Technology for a Quieter America (2010)

The science of environmental noise measurement has progressed rapidly in the past decade as computer technology has come online to provide rapid data acquisition and analysis in small portable packages. The end result has been a revolution in the type and complexity of measurements and calculations that can be made in analyzing environmental noise. The bulk of this discussion will be focused on the capabilities of modern measurement systems. Both sound-level meters and monitoring systems will be discussed in some detail. Finally, a summary of the findings from this analysis will be presented as to the capabilities and limitations of current measurements. Whether there are restrictions on the types of metrics that could be utilized in defining and limiting environmental noise will also be discussed.

The equations used to calculate the various metrics are not discussed here. The American National Standards Institute has a series of standards, the S12.9 series, listed as references in this appendix. Part 4 is particularly relevant to the mathematical definition of metrics for community noise. These standards are developed by ANSI Committee S12—Noise and are available through the Acoustical Society of America (ASA, 2010).

Sound-level meters and related filter characteristics have been standardized by the American National Standards Institute and are also available through the Acoustical Society of America (http://asastore.aip.org/shop.do?cID=7). International standards on the same subjects are developed by the International Electrotechnical Commission Technical Committee 29—Electroacoustics (IEC, 2010).

The Brüel & Kjær Type 2270 sound-level meter is a modern instrument and will be used as the typical example for this discussion. Other manufacturers make instruments with similar capabilities. This is an integrating sound-level meter with the ability to compute sound energy summations. This is the standard sort of capability found in high-end sound-level meters. There is a large amount of computing power using microprocessors built into the unit. This allows for sophisticated analysis, data communication, and programming. Figures E-1 and E-2 show examples of the screen display and use of this meter.

The types or measurements possible with this meter are listed below:

• for display and storage: L_dn, L_den, L_day, L_evening, and L_night

• selectable day, evening and night periods and penalties

FIGURE E-1 Screen display of discrete frequency analysis for Type 2270 monitor. Copyright © Brüel & Kjær.

FIGURE E-2 Type 2270 meter in use. Copyright © Brüel & Kjær.

• report period: from 1 minute to 24 hours with 1-minute resolution

• all broadband data and statistics stored at each reporting interval

• all spectrum data stored at each reporting interval

• spectral statistics stored at each reporting interval

• logging time: from 1 second to 31 days with 1 second resolution or continuous

• data are saved in separate projects for every 24 hours of logging

The sound-level meter market can be divided into three levels. The high end is the integrating analyzer with a tremendous amount of computing power. Some manufacturers use a laptop computer attached to the instrument for this category. At the lowest level, these instruments are meters that can merely report a sound level.

The Brüel & Kjær Type 3639 Noise Monitoring Terminal will be used as the example for this discussion. There are several competing products by other manufacturers with very similar capabilities. The Type 3639 is designed for use in all climate environments, as well as industrial, urban, and rural conditions. It can be left unattended as part of an environmental noise monitoring system for permanent, mobile, or semipermanent monitoring. The Noise Monitoring Terminal can be controlled by a remote PC. This unit is shown in Figure E-3.

Typical capabilities for these types of monitoring systems are summarized here:

• logging of broadband and 1/3-octave parameters every second or half-second

FIGURE E-3 Type 3639 monitoring station. Copyright © Brüel & Kjær.

• postprocessing that can create periodic statistical reports down to 1 minute, including L_N data

• GPS support

• sound recording

• weather data monitoring

• camera support

• remote operation via LAN, public telephone lines, mobile phone, or General Packet Radio Service (GPRS)

The definition of the measurements that can be done with these types of monitoring stations is quite lengthy. A short summary is presented here of typical calculations.

Broadband values:

• X = frequency weightings A and C, or A and Linear, or C and Linear (two weightings simultaneously)

• Y = time weightings Fast, Slow and Impulse (all simultaneously)

• L_Xeq, L_Xpeak, L_Xim, L_XYinst, L_XYmax/SPL, L_XYmin

Spectrum values:

• equivalent continuous level (L_eq) and I-weighted value also selectable (L_AIeq)

• 1/3-octave frequency range: 12.5 to 20 kHz

Events:

• settings: hourly, user-defined on the following parameters:

• detection: separate event start/stop triggers

• event start trigger: L_eq or SPL with minimum threshold exceedence duration

• event stop trigger: L_eq or SPL with minimum threshold exceedence duration

Table E-1 is a summary of the hardware options offered by the Brüel & Kjær system to illustrate the variety available. In addition, there is a wide array of software options as shown in Table E-2. One will note that all the energy summation options and most of the other metrics noted previously are included in the available software.

The drivers of the demand for monitoring systems have been studied extensively by manufacturers, including Brüel & Kjær (Denmark), Lochard (Australia, mostly focused on monitoring airport noise), 01dB-Metravib (France, mostly focused on monitoring urban noise), and Norsonic/Topsonic (Germany and Norway, a software partner of Norsonic on large systems).

A primary influence is the need to meet the monitoring requirement dictated by legislation and standards. Implementation of European Union environmental noise directive 2002/49/EC and similar statutes in other parts of the world has also been a major driver for the acquisition and use of monitoring systems. Cities, counties, countries, and industries are obliged to follow the national and local legislation and the standard that defines measurement and estimation of noise in the environment. In many instances the demand is driven by a desire to have a positive relationship with the public. There is also increased attention to quality of life. Public pressure on noisy transportation systems (roads and rail), industries (metal, chemical, mining, and construction), and communities to manage and inform on environmental issues has been a driver for the use of monitoring systems in the urban environment.

For airports, the major driver in the use of monitoring systems is to optimize profit or capacity. By carefully monitoring noise, airports can increase movements and hence profits by increasing the environmental capacity. It allows them to optimize the capacity utilization. An airport can also postpone or even avoid the need for new infrastructure such as runways, taxiways, or terminals by maximizing use of the available land and runways.

It is also necessary to manage relationships with regulatory bodies. This includes the use of monitoring equipment with regard to legislation, standards such as ISO 1996 Environmental Noise Assessment, Part 1 (definitions) published

2003, Part 2 (assessment techniques) DIS 2005, and ISO 20906 Aircraft Noise Monitoring (major revision of ISO 3891-1978). Finally, there is the need to manage relationships with adjacent communities. One way to accomplish this is to monitor and be able to provide noise levels to refute complaints and to demonstrate action to monitor and control noise levels.

One way to understand how this market is segmented is to look at the interests of customers:

1. Airport noise

2. Urban noise

3. City noise

4. Road noise

5. Railway noise

6. Industry—internal (facilities) and external(products)

7. Construction sites

8. Recreational areas

In each customer segment the buyer can be either the final customer, a consultant, or a system integrator. Another way to break down the marketplace is to look at solution segments:

1. short-term monitoring

2. long-term monitoring

3. permanent monitoring

Each segment represents a need for different types of software and hardware. In the case of short-term monitoring, a sound-level meter may be sufficient. For permanent monitoring a self-contained monitoring unit is required, and on-board analysis capabilities are probably desirable.

A large number of metrics are currently being used, ranging from A-weighted sound levels to day-evening-night average sound pressure levels with various corrections. There are still some issues when it comes to low-frequency noise, impulsive sounds, and certain sources—special cases may require unique metrics. Undoubtedly, new and more complex metrics will be developed.

Sophisticated modern sound-level meters and monitoring devices have the capability to record and report any metric that can be programmed. The level of sophistication currently available is sufficient to perform measurements and calculations required by all current metrics and some of the metrics used in product sound quality evaluation. These sound quality metrics may become more widespread in the future for the evaluation of community noise. The use of modern computer technology has effectively eliminated any limitations on measurement equipment in terms of the metrics that can be used.

Data management is now much easier. Embedding large amounts of memory in instrumentation is relatively inexpensive and wireless connection capability also means that a large amount of data can now be collected and stored automatically for future processing, which greatly facilitates

testing of proposed new metrics. It also means that the noise measurement component of large community surveys can be approached in a very different way from the way it was done in the past when data collection, memory, and storage capabilities were very limited.

In the competitive marketplace for sound-level meters and monitoring systems, the same sort of capability is available from several vendors. Prices and performance will continue to improve.

ASA. 2010. American National Standards Institute, ASC S1—Physical Acoustics. ASC S1 standards are available online from the Acoustical Society of America at http://asastore.aip.org/shop.do?cID=7. The following is a list of the standards available in the S12.9 series:

• ANSI S12.9-1988 (R 2003) American National Standard Quantities and Procedures for Description and Measurement of Environmental Sound, Part 1

• ANSI/ASA S12.9-1992/Part 2 (R2008) American National Standard Quantities and Procedures for Description and Measurement of Environmental Sound, Part 2: Measurement of Long-Term, Wide Area Sound

• ANSI/ASA S12.9-1993/Part 3 (R2008)—American National Standard Quantities and Procedures for Description and Measurement of Environmental Sound, Part 3: Short-Term Measurements with an Observer

• ANSI S12.9-2005/Part 4 American National Standard Quantities and Procedures for Description and Measurement of Environmental Sound—Part 4: Noise Assessment and Prediction of Long-Term Community Response.

• ANSI/ASA S12.9-2007/Part 5 American National Standard Quantities and Procedures for Description and Measurement of Environmental Sound—Part 5: Sound-Level Descriptors for Determination of Compatible Land Use

• ANSI/ASA S12.9-2008/Part 6 American National Standard Quantities and Procedures for Description and Measurement of Environmental Sound—Part 6: Methods for Estimation of Awakenings Associated with Outdoor Noise Events Heard in Homes

IEC. 2010. Technical Committee 29—Electroacoustics, International Electrotechnical Commission, Geneva, Switzerland. Available online at http://www.iec.ch/cgi-bin/procgi.pl/www/iecwww.p?wwwlang=e&wwwprog=TCpubs.p&progdb=db1&committee=TC&css_color=purple&number=29.

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