Environmental acoustics- Basic sound measuring system, sound level meter, Octave band analyzer

1. Environmental acoustics-
Basic sound measuring system
sound level meter
Octave band analyzer
Dr. Priyanka Tabhane
Department of Physics
Rashtrasant Tukadoji Maharaja Nagpur University,
Nagpur

2. Sound level meter
 Sound level meters work by calculating the
pressure of the sound waves travelling through
the air from a source of noise.
 It is also known as sound pressure level (SPL)
meters.
 They give a measurement of sound intensity in
units called decibels.
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

3. Block diagram of the principal elements of a sound level meter
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

4. Working:
 A microphone feeding a preamplifier (which function as a cathode
follower) which is turns to one of the weighting networks that is
selected by a switch.
 The weighted (or unweighted, if none of the weighting curves has
been selected ) signal then amplified and then passes through a
root-mean-square rectifier.
 It becomes converted to logarithmic (i.e. decibel) form, and is fed
to either a digital or analog readout device.
 The A and C networks are far more commonly used than B-
weighting, particularly when the low frequency acoustic energy is
present. Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

5. The integrating sound level meter :
the equivalent sound level was defined as
Or in terms of N sound-level measurements taken during N equal intervals.
The integrating sound-level meters are based on the application of above
equation in measurements of fluctuating noise over a considerable interval.
The integrating sound level meter is also capable of measuring the sound
exposure level (SEL), which characterizes a single event on the basis of both
the pressure level and the duration.
This parameter is defined by
(1)
(2)
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

6. Where T is measured in seconds.
If we consider a 2-s burst of sound at the rms pressure of 1 Pa,
using eq (2) will indicate an SEL of 97 dB.
On comparing equation (2) and (3) , we get the following
relationship between SEL and Leq:
(3)
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

7. Que. What is the sound exposure level SEL for an equivalent
sound-level pressure of 98 dB(A) lasting 8 seconds ?
Solution:
given : Leq = 98dB(A)
T = 8 seconds
Formula : SEL = Leq + 10 log T
SEL = 98 + 10 log 8
= 98 + 10(0.903089987)
=107.0308999
SEL = 107 dB(A)
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

8. Applications:
Sound level meters are used to measure and
manage noise from a variety of sources, including
industrial plants, road and rail traffic, and
construction work.
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

9. Advantages of sound level meter :
 No loudspeaker required.
 Automatic compensation for microphone distance.
Disadvantages of sound level meter :
 Only valid for a particular distance.
 Hard to keep the level of astable.
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

10. Octave band analyzer :
 Octave band analysis is a type of noise
measurement used to determine the type of
hearing protection needed in a specific setting.
 octave band analyzers are special sound level
meters that divide noise into its frequency
components.
 Electronic filter circuits are used to divide the
sound or noise into individual frequency bands.
 Dewesoft offers flexible octave band analyzers
for any sound measurement.
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

11. This device is capable of resolving the noise signal spectrum into frequency
bands that are one octave in width.
The centre frequency of octave band is √2 times the lower cut off frequency ,
and the upper cut off frequency is twice the lower cut off frequency .
The octave band in the audio range are designated by their center frequencies.
And are standardized internationally at 31Hz, 63Hz, 125Hz, 250Hz, 500Hz, 1kHz,
2kHz, 4kHz, 8kHz and 16kHz.
The typical relative bandwidth analyzers use 1/3-octave and 1/12-octave
bandwidths. These analyzers resolve the noise spectrum into third octave and
twelth octave.
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

12. Denoting f1 as the lower cutoff frequency , f2 as the upper cutoff frequency ,
and f0 as the centre frequency , then the relationship between the upper and
lower cutoff frequencies for a 1/nth octave filter is
The centre frequency is the geometric mean of the product of the upper and
lower cutoff frequencies.
And the band width bw is expressed as follows :
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

13. Applications:
 It is used in noise control, hearing protection.
 sometimes in environmental noise issues.
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University

14. THANK YOU
Dr Priyanka Tabhane
Department of Physics
RTM Nagpur University