Application notes

Application notes

   

Noise Reduction on a Superbike

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Large Gas Compressor Noise Assesment

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Gearbox Noise Assesment

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Home appliances: vacuum cleaner Typically sound intensity measurements are performed in anechoic room, with the purpose to rank the acoustic radiation of the object under test by Sound Power. Holography and beamforming are methods available on the market but they require high number of channels, so they are costly and time consuming. Furthermore sound pressure based methods cannot be applied in non-anechoic conditions.The Microflown sensor can measure both pressure and particle velocity, which in the near field is not affected by background noise and reflections. A novel method based on video and audio synchronization has been developed as a fast tool for sound source localization with only one sensor.

Scan&Paint

Sound source localization

MEMs noise problem detection MEMS or “Micro electrical mechanical systems” is a growing sector in which components are reducedto the minimum size possible in order to obtain high performance products in reduced casings.Locating a failing component in such devices has become a problem for many manufacturers as spatialresolution and sensor size are normally in dispute.The PU match Acoustic Camera is a very effective tool with which high spatial resolution noiseproblems can be approached.Once proven that the spatial resolution is small enough for this applications and the sensitivity of thesensor has a sufficiently low threshold to capture these non-audible noises, the purpose in the nearfuture is to use this technique to detect failing components in the production line.

Acoustic camera

Sound source localization

Small Electrical Devices To be able to find possible noise source in small electrical devices, it is necessary to describe the sound field with a very high spatial resolution. Due to the costs, many tests are not possible to perform in anechoic conditions, which makes the acoustic testing very difficult to approach.With the Microflown sensor it is possible to measure directly the particle velocity, which is not affected to background noise and reflections. Besides this property (near field effect) the sensor has a directivity pattern at figure of eight, so contribution of lateral sources are not measured. 

Scan&Paint

Engineering services

Driveline Noise A car’s driveline includes everything in the car’s drivetrain with the exception of the engine and transmission. The ability to detect problems with the car’s driveline is an important skill that can save the vehicle from potential irreparable damages. If there is a driveline problem, the car will make noise and vibrate. Many driveline components cannot be easily separated to verify the source of the vibration or noise. So, on the development stage of powertrain it is important to evaluate the noise radiation of the driveline, and separate its NVH behavior which is related only to this component.

Acoustic Camera

Engineering services

Cooling fans

To cool down the sensors that are used for investigations in aerospace and automotive industries, atype of cooling fan is needed, that is only allowed to produce a maximum noise level of 24 dB. In orderto ensure that the fans meet those requirements, each one is currently tested in an anechoic roominside a production hall. The fans have to be taken out of the production line and placed in theanechoic room where the End of Line test is conducted. All fans which successfully pass the test arereturned to the production line for further development.

End of Line Control

Mirror actuator

A mirror actuator adjusts the angle of car side mirrors. The actuators are made out of plastic parts andare driven by two electric engines with a gear. In a production line a high number (100.000+ per week)of mirror actuators are produced.The absolute sound level of a mirror actuator is a general quality index for many OEM manufacturers.However in this particular case the sound quality of the noise emission was more important than theabsolute level. In order to assess the sound quality impression, certain types of error sounds weredefined: grinding, waving, ticking, vibration and buzzing. If these sound types were measured, theactuator had to be rejected.

End of Line Control

Damping optimization for car interior

The interior noise of a car is a general quality index for many OEM manufacturers. A reliable method for sound source ranking is often required in order to improve the acoustic performance. The final goal is to reduce the noise at some positions inside the car with the minimum impact on costs and weight. The general sources perceived in the interior are: the tires, the engine, intake and exhaust, aerodynamic noise, and more. All of them affect the car interior through body borne vibrations or airborne transmission. In this measurement example a cobbled brick road is used to evaluate the low frequency noise in driving conditions. The measurements are designed to evaluate the impact of damping materials used on the chassis of the car, and their direct effect on the car interior.

Scan & Paint

Sound source localization

Stationary and transient noise
measurement on consumer goods’ design stage

The temperature variations of a fridge in a “cooling” phase directly affect the metal and plastic elements of its cover. As a result, these elements vary their size and produce the typical “cracking” noise.To locate the critical panels and to be able to modify them to the best combination of outside layers and installation distances It is necessary to adopt a multi-probe solution. With this setup is possible to monitor the whole cooling / de-cooling process and analyze the transient signals produced by the different panels.

Acoustic Camera

Sound source localization

Acoustic characterization of tires and pavement

Over the past few decades, measurements have been taken to limit noise exposure in the European Union caused by cars, trucks, buses, and motorcycles. Road traffic is considered the most significant noise source in urbanized, industrial areas. The noise emission of tires has been always an important issue in relation with the environmental and urban traffic noise but also with the perceiving passenger in the car. Noise radiation depends on the tire-pavement interaction and is produced by several mechanisms: those mechanisms and their effects depend on the tire type, the tread design and the absorption properties of the road surface. All these parameters can be tested and characterized by measuring the impedance of the interacting materials and structures.

In-situ absorption

Material testing

Rattle noise on carseats: low
frequency, transient noise localization
The acoustic optimization process of the seat often requires testing in non–anechoic condition and with strong background noise and reflecting walls. The frame of the seat is mounted on the 6 dimensional axis hydraulic shaker, a random low frequency excitation simulates the behavior of the seat during a driving condition.

Acoustic Camera

Sound source localization

Turbochargers: noise and vibration characterization In the recent engines development and engineering the request of low fuel consumption and better pollution emissions requires car manufacturer to downsizing the engine volume and use a turbocharger to improve the performance. The turbochargers have general typical noise phenomena. A complete characterization of these effects can be made by using the Microflown sensor.  
Windtunnel testing: external flow correlated to a perceiving position The main issue in aerodynamic noise in wind tunnel is to find the way to measure the property of the external flow (velocity, pressure) and also correlate it with the passenger perceiving using the transmission path and some interior noise measurements techniques. The microflown sensor is the only sensor that can measure directly the particle velocity in 3D out from the car and inside the car.

Acoustic Camera

Sound source localization
Seatbelt rolling mechanism transient noise mapping Measurements of noise in real working and transient conditions becomes applicable when using a Microflown particle velocity sensor. This in a broad bandwith so also on low frequencies.

Acoustic Camera

Sound source localization
Ricardo UK using PU probes Recently a case of measuring an engine run up with Microflown PU probes is being done at Ricardo UK. The case done was a combined project between four parties to research the benefits of using PU sound intensity probes instead of the traditional PP sound intensity probes.To verify the results, the sound power spectra obtained with the Microflown probes are to be compared to sound power measurements using a PP probe.

Acoustic Camera

Sound Intensity

Sound power

Sound source localization
Velocity vs acceleration
An acceleration signal is compared with a velocity signal by measuring the velocity of an accelerometer that is driven by a chirp.
Vibration
PU versus PP measurements
A PU and a PP measurement are compared. The mathematics is shown in small steps.
Sound Intensity
Velocity vs intensity visualisation of a thin plate
For an experiment the differences between surface velocity and sound intensity visualisation in a 33x43cm, 0.8mm thin plate are measured.
 
Scan and listen method: vibration measurement
For a lab experiment the modes in a 33x43cm 0.8mm thin plate are found with a simple scan and listen method. The method employs one PU-mini probe. The normal velocity of the surface is scanned and the signal is amplified and made audible trough headphones.

Scan & Listen

Vibration

Microflown Based non Contact Measurements of Structural Velocity in the Very Near Fields
Microflown acoustical particle velocity sensors are a viable alternative to both laser vibrometers and mini-accelerometers, enabling truly new testing opportunities whilst reducing often the overall system costs!
Close to an object (in the so called very near field), and without the need for advanced software, (an array of) Microflown acoustical particle velocity sensors can be used for the non contact measurement of the normal component of the structural velocity. For instance non contact multi channel measurements on (in) stationary sources become feasible, as well as capability of measuring airborne sound.
Due to the miniaturized size and working principle of the Microflown, measurements in confined spaces are possible now, at elevated temperatures up to 200 degrees Celsius and above and in situations with high levels of background noise.
 
Particle Velocity Based P-U Sound Probes for Car Panel Noise Analysis
The use of particle velocity based fully integrated p-u sound probes allows the development of new sound power based measurement methods to optimize the acoustical packages for car interiors.  
P-U Based in situ Characterization of Damping Materials
A new universal tool to the acoustical world has become available to characterise acoustical properties of materials under all sorts of real world conditions. Uniformity, ease of use and productivity of measurements are increased dramatically. Costs of infrastructure and samples are reduced significantly.
Includes paper presented at the ISMA 2004 in Leuven, Belgium.

In-situ absorption

Material testing

Very Near Field Structural Dynamics In acoustics concepts like the ‘far field’ and ‘near field’ are well known. The sound field at a position much closer to the source than the size of the source itself, is introduced as the ‘very near field’ It will be shown that in the very near field the particle velocity is frequency independent and almost independent of place whereas the sound pressure is almost independent of place but suppressed and frequency dependent.  
In situ Impedance Measurements
Measuring method of sound reflection and absorption characteristics based on the particle velocity and its applications to measurements on such as drainage pavement of road surface.  
Near Field and Very Near Field Source Localization
The availability of dedicated Microflown particle velocity sensors offers entirely new ways for solving numerical inverse methods for near field source localization. Furthermore, in the proximity of an object, e.g. in the so called very near field, uncomplicated direct measurements methods without computational power are available now.  
Structural Vibration Measurements
Microflown Scanning Probes offer the opportunity to measure 3D on a vibrating surface, either by using a three dimensional probe or by repositioning the single element Scanning Probe.  
Far Field Source Localization
The combination of dedicated particle velocity sensors, a sound pressure microphone and some advanced measuring techniques offers new possibilities to localize sound sources in the far field.  
Representation of 3D Sound Fields on Loudspeakers
Until recently, sound field and sound intensity measurements were scarcely used, mainly due to various practical and technical limitations. Here a representation method is given for the sound field of loudspeakers.  
Three Dimensional Impulse Response
The 3DP is a measurement system developed at Meyer Sound for architectural acoustic measurements. It consists of one pressure microphone, three Microflown velocity probes, and custom Meyer Sound hardware and software.  
Low DC flow Measurement with a High Spatial Resolution
A Scanning Microflown Probe is used to measure a spatial DC flow field that was generated by a high number of (250µm in diameter) little holes in line. The maximal air-velocity from the holes was in the order of 1mm/s.