2000 # Measuring Speech Intelligibility Using DIRAC — Type 7841 DIRAC PC software is used for measuring a wide range of room acoustical parameters. Based on the measurement and analysis of impulse responses, DIRAC supports a variety of measurement configurations. For accurate measurements according to the ISO 3382 standard, you can use the internally generated MLS or sweep signals through a loudspeaker sound source. Survey measurements are easily carried out using a small impulsive sound source, such as a blank pistol or even a balloon. Speech measurements can be carried out in compliance with the IEC 60268-16 standard, for male and female voices, through an artificial mouth-directional loudspeaker sound source or through direct injection into a sound system, taking into account the impact of background noise. DIRAC is not only a valuable tool for field and laboratory acoustics engineers, but also for researchers and educational institutions. Type: Application Note Year: 2003 PDFRead document # Modal Analysis using Multi-reference and MIMO Techniques The aim of this application note is to give a brief overview of the mobility measurement based modal analysis methods and give some practical explanations and hints for use of the different techniques. This includes multi-reference and Multiple-Input Multiple-Output measurement techniques. Type: Application Note Year: 2002 PDFRead document # Using NS-STSF to investigate Transient Phenomena in Automotive Applications Non-stationary Spatial Transformation of Sound Fields (NS-STSF) is a revolutionary technique for mapping noise in 3D-space and time. NS-STSF in effect allows you to film the noise emanating from a test object as a sequence of snapshots of instantaneous sound pressure using a microphone array. You can then map the noise distribution in time and space by transforming the measured sound-field to other planes, parallel to the measurement plane. All common soundfield descriptors such as SPL, intensity and spectral content are available from a single measurement. This system is the only truly transient implementation of the Acoustic Holography technique. Type: Application Note Year: 2002 PDFRead document # Envelope Analysis for Diagnostics of Local Faults in Rolling Element Bearings The Multi-analyzer System PULSE™ includes Envelope Analysis Type 7773. This application note briefly describes the ideas behind Envelope Analysis of local bearing faults, how Envelope Analysis is implemented in PULSE™, practical considerations, and two case studies. Type: Application Note Year: 2002 PDFRead document # Tone Assessment using the 2260 H Sound Level Analyzer This application note presents a case and explains the concepts and features of tone assessment in Sound Level Analyzer Type 2260 H. The description is based on the JNM2 method, since this is the de facto standard and the one specified in most detail. For computer-based tone assessment, the JNM2 method includes guidelines which are implemented in Type 2260 H. Type: Application Note Year: 2002 PDFRead document # Operational Modal Analysis of a Wind Turbine Wing using Acoustical Excitation 1990 # Dynamic Sound Testing of Earth-moving Machinery to ISO 6393-6 The Dynamic Sound Test System performs dynamic and static sound testing on earth-moving machinery according to ISO standards. The major components of the system are the AudiBel software and the PULSETM Multi-Analyzer platform. Due to an advanced system design, only one person, the machine operator, is required to perform a complete test. Type: Application Note Year: 1999 PDFRead document # Order Tracking of a Coast-down of a Large Turbogenerator In this application note, it is demonstrated how to use the order tracking facility of PULSE™, the Multi-analyzer System Type 3560. The data to be analysed is a coast-down of a large turbogenerator in a power station. Critical speeds were confirmed during the measurement. In addition, the 37th order component (and multiples thereof) were identified, caused by loose blades in the cooling fan system. Type: Application Note Year: 1999 PDFRead document # To Deal with Electrical Noise and Interference in the Measuring Chain using NEXU When making vibration measurements, it may happen that not all the signal measured comes from vibration of the object. Some of it may derive from electrical pollution in the environment. This application note describes some possible sources of spurious measurements together with recommendations on how to avoid them. Type: Application Note Year: 1998 PDFRead document # Using Modems with Sound Level Meters Sound Level Meters are often used for monitoring in remote places, and you may want to “monitor the monitor” or transfer measured data to your homebase PC, without going to the measurement site. A telephone connection — wired or wireless — is a convenient way to transfer measurement data. And modems are a vital link in the chain of transmission. This application note explains what equipment you need and how to use it. Type: Application Note Year: 1998 PDFRead document # 2-channel Measurement using 2260 Investigator To measure facade insulation using traffic noise you need to measure sound pressure outside and inside the façade simultaneously, i.e., 2-channel measurement. This can be done using 2260 Investigator™ with Sound Intensity Software module BZ 7205. In addition you need the reverberation time inside the facade, and this can be measured using 2260 Investigator Building Acoustics Software BZ 7204. Type: Application Note Year: 1998 PDFRead document # Improving Telephone Handset Performance When using the new Type 3.2 ear simulators, the measurement results obtained will in some cases be different (more realistic) than results obtained with the Type 1 ear simulator. This application note explains the reason for these differences. It also suggests some basic rules for designing handsets which are less sensitive to differences in ear simulators and hence also less sensitive to the different conditions under which the handsets are used. Eventually, using the new ear simulator types may lead to an improved performance of the telephone handset, in terms of a better perceived sound quality. Type: Application Note Year: 1997 PDFRead document # Improved Method for Complex Modulus Estimation In industrial products, vibration and the noise it creates is often a major parameter to be taken into account. It is therefore usually very important to measure the material properties i.e. stiffness and damping, that determine how vibrations are generated, transmitted and damped. This application note describes a method developed by Mr.Fuglsang Nielsen which will allow the standard non-resonant method for the determination of complex modulus to be used at higher frequencies than otherwise possible. It is also shown how this method can be implemented using the Multichannel Analysis System Type 3550. Type: Application Note Year: 1996 PDFRead document # Tyre Noise Measurement on a Moving Vehicle To obtain precise information about the noise radiation from tyres it is desirable to measure with the tyre in actual operation on a road. The STSF technique for tyre noise measurements is able to present detailed information about both the acoustical near-field, as intensity radiation mappings very close to the surface of the tyre, and farfield calculations such as pass by simulations and radiation patterns. Type: Application Note Year: 1996 PDFRead document # Sound Power Determination with or without ISO 9614-1 In Europe, a new "Machinery Directive" has been written, coming into force from 1/1/95. The purpose of this directive is to ensure the health of people using machines. The directive states, among other things, that equipment sold in Europe must fulfil specified noise demands. The equipment covered by this directive is everything from jacks and garden tractors, to chain saws and plastic moulding machines. What should be stated in the instruction manual for the equipment? If the A-weighted sound pressure level is below 70 dB(A), this must be indicated (Lp < 70 dB(A) re 20 Pa). Above 70 dB(A), the A-weighted sound pressure level should be stated. If the sound pressure level exceeds 85 dB(A), the A-weighted sound power level should also be stated. If the machine is very large, the sound power level is replaced by the sound pressure level measured at significant positions. If the noise contains peaks exceeding 130 dB(C), this must also be stated. Type: Application Note Year: 1995 PDFRead document # Mounted Resonance Measurements using Type 2525 With Measuring Amplifier Type 2525, Brüel & Kjaer has not introduced just a simple amplifier, but a sophisticated measurement system. Besides its ability to amplify signals and to display the signal's RMS and peak values, the Type 2525 has a number of other facilities. In this application note, we are going to focus on its capability to perform mounted resonance tests of piezoelectric accelerometers. With this feature the Type 2525 is able to measure the resonance frequency of the accelerometer, and by comparing the measured frequency with the one specified on the calibration chart, it is possible to determine whether the accelerometer is correctly mounted or not. Type: Application Note Year: 1995 PDFRead document # The Use of a Computer to Process 3550 Disk Data This application note shows how to store data on the built-in 3550 disk drive, and how to use the stored data in commercially available IBM-PC application software such as spreadsheets or word-processors. Type: Application Note Year: 1995 PDFRead document # Sound Power Determination according to ISO 374x This is a typical case story regarding noise labelling of a tape streamer, made in cooperation with Tandberg Data Storage A/S, Oslo. Type: Application Note Year: 1995 PDFRead document # Exterior Noise Measurements on a Rover 220 GSi The acceptable exterior noise level from passenger cars is constantly decreasing through national and international regulations. Most recently, the acceptable level within the European Union has been lowered to 74 dB(A). To fulfill these demands, still more advanced measuring techniques have to be used in the development process and for troubleshooting. In this example, traditional measuring techniques suggested that the main noise source was the exhaust orifice. Detailed analysis of the sound field using Spatial Transformation of Sound Fields showed that the engine air intake system was dominant. As a result the overall sound pressure level was reduced by minor adjustments to the intake system as opposed to major modifications to the exhaust system. Type: Application Note Year: 1995 PDFRead document # Practical use of the "Hilbert transform" The Brüel & Kjaer Signal Analyzer Type 3550 and 2140 families implement the Hilbert transform to open up new analysis possibilities in the time domain. By means of the Hilbert transform, the envelope of a time signal can be calculated, and displayed using a logarithmic amplitude scale enabling a large display range. Two examples which use the Hilbert transform are presented here: - The determination of the damping or decay rate at resonances, from the impulse response function. - The estimation of propagation time, from the cross correlation function. Type: Application Note Year: 1995 PDFRead document # Gated Tracking Applied on an Automobile Engine Using Multichannel Analysis... Vibrations in rotating and reciprocating machinery are caused by the acceleration of the moving parts and by impact activity in the machinery. Order tracking is applied to relate vibration to the various moving parts. Gated tracking is used to identify where in the engine cycle the vibration is generated. Gated tracking is especially interesting when dealing with reciprocating machines like combustion engines, pumps and compressors. Type: Application Note Year: 1995 PDFRead document # Calibration at Toyota Motor Corp. using Vibration Transducer Calib. System 9610 For several years, Toyota Motor Corporation have used a traditional manually operated back-to-back vibration transducer calibration system based on older Brüel & Kjær equipment. However, continuously adding vibration transducers, Toyota Motor Corporation developed a need for a more efficient means of calibrating these transducers. To ensure continued optimum vibration measurement results, reliability, high precision and high accuracy were vital factors when the Calibration Laboratory began looking for a suitable calibration system. Vibration Transducer Calibration System Type 9610, providing automated FFT-based sensitivity and phase calibration of vibration transducers over a wide frequency range, was chosen for reasons of accuracy, confidence and durability. This Application Note introduces the concept of FFT-based vibration transducer calibration and discusses the features, advantages and benefits of the Vibration Transducer Calibration System Type 9610 in connection with its use at Toyota Motor Corporation. Type: Application Note Year: 1994 PDFRead document # A Hand-held Exciter for Field Mobility Measurements This Application Note introduces a new excitation technique for exciting mechanical structures, in order to make mobility measurements. A small hand-held exciter or shaker has been developed for field measurements yielding the same advantages as those obtained using an impact hammer as well as those obtained using a shaker for the frequency response function measurements. The main advantages are: easy to use in the field, no elaborate fixturing, and best linear approximation of system under test as well as no leakage, assuming an appropriate excitation signal has been selected. The only disadvantage is that some degree of freedom (DOF) jitter may be introduced using this method, and the use of the hand-held exciter is only applicable for relatively small structures. A complete review of advantages/disadvantages of various excitation techniques is included in this Application Note in order to put the method into the right perspective. Type: Application Note Year: 1994 PDFRead document # Sound Power Determination according to ISO 9614-2 In Europe, a new "Machine Directive" has been written, coming into force from 1/1/95. The purpose of this directive is to ensure the health of people using machines. The directive states, among other things, that all equipment sold in Europe must fulfil specified noise demands. The equipment covered by his directive is everything from toothbrushes, washing machines, office machines and handheld drills to cars and heavy vehicles. What should be stated in the instruction manual? If the A-weighted sound pressure level is below 70 dB(A), this must be indicated (< 70 dB(A) re 20uPa). Beyond 70 dB(A), the A-weighted sound pressure level should be stated. If the sound pressure level exceeds 85 dB(A), the A-weighted sound power level should also be stated. If the machine is very big, the sound power level is replaced by the sound pressure level measured at significant positions. If the noise contains peaks exceeding 130 dB(C), this must also be stated. Note that all sound pressure levels should be measured under "free field" conditions at the typical position of the operators head. If that is not defined, the sound pressure level must be measured at a distance of 1 metre from the surface of the machinery at a height of 1.6 metres from the floor. Type: Application Note Year: 1994 PDFRead document # An Overview of Standards for Sound Power Determination This application note is an introduction to the large number of international standards existing regarding sound power determination. The standards mentioned are mainly ISO (International Organization for Standardization), IEC (International Electrotechnical Commission), ECMA (European Computer Manufacturers Association), DIN (Deutsches Institut for Normung e.V.), ANSI (American National Standards Institute) and some of the European "Council Directives". Type: Application Note Year: 1994 PDFRead document # Mobility Measurements Being modular and expandable, the Brüel & Kjaer Multi-channel Analysis System Type 3550 makes fast, easy and accurate mobility measurements on structures. In its standard dualchannel configuration, and equipped with only a force hammer and an accelerometer, even the novice can begin to explore the dynamic behaviour of structures. This note gives an introduction to this important application area and outlines the theoretical background and experimental techniques. Type: Application Note Year: 1994 PDFRead document # Time Domain Averaging Combined with Order Tracking Apart from spectrum averaging, there is another averaging method that can be used when measuring periodic signals, namely synchronous time domain averaging. The main advantage of this method is that unwanted noise components are averaged out. On the 3550 analyzer, time domain averaging can be combined with order tracking analysis to yield a very powerful method for measuring on reciprocating engines (internal-combustion engines, pumps, and compressor). Type: Application Note Year: 1994 PDFRead document # Run-up Order Analysis of Axial Vibrations in a 2190kW, MAN B&W In operation, the propulsion shafting of a ship is deformed axially and torsionally. Both deformations cause axial vibrations, which at critical RPM may become unacceptable. The vibrations are damped by an integral axial vibration damper. The critical RPM are calculated based on a model of the shafting, and measurements are performed to verify the calculated natural frequencies and the effect of the damper. The verification is required by some of the shipbuilding classification societies. It is demonstrated that Type 3555 fitted with Extended Analysis Software Type 7639 is suited for the measurements. Type: Application Note Year: 1994 PDFRead document # Multi-Reference Impact Testing for Modal Analysis using Type 3557 Four Channel Analyzer and CADA-PC This Application Note introduces the MRIT concept and demonstrates the techniques on a bi-symmetrical structure which has repeated roots in all the modal peaks. These are decomposed using the three-reference data set, measured with the Brüel & Kjaer Type 3557 four-channel analyzer, and Polyreference curvefitting as implemented in the CADA-PC modal analysis package. Type: Application Note Year: 1994 PDFRead document # Solving a Critical Propulsion Problem at Volvo Penta using Two Torsional Vib.... This Application Note describes and examines the use of two Torsional Vibration Meters Type 2523 in a critical, severely time-limited, trouble-shooting situation where the performance of a torsional vibration elastic coupling, fitted to the propulsion system of a new series of smaller navy vessels, had to be thoroughly investigated in order for the propulsion system to be cleared for operational service. Type: Application Note Year: 1994 PDFRead document # On the Working Principle of Torsional Vibration Meter In this Application Note, the basic optical design of the instrument is introduced along with a derived mathematical explanation of some of the important features offered by the technique and implemented in the Torsional Vibration Meter Type 2523. Furthermore, to verify the performance of the instrument, results from comparison measurements are presented and evaluated. Type: Application Note Year: 1994 PDFRead document # Time Windows FFT analyzers such as the Brüel & Kjaer Signal Analyzer families Type 3550 and Type 2140 (with FFT options) process finite blocks of digital information. The analyzer extracts, or “cuts out”, these blocks from the complete time record using time weighting functions, or “time windows”. Unless we can understand the basic concepts of time limited data, we can’t be sure that our interpretation of FFT analysis is correct. Neither can we be sure of the accuracy of our results. Type: Application Note Year: 1994 PDFRead document # Choose your Units! The Brüel & Kjaer Signal Analyzer families Type 3550 and Type 2140 (with FFT options) allow you to choose the appropriate units to suit your measurement signal, be it deterministic, random or transient. The frequency spectrum amplitude can be scaled in terms of: - Root mean square (RMS) for deterministic signals - Mean square, Power (PWR) for deterministic signals - Power spectral density (PSD) for random signals - Energy spectral density (ESD) for transients The noise bandwidth (B=Df´k, where k depends of the choice of time window) and record length (T) selected for the measurement affect the amplitude scaling of the frequency spectra. The analyzers of the 3550 and 2140 families will automatically compensate for these factors if the correct scaling has been selected. Type: Application Note Year: 1994 PDFRead document # Gearbox Analysis using Cepstrum Analysis and Comb Liftering Cepstrum analysis has many applications: for example echo detection and removal, or speech analysis, but the most important one in industry is related to machine diagnostics, where its ability to detect periodicities in the spectrum is taken advantage of. The Dual Channel Analyzer Type 3555 has a number of editing features that make it uniquely well suited for identification and separation of harmonic families using cepstrum analysis. Type: Application Note Year: 1994 PDFRead document # Sound Power Determination using Type 3554, with or without ISO 9614-1 The purpose of this application note is to show novices how easily the sound power measurements can actually be performed. For this purpose we have chosen a modern "Nilfisk" vacuum cleaner from the Danish manufacturer Fisker & Nilsen. The measurements are first done according to ISO 9614-1 and then as simply as possible. As you will see, the results are very close. Type: Application Note Year: 1994 PDFRead document # Laser Diagnostics of Machinery Health For reasons of both safety and economy it is desirable to avoid the breakdown at sea of heavy machinery in marine transport and offshore installations. Unscheduled loss of production or power during ‘downtime’ enhances vulnerability and often carries severe financial penalties. This has led to an increasing interest in the concept of monitoring machinery health to detect impending failure. This Application Note demonstrates how the Torsional Vibration Meter Type 2523 can be used to address the problem of diagnosing failure in viscous shear torsional dampers which are normally fitted to the crankshaft of large marine propulsion diesels and generator sets. The method allows condition diagnosis to be achieved while the engine is running and avoids the need for ‘downtime’ associated with traditional fluid sampling methods. Type: Application Note Year: 1993 PDFRead document # Measuring Torsional Operational Deflection Shapes of Rotating Shafts With the advent of the laser-based Torsional Vibration Meter Type 2523, general torsional vibration measurements were not only greatly facilitated but, moreover, the unique concept of the instrument opened up for a number of new innovative measurement techniques, including the possibility of measuring Torsional Operational Deflection Shapes on rotating shafts. This Application Note describes the concept and the basic technique of measuring torsional operational deflection shapes using the Torsional Vibration Meter Type 2523, the Multichannel Analysis System Type 3550 and the Operational Deflection Shapes Software WT 9380, running on a Personal Computer. Applying the Torsional Operational Deflection Shapes technique to a demonstration model, the features and benefits of the technique are discussed. Type: Application Note Year: 1993 PDFRead document # Audio Distortion Measurements In the never ending quest for better sound transmission, reinforcement, and reproduction, the electronics have been extensively analyzed for distortion. Distortion in the electro acoustic transducers, while typically several orders of magnitude greater, has often been neglected or not even specified because it has been difficult to measure and interpret. With a basic understanding of transducer limitations, some knowledge of human hearing, and the application of different distortion test methods, electroacoustic transducer distortion becomes easier to measure and assess. Type: Application Note Year: 1992 PDFRead document # Noise control survey on a pump using the gated technique When making noise control surveys on rotating machinery, one is often interested in parts of the rotational cycle and the noise events which occur during that part. By taking a trigger signal from a rotating part to initiate a measurement, the filters of the analyser start to respond and their outputs are detected at a specified number of "windows" or "gates" per revolution. Type: Application Note Year: 1992 PDFRead document # Sound field description using complex sound intensity instrumentation Complex sound intensity is a vector that describes the coherent relation between the sound pressure and the particle velocity in a sound field. The concept of complex sound intensity was introduced more than 40 years although the first descriptions of practical methods of measuring the quantity appeared much later. Sound intensity analysers capable of determining the active intensity have been commercially available since 1981 whereas equipment which can measure both active and reactive intensity directly has only been available since 1988. Type: Application Note Year: 1992 PDFRead document # The Use of a Computer to Process 2123/33 Disk Data This application note shows how to store data on the built-in 2123/33 disk drive and how to use the stored data in commercially available IBM-PC application software such as spreadsheets or word processors. Type: Application Note Year: 1991 PDFRead document # Measurement of Sound Reduction Index with the Single/Dual Channel Real-time analyzers Types 2123 and 2133 Determination of sound insulation according to the International Standard ISO 140 or equivalent standards can be accomplished directly by using the Single/Dual Channel Real-time Analyzer Type 2123 or 2133. This application note describes features important to measurement of the sound reduction index, and includes information about user-defined functions, data storage and presentation of results. Type: Application Note Year: 1990 PDFRead document # Measuring the Non-rigid Behavior of a Loudspeaker Diaphrahm using Modal Analysis When a loudspeaker vibrates at low frequencies, it behaves as a rigid piston, with all parts of the diaphragm moving in phase. Above a certain frequency, however, the diaphragm behaviour will become more complex. To examine this phenomenon, it is necessary to make reliable measurements of the diaphragm motion at a number of different points. Type: Application Note Year: 1990 PDFRead document # Measurement of Vehical Exterior Noise using the portable Real-time Frequency Analyzer Type 2143 Exterior noise is a major component of the environmental impact of cars, trucks, buses, motorcycles, and the like. Control of exterior noise has led to the development of several test procedures which can be categorized into two groups: stationary tests and pass-by tests. Type: Application Note Year: 1990 PDFRead document # Condition Based Maintenance and Quality Assurance of Production Machinery Production output and quality assurance are the key elements in any production facility. Techniques that help to maintain a high production throughput and provide a tool for both maintaining and monitoring finished quality are therefore of paramount importance. This Application Note details the role that vibration monitoring plays at the Ford Motor Co’s Düren plant, Germany. Considerable savings in maintenance costs and a high-level of output I quality have been achieved. Type: Application Note Year: 1990 PDFRead document # Applications of the Real-time Frequency Analyzer The 2143 can be described as the next logical step up from a sound level or vibration meter, while also providing a link to sophisticated laboratory systems, and in particular allows online laboratory-standard analysis in the field where otherwise tape recorders would be used to bring the data back to the laboratory. It has many applications in the analysis of sound, vibration, and other signals. The purpose of this application note is to describe how the features of the 2143 can be used in some of these applications. Type: Application Note Year: 1990 PDFRead document # Acoustical testing in the automotive industry using STSF # Dynamic Sound Testing of Earth-moving Machinery to ISO 6393-6 The Dynamic Sound Test System performs dynamic and static sound testing on earth-moving machinery according to ISO standards. The major components of the system are the AudiBel software and the PULSETM Multi-Analyzer platform. Due to an advanced system design, only one person, the machine operator, is required to perform a complete test. Type: Application Note Year: 1999 PDFRead document # Order Tracking of a Coast-down of a Large Turbogenerator In this application note, it is demonstrated how to use the order tracking facility of PULSE™, the Multi-analyzer System Type 3560. The data to be analysed is a coast-down of a large turbogenerator in a power station. Critical speeds were confirmed during the measurement. In addition, the 37th order component (and multiples thereof) were identified, caused by loose blades in the cooling fan system. Type: Application Note Year: 1999 PDFRead document # To Deal with Electrical Noise and Interference in the Measuring Chain using NEXU When making vibration measurements, it may happen that not all the signal measured comes from vibration of the object. Some of it may derive from electrical pollution in the environment. This application note describes some possible sources of spurious measurements together with recommendations on how to avoid them. Type: Application Note Year: 1998 PDFRead document # Using Modems with Sound Level Meters Sound Level Meters are often used for monitoring in remote places, and you may want to “monitor the monitor” or transfer measured data to your homebase PC, without going to the measurement site. A telephone connection — wired or wireless — is a convenient way to transfer measurement data. And modems are a vital link in the chain of transmission. This application note explains what equipment you need and how to use it. Type: Application Note Year: 1998 PDFRead document # 2-channel Measurement using 2260 Investigator To measure facade insulation using traffic noise you need to measure sound pressure outside and inside the façade simultaneously, i.e., 2-channel measurement. This can be done using 2260 Investigator™ with Sound Intensity Software module BZ 7205. In addition you need the reverberation time inside the facade, and this can be measured using 2260 Investigator Building Acoustics Software BZ 7204. Type: Application Note Year: 1998 PDFRead document # Improving Telephone Handset Performance When using the new Type 3.2 ear simulators, the measurement results obtained will in some cases be different (more realistic) than results obtained with the Type 1 ear simulator. This application note explains the reason for these differences. It also suggests some basic rules for designing handsets which are less sensitive to differences in ear simulators and hence also less sensitive to the different conditions under which the handsets are used. Eventually, using the new ear simulator types may lead to an improved performance of the telephone handset, in terms of a better perceived sound quality. Type: Application Note Year: 1997 PDFRead document # Improved Method for Complex Modulus Estimation In industrial products, vibration and the noise it creates is often a major parameter to be taken into account. It is therefore usually very important to measure the material properties i.e. stiffness and damping, that determine how vibrations are generated, transmitted and damped. This application note describes a method developed by Mr.Fuglsang Nielsen which will allow the standard non-resonant method for the determination of complex modulus to be used at higher frequencies than otherwise possible. It is also shown how this method can be implemented using the Multichannel Analysis System Type 3550. Type: Application Note Year: 1996 PDFRead document # Tyre Noise Measurement on a Moving Vehicle To obtain precise information about the noise radiation from tyres it is desirable to measure with the tyre in actual operation on a road. The STSF technique for tyre noise measurements is able to present detailed information about both the acoustical near-field, as intensity radiation mappings very close to the surface of the tyre, and farfield calculations such as pass by simulations and radiation patterns. Type: Application Note Year: 1996 PDFRead document # Sound Power Determination with or without ISO 9614-1 In Europe, a new "Machinery Directive" has been written, coming into force from 1/1/95. The purpose of this directive is to ensure the health of people using machines. The directive states, among other things, that equipment sold in Europe must fulfil specified noise demands. The equipment covered by this directive is everything from jacks and garden tractors, to chain saws and plastic moulding machines. What should be stated in the instruction manual for the equipment? If the A-weighted sound pressure level is below 70 dB(A), this must be indicated (Lp < 70 dB(A) re 20 Pa). Above 70 dB(A), the A-weighted sound pressure level should be stated. If the sound pressure level exceeds 85 dB(A), the A-weighted sound power level should also be stated. If the machine is very large, the sound power level is replaced by the sound pressure level measured at significant positions. If the noise contains peaks exceeding 130 dB(C), this must also be stated. Type: Application Note Year: 1995 PDFRead document # Mounted Resonance Measurements using Type 2525 With Measuring Amplifier Type 2525, Brüel & Kjaer has not introduced just a simple amplifier, but a sophisticated measurement system. Besides its ability to amplify signals and to display the signal's RMS and peak values, the Type 2525 has a number of other facilities. In this application note, we are going to focus on its capability to perform mounted resonance tests of piezoelectric accelerometers. With this feature the Type 2525 is able to measure the resonance frequency of the accelerometer, and by comparing the measured frequency with the one specified on the calibration chart, it is possible to determine whether the accelerometer is correctly mounted or not. Type: Application Note Year: 1995 PDFRead document # The Use of a Computer to Process 3550 Disk Data This application note shows how to store data on the built-in 3550 disk drive, and how to use the stored data in commercially available IBM-PC application software such as spreadsheets or word-processors. Type: Application Note Year: 1995 PDFRead document # Sound Power Determination according to ISO 374x This is a typical case story regarding noise labelling of a tape streamer, made in cooperation with Tandberg Data Storage A/S, Oslo. Type: Application Note Year: 1995 PDFRead document # Exterior Noise Measurements on a Rover 220 GSi The acceptable exterior noise level from passenger cars is constantly decreasing through national and international regulations. Most recently, the acceptable level within the European Union has been lowered to 74 dB(A). To fulfill these demands, still more advanced measuring techniques have to be used in the development process and for troubleshooting. In this example, traditional measuring techniques suggested that the main noise source was the exhaust orifice. Detailed analysis of the sound field using Spatial Transformation of Sound Fields showed that the engine air intake system was dominant. As a result the overall sound pressure level was reduced by minor adjustments to the intake system as opposed to major modifications to the exhaust system. Type: Application Note Year: 1995 PDFRead document # Practical use of the "Hilbert transform" The Brüel & Kjaer Signal Analyzer Type 3550 and 2140 families implement the Hilbert transform to open up new analysis possibilities in the time domain. By means of the Hilbert transform, the envelope of a time signal can be calculated, and displayed using a logarithmic amplitude scale enabling a large display range. Two examples which use the Hilbert transform are presented here: - The determination of the damping or decay rate at resonances, from the impulse response function. - The estimation of propagation time, from the cross correlation function. Type: Application Note Year: 1995 PDFRead document # Gated Tracking Applied on an Automobile Engine Using Multichannel Analysis... Vibrations in rotating and reciprocating machinery are caused by the acceleration of the moving parts and by impact activity in the machinery. Order tracking is applied to relate vibration to the various moving parts. Gated tracking is used to identify where in the engine cycle the vibration is generated. Gated tracking is especially interesting when dealing with reciprocating machines like combustion engines, pumps and compressors. Type: Application Note Year: 1995 PDFRead document # Calibration at Toyota Motor Corp. using Vibration Transducer Calib. System 9610 For several years, Toyota Motor Corporation have used a traditional manually operated back-to-back vibration transducer calibration system based on older Brüel & Kjær equipment. However, continuously adding vibration transducers, Toyota Motor Corporation developed a need for a more efficient means of calibrating these transducers. To ensure continued optimum vibration measurement results, reliability, high precision and high accuracy were vital factors when the Calibration Laboratory began looking for a suitable calibration system. Vibration Transducer Calibration System Type 9610, providing automated FFT-based sensitivity and phase calibration of vibration transducers over a wide frequency range, was chosen for reasons of accuracy, confidence and durability. This Application Note introduces the concept of FFT-based vibration transducer calibration and discusses the features, advantages and benefits of the Vibration Transducer Calibration System Type 9610 in connection with its use at Toyota Motor Corporation. Type: Application Note Year: 1994 PDFRead document # A Hand-held Exciter for Field Mobility Measurements This Application Note introduces a new excitation technique for exciting mechanical structures, in order to make mobility measurements. A small hand-held exciter or shaker has been developed for field measurements yielding the same advantages as those obtained using an impact hammer as well as those obtained using a shaker for the frequency response function measurements. The main advantages are: easy to use in the field, no elaborate fixturing, and best linear approximation of system under test as well as no leakage, assuming an appropriate excitation signal has been selected. The only disadvantage is that some degree of freedom (DOF) jitter may be introduced using this method, and the use of the hand-held exciter is only applicable for relatively small structures. A complete review of advantages/disadvantages of various excitation techniques is included in this Application Note in order to put the method into the right perspective. Type: Application Note Year: 1994 PDFRead document # Sound Power Determination according to ISO 9614-2 In Europe, a new "Machine Directive" has been written, coming into force from 1/1/95. The purpose of this directive is to ensure the health of people using machines. The directive states, among other things, that all equipment sold in Europe must fulfil specified noise demands. The equipment covered by his directive is everything from toothbrushes, washing machines, office machines and handheld drills to cars and heavy vehicles. What should be stated in the instruction manual? If the A-weighted sound pressure level is below 70 dB(A), this must be indicated (< 70 dB(A) re 20uPa). Beyond 70 dB(A), the A-weighted sound pressure level should be stated. If the sound pressure level exceeds 85 dB(A), the A-weighted sound power level should also be stated. If the machine is very big, the sound power level is replaced by the sound pressure level measured at significant positions. If the noise contains peaks exceeding 130 dB(C), this must also be stated. Note that all sound pressure levels should be measured under "free field" conditions at the typical position of the operators head. If that is not defined, the sound pressure level must be measured at a distance of 1 metre from the surface of the machinery at a height of 1.6 metres from the floor. Type: Application Note Year: 1994 PDFRead document # An Overview of Standards for Sound Power Determination This application note is an introduction to the large number of international standards existing regarding sound power determination. The standards mentioned are mainly ISO (International Organization for Standardization), IEC (International Electrotechnical Commission), ECMA (European Computer Manufacturers Association), DIN (Deutsches Institut for Normung e.V.), ANSI (American National Standards Institute) and some of the European "Council Directives". Type: Application Note Year: 1994 PDFRead document # Mobility Measurements Being modular and expandable, the Brüel & Kjaer Multi-channel Analysis System Type 3550 makes fast, easy and accurate mobility measurements on structures. In its standard dualchannel configuration, and equipped with only a force hammer and an accelerometer, even the novice can begin to explore the dynamic behaviour of structures. This note gives an introduction to this important application area and outlines the theoretical background and experimental techniques. Type: Application Note Year: 1994 PDFRead document # Time Domain Averaging Combined with Order Tracking Apart from spectrum averaging, there is another averaging method that can be used when measuring periodic signals, namely synchronous time domain averaging. The main advantage of this method is that unwanted noise components are averaged out. On the 3550 analyzer, time domain averaging can be combined with order tracking analysis to yield a very powerful method for measuring on reciprocating engines (internal-combustion engines, pumps, and compressor). Type: Application Note Year: 1994 PDFRead document # Run-up Order Analysis of Axial Vibrations in a 2190kW, MAN B&W In operation, the propulsion shafting of a ship is deformed axially and torsionally. Both deformations cause axial vibrations, which at critical RPM may become unacceptable. The vibrations are damped by an integral axial vibration damper. The critical RPM are calculated based on a model of the shafting, and measurements are performed to verify the calculated natural frequencies and the effect of the damper. The verification is required by some of the shipbuilding classification societies. It is demonstrated that Type 3555 fitted with Extended Analysis Software Type 7639 is suited for the measurements. Type: Application Note Year: 1994 PDFRead document # Multi-Reference Impact Testing for Modal Analysis using Type 3557 Four Channel Analyzer and CADA-PC This Application Note introduces the MRIT concept and demonstrates the techniques on a bi-symmetrical structure which has repeated roots in all the modal peaks. These are decomposed using the three-reference data set, measured with the Brüel & Kjaer Type 3557 four-channel analyzer, and Polyreference curvefitting as implemented in the CADA-PC modal analysis package. Type: Application Note Year: 1994 PDFRead document # Solving a Critical Propulsion Problem at Volvo Penta using Two Torsional Vib.... This Application Note describes and examines the use of two Torsional Vibration Meters Type 2523 in a critical, severely time-limited, trouble-shooting situation where the performance of a torsional vibration elastic coupling, fitted to the propulsion system of a new series of smaller navy vessels, had to be thoroughly investigated in order for the propulsion system to be cleared for operational service. Type: Application Note Year: 1994 PDFRead document # On the Working Principle of Torsional Vibration Meter In this Application Note, the basic optical design of the instrument is introduced along with a derived mathematical explanation of some of the important features offered by the technique and implemented in the Torsional Vibration Meter Type 2523. Furthermore, to verify the performance of the instrument, results from comparison measurements are presented and evaluated. Type: Application Note Year: 1994 PDFRead document # Time Windows FFT analyzers such as the Brüel & Kjaer Signal Analyzer families Type 3550 and Type 2140 (with FFT options) process finite blocks of digital information. The analyzer extracts, or “cuts out”, these blocks from the complete time record using time weighting functions, or “time windows”. Unless we can understand the basic concepts of time limited data, we can’t be sure that our interpretation of FFT analysis is correct. Neither can we be sure of the accuracy of our results. Type: Application Note Year: 1994 PDFRead document # Choose your Units! The Brüel & Kjaer Signal Analyzer families Type 3550 and Type 2140 (with FFT options) allow you to choose the appropriate units to suit your measurement signal, be it deterministic, random or transient. The frequency spectrum amplitude can be scaled in terms of: - Root mean square (RMS) for deterministic signals - Mean square, Power (PWR) for deterministic signals - Power spectral density (PSD) for random signals - Energy spectral density (ESD) for transients The noise bandwidth (B=Df´k, where k depends of the choice of time window) and record length (T) selected for the measurement affect the amplitude scaling of the frequency spectra. The analyzers of the 3550 and 2140 families will automatically compensate for these factors if the correct scaling has been selected. Type: Application Note Year: 1994 PDFRead document # Gearbox Analysis using Cepstrum Analysis and Comb Liftering Cepstrum analysis has many applications: for example echo detection and removal, or speech analysis, but the most important one in industry is related to machine diagnostics, where its ability to detect periodicities in the spectrum is taken advantage of. The Dual Channel Analyzer Type 3555 has a number of editing features that make it uniquely well suited for identification and separation of harmonic families using cepstrum analysis. Type: Application Note Year: 1994 PDFRead document # Sound Power Determination using Type 3554, with or without ISO 9614-1 The purpose of this application note is to show novices how easily the sound power measurements can actually be performed. For this purpose we have chosen a modern "Nilfisk" vacuum cleaner from the Danish manufacturer Fisker & Nilsen. The measurements are first done according to ISO 9614-1 and then as simply as possible. As you will see, the results are very close. Type: Application Note Year: 1994 PDFRead document # Laser Diagnostics of Machinery Health For reasons of both safety and economy it is desirable to avoid the breakdown at sea of heavy machinery in marine transport and offshore installations. Unscheduled loss of production or power during ‘downtime’ enhances vulnerability and often carries severe financial penalties. This has led to an increasing interest in the concept of monitoring machinery health to detect impending failure. This Application Note demonstrates how the Torsional Vibration Meter Type 2523 can be used to address the problem of diagnosing failure in viscous shear torsional dampers which are normally fitted to the crankshaft of large marine propulsion diesels and generator sets. The method allows condition diagnosis to be achieved while the engine is running and avoids the need for ‘downtime’ associated with traditional fluid sampling methods. Type: Application Note Year: 1993 PDFRead document # Measuring Torsional Operational Deflection Shapes of Rotating Shafts With the advent of the laser-based Torsional Vibration Meter Type 2523, general torsional vibration measurements were not only greatly facilitated but, moreover, the unique concept of the instrument opened up for a number of new innovative measurement techniques, including the possibility of measuring Torsional Operational Deflection Shapes on rotating shafts. This Application Note describes the concept and the basic technique of measuring torsional operational deflection shapes using the Torsional Vibration Meter Type 2523, the Multichannel Analysis System Type 3550 and the Operational Deflection Shapes Software WT 9380, running on a Personal Computer. Applying the Torsional Operational Deflection Shapes technique to a demonstration model, the features and benefits of the technique are discussed. Type: Application Note Year: 1993 PDFRead document # Audio Distortion Measurements In the never ending quest for better sound transmission, reinforcement, and reproduction, the electronics have been extensively analyzed for distortion. Distortion in the electro acoustic transducers, while typically several orders of magnitude greater, has often been neglected or not even specified because it has been difficult to measure and interpret. With a basic understanding of transducer limitations, some knowledge of human hearing, and the application of different distortion test methods, electroacoustic transducer distortion becomes easier to measure and assess. Type: Application Note Year: 1992 PDFRead document # Noise control survey on a pump using the gated technique When making noise control surveys on rotating machinery, one is often interested in parts of the rotational cycle and the noise events which occur during that part. By taking a trigger signal from a rotating part to initiate a measurement, the filters of the analyser start to respond and their outputs are detected at a specified number of "windows" or "gates" per revolution. Type: Application Note Year: 1992 PDFRead document # Sound field description using complex sound intensity instrumentation Complex sound intensity is a vector that describes the coherent relation between the sound pressure and the particle velocity in a sound field. The concept of complex sound intensity was introduced more than 40 years although the first descriptions of practical methods of measuring the quantity appeared much later. Sound intensity analysers capable of determining the active intensity have been commercially available since 1981 whereas equipment which can measure both active and reactive intensity directly has only been available since 1988. Type: Application Note Year: 1992 PDFRead document # The Use of a Computer to Process 2123/33 Disk Data This application note shows how to store data on the built-in 2123/33 disk drive and how to use the stored data in commercially available IBM-PC application software such as spreadsheets or word processors. Type: Application Note Year: 1991 PDFRead document # Measurement of Sound Reduction Index with the Single/Dual Channel Real-time analyzers Types 2123 and 2133 Determination of sound insulation according to the International Standard ISO 140 or equivalent standards can be accomplished directly by using the Single/Dual Channel Real-time Analyzer Type 2123 or 2133. This application note describes features important to measurement of the sound reduction index, and includes information about user-defined functions, data storage and presentation of results. Type: Application Note Year: 1990 PDFRead document # Measuring the Non-rigid Behavior of a Loudspeaker Diaphrahm using Modal Analysis When a loudspeaker vibrates at low frequencies, it behaves as a rigid piston, with all parts of the diaphragm moving in phase. Above a certain frequency, however, the diaphragm behaviour will become more complex. To examine this phenomenon, it is necessary to make reliable measurements of the diaphragm motion at a number of different points. Type: Application Note Year: 1990 PDFRead document # Measurement of Vehical Exterior Noise using the portable Real-time Frequency Analyzer Type 2143 Exterior noise is a major component of the environmental impact of cars, trucks, buses, motorcycles, and the like. Control of exterior noise has led to the development of several test procedures which can be categorized into two groups: stationary tests and pass-by tests. Type: Application Note Year: 1990 PDFRead document # Condition Based Maintenance and Quality Assurance of Production Machinery Production output and quality assurance are the key elements in any production facility. Techniques that help to maintain a high production throughput and provide a tool for both maintaining and monitoring finished quality are therefore of paramount importance. This Application Note details the role that vibration monitoring plays at the Ford Motor Co’s Düren plant, Germany. Considerable savings in maintenance costs and a high-level of output I quality have been achieved. Type: Application Note Year: 1990 PDFRead document # Applications of the Real-time Frequency Analyzer The 2143 can be described as the next logical step up from a sound level or vibration meter, while also providing a link to sophisticated laboratory systems, and in particular allows online laboratory-standard analysis in the field where otherwise tape recorders would be used to bring the data back to the laboratory. It has many applications in the analysis of sound, vibration, and other signals. The purpose of this application note is to describe how the features of the 2143 can be used in some of these applications. Type: Application Note Year: 1990 PDFRead document # Acoustical testing in the automotive industry using STSF * Primer: Measurements in Building Acoustics The influence of acoustics on the design of buildings can be observed through the ages from Roman amphitheatres to the modern houses or buildings in which we spend our working hours and our leisure. The great difference, however, between life in ancient Rome and life in our crowded modern cities is the presence of noise from an ever increasing number of sources, from neighbours, traffic and industry. Type: Primers Pages: 46 Size: 921 kb PDFRead document * Primer: Measuring Sound This booklet gives answers to some of the basic questions asked by the newcomer to a noise measuring programme. It gives a brief explanation to questions like: What is sound ? Why do we measure sound ? What units do we use ? How do we hear ? What instruments do we use for measurement ? What is a weighting network ? What is frequency analysis ? Type: Primers Pages: 44 Size: 1061 kb PDFRead document * Primer: Measuring vibration This booklet answers some of the basic questions asked by the newcomer to vibration measurement. It gives a brief explanation to the following: Why do we measure vibration? Where does it come from? What is vibration? How to quantify the vibration level, The vibration parameters, Acceleration, Velocity and Displacement, Measurement Units, Which parameter to measure, The piezoelectric accelerometer Type: Primers Pages: 42 Size: 771 kb PDFRead document * Primer: Structural Testing - Part 1 Modal analysis is an efficient tool for describing, understanding, and modeling structural behaviour. The study of modal analysis is an excellent means of attaining a solid understanding of structural dynamics. "Structural Testing" consists of a comprehensive introduction to the theoretical background to modal analysis and structural dynamics. Type: Primers Pages: 49 Size: 1235 kb PDFRead document * Primer: Structural Testing - Part 2 Modal analysis of the data obtained from structural testing, provides us with a definitive description of the response of a structure, which can be evaluated against design specifications. It also enables us to construct a powerful tool, the modal model, with which we can investigate the effects of structural modifications, or predict how the structure will perform under changed operating conditions. Type: Primers Pages: 56 Size: 1310 kb PDFRead document * Primer: Sound Intensity This booklet sets out to explain the fundamentals of sound intensity measurement. Both theory and applications will be covered. Although the booklet is intended as a basic introduction, some knowledge of sound pressure measurement is assumed. If you are unfamiliar with this subject, you may wish to consult our companion booklet "Measuring Sound". Type: Primers Pages: 38 Size: 966 kb PDFRead document * Environmental Noise This booklet deals with environmental noise - for example, noise from industrial sites, road and rail traffic, airports and fairgrounds. It does not cover related issues such as building acoustics, building vibration or domestic noise. Type: Primers Pages: 69 Size: 4845 kb PDFRead document * Microphone Handbook This handbook gives an insight into the theory behind the development of microphones and preamplifiers and explains the terminology used to describe these products. The aim of this volume is to promote a full understanding of measurement microphones and to provide sufficient background information for customers to get the best out of these products. It also gives adequate information for customers to be able to make informed and qualified decisions about the microphone products which are most suitable for their measurement requirements. Type: Primers Pages: 155 Size: 10500 kb PDFRead document *