Sound management by lt ns wickramasinghe b sc e & e

SOUND MANAGEMENT

26 February 2014

nswickramasinghe@gmail.com/nswickramasinghe@yahoo.com

1

what your ears capture

Sound is a vibration
in
an
elastic
medium such as air,
water,
building
materials and earth.

- Wave Length
- Amplitude
Rarefaction

26 February 2014

Compression

Sound
is
the
physical phenomenon
that encourages the
sense of hearing. It is
generated by vibrated
bodies in the form of
waves rarefaction of
compression
and
rarefaction in the air.


2



Interference
there can be two kinds of interference patterns;



Constructive- Two waveforms are added together and creates a louder sound



Destructive - Occurs when two waves are out of phase and creates a diminished waveform

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3



Standing Waves
A standing wave is the result of the wave reflecting off the end of the tube
(whether closed or open) and interfering with itself and sound is produced in an instrument
by blowing it, only the waves that will fit in the tube resonate, while other frequencies are
lost.
The longest wave that can fit in the tube is the fundamental, other waves
that fit are overtones

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4



Overtones
Overtones are the other frequencies besides the fundamental that exist in
musical instruments. Instruments of different shapes and actions produce different
overtones

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5

Sound has two main characteristics;


Frequency – measured in Hz (Hertz)



Pressure level – measured in dB (decibels)

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6

Quality of sound depend on following;
Pitch-

Pitch is roughly equivalent to the frequency of a sound wave.
Frequencies are measured in vibrations per second, or Hertz
(Hz).Higher
pitches vibrate more quickly, whereas low pitches
vibrate more slowly

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7

Amplitude- determines the intensity, or loudness the size of the vibration

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8

In engineering the argument of the logarithm is
always a ratio of two quantities having the same
dimensions. In mathematics the argument of a
logarithm function is simply a number. No
dimensions involved.
Example

102 = 100

log10(100) = 2

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9

Gain

1

0 dB

2

3 dB

3

4 dB

4

6 dB

5

7 dB

200

23 dB

6

7 . 7 dB

100

20 dB

7

8.4 dB

80

19 dB

8

9 dB

40

16 dB

9

9 dB

20

13 dB

10
26 February 2014

Level
10 log (x)

10 dB

16

12 dB


10

logb(mn) = logb(m) + logb(n)
logb(m/n) = logb(m) – logb(n)
logb(mn) = n · logb(m)
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11

dB can be used to express the absolute level of the physical quantity. The
decibel is also commonly used as a measure of gain or attenuation, the
ratio of input and output powers of a system, or of individual factors that
contribute to such ratios.
Examples;
Voltage

Acoustics

Audio
electronics

Antenna
measurements

dBV(Rms)

dB SPL

dB(mW)

dBi

dBmV(Rms)

dB SIL

dBTP

dBd

dBμV

dB SWL

dBq

dB HL
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12

The power P(dBm) in dBm is equal to 10 times the base 10 logarithm of the power
P(mW) in mill watts (mW) divided by 1 mill watt (mW):
P(dBm) = 10 · log10( P(W) / 1mW)

dBmV (decibels relative to one mill volt) is a measure of the signal strength in
wires and cables at RF and AF frequencies. This unit is defined in terms of rootmean-square ( rms ) alternating current ( AC ) signal voltages in circuits in which
the impedance is a pure resistance of some specified value.
P(dBmV) = 20 · log10( P(V) / 1mV)

26 February 2014


13

The power P(dBm) in dBm is equal to 10 times the base 10 logarithm of the power
P(mW) in mill watts (mW) divided by 1 mill watt (mW):
P(dBm) = 10 · log10( P(W) / 1mW)

dBmV (decibels relative to one mill volt) is a measure of the signal strength in
wires and cables at RF and AF frequencies. This unit is defined in terms of rootmean-square ( rms ) alternating current ( AC ) signal voltages in circuits in which
the impedance is a pure resistance of some specified value.
P(dBmV) = 20 · log10( P(V) / 1mV)

26 February 2014


14

dBm + dB = dBm

dBm – dB = dBm

dBm – dBm = dB
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15

3 dBm
1 dBm

+

0 dBm

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16

What will happened when this knobs are rotate
0
-3

0 dBm
3

-3 dBm

6

-6

-9

26 February 2014

9

-6 dBm

-9 dBm


3 dBm

6 dBm

9 dBm

17

Take two short audio samples and play them, Human
listeners can detect the difference between two sound
sources that are placed as little as three degrees apart, about
the width of a person at 10 meters. Or play them
30microseconds apart

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18

Convex Surface

Concave Surface

Corners

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19

Smooth Surface
θ1

Absorption Surface

P1

P2
P1
P1 = P2 = P3

θ2

θ1

θ2
θ3

P3

P3

P2
θ3 θ4

θ4
P1 > P2 > P3

θ1 = θ2 = θ3 = θ4

θ1 = θ2 = θ3 = θ4

Diffusion Surface

P5
P2
P1
26 February 2014

P3

P4

P1 = P2 = P3 = P4 = P5


20

The purpose of acoustic treatment is to improve the quality
of sound in a room/studio.
Diffusers
Traps
Absorbers

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21

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22



Two long sides and two
short sides from planks of
planed (using 15mm thick,
125mm wide, 2.4m)



then glued and screwed the
corners.



Rockwool and foam fit
inside the frame.



To secure the 30 mm
Rockwool slab, then fitted
20mm wooden batten
around the inside of the
frame, set back from the
front edge by 35mm

It would sit 5mm behind
the front of the frame. This
meant that when the
23
Auralex foam was glued.


26 February 2014

Main Isolation Window
2” Regiform Gap

Isolation Wall
Shell Wall

Cable Duct
Dry Wall
2”x2” wooden poles

26 February 2014


24

Main Window Arrangement

Wooden poles

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25

Dynamic Microphone - A paper cylinder, onto which fine copper wire is
wound, is connected to a membrane which moves under the force of sound
pressure created by the sound source. This coil is in a narrow gap with a high
magnetic field created by a permanent magnet. When the coil moves in this
magnetic field, it produces a voltage identical to the sound causing the
movement.

26 February 2014


26

Crystal Microphone - The crystal microphone uses a thin strip of
piezoelectric material attached to a diaphragm. The two sides of the
crystal acquire opposite charges when the crystal is deflected by the
diaphragm. The charges are proportional to the amount of deformation
and disappear when the stress on the crystal disappears.

26 February 2014


27

Ribbon Microphones The air
movement associated with the sound
moves the metallic ribbon in the
magnetic field, generating an imaging
voltage between the ends of the ribbon
which is proportional to the velocity of
the ribbon - characterized as a "velocity"
microphone.
Condenser Microphones- Sound pressure
changes the spacing between a thin
metallic membrane and the stationary
back plate. The plates are charged to a
total charge
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28

Work through each of these characteristics and determine your needs



Frequency Response



Impedance



Handling Noise



Transient Time


26 February 2014

Directionality

Sensitivity


29

Omni directional

Cardioid

Captures sound equally from all
directions.

Cardioid means "heart-shaped", which is
the type of pick-up pattern these mics use.
Sound is picked up mostly from the front,
but to a lesser extent the sides as well.

Uses
Capturing ambient noise; Situations
where sound is coming from many
directions; Situations where the mic
position must remain fixed while the
sound source is moving.

26 February 2014

Uses
Emphasising sound from the direction the
mic is pointed whilst leaving some latitude
for mic movement and ambient noise.


30

Hypercardioid
This is exaggerated version of the cardioid
pattern. It is very directional and eliminates
most sound from the sides and rear. Due to the
long thin design of hypercardioids, they are
often referred to as shotgun microphones.

Bidirectional
Uses a figure-of-eight pattern and picks
up sound equally from two opposite
directions.

Uses
As you can imagine, there aren't a lot of
situations which require this polar
Uses
pattern. One possibility would be an
Isolating the sound from a subject or direction
interview with two people facing each
when there is a lot of ambient noise; Picking up
other (with the microphone between
sound from a subject at a distance.
26 February 2014
31
them).

Frequency response refers to the way a microphone responds to different
frequencies. It is a characteristic of all microphones that some frequencies are
exaggerated and others are attenuated (reduced)

More importantly, it should be noted that a flat frequency response is not always the most
desirable option. In many cases a tailored frequency response is more useful. For example, a
response pattern designed to emphasise the frequencies in a human voice would be well
suited to picking up speech in an environment with lots of low-frequency background noise.
26 February 2014


32

All microphones have a specification referring to their impedance. This spec may be
written on the mic itself (perhaps alongside the directional pattern), or you may
need to consult the manual or manufacturer's website.
You will often find that mics with a hard-wired cable and 1/4" plug are high
impedance, and mics with separate balanced audio cable and XLR connector are
low impedance.


There are three general classifications for microphone impedance. Different
manufacturers use slightly different guidelines but the classifications are roughly:





Low Impedance (less than 600Ω)
Medium Impedance (600Ω - 10,000Ω)
High Impedance (greater than 10,000Ω)

Note that some microphones have the ability to select from different impedance
ratings.
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33

Remember that the diaphragm works by converting vibrations from
sound waves into an electrical signal. Unless the microphone has
some sort of protection system, the diapragm can't tell the
difference between a desirable sound wave vibration and any
other sort of vibration (such as a person tapping the microphone
casing). Any sort of vibration at all will become part of the
generated audio signal.
If your mic is likely to be subjected to any sort of handling noise or
vibration, you will need a mic which will help prevent this noise
from being picked up. High quality hand-held mics usually attempt
to isolate the diaphragm from vibrations using foam padding,
suspension, or some other method. Low quality mics tend to
transfer vibrations from the casing right into the diaphragm,
resulting in a terrible noise.

26 February 2014


34

One of the most important factors in a
microphone is it's ability to respond
to rapidly changing sound waves. This
is known as "transient response".
The acoustic sound wave physically
moves the diaphragm. The amount of
time it takes for this to happen
depends on the weight of the
diaphragm material. Of course, the
response time is longer for the
heavier diaphragm material of the
dynamic to react over the
lightweight,
thinner
condenser
element.
26 February 2014

Transient time of Condenser Mic,
Ribbon Mic and Dynamic Mic


35

Sensitivity expresses the microphone's ability to convert
acoustic pressure to electric voltage. The sensitivity states what
voltage a microphone will produce at a certain sound pressure
level. A microphone with high sensitivity will give a high voltage
output and will therefore not need as much amplification (gain)
as a model with lower sensitivity. In applications with low sound
pressure levels, a microphone with a high sensitivity is required
in order to keep the amplification noise low.
According to the IEC 268-4 norm, the sensitivity is measured in
mV per Pascal at 1 kHz (measuring microphones at 250 Hz).

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36

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37

XLR Balance Connector

TRS Balance Connector

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38

RCA
(Radio Corporation of America)
connector, sometimes called a phono
connector or cinch connector, is a type of
electrical connector commonly used to carry
audio and video signals.

TS Unbalance Connector

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39

XLR Balance Cable

26 February 2014

This means that much of the electromagnetic
interference will induce an equal noise voltage in
each wire. Since the amplifier at the far end
measures the difference in voltage between the
two signal lines, noise that is identical on both wires
is rejected. The wires are also twisted together, to
reduce
interference
from
electromagnetic
induction.


40

26 February 2014


41

1/4″ on the other hand comes in two styles:
balanced TRS (tip, ring, sleeve) and unbalanced
TS (tip, sleeve).

To be continued with Public Address Systems

26 February 2014


42

nswickramasinghe@gmail.com
Electrical and Electronic Engineer

26 February 2014


43

Sound management by lt ns wickramasinghe b sc e & e

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