NVH Reduction Trends Engineers are tackling buzzes, squeaks, rattles, grunts, groans, grinding, and moans in their efforts to improve customer satisfaction.

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Reducing noise, vibration, and harshness (NVH) generated in vehicles is a major priority within the automotive industry. Overall noise and vi-bration levels now are directly linked to vehicle quality. Development engineers are expending considerable effort to eliminate or reduce noise sources and determine their transmission path so the coupling of these sources to chassis modes can be eliminated.

Squeak and rattle (S&R) noise, in particular, conveys an impression of poor quality to the customer. Addressing these complaints in the field can be a significant warranty cost issue. The "design-right-the-first-time" approach is replacing the "find-and-fix" approach.

NVH problems have taken on new significance with improvement in overall noise control inside the vehicle. Pushed by buyer demand for audio system quality rivalling in-home system, powertrain, wind, and tire noise have been reduced significantly. Noises that traditionally were masked by these operating noises easily become as audible as whispers during a church service. Here are several examples of improving NVH characteristics with better engineering development.

Pressure ripples in steering hydraulics

Identifying rattle noise in a hydraulic steering system involves separating mechanical from hydraulic noise. Certain conditions generated by a road-load feedback frequency to the steering gear result in a hydraulic sound much like that of mechanical rattle.

Pressures in the gear at low speeds in a left turn illustrate a large, unwanted pulse in the return line The noise heard inside the vehicle corresponded to this pressure spike. Pressure fluctuations in the return line occur at about 20 Hz, or roughly twice the frequency of tie-rod loads during normal driving. The pressure pulse reacts more quickly with the steering hydraulics. When the hydraulic steering system is pressurized quickly in one direction and then suddenly released, a pressure pulse occurs simultaneously in the opposite cylinder and return lines. The result is hydraulic rattle experienced by the driver.

The amount of steel tubing in the return line amplifies hydraulic rattle. During vehicle evaluations of hydraulic rattle, the return pressure trace was the main verification for damping unwanted pressure pulses.

Figure 1. Left turn on gravel surface at 25 km/h (15.5 mph) (w/o standpipe).

Hydraulic rattle noise can be isolated from mechanical rattle with installation of a standpipe in the return line (Figure 2). The standpipe contains a compressible column of air, which dampens the unwanted pressure pulse to a very low level. The standpipe used was a 250-mm (10 in) length of rubber return hose, positioned as close to the valve housing return port as possible. The farther away from the return port the standpipe, the lower its effect on dampening the pressure pulse. The standpipe is secured upright, with its upper end above the pump reservoir. Vehicle preparation must not purge air from the pipe.

Figure 2. Power-assisted rack and pinion steering gear assembly.

Reducing the pressure spike with a standpipe eliminated the audible noise (Figure 3). A sound track recorded during the noise evaluations and the identification on the sound track was matched in time with the pressure spikes.

Figure 3. Left turn on gravel surface at 25 km/h (15.5 mph) (with standpipe).

Evaluating the steering system under both low and high-speed conditions is important to determine if a certain feedback frequency through the tie rods excites the hydraulic system. Once the true source of steering noise has been resolved, further analysis will determine the necessary changes to meet vehicle validation acceptance levels for the vehicle.

Active reduction of steering pressure pulses

Various passive techniques have been tried to reduce the pressure pulse in the fluid with limited success. These methods often fail because they are based on formation of standing waves, or because they cannot accommodate changes in the system's characteristics during operation. Satisfactory performance over normal engine speeds from 700 to 2500 rpm requires a wideband solution.

An active system that can neutralize pressure ripples over a broad frequency range would be an ideal solution. To neutralize the pressure ripple completely, an active system would produce a 180° phase-shifted pressure field in the fluid with the same volume displacement of the pressure ripple. The phase of the control circuit should be maintained at 180° over the entire frequency band in which the pressure ripple is to be neutralized.

Piezoelectric actuators have been widely proven in vibration control. These ceramic materials can withstand high hydrostatic pressures and still respond to pressure fluctuations within microseconds. Displacements produced by these actuators are precise. Although the displacement is small, generated force can be extremely high.

With the small displacements generated by the piezoelectric actuator, efficient coupling with the power steering fluid is important. The actuator, mounted in a steel cell with a 0.25-mm (0.01-in) thick membrane separating the fluid and the actuator, acts like a diaphragm to send the actuator's displacement to the fluid. A piezoelectric sensor upstream detects the pressure pulsation field.

The amplitudes of different frequency components associated with the ripple observed under the two conditions—first without, and then with activation of the piezoelectric actuator—were compared with each other.

Pressure pulses at various dominant frequencies are reduced by as much as 80% with active noise cancellation and an electrohydraulic power steering (EHPS) pump. All four frequencies in the pressure ripple are reduced in amplitude, making the method broadband in nature. This system, being insensitive to ripple frequency, can reduce pressure pulses of all frequencies within the given bandwidth. Thus if one or all the frequencies shift, their amplitudes still will be reduced by this active attenuation.

With a conventional power steering pump, only a 33% reduction in the pulse has been seen. The fundamental frequency of the ripple in a conventional power steering system is much lower at 140 Hz, and the volume associated with the pressure ripple is higher in comparison to that generated by the EHPS pump. This emphasizes how an active control system must be optimized for the frequencies and volumes of a particular system to achieve maximum benefit. With careful design of the feedback control system, a bandwidth of about 1 kHz has been achieved for the frequency of pressure pulse control.

Buzzes, squeaks and rattles—present and future

Sound inside a passenger compartment has many elements, with a basic one being irritating noises made up of buzzes, squeaks, and rattles (BSR). Manufacturer warranty bills for BSR problems are estimated to be about 10% of total things-gone-wrong (TGW) costs. Instrument panels (IPs), seats, and doors are responsible for more than 50% of all BSR problems, with IPs the most common offender.

Lightweight body construction and materials, combined with increased general content in the subsystems, keeps growing. Controlling BSR thus increases in difficulty. Electric vehicles with their low level of powertrain noise further highlight even subtle BSR problems.

Squeak is friction-induced noise caused by relative motion resulting from a slipstick phenomenon between interfacing surfaces. Elastic deformation of contact surfaces stores energy that is released when the static friction exceeds the kinetic friction, producing the audible squeak noise. The release of energy produces a vibration of the surfaces that causes audible squeaks in the 200 to 10,000 Hz range.

Rattle is an impact-induced event that occurs when relative motion between parts causes a brief loss of contact. The usual cause is loose or excessively flexible elements under forced excitation. Insufficient attachments or inadequate structural strength force repeated separation and contact. A rattle's exciting force often is road surface-induced. The frequency range of audible rattles is between 200 and 2000 Hz. Higher frequency rattles are often perceived as "buzz."

A stiff suspension causes input forces to be large. A vehicle with a sport suspension and low-profile tires had about 30% higher response levels on the IP than the same vehicle with its base suspension as standard.

Effective BSR prevention involves structural integrity, material pair compatibility, manufacturing control and smart design. Minimizing relative motions effectively controls BSR. Reduced warranty costs easily can offset the initial cost of method development and implementation. Superior structural integrity implies adequate static and dynamic stiffness. Stiffer usually is better, but too stiff often is too expensive and too heavy.

Some relative motion always occurs, so judicious selection of material mating pairs will reduce BSR. Squeaks, itches or creaks usually occur at elastomeric contacts along windshield and backlight headers, roof and door weatherstrips, and IP seals. With so many entities involved in a single squeak, no single material is the ultimate solution.

Many BSRs happen with poor manufacturing control or large process variations. Tighter manufacturing control reduces BSR, but at a higher cost that is clear with the low BSR levels in luxury vehicles. Corporate best-in-class vehicles often perform 30% better than average.

Smart design consists of incremental factors effective on niggling BSR problems. Many design practices are employed as a result of poor experiences in past models. Often, design engineers compromise BSR over aesthetics when a mutually acceptable solution is possible. A database of both BSR lessons learned and effective competitor BSR solutions can prove invaluable to design engineers.

An integrated BSR prevention design strategy encompasses several facets and phases of vehicle development from concept to production. It depends heavily on continuing research and development efforts to advance the art, and critical feedback from all phases of the process must be efficiently communicated for corrective actions, and the ultimate success of the process.

Detecting squeaks and rattles

S&R noise is highly dynamic, presenting difficulties for some types of analysis. In one study, the duration of a particular S&R was less than 10 ms. Furthermore, S&R events measured in real driving environments often have other, higher-level acoustic events. For example, when a vehicle crosses a large, abrupt road irregularity, a non-S&R acoustic event usually will be generated by the impact. There also can be a corresponding S&R event, but at a very low level compared to the acoustic impact. This low relative level merely adds to the analysis difficulty.

The final arbiter of an S&R event is the customer. Since humans do not perceive sound linearly in sound pressure level (SPL) or sound power, measures of physical quantities such as decibels for SPL are not ideally suited for measures of S&R audibility and subjective intensity. However, psychoacoustic techniques provide an estimate of the subjective audibility and character of an S&R event, more accurate than one based on purely objective signal analysis. One psychoacoustic method that is particularly well suited for S&R events is time-varying, or instationary, loudness analysis.

There is no published standard for estimating the subjective loudness of instationary and transient acoustic events. However, a Deutsche Industrie Normen (DIN) committee has agreed upon a definition of the required behavior of such a model. The model uses the output of a one-third octave analysis as an input. Like other analysis methods, the instationary loudness model provides magnitude versus frequency versus time information (e.g., a subjective loudness-time-frequency representation).

Beyond simply detecting S&R events, a measure of the audibility of an event can be useful. It is tempting to assume that the instationary loudness peaks corresponding to S&R events are measures of their audibility. For test data from an ultraquiet test stand, this can be considered reasonable. However, in a real driving environment the absolute loudness level of an S&R event does not predict audibility, due to masking and other effects of ever-present background noise.

Percentile statistical measures N10 and N50 are used to describe a set of noise measurements as a single value. N50 is defined as the level that is reached or exceeded by 50% of the measurements in a set, or the median of the measurement set. Similarly, N10 is that level reached or exceeded by 10% of the values. It sometimes is used to represent the level of transient peaks in a measurement, while N50 represents the mean level.

However, using N10 as an S&R threshold statistic falsely assumes that the S&R events of interest always occur in more than 10% of the analysis points. A signal whose instationary loudness measurement contains 9% rattle peaks of level equal to 10 sones could have a lower N10 value than a signal that contains rattle peaks of 2 sones 10% of the time. N10 as a S&R threshold also assumes that the level of each S&R event is unimportant. A signal with N10 = 5 sones, whose rattles peak at 10 sones, is considered equivalent to a signal with the same N10 level but whose rattles peak at 100 sones.

The value of N10 for part A is much higher than that for part B. It is easy to say that part A has worse rattle performance than part B. Part A rattles more than part B, but when part B rattles, its rattles are louder. This information is not available from the single number statistics of N10 and N50.

In another case, the subjective impression did not agree with the N10 threshold. N10 for C is twice the value it is for D. There is no reversal in relative order.

The key to understanding why part C can be more objectionable than D is realizing that subjective loudness of the rattles can be interpreted in two distinctly different ways: absolute loudness of each rattle, as represented by the instationary loudness peak value; and relative rattle loudness with respect to background noise. A rattle with peak loudness of 20 sones is inaudible if the background level (in the same frequency band) is 30 sones. In contrast, the same 20-sone rattle in a background of 15 sones will be readily audible. Audibility and loudness of an S&R event, with respect to any background noise present, is a function of the level of background noise. Comparing relative loudness is important for understanding how to interpret analysis of data from onroad S&R tests.

Squeak and rattle of polymers

Driving sounds affect a driver's opinion of a vehicle. The only desirable sounds are those telling the driver that the car is functioning properly. It is difficult to quantify sounds in the passenger compartment because everyone perceives sound differently. Setting a maximum noise limit before onset of driver dissatisfaction is almost impossible.

Many squeaks and rattles occur from sliding contact between interior plastic parts. A tensile tester was used to measure the friction force of a plastic sliding on itself. When stickslip occurred during

sliding, amplitude of the stickslip was used to describe the tendency for the sliding pairs to make noise. The effects of normal load, stiffness of the connection between the force transducer and the sliding polymer, the temperature, surface roughness and sliding speed on the amplitude of the stickslip also were determined.

The plastics examined are polypropylene (PP), polycarbonate (PC), acrylonitrilebutadienestyrene (ABS), polyamide 6 (PA6), polyoxymethylene (POM), PC/ABS blend and ABS/PA blend. PP had the lowest stickslip amplitude. Its mean and standard deviation also were the lowest of all the polymers tested. The PP's surface energy was 60 % of those of all other polymers, and it had the highest internal damping.

PP produces sliding curves with double amplitude that ranges between 0.1 and 0.3 N. PA6 showed highest double amplitude response, ranging between 1.1 and 14.8 N. PP exhibits superior squeak behavior compared to the remaining investigated materials. The ranking of the test materials, according to increasing stickslip amplitude, is: PP, ABS, PC/ABS, PC, ABS/PA, POM, and PA6.

The low surface energy of the PP is caused by the absence of polar groups on its surface. When PP was etched with chromic acid, oxygen containing groups were introduced on its surface. As a result, both surface energy and stickslip amplitude increased. PP also had the highest internal damping of the polymers tested and was one of the three polymers that was semicrystalline.

Stickslip amplitude can be reduced by using polymers with low adhesion at the contact points (i.e., low surface energy). In addition, crystallinity inhibits mobility of the polymeric chains and minimizes diffusion across the interface that promotes better adhesion. Finally, high internal energy dissipation damps vibrations that are excited by sliding motion.

Investigating disc brake noise

Low frequency disc brake noise typically occurs between 100 and 1000 Hz. Typical noises in this group are grunt, groan, grind and moan. These noises are caused by friction material excitation at the rotor and lining interface. The energy is transmitted as a vibrational response through the brake corner and couples with other chassis parts.

The typical failure mode for front disc brake groan occurs at deceleration rates of 1.5 to 6 m/s2 (5 to 1.8 ft/s2), with lining temperatures from 65° to 120°C (149° to 248°F), and vehicle speeds between 16 and 32 km/h (10 and 20 mph). The noise normally occurs through the entire stop in the most severe cases, but it often happens from the middle to end of the braking event.

Changes to the vehicle's response to groan's forcing function were unsuccessful. Reducing the forcing function itself through lining material changes was the alternative. Statistically significant ingredients or a combination of ingredients that can influence groan are abrasive, lubeabrasive filler, and filler.

Low-frequency squeal is classified as noise having a narrow frequency bandwidth in the range above 1000 Hz yet below the first circumferential (longitudinal) mode of the rotor. The failure mode for low frequency squeal occurs with low deceleration of 1.2 to 1.8 m/s2 (4 to 6 ft/s2), vehicle speeds of 8 to 16 km/h (5 to 26 mph), and initial lining temperatures of 1° to 4°C.

Sound data during a squeal event showed that its frequency was between 2500 and 2600 Hz. Structural dynamic measurements taken on the rotor and caliper of the vehicle indicated that both had resonances in that frequency range. Rotor changes were seen as a more practical short-term solution. The simplest available solution was a material change for gray cast iron. The alternative

material was classified as "damped iron," with a goal to reduce the amplitude of the rotor response.

The damped iron rotor eliminated the low frequency squeal, but damping was not a factor in the solution. The resonance at 2600 Hz was shifted down in frequency about 400 Hz with the damped iron rotor. Damping values measured at these frequencies are the same, so the modulus change of the rotor, not its damping characteristic, was the key to the noise reduction.

High-frequency brake squeal is a troublesome problem in brake development. It typically occurs at frequencies above 5000 Hz. Several methods have been developed over the years to reduce squeal, but no absolute solution has ever been developed.

Each brake system has particular frequencies at which high frequency brake squeal commonly occurs. These frequencies remain constant for a particular brake rotor, independent of the rest of the brake system. This supports the theory that the brake rotor is a controlling element in determining the squeal frequency.

Rotor stiffness is also a factor in squeal. Increased rotor stiffness can reduce its squeal tendency. This can be looked upon as increasing the mechanical impedance of the rotor, making it more resistive in responding to input forces.

A potentially more significant factor is the shifting of normal response modes and the resulting reduction in modal density. Rotors of increased and decreased thickness were used to achieve rotor stiffness variations. The resulting sound pressure data from brake dynamometer tests revealed the large influence that rotor dynamics can have upon high frequency squeal.

The baseline rotor produced the most noise, and rotors of increased and decreased thickness produced lower noise levels. The expected benefits of increased overall stiffness were not seen. Further analysis of these rotors revealed differences in dynamic stiffness at the predominant squeal frequency. This dynamic stiffness variation is related to the modal alignment of normal and circumferential modes.

Though decreased modal density of the rotor disc is directionally correct for brake squeal reduction, in this instance modal alignments of the normal and circumferential resonance frequencies were more important than modal density as a single parameter.

Two configurations proved to be significant noise reducers: in-board pad trailing edge and out-board pad leading edge chamfers, and chamfers on all leading and trailing edges. A center slot in the pad intensified squeal.

Brake noise insulators, constructed of layers of steel and viscoelastic material applied to the back of the disc brake shoe plate, are commonly used in systems as a "noise fix."

Since dynamic properties of these materials can vary widely with temperature and frequency, the performance of brake noise insulators can vary significantly in the exposed operating environment. Potential gains or losses in squeal control depend on a properly tuned brake noise insulator for the application.

Whatever their sources in the vehicle, unwanted noises and their control will continue challenging development engineers in the future.

NVH is an industry term that stands for noise, vibration, and harshness.

It is a search for the source of a noise, shake, or vibration, and it refers to the entire range of vibration perception, from hearing to feeling.

Noise is unwanted sound; vibration is the oscillation that is typically felt rather than heard. Harshness is generally used to describe the severity and discomfort associated with unwanted sound and/or vibration, especially from short duration events.

NVH is also called sound quality analysis, which involves metrics such as loudness, sharpness, sound exposure level, and others.

NVH Reduction: Gaining in Prominence

The Sound and Vibration Effect

As a natural consequence of modern society's frenetic manufacturing, transportation and communication activities, sound and vibration affect environment and all of us. They affect the safety of our vehicles, the construction of our buildings, and the level of noise at home and work. Our escalating demands for safety and physical well being mirror our increased awareness of the effects of noise and vibration.

Our cars are extensively tested to make sure they can withstand the mechanical shocks imposed on them. Likewise, any safety equipment, such as airbags, will make good use of vibration transducers to act as critical sensors that signal danger and trigger appropriate action. The noise that your car makes will have been analyzed to make sure that it does not spoil the environment of those around you. There are many other examples of how sound and vibration affects all of us, such as the noise from planes flying overhead, dishwasher, your neighbors, or tiresome use of lawnmower.

It is fortunate then, that in every sector of industry, in every part of the scientific community, and in all aspects of our daily lives, there are people who dedicate their working lives to sound and vibration, controlling their harmful effects. Noise is a controllable pollutant that deserves the attention of lawmakers, health and occupational specialists, and consumers. Modern research affords us the opportunity to understand the subject better and to develop abatement technologies.

NVH reduction seems to be the primary objective, continuing slogan and goal of any industry today. Competition has been growing rapidly to see who can make the quietest and smoothest running cars, vacuum cleaners, and washing machines. In crowded and mature markets, such as domestic appliances, sound quality testing is one way to differentiate a product from that of competitors. It also plays a vital role in the saleability of a product.

Regulation Trends

EPA regulations on snowmobiles

Regulations for off-highway equipment

Noise norms for automotive industries and aircraft

And many more stringent regulations are being introduced in the aerospace, defense, automotive, and industrial sectors

Who Will Benefit from it?

Definitely, people will appreciate such measures and benefit from such regulations.

Who else Will Benefit?

The answer is NVH test equipment manufacturers. The demand for NVH equipment is already witnessing a spike, and hence there is a huge potential for this market. NVH is an integral part of product development where all the processes can be bundled: design, predictive analysis development, and validation. Hence, the market for the same will remain. End users of NVH test equipment include aerospace & defense, automotive, industrial, consumer products, and building construction among others.

The NVH test equipment manufacturers can be classified as product vendors and solution providers.

Product vendors supply devices that fulfill certain end users, usually called application specialists, whereas solution providers design products that cater to the clients’ requirements.

NVH Test Equipment Include

Analyzers, shakers and controllers, accelerometers, noise dosimeters, octave band filters, transducers for vibration and acoustics, dynamometers, sound level meters, microphones, and analysis software.

With technology changing everyday, focus is shifting more toward the development of PC based analyzers, multichannel NVH data acquisition systems, acoustic holography devices, laser vibrometers, and anechoic test cells.

Applications

NVH test equipment are used for various applications such as:

Engine noise vibration testing

Acoustic performance testing

Sound power testing

Pass by noise testing

Telephone testing

Environmental noise measurements and noise field mapping

Structural dynamics and vibration testing

Occupational health and safety

Advantages of NVH Test Equipment

Real-time multi-analysis is possible in one test run

Results obtained are accurate and precise

Report generation is made easy

Shorter lead times, and hence improved productivity

Conclusion

The need to improve product quality and differentiate from the competition, concerns about human health and safety combined with stringent regulations, create a viable market for NVH test equipment. This market has a huge potential and it can be

expected that this market would grow for the next couple of years. The future is for us to see.

For additional information on this market, please refer to the upcoming Frost & Sullivan study on the "World NVH Test Equipment Market".

The NVH test equipment market is going through a changing phase in terms of instruments’ features, technology development, and customer service. It has evolved from a precautionary, difficult to use, and expensive tool to being an integral part of the product development and validation cycle. Integral to this cycle is the modern society's frenetic manufacturing, transportation and communication activities. Manufacturers and suppliers are turning to NVH testing to gain competitive advantage and strengthen their market position. Easy-to-use solutions capable of executing tests quickly, efficiently, and accurately are on top of the wish list for NVH test equipment customers.

The market for NVH test equipment is huge and diversified and continues to be driven by growing consumer need for improved product safety, quality, reliability, comfort, and sound quality. Apart from growing focus on product quality; advancement in technology, growing environmental, occupational and health concerns and emergence of new end-user segments, are some of the factors that are expected to aid growth of this market. Frost & Sullivan’s research indicates that this market will be valued at $1,388.2 million by 2014.

Chart 1.1 represents global NVH test equipment market revenues in 2007.

Wireless NVH Testing: The Future?

The advancements in wireless technology have significantly benefited the NVH test equipment market. Wireless data transmission is particularly beneficial for applications such as environmental noise, building acoustics, noise mapping, and structural vibration testing, as it allows the user to acquire data on the move and view it from a centralized location.

The automotive industry has also been quick to embrace evolving wireless technologies. There is a growing trend of NVH moving out of the traditional laboratory-based testing into real world conditions. This trend is particularly evident in the automotive industry, where the need to test automobiles in driving conditions forms a critical part of the manufacturing process. Although virtual testing is gaining popularity within this industry, it will not be able to replace component and vehicle durability testing, which is expected to aid the growth of wireless testing.

Although the advantages of using wireless technology is undeniable, end users have been hesitant to invest in it due to lack of standardization and challenges associated with synchronization, performance, and security.

End-of-Line NVH Testing

In today’s competitive market scenario product quality has become a key differentiator and is not limited only to luxury and expensive commodities. Customer demands for high quality and stringent government regulations have necessitated end-of-production line testing, which guarantees that every item coming off the production line meets required specification. While this type of testing has been around for a long time, in recent times it has become increasingly sophisticated and cheaper. In the manufacturing arena NVH testing has been comparatively more challenging, as a variety of manufacturing and assembly faults often result in unacceptable noise and vibration levels in manufactured products. The last few years have seen significant advancement in end-of-line technology driven primarily by the automotive industry. Other industries such has construction, consumer electronics, industrial equipment, and military among others, could leverage the investments made by the automotive industry to meet the ever increasing quality demands of customers, as well as reduce overall operating costs.

Technological Advancement

NVH testing differs from other test equipment markets in terms of the sheer volume of data that need to be tested as well as stored. The evolution to multi-core processors is a key advancement in the computer industry, which will aid the growth of the NVH test equipment market. Besides, as processors get cheaper as well as faster, the increased processor speed will help improve throughput and help reduce the cost of test. Companies are leveraging Intel’s multiprocessor technologies to split up the analysis, which speeds up the analysis process by two to four times. Advancements in sensor and communications technology have also aided greatly in improving adopting of NVH testing.

The above article is a snapshot of "World NVH Test Equipment Markets", which is due to be published in November 2008. This research service provides detailed information regarding individual product trends and revenue growth rates, unique drivers and restraints influencing the market, and industry challenges as well as strategies followed by major participants to deal with those obstacles.

Introduction

NVH (noise, vibration, and harshness) is an integral part of product development where all the processes, including design, predictive analysis development, and validation, can be tied up. NVH test equipment includes analyzers, shakers and controllers, accelerometers, noise dosimeters, octave band filters, transducers for vibration and acoustics, dynamometers, sound level meters, microphones, and analysis software. These are used for a plethora of applications such as testing of engine noise vibration, acoustic performance, sound power, pass by noise, noise field mapping, occupational health and safety, structural dynamics, and vibration testing among others.

Where is the Market Heading?

The market for NVH test equipment is huge and diversified and the demand for the equipment is already witnessing a spike. Hence, there is huge potential for this

market. End users of NVH test equipment include aerospace and defense, automotive, industrial, consumer products, and building construction among others.

Technology Trends

"Technology is changing its face everyday"

Multichannel Analysis Broadens Applications

Multichannel analysis is increasingly gaining significance, with equipment manufacturers generally looking to increase the number of channels. This is mainly due to end-user preferences and the scope of application that it offers. Acceleration and deflection are few measurements that are increasingly being taken, especially in the automotive industry where simulated analysis of both sound and vibration are of extreme importance. Most vendors today offer products that range from 2 to 16 channels. However, companies that offer 32 to 64 channels are finding a viable market for their products. End users such as auto manufacturers, industrial product manufacturers, and so on are looking for solutions that have over 80 to 100 channels. Hence, the focus, today, is more on multichannel NVH test equipments and this is becoming an increasingly important trend in this market.

Preference for High Performance, Accuracy, and Analysis

Customers today are looking for NVH test equipment that offers improved performance, greater accuracy, and better analysis. Vendors are in a position to use the benefits of high-performance processors at lower costs than ever before. This has made PC-based analyzers a popular option among end users. Further, software packages and options are constantly improving. Some of the value-added features, vendors in the industry are offering today include real-time analysis, ability to store and retrieve data, as well as the ability to analyze data as required by the end-user. Improved hardware coupled with better analysis using software is likely to become the norm in the market over the next couple of years.

Trend Toward Portability and Miniaturization of NVH Test Equipment

Improvements and advancements in electronics have enabled vendors to reduce the size of NVH test equipment without comprising on performance. Increasingly, the industry is witnessing the introduction of portable NVH analyzers, which are predominantly used in applications such as field testing. However, with the trend of sharing test equipment in research and development laboratories becoming common, portable products are a perfect option. This is certainly becoming an important trend in the market.

Flexible Modular Instrumentation Leverages the Power of the PC

Modular instrumentation is being widely used, especially in noise measurement systems that demand higher channel counts. Today, flexible modular instrumentation employs the latest software technology and is used in applications that include high-precision noise measurements where higher sampling rates, higher channel counts, increased dynamic ranges, and distributed architecture are needed in smaller packages.

Factors Challenging the Market

Maintaining the quality of services offered challenges test vendors significantly

Need to evolve technologies to cater to new application requirements and the diverse needs of end users

Virtual testing replaces physical testing in R&D

Software compatibility and portability challenge NVH test equipment vendors

Factors Driving the Market

The need to improve product quality and the necessity to differentiate from the competition

Stringent regulations creating a viable market for NVH test equipment

Increasing focus on NVH attributes in the design stage to diagnose problems spurring the demand for NVH test equipment

Concerns about human health and safety drive the demand for increased NVH testing

Factors Restraining the Market

High price of NVH test equipment limits sales

Second hand market limits the purchase of new NVH test equipment

Improper distribution and support network affects growth

Economic downturn impacts the demand for test equipment

Conclusion

The growing focus on product quality and the increased drive to test products creates a demand for NVH test equipment. This market has a huge potential and is certainly poised for growth.

Arctic Cat makes fast moves in the power sports marketRiders hop on a snowmobile or ATV not just to get from one place to another but to enjoy the thrill of power sports. As indicated from their market success, the company clearly knows how to give these customers the ride they want – and naturally expect – when they rev up an Arctic Cat vehicle and go where they need no roads.

Arctic Cat is one of the early pioneers in the power sports industry and has firmly established itself as a leading manufacturer of these vehicles. Plans are to double its international business over the next three years, and for the first time ATV sales now account for more than half of the company’s total sales. Unlike competitors seeing flat sales or downturns, Arctic Cat has continued to gain market share in the ATV segment every year since it started selling these popular vehicles.

As for snowmobiles, the 2007 line-up has over 75% new models, the most extensive introduction of new vehicles in the company’s history – and possibly the largest in the industry for a single year. The new snowmobile designs include an innovative twin-spar chassis that provides leading-edge ride and comfort. The company’s product line-up has a range of characteristics targeted toward different types of riders: touring snowmobiles that cruise along quietly, high-performance models that provide speed and lots of sporty acoustic feedback, and mountain vehicles with added pulling power at lower gears.

Likewise, ATV models include models for sport, general utility, multi-rider and young drivers.

This full line-up of models includes unique designs based on latest technology to attract new buyers and retain them with a steady stream of new products designed around the unique Arctic Cat identity. "Snowmobile customers are intensely brand loyal and driven to purchase machines which capture their imagination with innovation and advances in technology," says Arctic Cat Chairman and CEO Chris Twomey. "Overall, 92 percent of snowmobile customers are repeat buyers – and new, innovative products are what drive them to buy. To maintain a fast, steady stream of new designs, we have implemented

product development technologies as innovative as our vehicles."

Leading-edge NVH technology

According to Twomey, an essential part of Arctic Cat’s ability to develop such a wide range of innovative new vehicle models so quickly is the company’s investment in an NVH center that rivals those found at automotive companies and is a first in the power sports industry. The 3,500-square-foot facility has some of

the most advanced NVH testing equipment available including a chassis dynamometer for simulating trail and high-performance riding conditions, a semi-anechoic sound chamber, and a sound-quality room for juried evaluations.

NVH Engineering Manager Bala Holalkere notes that running tests and taking measurements such as vehicle sound levels in the controlled environment of the lab overcomes the limitations of outdoor measurements where variables such as background noise, temperature and wind direction can affect readings, and additional time often is needed for travel to locations with satisfactory conditions.

According to Holalkere, "LMS technology is a key element in Arctic Cat’s NVH efforts." Vibro-acoustic testing of vehicle hardware is performed using LMS Test.Lab with two high-speed multichannel SCADAS III front end units, each with 20 input channels and two tachometer channels to accommodate data acquisition typically from two microphones, 14 accelerometers and engine sensors. The units each have an integrated suite of built-in tools for test control, measurement, result analysis, data management and report generation.

He explains that LMS Test.Lab is particularly useful in efficiently running repeated tests. Test setup and required signal processing tasks only need to be defined once, after which they are saved in a dedicated template. These procedures can then be performed automatically test after test with highly consistent results. Tests are thus able to be performed very quickly and are highly repeatable, allowing engineers to build up a knowledge base of sound signatures from various vehicle models and different part configurations, for example. This is valuable information for comparing results and working with designers in optimizing vehicle behavior.

Another aspect of LMS Test.Lab that greatly improves testing productivity is on-line data processing. "Data is automatically processed as measurements are being taken, so

engineers can see results immediately instead of waiting hours for postprocessing," he says. "This provides greater insight into the noise and vibration behavior of the

vehicle, and enables the verification of test data on the spot.

In combination with physical testing, Arctic Cat engineers use two simulation software programs for virtual modeling to predict the behavior of vehicles and subsystems: LMS SYSNOISE for determining radiated sound levels and LMS Virtual.Lab Motion, a multi-body dynamics program for studying the paths and loads of moving parts and mechanical

behavior of vehicles.

"Simulation provides the capability to study and optimize vehicle designs early in the development cycle," says Holalkere. He notes that design of snowmobiles and ATVs must satisfy multiple requirements. The sound of the machine must have a tone and quality geared to rider expectations while complying with government noise limits, structure-borne engine vibration must be minimized for rider comfort, and the chassis and suspension have to provide the required levels of stiffness and

damping for smoothing out bumps while maintaining good vehicle maneuverability.

"The challenge is to balance these attributes for the right sound, feel, ride and handling that altogether make up the overall riding experience," he explains. "By performing this work up front with the predictive capabilities of virtual prototyping, we can identify problems early, quickly evaluate alternatives and refine designs in the early stages of development. In this way, LMS technology helps our engineers design many more products much faster than is otherwise possible."

Shaping sound profiles and quieting noise

One major issue for power sports equipment manufacturers is ensuring strict compliance with pass-by noise regulations outlined in the SAE J192 standard that specifies a maximum sound level of 78 dB at 50 feet with wide-openthrottle acceleration.

"LMS Test.Lab is instrumental in improving our turnaround times for noise compliance tests," says Arctic Cat Test Engineer Abhay Rawal. "Efficient set-up, task automation and on-line monitoring mean that in a few hours we can typically complete a pass-by test that otherwise could possibly drag on for days without these capabilities."

Another critical element is acoustic quality, which defines Arctic Cat’s brand value. Engineers aim for a specific tone not corrupted by mechanical clanging or other secondary noise. The goal is an overall linearity in loudness, with amplitude increasing steadily as a function of engine speed. This acoustic behavior is often difficult to achieve with two-cycle and four-cycle engines, which often exhibit sound amplitude fluctuations at various speeds.

Arctic Cat’s process of shaping the vehicle sound profile generally involves comparing a target signature with prototype test data. Frequency analysis with LMS Test.Lab enables NVH engineers to study overall sound quality and identify the influence of various

subsystems including the engine, air intake, exhaust as well as gears, tracks and chassis resonances. Using LMS SYSNOISE, engineers can quickly study the impact of various vehicle modifications to muffle unwanted noises and attenuate the desired sounds.

NVH Analyst and Design Engineer Mark Claywell explains that the LMS acoustics prediction software provides greater insight into finding ways of modifying the design to change the sound profile. Considerable attention is focused on the intake system in which ambient air enters a small port and is drawn into the engine through a circuitous plenum

and air box chamber. Often several feet in total length, the relatively thin-walled intake system can reverberate from combustion pulsations. The multiple internal compartments and complex, winding shape of the system – contoured to fit tight vehicle packaging requirements – make the task of predicting noise generation difficult.

"In the past, manual calculations would be used in trying to figure out the best shape of the intake as well as the size and placement of resonators inside the air box. Then physical prototypes would be built, tested and modified until an

adequate sound profile was achieved," says Claywell. "LMS SYSNOISE enables us to compress the time to evaluate an intake design from a week to a few hours. Moreover, the final sound is closer to our target profile because we can go through many more change iterations than is practical otherwise."

Feel, ride and handling –becoming one with the machine

Arctic Cat engineers utilize LMS Test.Lab in combination with LMS Virtual.Lab Motion in studying structure bornetransmission of engine vibration and trail bumps, and the maneuverability of the vehicles in making turns. By studying various rider demographics, Arctic Cat applies the LMS tools in quantifying these otherwise subjective characteristics. Target requirements then can be cascaded from overall system-level behavior to development of subsystems and components in an approach similar to that used in the automotive industry.

A major strategy in Arctic Cat’s rapid introduction of multiple new models is to use common part types wherever possible, with 80% of the company’s 2007 vehicles having the same chassis, for example. "We put considerable effort into ensuring chassis performance is optimal in meeting the requirements of a broad range of vehicles," says test engineer Abhay Rawal, who notes that throughout much of the power sports industry this is a "black art" involving considerable engineering experience, manual calculations, guesswork and trial and-error iterations.

In Arctic Cat’s process, LMS Test.Lab is used in quantifying chassis compliance – essentially an inverse measure of structural stiffness. Modal tests determine resonate frequencies by exciting the structure to vibrate with an instrumented hammer. Results from these dynamic tests are then correlated with static tests where the structure is bent and twisted under various torsional, vertical and lateral loads. From these measurements, Abhay readily determines the compliance level of the chassis.

"The goal is to strike a balance of stiffness for optimal maneuverability without having compliance so low that riders feel excessive bumps and vibrations," explains Abhay. "LMS Test.Lab is a valuable tool in quickly determining the critical chassis compliance level by performing tests so efficiently and accurately."

NVH Product Development Engineer Dale Hahn explains that LMS Virtual.Lab Motion is used in an increasing number of simulation projects at Arctic Cat involving mechanical performance of vehicles. In a recent redesign of a snowmobile suspension from a torsion spring to a coil spring configuration, for example, the software was used in quickly predicting the stiffness and loadcarrying capabilities of the new design to help engineers better understand the ride and handling.

In another example, the software was used to model a clutch for a continuous variable transmission (CVT) for studying the vibration and reliability of the assembly. "Since the unit operates on centrifugal force, using LMS Virtual.Lab Motion is of considerable value in accurately representing the masses and inertia of these complex components – as well as all the interrelated physics of the mechanism. In a few hours we obtained detailed load data that could not have been produced from weeks of prototype testing."

Business value of NVH engineering

According to Roger Skime, Arctic Cat Vice President of Engineering and International Snowmobile Hall of Fame inductee, NVH engineering is an integral part of the company’s product development process and business strategy.

"Efficient and targeted testing with LMS Test.Lab enables our engineering teams to build a valuable NVH knowledge base of existing hardware that helps guide the design of innovative new models. The predictive capabilities of LMS Virtual.Lab simulations enable engineers to change new designs up-front in development to achieve the right performance, before any hardware is built. Simulation saves time and money in development and lets us deliver the required sound, feel, ride and handling for our vehicles," says Skime.

"This combination of test and simulation is where the future lies in NVH for the power sports industry, and Arctic Cat is proud to be leading the way with advanced tools that leverage the expertise of our dedicated and talented engineering staff in developing some of the most innovative and popular snowmobiles and ATVs on the market."

NVH Challenges

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Unwanted automobile noise and vibration irritates drivers as much as fingernails scrapping a chalkboard. by Kami Buchholz, Detroit Editor

Engineering a pleasant-sounding, smooth-riding vehicle means evaluating material choices from a noise/vibration/harshness (NVH) perspective, designing systems to squelch NVH influencers like wind and road noise as well as matching customers' NVH expectations. "NVH is one of the top things we're constantly thinking about," says DaimlerChrysler's Peter Gladysz, a Senior Manager in vehicle development and synthesis. "It's as relevant as performance, handling, and overall styling."

Sources of ugly noise emanating from the powertrain, the roadway, and the wind impacted design/engineering cues on Neon 2000 (sold as Plymouth Neon, Dodge Neon and Chrysler Neon). "Daimler- Chrysler's NVH lab works on all platforms simultaneously, so if anything can be utilized cross-platform — like going to a spiral cut antenna to stop whistle noise — it spreads throughout the product line-up," Gladysz explains. (The spiral cut antenna first appeared on Neon 1999.)

Neon 2000 NVH attributes include:

A higher volume muffler and an exhaust flex joint to make engine operation quieter.

A four-point engine mount system to reduce steering wheel vibration at idle speed.

Stiffer suspension crossmembers and control arms to minimize the resonance from powertrain vibrations.

Full frame doors (replacing glass roll-up side windows) to form a tight-fitting body seal/noise barrier.

All-season single ply tires (replacing previous Neon's two-ply tires) to dampen road noise and beef up fuel economy.

Moving front windshield 76 mm (3 in) farther forward to calm errant wind noise. Adding expandable foam baffles inside the A, B, and C pillars as well as in the fore and

aft frame rail to cause a drop in decibels.

"The foam baffles expand to fill up the body cavities as the vehicle goes through the e-coat bake process in temperatures of 149°C plus," says Gladysz. Sika Automotive developed and supplied the one dozen foam baffles used on the new four-door Neon. In a typical automotive application, between six and 12 baffles — each expanding three to 20 times pre-bake size — essentially impede noise, water, and dust entrance.

One of the real world simulation chambers at Sika Automotive features a hemi-anechoic chassis dynamometer. "The unique aspect of this chamber is it provides for up to 97 km/h (60 mph) wind. It's not a wind tunnel, but it does generate wind loading at appropriate frequencies. We can also synchronize the wind speed to vehicle speed," explains Phil Weber, Sika Automotive's Manager of Technical Services.

Test rooms feature a suite of anechoic and reverberant chambers for test and development of acoustic materials and applications; a materials testings lab; a sound quality lab and adjoining

Scanning laser vibrometer, one tool with DuPont Automotive NVH lab.

Sika Automotive acoustic baffle.

jury evaluation room for playback of collected vehicle noise measurements; a quiet room with bedplate and carbon monoxide extraction for modal analysis and other structural testing; a full-size body-in-white bake oven for simulation of production bake processes; and a computer room for design and analysis of acoustic, bonding, and sealing applications.

Having a dedicated NVH laboratory is of growing importance to suppliers. "Some suppliers are differentiating themselves with NVH (labs), and in other cases it's expected, so why not make necessity a virtue. For full service suppliers, the new challenge is the difficult task of managing fit and function pieces as well as the NVH piece," says Peter Greer, Principal Automotive Consultant for A.T. Kearney in Southfield, MI.

Vibracoustic North America, an independent wholly owned subsidiary of Freudenberg-NOK, has opened a new noise and vibration testing/product development/headquarters in Plymouth, MI. The $7 million center has counterpart NVH lab operations in Europe and Asia. "With the ever-increasing importance of vehicle NVH, our customers are looking for global suppliers with leading-edge technology, a broad portfolio and complete regional capabilities that are consistent everywhere in the world," notes Mehdi Ilkhani-Pour, President of Vibracoustic North America and former president of Freudenberg-NOK's Automotive Vibration Division

Products to address unwanted NVH in chassis and powertrain represent the Freudenberg-NOK portfolio of body and cradle mounts, engine mounts, torsional vibration dampers, jounce bumpers, suspension bushings, and spring isolators.

Vibracoustic North America expands the product line-up with such offerings as air springs, conventional and hydraulic chassis bushings while adding a testing framework for complete noise path analysis.

As one example of ongoing NVH-related development work, microcellular polyurethane functions as the material for body mounts. When compared to traditional rubber body mounts, microcellular polyurethane body mounts weigh less, improve vibration characteristics, and in most cases lower noise by an average five decibels. "These body mounts are expected to go into production in a few months. This is the first microcellular polyurethane use of its kind. It's a very exciting opportunity for us," Ilkhani-Pour says. The Vibracoustic group's sharing of best practices and self-contained NVH testing laboratories in North America, Asia, and Europe help speed up development cycles for components and systems.

"It's important for us to have very sophisticated, very advanced test equipment as it gives us the capability to better investigate NVH issues," Ilkhani-Pour says. The North American vibration control business currently has $150 million-plus in annual revenues; business is projected to double in the next five years. "The primary growth method is internal, not acquisitions," Ilkhani-Pour says.

NVH product solutions are forecast to reap substantial monies for 3M Automotive, due in part to work unfolding inside a two-story ideas center that opened this summer. "We expect the Thinsulate product line to double in sales in the next two years, and then again in the two years after that," says Tom Merkling, Business Development Manager for the 3M Automotive Innovation Center in Livonia, MI.

Thinsulate Acoustic Insulation — composed of polyester and polyolefin — employs 3M's advanced microfiber technology. Application areas for the NVH automotive product include headliners, door panels, door pillars, and instrument panels. "The next vehicle target areas for Thinsulate technology are under carpet, and under hood — which will mean a high-heat version of the product," Merkling says.

A few months ago, DuPont Automotive expanded its NVH-attuned research and development resources with the opening of a NVH lab in Troy, MI. In-house testing equipment includes holographic acoustic microphone system, scanning laser vibromometer, white noise box, and an anechoic chamber. "This is our first NVH lab in North America," says Ken Nelson, Senior Technical Consultant at DuPont Automotive. The newest NVH testing and analysis environment — a counterpart to a United Kingdom facility — was added to meet regional customer demands. DuPont's lab served as test site for modifications to an air intake manifold that was producing an unwanted hiss sound.

Nelson and Ping-Kang Chao of Ford Motor Company believe their analysis may be the first examination of a composite manifold to use objective noise data (microphone and laser scanning) as well as subjective characterizations (human jury) of the same NVH information. Since a cast aluminum intake manifold was found to essentially mask a high frequency hiss noise, system components were not optimized for minimum noise output. "This study has led to changes to the intake manifold, throttle body, and idle air bypass valve. The findings show that the noise source involves more than one component," Nelson says.

The now-altered composite air intake manifold is mated to a 3.0-L Ford V6 engine on select model year 2000 vehicles.

As the industry increases usage of lightweight materials, precision engineering for component and systems is crucial. "NVH performance is traditionally at odds with weight reduction. And that's because mass is proportional to the attenuation of sound and vibration; a principal casually known as the mass law," stresses John Feng, President of Muller-BBM in North America, an acoustic/vibration test system supplier, and an NVH consultant firm in Ann Arbor, MI.

Regardless of the weight, engines and brakes continue to be heavy noise generators. But where some consumers consider noise a signal of power and performance, others consider noise a symptom of problems. "Simply stated, our powertrain NVH strategy is to match customer expectations," says Tom Mitchell, General Motors' department manager for powertrain noise and vibration.

In the 2001 model year, a direct-injection, common rail DURAMAX 6600 diesel V8 engine debuts as an optional powerplant in the Chevrolet Silverado and GMC Sierra full-size pickup trucks. (Designed by Isuzu, the engine will be manufactured by DMAX, Ltd, the GM and Isuzu joint venture in Moraine, OH.)

The new 6.6 liter, four-valves-per-cylinder turbocharged engine produces power in a relatively quiet operation — something of particular relevance to the North American market. "Does a customer expect a diesel to sound different; we think they do in North America. The expectations are different in different markets, but it still needs to sound pleasant and powerful," Mitchell stresses.

In contrast, brake noise is generally not tolerated regardless of the market locale.

The initial rear brake design for a 2001 model year North American passenger vehicle produced a howl in the frequency range of 700 to 800 Hz. Using the first set of prototype parts, the bothersome noise was reproduced on a dynamometer and analyzed through various techniques, including a scanning laser vibrometer. A first fix to the drum's exterior eliminated the howl, but caused a vibration because the drum now had uneven stiffness.

The team's redesign meant re-configuring the stiffeners. It turned out to be a two-step solution process. The added material is cast right into the drum, so it's still a one-piece construction,"

explains George Schumacher, Senior Manager of CAE/NVH Department for TRW Automotive in Livonia, MI.

Redesigns may be less commonplace once predictive analysis becomes refined. Today's faster computing time, which permits 250,000 to 500,000 degrees of freedom, is a major enabler to advanced predictive NVH analysis. "For model year 2003-2004 production platforms, the team will use predictive models to solve NVH issues. That will enable us to conduct noise screening on the computer using entire system models (axles, knuckles, suspension) before prototype parts are built," says Schumacher.

Although dampening and deadening sounds remain a common method to hinder noise paths, Siemens Automotive is developing a unique approach to enhancing desirable sounds. "We recognize the subjective nature of NVH," says David Geran, Director, Business Development for Siemens Automotive Powertrain Air Induction Division in Windsor, Ontario, Canada.

Satisfying consumer wants does follow patterns. For instance, the public expects a sports car's engine to sound different from a luxury car's engine. "A V6 engine could have an enhanced growl in one application, but purr like a kitten in another application because we can focus on frequency sounds via the air induction system to create a noise signature," Geran says. As an engine accelerates through higher and higher rpms, electronics could be used to null and void certain frequencies that only occur at certain rpms.

"We're working on electronic cancellation of noise frequencies, which is different from passive resonators that only address one noise frequency. By using electronics to cancel or enhance sounds, plastic hollow resonators could be eliminated. That's a huge issue from a packaging and cost standpoint," explains Geran.

Ford Motor Company engineers plotted a comprehensive vehicle, systems and components engineering approach on a new vehicle platform. "We set very specific goals/targets relating to NVH," Tom Lahvic, Ford Motor Company's Vehicle NVH Department Manager for Research and Vehicle Technology, says about 2000 Lincoln LS and Jaguar S-Type. "There was no unique technology used to address NVH, it's just conventional techniques executed very well."

Even small components influenced sound quality on the luxury cars powered by a new 3.9-L V8 DOHC engine. "It's probably the stiffest bracket design we've ever had. Each of the engine-to-body brackets are a small, pyramid shaped design. The design of the engine was driven by achieving noise and vibration goals." Noise and vibration targets helped Ford engineers bypass costly and time consuming re-engineering.

"NVH can be an Achilles' heel because it can actually slow or delay the release of a product," Lahvic says. Since a vehicle's interior is the ending route for NVH, a cabin devoid of unwanted noises helps generate and maintain vehicle brand loyalty.

"If seats are properly designed, they can absorb more than half the sounds reaching the inside of a vehicle," says Mike Dinsmore, Manager of Business Development and Product Planning for Acoustics and Materials at Johnson Controls, Inc. in Holland, MI. More than 60 seat cover materials are undergoing standardized acoustics measurement tests at Johnson Controls as part of the supplier's concentrated efforts to design and engineer improved NVH seat systems.

Although other interior zones such as instrument panels, headliners, and carpeting possess untapped noise absorption possibilities, seats are a primary focal point. "Right now, seats have the most potential for improved interior noise control. There's not much yet being done with instrument panels as a noise absorber, and one reason is because of knee bolsters, airbags, and other structural concerns," Dinsmore says.

In the future, tools that help engineers develop noise-appropriate vehicles may mix subjective and objective considerations. "The trend is to develop scientific models to predict subjective responses. That's an important goal because we are designing our cars to satisfy the subjective impressions of real customers," expresses Muller-BBM's Feng. In the meantime, automakers and suppliers use other methods to predict consumer NVH preferences.

"We do not know how to model how humans perceive the noises of a vehicle, which is why we rely very heavily on jury testing," as well as objective measurements, concludes Peter Laux, PhD, and technical expert in acoustic integration at Johnson Controls.