American National Standards for noise emission measurements

Details

• Personal Author:
  Murphy, William J.
• Description:
  When determining sound power, three different room designs are described in the standards: anechoic (meaning free from echo), hemi-anechoic, and reverberant. A typical anechoic room is rectangular and has wedges on the six interior walls and a mesh trampoline to permit positioning the device being tested in the center of the volume of the room. In a hemi-anechoic room the floor is a reflective surface meant to simulate what might happen during outdoor measurements, in quiet without any reflections except for the ground. A reverberant room is designed to be highly reflective with non-parallel walls and diffusers on the walls to prevent the development of standing wave modes that are characteristic of rectangular rooms. For measuring in the three types of rooms, several measurement methods exist. Perhaps the most common is the pressure-over-area method. In this configuration, a set of microphones sample the sound level at a prescribed distance from the source outside of the nearfield of the device under test. The microphones are distributed over an imaginary surface that encompasses the device under test (DUT), and the pressure over a given area is used to determine that average power output of the DUT. The pressure over area method requires that the noise be coming from the source and that there not be other sources which are acting as sources outside the imaginary volume. For instance ANSI S12.55 is used to measure sound power in fully anechoic spaces and in hemi-anechoic spaces. ANSI S12.54 and S12.56 are used in hemi-anechoic environments, and ANSI S12.51 and S12.53 are used to determine sound power in reverberant environments. The different standards reflect varying degrees of precision involved in conducting the measurements. The NIOSH sound power laboratories in Pittsburgh and Cincinnati conduct measurements at the Engineering grade, +/-2dB. To achieve Precision grade, +/- 1dB, requires greater control of temperature and humidity. In the substitution, or comparison, method, a calibrated reference sound source is tested in the space to establish the room constant and understand how the sound might be absorbed by the space. The substitution or comparison method can be conducted in just about any space, the most satisfactory being a reverberation room. The sound absorptive characteristics of the space affects the sustained sound pressure level of the reference sound source when it produces a continuous noise in the room. The sound source is tested in the room with the other equipment turned off. The device of interest is turned on and the sound source is turned off. The sustained level in the room while the device under test (DUT) is running is a function of the sound power of the DUT and the room constant. By measuring the room constant with a known source, the sound power can be determined. More sound absorption equates to less buildup of sound energy in the space. Once the reference sound source has been measured, the microphones are kept in the same position and the DUT is operated and assessed. From the two measurements, the sound power of the DUT can be determined. When a product is purchased that has a Noise Declaration provided, the validity of that declaration can be tested after the product has been installed. Finally, the sound intensity method is best suited for in situ sound power measurement because it can be performed in any environment. It relies upon making measurements over a measurement surface enclosing the DUT with a pair of phase- and amplitude-matched microphones. The sound intensity is determined as the product of the average pressure of the point between the microphones and the derived particle velocity estimated by the difference between the microphones. [Description provided by NIOSH]
• Subjects:
  Engineering Manufacturing And Industrial Facilities Noise Noise, Occupational Occupational Health Safety
• Keywords:
  Analytical Processes Engineering Controls Manufacturing Noise Analysis Noise Control Noise Levels Noise Measurement Noise Sources Sound
• ISBN:
  9780989943123
• Publisher:
  Institute of Noise Control Engineering of the USA
• Document Type:
  Text
• Genre:
  Proceedings
• Place as Subject:
  District of Columbia ; Illinois ; Ohio ; OSHA Region 3 ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  DART - Division of Applied Research and Technology
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  37-41
• NIOSHTIC Number:
  nn:20048370
• Citation:
  Reducing employee noise exposure in manufacturing: best practices, innovative techniques, and the workplace of the future. Maling GC Jr., Wood EW, Lotz G, Lang WW, eds. Springfield, IL: Institute of Noise Control Engineering of the USA, 2016 Jul; :37-41
• Editor(s):
  Maling GC Jr.; Wood EW; Lotz G; Lang WW
• Federal Fiscal Year:
  2016
• NORA Priority Area:
  Construction ; Manufacturing
• Peer Reviewed:
  False
• Source Full Name:
  Reducing employee noise exposure in manufacturing: best practices, innovative techniques, and the workplace of the future
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:3ba0a5185f8131098551f11d514d6efe7d22472a13d459dc2b051852fb716bdd7cff9617ac547d7813b82cefc9464c76644c2f72f8f178a5a6458b9e1fffe31f
• Download URL:
  https://stacks.cdc.gov/view/cdc/203136/cdc_203136_DS1.pdf
• File Type:
  [PDF - 3.05 MB ]