, requiring smart trade-offs and advanced testing methods. The need for better testing and more accurate data has never been more urgent.
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Audiology: The hearing aid industry has seen remarkable advancements in recent decades. Intelligent, adaptive devices now present new testing challenges, including how they respond to environmental changes and shift channels to optimize sound quality and the user’s perception of their own voice.
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Environmental Noise & Monitoring: Environmental noise, whether from a distant power station or traffic, affects everyone. Noise monitoring, driven by regulations and legislation, aims to protect both the environment and public health from noise pollution.
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Regulatory: International regulatory bodies require manufacturers to declare the acoustic noise emissions of various equipment types before they can be sold. In addition to helping manufacturers meet compliance requirements, we are frequently invited to contribute to the development of ISO standards.
What is the difference between sound and vibration, and how are they related?
Sound is produced by the vibration of air molecules. When an object vibrates, it generates sound waves that travel through the air. This movement of air caused by vibrations is what we recognize as sound.
Vibrations are the source of sound. For example, when a drum is struck with a mallet, the drumhead vibrates and produces sound waves. As the drumhead moves back and forth, it pushes the surrounding air, causing the air to move faster than usual. This faster-moving air collides with surrounding air molecules, transferring energy outward. This chain reaction of vibrating air molecules continues until the energy disperses and the sound fades.
Several factors influence vibrations, and therefore sound. For instance, increasing the intensity of vibrations results in louder sounds, while increasing the frequency of vibrations leads to higher-pitched sounds. The frequency of these vibrations determines what organisms can hear. Humans can perceive a specific range of frequencies, while other animals, such as dogs, can detect sounds at frequencies beyond human hearing.
Source of Sound
When measuring sound, most people think of measuring sound pressure using a microphone. But is this the best method to assess an acoustic source? When a metal plate vibrates, it causes the air particles around it to move. As the sound wave interacts with a particle, it temporarily displaces it from its resting position. The excited particles pass momentum to one another, and what we measure with a microphone is the disturbance of these air particles. However, depending on the microphone’s location or whether it's indoors or outdoors, the recorded sound pressure will vary.
To objectively evaluate the source of sound, we must measure sound power, which is the acoustic energy emitted by the vibrating object (such as the metal plate) and is expressed in watts (W). Sound power is independent of factors like environment, distance, or direction—while sound pressure is an easily measurable effect, sound power represents the actual cause.
A comparable phenomenon is how we measure heat. For example, a household radiator emits heat, but we use a thermometer to measure the effect, shown as temperature (in degrees Celsius or Fahrenheit). The temperature will vary depending on the environment—whether the radiator is in a desert or an igloo—but the heat emitted by the radiator remains constant. Measuring sound power allows for objective comparisons and is often required by legislation. Before launching a new product, manufacturers must often certify it according to ISO (International Organization for Standardization) standards, as well as local and regional regulations.
In addition to certification, sound power testing supports the development of products that comply with industry standards, allowing firms to exceed expectations, improve their competitive advantage, and strengthen their branding strategies.
Sound power levels are useful for:
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Certifying the noise emissions of machines or equipment
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Verifying declared noise levels
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Comparing noise emissions from different machines, regardless of type or size
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Engineering efforts to reduce machinery noise
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Predicting noise levels
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Characterizing noise sources
Measuring Sound Power
Measuring sound power is a complex process. It can be determined either through measuring sound pressure (Pa) or sound intensity, which represents the rate of energy flow per unit area and is expressed in watts per square meter (W/m²).
There are also alternative methods, like acoustic holography, which provide added benefits such as localization information through quantitative array techniques. However, these methods are not ISO compliant, and results from tools like acoustic cameras cannot be used for regulatory purposes.
Sound pressure-based sound power measurements must be conducted under very specific environmental conditions, typically found in acoustic rooms like anechoic or reverberant chambers. This method is most commonly used for certification purposes, as it follows ISO standards that outline the procedures necessary to achieve accurate results.
On the other hand, sound intensity-based sound power measurements can be performed in any sound field, as long as certain sound-related requirements are met. This method is advantageous because it allows measurements on individual machines or sound sources, even in the presence of other noise-emitting components. Since steady background noise does not affect the measured sound intensity, this method can be used in less controlled environments. However, it has some limitations, such as a restricted usable frequency range, time-consuming measurement procedures, and restrictions on the noise source's characteristics. Like sound pressure-based measurements, sound intensity-based measurements are also governed by ISO standards to ensure high-quality results.
Choosing the appropriate method depends on the test's purpose, the available equipment, the required accuracy, the level of background noise, and the test environment.
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Precision Method: This is a grade 1 method that provides the most accurate results. It requires laboratory conditions and the highest-quality equipment to achieve minimal uncertainty. While it ensures the greatest precision, it also demands significant effort during the measurement process.
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Engineering Method: A grade 2 method that delivers highly accurate results. This approach takes into account the influence of the acoustic environment and the nature of the sound source. It is ideal for engineering tasks, such as proactive or corrective sound design initiatives.
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Survey Method: A grade 3 method that requires the least time and equipment. While this method is suitable for comparing sources with similar characteristics, it has limited value when it comes to detailed noise evaluation.
Equipment Used to Determine Sound Power
Achieving results that meet ISO standards and can be used for noise marking and noise-limiting purposes requires high-quality measuring equipment. The ISO 3740 and ISO 9614 standards outline specific requirements for the equipment based on the chosen measurement method and the desired level of accuracy.
Common equipment for determining sound power includes microphones, intensity probes, cables, filters, and calibrators.
Active Sound Design
In the automotive industry, the shift toward powertrain electrification has elevated the importance of active sound design. While artificial sound in internal combustion engine (ICE) vehicles primarily focused on enhancing sound quality and evoking an emotional response, sound design in electric vehicles now plays a functional role, becoming an integral part of the driving experience.
In hybrid vehicles, active sound design technology can acoustically cancel out disruptive interior noise, such as the transition when the engine switches on or off. For electric vehicles, this technology allows for the creation of consistent acoustic feedback, reflecting driving conditions like acceleration and braking—sounds typically absent in electric motors.
Active sound design also helps meet the legal requirements for Acoustic Vehicle Alerting Systems (AVAS) in electric vehicles, ensuring minimal noise levels to alert other road users. The system can emit exterior sounds, with the sound signature being unique and easily identifiable to the brand.
The demand for new vehicle sounds—whether technical or emotional—presents fresh challenges for acoustic development teams. We provide a comprehensive toolset to help tackle these challenges in an integrated way.
Aero-acoustic Wind Tunnel Testing
In the automotive industry, vehicle wind tunnel testing is an effective way to measure and optimize wind noise, following thorough CFD (Computational Fluid Dynamics) and 3D vibro-acoustic simulations during the early development stages. With the growing trend of vehicle electrification, the demand for wind tunnel testing has surged. Without the masking effect of combustion engines, wind noise has become a top priority for refinement.
Given the high costs associated with wind tunnel testing, testing facilities are under pressure to improve procedures to balance demand with cost. Capturing as much data as possible during each test run is now essential. This has led to a shift from basic testing systems to more advanced, high channel-count systems, which offer greater data collection capabilities.
Engineers are tasked with maximizing the value of test campaigns and must choose the right combination of methods and technologies. By integrating various technologies into a single platform, new insights can be gained to enhance vehicle aero-acoustic performance. Our solutions provide cutting-edge technologies that ensure maximum productivity and reliability, making them a safe and effective choice for current and future testing needs.
Pass-by Noise Engineering
In urban areas, traffic noise is a significant source of discomfort, impacting the daily lives and well-being of millions of people. To foster a more peaceful living environment and reduce the risks associated with noise exposure, legislators are setting acceptable noise emission levels and imposing limits on pass-by noise (PBN) levels. ISO certification standards are used to ensure vehicles meet these regulations, and certification is mandatory for all road vehicles, including trucks, buses, motorcycles, passenger cars, and recreational vehicles.
For hybrid and electric vehicles, new standards have been introduced to measure minimum noise emissions. These vehicles are also equipped with Acoustic Vehicle Alert Systems (AVAS), which add exterior noise to enhance pedestrian safety.
We offer a complete range of microphones and accessories for reliable data acquisition, ensuring accurate and efficient measurements. Our solutions not only help with certification procedures but also provide valuable engineering insights, such as identifying the root causes of dominant noise contributors.
Sound Quality Engineering
An emerging trend in product design is the growing variety of design variants available to consumers. This trend places increased pressure on noise, vibration, and harshness (NVH) engineers in development and validation teams, who are expected to deliver test results more quickly and efficiently. Engineers, regardless of their experience level, need tools that help them achieve faster results without compromising the quality or confidence in their analyses and methods.
Our solutions are specifically tailored to meet these needs. They allow you to troubleshoot sound-quality issues, benchmark against competitors, improve productivity in NVH testing, and gain valuable insights into how customers perceive your product’s sound. This combination of enhanced productivity, deeper customer understanding, and faster decision-making will help you bring high-quality, great-sounding products to market more quickly.
Sound Power Testing
Measuring the sound power produced by a product is essential across many industries. Sound power values are necessary not only for certification but also for engineering and benchmarking. Our sound power testing solutions ensure compliance with international standards and regulatory requirements, while also providing the flexibility to integrate custom, detailed acoustic engineering workflows.
Summary
Sound and vibration quality impact our everyday lives, from the smartphones we use and the cars we drive to the machines we operate and the environments we live in. Leading companies face the challenge of delivering innovative, efficient, and customized products that provide a distinctive sound and vibration experience, all within tight timelines.
GRAS Sound and Vibration helps acoustic engineers make smarter decisions, increase testing productivity, and ensure compliance with industry standards. We achieve this through our comprehensive range of microphones and peripherals, our collaborative approach to co-creating customized solutions, and our exceptional after-sales support. Ultimately, this enables engineers to deliver a unique sound and vibration quality experience.
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