IEEE 656-1985 pdf free.IEEE Standard for the Measurement of Audible Noise fromOverhead Transmission Lines.
IEEE 656 system consists of asound transducer，an amplifier，filters,a detector, and an indicating device. Such systems maybe manually operated for shortterm measurements or designed to automatically record repeated measurements on a long-term basis.
Sound-Level Meters.‘The basic sound-measurement system is the soundlevel meter.The standard soundlevel meter contains a microphone, weighting networks, an rms detector anda sensitive voltmeter or digital display that showsthe weighted electrical signal from the microphone. It may also have various response times.lt is calibrated to a standard reference soundpressure level 20 uPa .
The characteristics of soundlevel meters arecovered by several current standards. For trans-missionline noise measurements,a precisionsound-level meter as specified by ANSI S1.4-1983[2] shall be used.
Microphone Protective Devices. To mini-mize windgenerated noise, a windscreen shall beplaced over the microphone. A windscreen willalso afford a certain degree of protection fromrain. The insertion loss of the windscreen shallnot exceed 2 dB over the frequency range ofthe microphone. For short-term measurementsin light rain, no additional weather protection isnecessary.
For long-term unattended operation of anytype of microphone,an all-weather protectionsystem shall be used.The effect of the protectionsystem on the directivity pattern of the micro-phone,on its frequency response,and on thelocal noise level shall be evaluated and recorded.
Frequency Analyzers. When a frequencyanalysis is performed, data shall be obtainedfrom 31.5 Hz to 8 kHz inclusive and extendingto 16 kHz if system response permits，with instrumentation conforming to ANSI s1.11-1966(R 1976)[3], and in frequency bands conformingto ANSI/AsC s1.6-1984 [4]. For all but the puretone components of ac transmission-line audiblenoise,octaveband measurements give sufficientdetail of the frequency spectrum, and are recom-mended. For pure tones, measurements shall bemade with one-third octave band or narrowerbandwidth filters.
Recorders.Chart recorders and magnetictape recorders can be used for the shorttermand the longterm monitoring of audible noise. Ifchart recorders are used, chart span and speedshall be sufficient to display the full range oflevels of interest.
When a magnetic tape recorder is used torecord sounds for later analysis,it shall have a response which is flat within 3 dB over thefrequency range from 20 Hz to 15 kHz. For a fre-quency-spectrum analysis, both the recorder andthe spectrum-analyzer instrumentation shall havea response which is flat within  1 dB over thefrequency range of interest. The electronic noiselevel of the recorder shall be at least 10 dBbelow the lowest acoustical signal level in eachfrequency band to be analyzed.IEEE 656 pdf download.