RELIABLE AND REPEATABLE MEASUREMENTS THE FIRST TIME, EVERY TIME!

The new and improved GRAS microphones secure efficient and reliable acoustic NVH testing.

Explore the rugged and versatile GRAS 146AE standard microphone that applies to a variety of acoustic NVH applications and the highly specialized microphones designed for specific applications.

Brake Noise Testing

GRAS NEVS 2018 3081

Brake noise is a chassis-related noise and a big problem for car manufacturers. The noise is caused by friction-induced vibrations, which make the brake system radiate noise. This will in turn cause a lot of irritation and disturbance to the car owner and any person near the vehicle when it occurs. The brake noise can lead to poor results in surveys of customer satisfaction and high warranty costs. Therefore, the development of brake systems with minimum noise issues are highly prioritized in the automotive industry. Brake noise is a very complex problem and the research in this area is in continuous progress.

THE CHALLENGE

The major challenge for brake noise testing is to be able to reproduce the numerous driving conditions that can cause the noise. For example, brake squeal during city traffic, or creep groan during parking. When this happens, during any of the thousands of brake applies, the noise must be recorded at the best possible quality.

SELECTING THE RIGHT MICROPHONE

Brake dynamometer squeal noise test

The SAE J2521 standard recommends a ½” free-field microphone with windshield. The microphone should be able to handle temperature variations and brake dust. For noise source identification, use intensity microphones or array microphones configured according to the relevant equipment needs.

For test cell, we recommend GRAS 146AE ½’’ CCP Free-field Microphone Set with GRAS AL0004 Small, Lightweight Microphone Tripod and GRAS AL0008 1/2" Microphone Holder, POM or GRAS RA0093 Microphone Holder and GRAS AM0069 Spherical Windscreen for ½’’ Microphones when exposed to wind flow. Also consider GRAS RA0504 GoPro Adapter.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

Wheelhouse test

The recommended microphone inside the vehicle is a ½“ free-field or random-incidence microphone as defined by company standards. For the wheelhouse measurements, there is a need for an extremely ruggedized measurement microphone with good performance. It should be able to endure long-term measurements at extremely tough conditions, different environmental conditions and exposure to dust, water, salt and gravel.

For wheelhouse, we recommend GRAS 147EB CCP X-Rugged Microphone Set with GRAS AA0121 5 m Waterproof BNC-BNC Cable (other lengths available) and Plastic Strips.

For in vehicle, GRAS 146AE ½’’ CCP Free-field Microphone Set with GRAS RA0357 Random-incidence Corrector for 146AE and GRAS RA0504 GoPro Adapter are recommended options.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

 

Meet the new specialized microphone set

GRAS 147EB CCP X-rugged Microphone Set

Prolonged on-road testing on all surfaces and in all climate zones and weather conditions

Engine Noise Testing

GRAS NEVS 2018 4N2A3123

A lot of noise originates from the engine itself of course, the gear box, the belt drive system, pumps, cooling fans, but also other components like the A/C compressor and the power steering motors. These systems contribute to the vehicle acoustic comfort and some parts of the noise provides important feedback to the driver while other parts are just annoying.

THE CHALLENGE

A lot of vehicle design concept selections are critical for successful reduction of unwanted airborne noise from the engine bay. Firstly, it is essential to minimize the leakage in the firewall and to optimize the acoustic insulation package. Secondly, you should make sure that the actual noise sources are as silent as possible, maybe with the help of acoustic insulation covers. To quantify all this in a measurable and comparable way, it is important to be very structured during the testing so that requirements for systems and components can be derived from the vehicle level targets.

SELECTING THE RIGHT MICROPHONE

Acoustic transfer function measurements

The 147AX Pressure Rugged Microphone has been specially designed to achieve repeatable measurements in positions that are hard to reach with other types of microphones. This makes it a perfect choice to place in the response positions for TPA measurements in the engine bay of a car. Its small and rugged design allows for microphone mounting in places that were otherwise impossible. Furthermore, the magnetic base of the 147AX enables easy positioning on any metal surface and the included mounting disc will ensure the exact same microphone position for future measurements.

For engine bay, we recommend GRAS 147AX CCP Rugged Pressure Microphone.

For inside car, we recommend GRAS 146AE ½” CCP Free-field Microphone Set with RA0357 Random-incidence Corrector for 146AE and RA0504 GoPro Adapter.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

 

Meet the new specialized microphone

GRAS 147AX CCP Rugged Pressure Microphone

Rugged surface microphone for cold and hot engine testing

 

Powertrain NVH Testing

GRAS NEVS 2017 A4A5655

Powertrain noise, vibration and harshness (NVH) testing concerns the overall driver experience of the vehicle propulsion system, and this includes everything that makes the vehicle move. The noise level and sound quality are both very important since some parts of the sound provides important feedback to the driver while other parts are just annoying. The noise from all these sources, i.e. the internal combustion engine (ICE) with air induction, exhaust system, tail pipe, gear box, belt drive system, pumps and accessories like cooling systems and fuel pump is transmitted both airborne and structure-borne into the vehicle and contribute to the vehicle acoustic comfort. The powertrain noise also affects the external noise (the pass-by noise), which is regulated by legislation.

THE CHALLENGE

Challenges R&D typically deals with when working on powertrain NVH include

  • Concept selection for engine installation, engine content, layout and insulation

  • Exhaust system installation and optimization

  • Transmission design

  • Concepts for auxiliary components

  • Predictions of noise radiation

  • Compromising between NVH and other important attributes like performance, fuel consumption and emission

SELECTING THE RIGHT MICROPHONE

Powertrain test

GRAS provides a wide variety of standardized measurement microphones that can be used in the many different stages of powertrain testing.

We recommend GRAS 146AE ½’’ CCP Free-field Microphone Set and GRAS 147AX CCP Rugged Pressure Microphone with AL0005 Swivel head, AL0006 Microphone Tripod and AL0008 ½” POM, or RA0093 ½” 5-click Stainless Steel, Microphone Holder. When using 146AE, RA0357 Random-incidence Corrector for 146AE is recommended.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

Sound intensity and sound source location

Array microphones like the 40PH and the 40PL CCP Free-field Array Microphones are cost-effective, free-field acoustic sensors designed to be mounted on large or small array modules like the PR0002 Array Module for the analysis of sound fields. These types of microphones can be used in powertrain testing for measuring and locating sound sources using techniques like beamforming, near-field acoustic holography (NAH) and acoustic cameras. The 42AG can be used for calibration of array microphones too.

We recommend GRAS 40PH CCP Free-field Array Microphone and GRAS 40PL CCP Free-field Array Microphone, High Pressure with PR0002 Array Module and GRAS 50GI-P CCP Rugged Intensity Probe.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 and 51AB Phase Intensity Calibrator are ideal choices.

 

Exhaust Noise Testing

GRAS NEVS A4A5598

The exhaust noise from vehicles with internal combustion engines is very important. It must support a good engine sound quality while not being disturbing or violating noise legislation. The intake system and exhaust system are highly responsible for the engine noise character and sound pressure level (SPL) and must be tuned to meet the required performance. The engine sound quality should provide driver information about engine rpm as well as a suitable sound for the vehicle type, e.g. powerful and sporty during acceleration, but silent during constant speed driving. This also applies to the exterior sound where the sound character should match the vehicle brand identity.

THE CHALLENGE

The hot and dusty environment must be considered for measurement setup and equipment selection. Other important issues are exact positioning of microphones to be able to verify calibration before testing. The environmental conditions during the operational measurements are harsh with heat, dust, humidity and exhaust flow. The transducers are often moved to different positions so they must withstand handling and occasionally being dropped to the floor. It is also important to be able to position the microphones precisely and thus verify calibration before testing.

SELECTING THE RIGHT MICROPHONE

Sound transmission loss (measurements on dynamometer)

The operating measurements are done with ruggedized ½” pressure or free-field microphones as per the company standards. For extremely hot positions close to e.g. the exhaust catalyst or in the direct exhaust flow, use a probe microphone. Windshields are recommended both to minimize wind noise and to provide some microphone protection.

For test cell, we recommend GRAS 146AE ½'' CCP Free-field Microphone Set and GRAS 40SC CCP Probe Microphone with AL0004 Small, Lightweight Microphone Tripod and AL0005 Swivel Head and AL0008 ½”  POM, or RA0093 ½” 5-click Stainless Steel, Microphone Holder and AM0069 Spherical Windscreen for ½’’ Microphones when exposed to wind flow. Also consider the RA0504 GoPro Adapter.

For calibration GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

Sound transmission loss (test rig)

A sound transmission loss rig for exhaust systems typically uses four class 1 ¼” microphones.

For test cell, we recommend GRAS 46BD-FV ¼" CCP Pressure Standard Microphone Set, Front Vented.

For calibration GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

Pass-by noise

The microphones for pass-by noise testing must fulfill the test procedures. Typically, a class 1, free-field microphone is used. Outdoor microphones with weather protection and internal heating are preferred for permanent installations.

For outdoor, we recommend GRAS 146AE ½'' CCP Free-field Microphone Set with AL0006 Microphone Tripod and AL0005 Swivel Head and AL0008 ½”  POM, or RA0093 ½” 5-click Stainless Steel, Microphone Holder and AM0069 Spherical Windscreen for ½’’ Microphones when exposed to wind flow.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

 

Wind Noise Testing

gras 171105

Wind noise is an aerodynamic noise related to the body design and turbulence from components such as side view mirrors, wipers, cavities, etc. It is most disturbing at speeds above 100 km/h (approx. 60 miles/h), but is becoming more and more important when powertrain and road noise is being reduced. Careful design minimizes the problem, so early concept studies are important. Wind noise is, however, often an issue which is discovered late in the development process. It requires fast and efficient analysis since measures like extended seal systems or sound packages are expensive.

THE CHALLENGE

The variation in production for critical design areas must be low. The tolerance chains need to be investigated and, if necessary, compensated for with good seal systems.

SELECTING THE RIGHT MICROPHONE

Intensity microphones or surface microphones are used for noise source investigations. Microphones used for wind noise testing must be very robust and able to withstand dust and humidity.

For wind tunnel, we recommend GRAS 40LA ¼” CCP Precision Surface Microphone and 40LS ¼” CCP Precision Surface Microphone,

For calibration, GRAS 42AP Intelligent Pistonphone, Class 0 and GRAS 42AA Pistonphone, Class 1 with OP0025 Kit for sensitivity calibration of surface microphone are ideal choices.

 

 

 

 

Meet the rugged and very versatile standard microphone for a wide variety of acoustic NVH applications

GRAS 146AE ½" CCP Free-field Microphone Set

Automotive noise testing can be extremely demanding, so you need a robust solution to meet your expectations. This is why GRAS has developed the 146AE - a measurement microphone specially designed to perform under realistic test conditions.

 

 

 

 

 

 

Buzz, Squeak and Rattle Noise Testing

GRAS NEVS 2017 layout A4A5683

Buzz, squeak and rattle are all noises produced by parts installed in such a way that they create annoying sounds. Buzz, squeak and rattle is thus caused by the relative motion between installed parts, which make them interact, sometimes only at certain environmental conditions.

THE CHALLENGE

Design guidelines and computer-aided engineering (CAE) methods to predict buzz, squeak and rattle in combination with production tolerances are continuously improving, but squeak and rattle problems are often detected at a very late stage, even after production start, and can be the reason for high warranty costs. Good tools are important for fast problem identification and verification of measures like adding felt tape. Improved correlation of measurements to subjective valuation is also a continuous task for the engineers.

SELECTING THE RIGHT MICROPHONE

Silent shaker test

For optimum results, ½” measurement microphones should be used. The measurement in the NVH test cell with silent shaker requires low noise performance. The transducers must also withstand exposure to harsh environmental conditions such as strong vibrations, shock, drop, extreme temperatures and wet or dusty conditions.

For test cell, we recommend GRAS 146AE ½’’ CCP Free-field Microphone Set and AL0005 Swivel Head with AL0006 Microphone Tripod and AL0008 ½” POM, or RA0093 ½” 5-click Stainless Steel, Microphone Holder.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

Test track

The RA0504 GoPro Adaptor will help to ensure quick and easy positioning of the 146AE microphone inside the car. The adaptor is also applicable for mounting of any other ½” measurement microphone and can be used on the wide variety of GoPro tripods, mounts and clamps available on the market.

For vehicle interior, we recommend GRAS 146AE ½’’ CCP Free-field Microphone Set with RA0357 Random-incidence Corrector for 146AE and RA0504 GoPro Adapter.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

 

Vehicle Interior NVH Testing

NEVS 146AE kabine

Vehicle interior noise, vibration and harshness (NVH) involves a number of different tests – all related to noise inside the vehicle originating from road, body, chassis and components of the vehicle.

THE CHALLENGE

There are a number of general challenges within vehicle interior NVH:

  • Testing time should be short since the access to prototypes is limited.

  • Microphone positioning should be done fast and easy, and in a way to record repeatable results.

  • The microphones should be placed so that they minimize structure-borne sound.

  • Microphone holders and cables should not introduce any rattling noise.

  • The installation should be safe for the test engineer to perform during vehicle testing.

  • Calibration verification should be easy to perform.

SELECTING THE RIGHT MICROPHONE

The transducers should be able to withstand exposure to harsh environmental conditions such as strong vibrations, shock, drop, extreme temperatures and wet or dusty conditions without sacrificing performance or lifetime.

Vehicle interior and component/system level noise measurements

GRAS provides solutions that can be used at the different project levels and under a wide variety of measurement conditions encountered in vehicle interior testing.

We recommend GRAS 146AE ½’’ CCP Free-field Microphone Set with RA0357 Random-incidence Corrector for 146AE and AL0005 Swivel head, AL0006 Microphone Tripod and AL0008 ½” POM, or RA0093 ½” 5-click Stainless Steel, Microphone Holder. Also consider the RA0504 GoPro Adapter.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

Vehicle interior sound source location

Array microphones like the 40PH and the 40PL CCP Free-field Array Microphones are cost-effective, free-field acoustic sensors designed to be mounted on large or small array modules like the PR0002 Array Module for the analysis of sound fields. These types of microphones can be used in vehicle interior testing for measuring and locating noise sources using techniques like beamforming, near-field acoustic holography (NAH) and acoustic cameras. The 42AG Multifunction Sound Calibrator can be used for calibration of array microphones too.

We recommend GRAS 40PH CCP Free-field Array Microphone and GRAS 40PL CCP Free-field Array Microphone, High Pressure with PR0002 Array Module and GRAS 50GI-P CCP Rugged Intensity Probe.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 and 51AB Phase Intensity Calibrator are ideal choices.

 

Road Noise Testing

Road Noise 8612012

Road noise is one of the most annoying interior noises in any vehicle and this problem is even more accentuated with more and more electrical vehicles on the market, leaving road noise, aero acoustic noise and, at certain conditions, heating, ventilation and air conditioning (HVAC) noise to be the dominating noise sources. External tire noise is also more and more critical for fulfilling pass-by noise regulations.

THE CHALLENGE

Reliable equipment is critical since testing often is performed at a test track off-site. Rattle-free installation is extremely important to be able to evaluate high-frequency content that is not contributing to SPL, but to sound quality. The measurement microphone field type is important since road noise is often analyzed above 5 kHz, and time data is sometimes also used for later playback for subjective noise comparison.

SELECTING THE RIGHT MICROPHONE

Vehicle interior noise testing

Microphones used for vehicle interior noise testing should have a frequency range up to at least 11,22 kHz to allow for the analysis to include the 10 kHz third octave band. Free-field or random-incidence ½” class 1 measurement microphones are used at ear position, and six or more microphones are used for far-field sound power measurements. The choice depends on the test procedures. Pressure or random-incidence microphones with low noise performance are recommended for acoustic transfer function (ATF) measurements where frequencies above 3-4 kHz are of importance.

For in vehicle, we recommend GRAS 146AE ½” CCP Free-field Microphone Set with RA0357 Random-incidence Corrector for 146AE and RA0504 GoPro Adapter.

For far-field, complement GRAS 146AE ½” CCP Free-field Microphone Set with AL0006 Microphone Tripod and AL0008 ½”  POM, or RA0093 ½” 5-click Stainless Steel, Microphone Holder.

In both instances, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice for calibration.

Acoustic transfer function testing

For near-field measurements or troubleshooting of the tire, intensity probes and microphone arrays can be used and configured as per the analysis equipment needs. Measurements at the tire on road require nose cones or high-performance windshields. The possibility of easy verification of calibration will minimize test time and enable repeatable measurement results. The transducers are exposed to a lot of wear, often moved and even at worst case dropped to the floor. It is important to ensure that variation in environmental conditions do not influence the measurement performance.

For laboratory, we recommend GRAS 147AX CCP Rugged Pressure Microphone or GRAS 146AE ½’’ CCP Free-field Microphone Set with RA0357 Random-incidence Corrector for 146AE and AL0004 Small, Lightweight Microphone Tripod. Or use GRAS 46AO ½” CCP Standard Pressure Microphone Set or 46BD¼” CCP Standard Pressure Microphone Set. Also consider the RA0504 GoPro Adapter.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

 

The best result every time

With the new rugged automotive microphone, we have elaborated our HALT test to reflect the harsh environments and conditions in NVH measurements.


NVH measurement conditions
Strong vibrations, shock, drop, extreme temperatures and wet or dusty conditions are all par for the course for a automotive microphone. And at the end of the day you need to be confident that you have valid data, reliable repeatability and minimal downtime or re-tests.

Pass-by Noise Testing

GRAS NEVS A4A5719

Environmental noise pollution must be minimized to ensure people’s health and comfort. Traffic noise is, therefore, regulated and without fulfilling the regional targets for pass-by noise, a vehicle model cannot get a type approval or be put on the market. International test methods have been developed to simulate as realistic driving conditions as possible and the noise level limits have been reduced all over the world. This, obviously, puts a lot of focus on vehicle development and robustness in production. The methods for measuring pass-by noise requires dedicated facilities like specialized test tracks, large indoor noise, vibration and harshness (NVH) chassis dynamometer test cells and high-performance test equipment to produce comparable measurement results. Before running verification tests, thorough investigations of the most contributing sources (engine and intake/exhaust system, tire noise) are performed to predict the total noise level.

THE CHALLENGE

Early tests and predictions become more and more important to be able to fulfill legislation within tightly planned vehicle development projects. Tire noise will also be more critical for future vehicles and, especially, for electrical vehicles. The acoustic vehicle alerting systems (AVAS) in electrical vehicles must not only fulfill target sound levels, but also sound quality design. Pass-by noise is an important part of the branding efforts of vehicles and should of course also be considered.

SELECTING THE RIGHT MICROPHONE

Outdoor testing

The 146AE ½” CCP Free-field Microphone Set, which is IP67 rated dust and waterproof, is the ideal microphone for pass-by noise measurements. Even when temporary rain will stop your outdoor measurements, it is not necessary to disassemble your measurement setup, if you use the 146AE, so that when the rain stops it is possible to quickly resume the measurement.

We recommend GRAS 146AE ½’’ CCP Free-field Microphone Set with AM0069 Spherical Windscreen for ½” Microphones mounted on AL0004 Small, Lightweight, or AL0006, Microphone Tripod with AL0005 Swivel Head and AL0008 ½” POM Microphone Holder.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

Permanent outdoor testing

The microphones must fulfill the test procedures, typically a class 1, free-field microphone. Outdoor microphones with weather protection and internal heating are preferred for permanent installations.

We recommend GRAS 41AC LEMO Outdoor Microphone with RemoteCheck.

Indoor testing

A microphone array consisting of the 146AE microphone sets can be mounted on each side of the vehicle suitable for making the pass-by driving simulation. The AL0006 tripod or the AL0004 in combination with the AL0008 microphone holder can be used for positioning the microphones on both sides of the dynamometer. The AL0008 also requires the use of the AL0005 Swivel Head. The power-on LED indicator in the 146AE will help the test engineers to swiftly check that all the microphones are working correctly. In addition, the transducer electronic data sheet (TEDS) capabilities of these sensors will contribute to the fast setup of these multi-channel systems.

We recommend GRAS 146AE ½’’ CCP Free-field Microphone Set mounted on AL0004 Small, Lightweight, or AL0006, Microphone Tripod with AL0008 ½” POM Microphone Holder and AL0005 Swivel Head.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.

 

Electric and Hybrid Vehicle Technology Testing

Electric Hybrid Vehicle 28443514

Electrical propulsion is rapidly becoming more or less mandatory to include in every OEM’s vehicle range. Many naming conventions exist for the different vehicle technologies presently available. The main categories are the battery electric vehicle (BEV) and the hybrid electric vehicle (HEV) which also includes an internal combustion engine (ICE). The main difference between traditional powertrain testing and HEV/BEV testing is this addition of one or more electric motors, including inverter technology, battery cooling and the transmission design. The electric motor means new challenges compared to the combustion engine.

THE CHALLENGE

The main challenges are the low sound levels and tonal noise at much higher frequencies compared to traditional vehicles. The testing, therefore, requires high-quality equipment and careful measurement setup. Obviously, there is also less experience of customer reactions in this field.

SELECTING THE RIGHT MICROPHONE

Microphones used for electric and hybrid driveline testing must be robust and handle any electromagnetic fields. A small size is important for easy positioning when measuring acoustic transfer functions. Free-field or random-incidence microphones are most often used, and the choice depends on the test procedures. Low-noise performance and full audible frequency range is also required.

We recommend GRAS 146AE ½’’ CCP Free-field Microphone Set or GRAS 147AX CCP Rugged Pressure Microphone with AL0005 Swivel Head and AL0006 Microphone Tripod and AL0008 ½” POM, or RA0093 ½” 5-click Stainless Steel, Microphone Holder. For 146AE, also RA0357 Random-incidence Corrector for 146AE is recommended. Also consider the RA0504 GoPro Adapter for in car mounting.

For calibration, GRAS 42AG Multifunction Sound Calibrator, Class 1 is the ideal choice.