Sound level meter.pptx

Sound level meter

1. Sound Level Meters Presented by Roba Fikadu

2. WHAT IS SOUND LEVEL METER? A Sound Level Meter (SLM) is an instrument (commonly hand-held) that is designed to measure sound levels in a standardized way. It responds to sound in approximately the same way as the human ear and gives objective, reproducible measurements of sound pressure levels.

3. What is Sound Pressure? Sound pressure (p) is the average variation in atmospheric pressure caused by sound. The unit of pressure measurement is the Pascal (Pa). Since it is not intuitive to use Pascal (Pa) to refer to the volume of sound in our daily lives, it is easier to describe them in decibels.

4. As a result, sound pressure (Pa) is typically converted into “sound pressure level” in decibels (dB) to represent the sound volume. The conversion of “sound pressure” (Pa) to “sound pressure level” (dB) is as follows. SPL = 20*Log10 ( P / P ref )

5. Classes of Sound level meters According to the International Standards (IEC 60942:2017), Sound Level Meter is categorized into two different classes based on its accuracy

6. Classes Class 1 —Precision grade with a tolerance of ±0.5 dB. It is ideal for industrial and laboratory use.  Class 2 —General purpose grade with a tolerance of ±1.0 dB. It is ideal for basic noise environmental measurements.

7. WHAT IS A SOUND LEVEL METER USED FOR? Sound level meters are used to measure and manage noise from a variety of sources, including I ndustrial plants, R oad and rail traffic, Construction work, etc

8. What is a normal sound level? The World Health Organization (WHO) defines a “normal” sound level as anything below 35 decibels (dB). This is roughly equivalent to the noise of a whisper or rustling leaves. Above this threshold, any increase in loudness can cause stress, fatigue, and even hearing loss over time.

9. How will you measure the sound level? Measuring the sound level is essential to evaluate the acoustic environment of a particular space. Many different techniques and instruments are used to measure sound levels, including sound level meters, sound analyzers, and noise dosimeters.

10. Sound level meters measure the instantaneous sound pressure level in decibels (dB) and are usually used to determine the overall sound pressure level in a given area By measuring the sound levels of a particular area, it is possible to determine if the noise levels are suitable for workers and occupants How will you measure the sound level?

11. HOW DOES A SOUND LEVEL METER WORK? A sound level meter comprises a  microphone , a  preamplifier ,  signal processing , and a display. The microphone converts the sound signal to an equivalent electrical signal. The most suitable type of microphone for sound level meters is the condenser microphone, which combines precision with stability and reliability.

12. The electrical signal produced by the microphone is at a very low level, so it is made stronger by a preamplifier before it is processed by the main processor. Signal processing includes applying frequency and time weightings to the signal as specified by international standards such as IEC 61672 – 1, to which sound level meters conform.

13. TIME WEIGHTING Time weighting specifies how the SLM reacts to changes in  sound pressure . It is an exponential averaging of the fluctuating signal, providing an easy-to-read value.

14. TYPES OF TIME WEIGHING The analyzer applies Fast, Slow, and Impulse (or ‘F’, ‘S’ and ‘I’) time weightings, which are the required weightings according to most international and national standards and guidelines. Environmental assessment standards usually specify which time weighting to use.

15. The signal is processed through the weighting filters, and the resulting  sound pressure level  is displayed in decibels (dB) referenced to 20 μ Pa on the analyzer’s screen. The sound pressure level values are updated at least once per second.

16. FREQUENCY WEIGHTING Frequency weighting adjusts how the sound level meter responds to different sound frequencies. This is necessary because the human ear’s sensitivity to sound varies according to the sound’s frequency.

17. TYPES OF FREQUENCY WEIGHTING IEC 61672-1 defines frequency weightings A, C and Z, but other frequency weightings are occasionally used in specialized applications.

18. A-weighting – dBA /dB(A) A-weighting adjusts a signal in a way that resembles the human ear’s response at medium-range levels. It is based on the 40 dB equal loudness curve. The symbols for the noise parameters often include the letter ‘A’ (for example, L Aeq ) to indicate that frequency weighting has been included in the measurement.

19. A-weighting is required for nearly all environmental and  workplace noise  measurements and is specified in international and national standards and guidelines. A-weighting filters cover the full audio range, 10 Hz to 20 kHz.

20. C-weighting – dBC /dB(C) The response of the human ear varies with the sound level. C frequency weighting corresponds to the 100 dB equal loudness curve, that is to say, the human ear’s response at fairly high sound levels. C-weighting is mainly used when assessing peak values of high sound pressure levels. It can also be used, for example, for entertainment noise measurements, where the transmission of bass noise can be a problem.

21. Z-weighting – dBZ /dB(Z) Zero’ frequency weighting is a flat frequency response between 10 Hz and 20 kHz ±1.5 dB excluding microphone response.

22. Today, the A-weighting network is the most widely used frequency weighting. C-weighting does not correlate well with subjective tests because the equal loudness contours were based on experiments that used pure tones — and most common sounds are not pure tones, but very complex signals made up of many different tones

23. FREQUENCY ANALYSIS When more detailed information about a complex sound is required, the frequency range can be divided up into sections or bands. This is done with electronic or digital filters, which reject all sound with frequencies outside the selected band. These bands usually have a bandwidth of either one octave or a third of an octave.

24. Octave An octave is a frequency band where the highest frequency is twice the lowest frequency. For example, an octave filter with a center frequency of 1 kHz admits frequencies between 707 and 1414 Hz but rejects all others. The name octave stems from the fact that an octave covers eight notes of the diatonic musical scale. A third octave covers a range where the highest frequency is 1.26 times the lowest frequency.

25. spectrogram

26. spectrogram The process of thus dividing a complex sound is termed frequency analysis and the results are presented on a chart called a spectrogram. After the signal has been weighted and/or divided into frequency bands, the resultant signal is amplified, and the Root Mean Square (RMS) value is determined in an RMS detector.

27. RMS The RMS is a special kind of mathematical average value. It is of importance in sound measurements because the RMS value is directly related to the amount of energy in the sound being measured.

28. THE DISPLAY The display shows the sound level in decibels, typically with a descriptor showing the selected combination of time and frequency-weighting ( eg ; L Aeq  or L Cpeak ). The signal may also be available at output sockets, in either AC or DC form, for connection to external instruments such as a data acquisition system, to provide a record and/or for further processing.

29. CALIBRATION Calibration is an adjustment of your SLM to measure and display correct values. The sensitivity of the transducer, as well as the response of the electronic circuitry, can vary slightly over time or could be affected by environmental conditions such as temperature and humidity.

30. THANK YOU!!