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132 The noise monitoring for this study was performed using four identical systems of two sound level meters (SLMs). Each system consisted of one Larson Davis (LD) 831 Sound Level Meter and one LD 824 Sound Level Meter connected to a Zoom H4 recorder. Table D-1 presents a list of the SLM used along with the microphone and preamplifier used with each SLM and their serial numbers. The LD 831 SLMs were set to record the overall A-weighted and C-Weighted Leq and maxi- mum noise levels as well as 1/3 octave band Leq noise levels every second. The LD824 SLMs were set to record the overall A-weighted and C-weighted Leq noise levels and maximum level every second. The audio output of the LD824 SLM was connected to the input of the Zoom H2 digital recorders which were set to record uncompressed WAV audio files at a sampling rate of 44.1 kHz and a bit rate of 16 bits/sample. Prior to the commencement of monitoring, the performance of each SLM, preamplifier, and microphone combination was verified using a Brüel and Kjær (B&K) 4231 calibrator producing a 1 kHz test tone at 93.8 dB (Serial Number 2528535) and a B&K 4420 pistonphone producing a 250 Hz test tone at 124.0 dB (Serial Number 147402). Certificates of Performance showing the measured calibration levels for each of the SLM systems prior to each measurement period are attached. The calibrator and pistonphone were calibrated by Odin Metrology using standards with values traceable to the National Institute of Standards and Technology. Calibration certifi- cates for these units are attached. At the commencement of each measurement period, one system, consisting of two SLMs and a Zoom audio recorder, were set up at each measurement location. The SLMs and audio recorder were located in weather resistant cases with access ports for microphone cables and power. The microphones were placed on tripods to mount them at a height of approximately five feet AGL. The microphone tripods were located near the center of the yards at least 10 feet away from any building or wall. Each SLM was calibrated using the B&K 4231 calibrator in the field prior to starting each mea- surement period and calibration levels recorded. Data capture on the SLMs was started along with the Zoom audio recording. A calibration tone was recorded to the Zoom recorder and an audible time stamp was recorded. The systems were locked within their cases, and left unattended. Data storage limitations on the LD 824 SLM and Zoom H4 recorders required downloading of data from the units every other day. Data from the LD 831 SLM were generally downloaded every fourth day. Upon approaching the meters, an audible time stamp was recorded to the Zoom audio file. Data capture on the LD 824 and audio recording on the Zoom were paused and their data was transferred to a portable hard drive. This process was generally repeated for the LD831 SLM on every other visit. After the data was downloaded from the SLMs, the calibration A P P E N D I X D Noise Measurement Protocol
Noise Measurement Protocol 133 was checked and recorded using the B&K 4231 calibrator. The SLMs were recalibrated if the measured level differed from the calibration level by more than 0.4 dB. After this process was completed, data capture on the SLMs and recording on the Zoom were restarted. A calibration tone and audible time stamp were recorded on the audio file. The time the technician approached and departed each measurement site was recorded along with file names, measurement start and stop times, and calibration levels. At the end of each measurement period an audible time stamp was recorded to the Zoom audio file as the meters were initially approached. Audio file recording and SLM data capture were paused and transferred to a portable hard drive. Calibration levels were checked using the Brüel and Kjaer calibrator and recorded. The calibration checks for the SLMs are attached. COMPONENT MANUFACTURER MODEL SERIAL # System A - Monitor 1 SLM Larson Davis 831 2564 Preamplifier Larson Davis PRM831 12422 Microphone GRAS 40AQ 83680 System A - Monitor 2 SLM Larson Davis 831 A1460 Pre-Amp. Larson Davis PRM902 1983 Mic. Larson Davis 2551 178 System B - Monitor 1 SLM Larson Davis 831 2562 Preamplifier Larson Davis PRM831 15267 Microphone GRAS 40AQ 101907 System B - Monitor 2 SLM Larson Davis 831 A1459 Preamplifier Larson Davis PRM902 1987 Microphone Brüel & Kjær 4176 2316550 System C - Monitor 1 SLM Larson Davis 831 2565 Preamplifier Larson Davis PRM831 15268 Microphone GRAS 40AQ 101963 System C - Monitor 2 SLM Larson Davis 831 A1458 Preamplifier Larson Davis PRM902 1976 Microphone Brüel & Kjær 2551 2316551 System D - Monitor 1 SLM Larson Davis 831 2566 Pre-Amp. Larson Davis PRM831 15270 Mic. GRAS 40AQ 101912 System D - Monitor 2 SLM Larson Davis 831 A1457 Pre-Amp. Larson Davis PRM902 1989 Mic. Larson Davis 2551 177 Table D-1. Sound level monitoring equipment.
