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 81818services@nvdynamics.com | 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

krishna@nvdynamics.com

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

Home

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.