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874 Lewelling Blvd. <br />Noise Study <br />9 July 2018 <br />Page 7 of 8 <br /> <br /> <br /> <br />APPENDIX A <br />DEFINITIONS OF COMMON ACOUSTICAL TERMS <br /> <br />Decibel, dB – A unit describing the amplitude of sound, defined as 20 times of the logarithm of the ratio of the <br />sound pressure measured to the reference pressure (20 µPa). <br />A-weighted Sound Level, dBA – The sound pressure measured using the A-weighting filter network that de- <br />emphasizes the very low and very high frequency components of the sound spectrum in a manner similar to the <br />frequency response of the human ear and correlates well with subjective reactions to noise. <br />Ambient Noise – The sound level in a given environment, usually comprised of many sources near and far, with no <br />particular sound dominant. It is often defined as L99 or the noise level exceeded 99% of the time. <br />Background Noise - The total noise from all sources other than the source of interest. It is often defined as L90 or <br />the noise level exceeded 90% of the time. <br />Community Noise Equivalent Level, CNEL – The average, 24-hour A-weighted noise level, obtained by adding 5 dB <br />to evening hours (7:00 pm to 10:00 pm) and 10 dB to night hours (10:00 pm and 7:00 am). <br />Day/Night Noise Level, Ldn (or DNL) – The average, 24-hour A-weighted noise level, obtained after adding 10 dB to <br />levels measured at night (10:00 pm to 7:00 am). <br />Integrated or Equivalent Noise Level, L eq – The energy average A-weighted noise level during the measurement. <br />Sound level meter - An instrument that measures sound in dB. Various instrument features include frequency <br />bands, integration of sound over time and display of average, minimum, maximum and statistical levels. <br />Sound pressure level - the ratio, expressed in decibels, of the mean -square sound pressure to a reference mean - <br />square sound pressure selected by convention to approximate the threshold of hearing (0.0002 µbar or 20 µPa). <br />Frequency – The number of times per second that the oscillation of a wave of sound or that of a vibrating body <br />repeats itself, expressed in Hertz (Hz). <br />Octave band - The frequency range of one octave of sound frequencies. The upper limit is always twice the <br />frequency of the lower limit. Octave bands are identified by the geometric mean frequency or center between the <br />lower limit and the upper limit. <br />Outdoor-Indoor Transmission Class (OITC) – A single-number rating system based on laboratory testing performed <br />in accordance with ASTM Standard E1332. It is used to define the sound isolating characteristics of exterior building <br />elements using a standardized automobile traffic spectrum. <br />Sound Transmission Class (STC) – A single-number rating system based on laboratory testing per ASTM Standard <br />E90. It is used to define the sound isolating characteristics of partitions separating occupied spaces. <br />Noise Isolation Class (NIC) - A single-number rating system based on field testing per ASTM Standard E336. It is <br />used to compare the sound isolating characteristics of the total construction between two enclosed spaces. <br />Impact Insulation Class (IIC) – A single-number rating system based on laboratory testing per ASTM Standard E492. <br />It used to compare the acoustic impact isolation characteristics of floor/ceil ing partitions using a standardized <br />tapping machine test method. <br />Field Impact Insulation Class (FIIC) – Similar to the IIC rating system except it is measured in the field. <br />64