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NV sage VOL-073 April 2020
NV Dynamics 2020 All rights reserved©
NVsageThe Noise & Vibration Newsletter
VOL- 073 | April 2020
NV Dynamics, Bangalore INDIA | Maryland USA+91 80 4161 0660 | +91 77603 [email protected] | www.nvdynamics.com
Qualified NVH Engineering Services since 2001
Foreword
Discussion Board
Know How Tit Bits
Recent Tasks
o Vibration Assessment at apartment floor building.
o Noise and Vibration validation assessment on DG floor area.
o Noise and Vibration assessment for ceiling fan.
o Noise Fundamentals Part - 04
o Subtraction of Sound Pressure Levels & Noise Reduction
o Noise measuring instrumentation – Microphones & its types
Cicadas Summer Sound!!!
NV sage VOL-073 April 2020
NV Dynamics 2020 All rights reserved©
Foreword
01
Home
Dear Customer
We are all in a grim situation caused by pandemic Covid 19.
I suppose the whole spectrum of industry has come to a grinding halt in
the wake of this, as we resolve to fight back this deadly outbreak, let us
do our part of sharing the social responsibility to minimize the spread of
this virus
As a sensible society, we all are following some of the precautionary
measures to this effect, I found the following 2 bills as good once and
share them here.
NV Dynamics made its small contribution to the Prime Minister CARES,
Covid fund; through this media, I request all to make your generous
donation to this fund in this hour of crisis. Lets put our firm determination
by our practices, responsible actions and by donations and come out
successfully in contain the menace of this virus and its effects.
As for our activities, just before the stoppage due to Corona, we finished
one large building vibration analysis and were preparing for designing a
large Noise barrier for containing the Acoustic energy radiated by
Commercial Aircraft during engine testing trails. There were also
CASE-1
Shapoorji Pallonji, a large multi-faceted Indian conglomerate with varied
interests of business both in India and abroad. In one of their real estate
projects, a validation study of long time vibration monitoring was
conducted to assess and qualify the impending magnitudes and their
compliance to applicable International Standards.
NV Dynamics deployed its multiple data acquisition systems and other
supporting add-ons to site and completed the detailed study; data is
being processed and report on the findings are being prepared.
CASE-2
The International Airport in Bangalore is building a facility for testing
Commercial flight engines for their performance as a part of routine
maintenance program. NV Dynamics had earlier tested and quantified
the sound pressure levels originating from these planes and now are
working on designing an acoustic barrier around the testing facility; once
implemented, this barrier will address Noise propagation effects around
the testing facility and in specific to some of the critical installations
around this facility.
Warm Regards
Krishna Balamurali
NV sage VOL-073 April 2020
NV Dynamics 2020 All rights reserved©
Discussion Board
02
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Noise Fundamentals – Part 04
In the previous edition of this newsletter, we discussed about the
descriptors, unit, perception of Sound & Addition of Sound Pressure
Levels.
In this edition, we will discuss about Subtraction of Sound Pressure
Levels, Noise reduction/isolation & its Instrumentation.
Subtraction of Sound pressure levels
Noise source identification from the complex machines with background
Noise is very critical. To discrete the Noise levels from the individual
components, Subtraction of Noise levels helps to identify individual local
source.
It is difficult to measure actual Noise level with all the Background Noise
being absent. A solution for this is to measure the Background Noise
alone and then with the source/machine in operation along with
Background Noise. Subtracting the Background Noise Level from the
Total Noise Level will give the level of the noisy piece of equipment on its
own. Let’s assume the Total Noise level is 60 dB and the background
alone is 53 dB.
Noise Control – Reduction/Isolation
In this advanced country, people always opt to comfortable life. Due to
rapid urbanization the usage of machinery, automotive and other
equipment is gradually increasing. Noise is one of the characteristics of
all the machinery that must be isolated to make it’s user comfortable.
Noise can be reduced by isolating at source, path and receiver.
At source: It is the most
convenient method to do the
isolation at source by
Engineering modifications at
the design stage, covering
them with acoustic absorbent
material. However sometimes
it is critical to isolate at
source.
At path: The second method
of isolation is to build an
acoustic barrier in between
the source and receiver such
that the Noise will be
absorbed and isolated.
At receiver: Most of the
recipients are human ears.
Using ear muffs or hearing
protectors is the easiest way
to reduce Noise at the
receiver end.
Method: The difference
between the Total Noise
level and the Background
Noise level alone is 7 dB.
The difference value to be
subtracted from the higher
Total Noise is 1 dB(Refer to
graph), which makes the
true Noise of the equipment
to be 59 dB on its own.
NV sage VOL-073 April 2020
NV Dynamics 2020 All rights reserved©
03
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Discussion Board
Noise Measuring Instrumentation – Microphone
To measure and quantify anything in Physics, it requires an instrument.
Microphone is a device used to measure Sound Pressure in air.
The basic measurement microphones with calibration always has
traceability to the fundamental quantities of Physics.
Microphones consist of a thin membrane in close to a metal plate. This
forms like capacitor and converts motion (Displacement) of diaphragm to
electrical signal (Voltage).
As the sound pressure level changes the motion of the diaphragm also
changes results in voltage deflection. The displacement of diaphragm is
directly proportional to sound pressure levels.
Types of Microphone
1. Depending on the Polarization method
• Externally Polarized Condenser Microphone
• Pre-polarized Condenser Microphone
2. Depending upon Sound Field(s)
• Free Field Microphone
• Diffuse Field Microphone
• Pressure Field Microphone
3. Depending on the diameter
• One inch (1’’) Microphone
• Half inch (1/2’’) Microphone
• Quarter inch (1/4’’) Microphone
• One-eighth inch (1/8’’)Microphone
4. Depending on the measurement tolerance or accuracy
• Laboratory Standard Microphone
• Working Standard Microphone
NV sage VOL-073 April 2020
NV Dynamics 2020 All rights reserved©
Know How
04
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Acoustics of Snoring!!!!
The Goldfish can see both infrared and ultraviolet light.
Great minds & their contribution to the world of Science
o Cicadas emit a wide range of Sounds from
sunrise to sunset during summer months
o They emit these sounds by stridulatory
organs located in the abdomen and are
received by an auditory organs located on
their legs or thorax.
o Some Cicadas are able to emit sounds that
exceed 120 decibels (they almost reach the
human ear pain threshold!
o However, some small Cicadas species emit
sounds at higher frequencies that the humans
cannot detect/hear, but could be painful for
other animals.
o The sounds of Cicadas have many
purposes, although they use it specially for
finding a mate or to delimitate their territory.
o
Cicadas Summer Sound…
Dr. APJ Abdul Kalam(October 15th , 1931 – July
27th 2015), son of Jainulabiddin and
Aashiyamma, lives in the heart of the Indian
people as Missile Man of India.
After his graduation from Madras Institute of
Technology, He joined the Defence Research and
Development Organization (DRDO). He has
worked under a legendary Space Scientist,
Vikram Ambalal Sarabhai (Father of India’s
Space Programme). In 1969, he became the
Project Director of India’s first indigenous
Satellite Launch Vehicle, SLV-III.
Kalam was elected as the 11th President of India
in 2002. Widely referred to as the “People’s
President”, He returned to his civilian life after a
single term. He is the recipient of several
prestigious awards, including the Bharat Ratna.
He has also been awarded with Padma Bhushan
in 1981 and Padma Vibhushan in 1990 for his
contributions at ISRO, DRDO and Government of
India as a Scientific Advisor. He has written many
books such as Wings of Fire, Ignited Minds,
Target 3 Billion in 2011, Turning Points, India
2020, My Journey and many more.
o Harsh sound from Nose during breathing
got obstructed while sleeping.
o Snoring sound energy from 652 to 1500 Hz
is compatible with obstructive level and
snoring generators in the respiratory tract
close to the carotid artery bifurcation.
o These sounds occurs when the air flows
past relaxed tissues in the throat, causing the
tissues to vibrate as you breathe.
o Snoring levels vary from person-to-person.
The mean peak level of snoring recorded is
between 50 and 65 decibels.
o Snoring could reach high Noise-level in the
range of 80-90 decibel that matches the
decibel levels of a vacuum cleaner.