Sound Level Meters.pptx

1. Sound Level Meters

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.

4. 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.

5. • 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 / Pref)

6. 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

7. 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.

8. WHAT IS A SOUND LEVEL METER USED FOR?
• Sound level meters are used to measure and
manage noise from a variety of sources, including
• Industrial plants,
• Road and rail traffic,
• Construction work, etc

9. 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.

10. 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.

11. • 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?

12. 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.

13. • 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.

14. 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.

15. 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.

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

18. 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.

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

20. 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, LAeq) to indicate that frequency
weighting has been included in the measurement.

21. • 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.

22. 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.

23. 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.

24. • 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

25. 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.

26. 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.

27. THE DISPLAY
• The display shows the sound level in decibels, typically
with a descriptor showing the selected combination of
time and frequency-weighting (eg; LAeq or LCpeak).
• 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.