VOL-058
NVDYNAMICS
July 2016
Vibration | Acoustics | Beyond
Qualified NVH Engineering Services since 2001
IN THIS ISSUE
Foreword
Large scale Ground Vibration /
Airport Noise Assessments
Vibrating screen foundation Analysis
Discussion Board
Acoustics – Part 4, Tones, Hearing,
octaves and diatonic
Fact File
Vibrations, as used by animals
Tit Bits
NV Dynamics Bangalore INDIA | Maryland USA
+91 80 4161 0660 | +91 777603 81818
[email protected] | www.nvdynamics.com
©NV Dynamics 2016 | all rights reserved
FOREWORD
Dear Customer
The last quarter of business activity was very interesting both in terms of the uniqueness of the tasks
handled and the sheer busy schedules we had, so much so that our news letter couldn’t be completed on
time and hence this delay. I have two important tasks to share with you for the present
Aerocity Ground vibration and Aircraft induced Noise analysis
Indira Gandhi International Airport (IGI) at New Delhi is one of the leading airports of the world both in terms of
overall traffic handling and passenger satisfaction. The integrated development of Multiplexes, Hotels and
Convention centres around the IGI has made the Airport area a complete business district catering to a host of
local and international companies to work on.
One of the leading real estate and land development companies who are engaged in creating a large business
facility in the AeroCity area approached NV Dynamics to assess the effects of ground borne vibrations (mostly
due to Metro Rail Operations) and to quantify the Airborne noise induced by Flight operations; both of the
parameters were essentially required to work on the design considerations of the foundation & structure, isolation
requirements, facade and elevation design and to comply with governing standards of human comfort and
occupational safety.
Extensive test preparations were made for getting the site readiness for conducting the tests. Working closely
with international consultants for Acoustics and Vibration, qualified test procedures were devised and configured
at site for a 20 Hour continuous monitoring / recording and assessment of Noise and Vibration parameters. A
series of output data were derived validated and shared with the customer’s consultants for further usage.
Vibratory screens, investigating effects of higher vibrations on the support structure.
A large Aluminium processing company in Eastern India has boiler house facilities for production of electrical
power; coal is the primary fuel and this passes through various stages of sieving and re-sizing before being used
in furnace.
One of the stages of coal feed is through the vibratory screens; by design, the screens work on eccentric
mass/force principle thus generating significant magnitudes of vibration and helping the coal chunks to move to
next stages. However, due to this highly dynamic state of operation, large forces are generated (mostly of 1st
order and their harmonics), thus creating higher vibrations on the connected structure and support foundation.
NV Dynamics conducted a series of tests and data analysis to closely understand the induced magnitudes of
vibration and their consequential effect on the support floor and structures. A number of valuable observations
and recommendations are made upon data inference; these are now being considered for execution by the
customer.
Warm Regards
Krishna Balamurali
[email protected]
NVsage – Noise & Vibration Newsletter July 2016
©NV Dynamics 2016 | all rights reserved
DISCUSSION BOARD
Part -4 Acoustics - Sound, Tones, Octaves and Diatonic
SOUND AND TONE
Sound is mechanical vibration that oscillates at a frequency within the range of the (human) ear. The vibration
that propagates through air (or any other medium) creates pressure variations that are interpreted as sounds by
the ear when the oscillations make the auditory membrane of the ear move. If the pressure variations are highly
erratic, the resulting sound is noise. Recurrent, regular pressure variations, however, produce distinct tones with
an observable musical pitch.
Sound propagates through air in the form of longitudinal sound waves with a speed of approximately 340 metres
per second. The exact speed depends on factors such as temperature. As sound waves propagate through a
medium, they create compressions and rarefactions. The volume of the sound depends on the pressure
difference between these compressions and rarefactions.
The top wave in the figure below has only one compression [f]. It represents a single vibration occurring within a
certain period of time. If two or more vibrations occur within the same period of time, they can be illustrated with
the waveforms below the top one [f, 2f, 4f and 8f].
If the time period is a only couple of seconds, the
individual vibrations can be heard as (for example)
regularly repeating whooshing sounds.
When the number of pressure variations within a given
period of time exceeds a certain limit (approximately 16–
20 variations per second), distinguishing them as
individual sounds becomes difficult, and they gradually
start to become audible as a pitch. If the frequency
increases, the pitch of the sound rises
When the frequency exceeds approximately 10 000 oscillations per second, the human ear can no longer detect
it. The sound can still be sensed as a “whining”, but making it audible requires a sound pressure that will
invariably be experienced as unpleasant by the listener.
HE ARING R AN GE, THE C ONCEPT OF THE OCT AVE AND DI ATONICS

The limits of human hearing depend on both frequency and intensity of the sound. The sensitivity of the
human ear peaks within the range of approximately 2000 to 4000 oscillations per second (2000–4000 Hz).
NVsage – Noise & Vibration Newsletter July 2016
©NV Dynamics 2016 | all rights reserved
DISCUSSION BOARD
Humans can detect frequencies up to 270,000 Hz, if the signal is strong enough, but what is commonly
referred to as the hearing range is (roughly) between 20 and 20,000 Hz.

A certain range may also be examined separately. The range between 110 and 220 Hz forms an octave.
The two tones at both ends of the range are recognised as the same regardless of the culture of the
listener. The numerical values of the frequencies have a simple numerical ratio: the frequency of the
higher sound is twice the frequency of the lower sound. The mathematical ratio and the perception of
sameness are clearly related. The relation between the tones cannot, however, be explained only in terms
of mathematics, because human beings tend to perceive two frequencies with a numerical ratio of 2:1 as
being just slightly too close to each other, whereas the tones with a ratio of approximately 2.02:1 are
perceived as forming a pure octave.

In Western cultures, the octave (which refers not only to the distance between the two tones at the either
end but also to the range of tones between them) has been divided diatonically since antiquity. Each
octave has seven tone positions that are not distributed evenly, but form two different types of intervals
instead: whole tones (or whole steps) and semitones (or half steps). The size of the whole tone (from F to
G, for example) equals the size of two semitones (such as from B to C).

In a medieval letter-based musical notation used since approximately the 10th century onward, the same
letters were first used to denote tones one octave apart from each other. The names we now give to tones
also originate from this period. In this letter-based notation, the same letters (usually the first letters of the
alphabet) appeared first as single capital letters, were then repeated as single small letters and then (for
example) as two small letters. A, a and aa would therefore all be one octave apart from each other.

On the diatonic scale, each octave contains 5 whole tones and 2 semitones. The principles of musical
notation, as well as many musical instruments such as the piano, are based on the diatonic scale. The
major and minor scales as well as all church modes are diatonic, or, in other words, can be understood as
parts of the diatonic scale.

We are so used to the diatonic scale that we cannot hear any difference between whole tones and
semitones when, for example, going up the major scale in a singing exercise. Deviating from the diatonic
scale (such as being able to sing several successive whole steps) requires musical experience or training.

How the tone positions are defined in relation to their frequencies is not manifest in musical notation or the
names we give to the tones. The tone positions, nevertheless, are best understood as narrow ranges
instead of exact points within each octave. The size of the whole tones, semitones and the intervals
created by adding them together may differ, though within certain limits. The notions of “pure” and “out of
tune” are, therefore, highly relative. An octave can be divided into 12 semitones. If the distance between
each semitone is equal, the tuning system is called equally tempered.
Let’s learn about Hertz, Cent and Decibel in the coming issues...
NVsage – Noise & Vibration Newsletter July 2016
©NV Dynamics 2016 | all rights reserved
FACT FILE
Animals using vibration for navigation and communication
Living underground, moles experience a world very different from our own. The dark, subterranean
environment lacks the usual cues for direction, distance, or time, forcing moles to use other methods to perceive
their habitat. Using senses like smell and touch, they can understand their immediate environment. But to
understand a wider zone and to communicate with other animals hidden behind layers of earth, moles use
vibrations. Species like the blind mole rat (genus Spalax) use a type of head drumming to send and receive
information about their subterranean world.
For example, they drum their heads against the tunnel
walls to send messages to other mole rats in separate
tunnels and they sense vibrations rebounded off of
hidden obstacles as they dig. But subterranean
animals are not the only one to communicate using
vibrations; in fact, vibrational, or seismic,
communication is an ancient and widespread
phenomenon.
Examples of blind mole-rats using head drumming
to communicate and navigate “vibrationally”
To communicate “vibrationally”, animals act on a substrate, or medium, to send signal waves. Much like we
communicate with sound by causing air molecules to vibrate back and forth in longitudinal waves, vibrational
communication involves sending waveforms of energy through things like soils, plants, or webs. (To learn more
about waves, see our Waves and Wave Motion module). To generate these waves, animals can use a variety of
methods: drumming or pounding on the substrate, stridulation (rubbing together parts of the body), and
tremulation (vibrating the entire body on a substrate).
The first Computer based Real Time Fast Fourier Transformation device
was available in the market in the year 1956, A single Channel (ONE
INPUT) device measured about 10ft x 8ft and took 15 minutes to startup….
NVsage – Noise & Vibration Newsletter July 2016
©NV Dynamics 2016 | all rights reserved
All inputs to this publication are duly acknowledged