SOUND FUNDAMENTALS Prepared by:SHUBHAM UMAKANT GUPTA En no

PHYSICS OF SOUND Sound is a longitudinal wave motion consisting of train of compression and rarefaction travelling in a medium. Being wave motion, sound has all the characteristics of waves. i.e. Amplitude, frequency, velocity, wavelength, and phase.

AMPLITUDE Intensity of Compression and Rarefaction

FREQUENCY(f):  No. of successive compression and rarefaction in 1 sec.  It expressed in Hertz(Hz).  Frequency range of audible sound:16Hz-20KHz TIME PERIOD(T):  Time taken in completing one cycle is called …. T=1/f second VELOCITY(v):  Distance travels in one second  Sound moves in air with v=344 m/s at 20 0 C. v=332 m/s at 0 0 C. Relation between velocity and Temperature is given by…. V2=V1(T2/T1) 1/ (1) V1=velocity at T1 K 0 V2=velocity at T2 K 0 (0 0 C = 273 K)

WAVELENGH

SOUND & EAR  EAR is the organ of human that detect the sound and convert sound pressure variation into electrical signal which are fed to brain through the auditory nerves.  The EAR performs the major function of receiving the sound and send them to brain.  Audible frequency = 16Hz - 20KHz  Freq. range of human voice = 2KHz-5KHz  The ear response to the sound is logarithmic.

Different part of human ear

Hearing sound  The eardrum vibrates in response to sound waves in the ear canal.  The three delicate bones of the inner ear transmit the vibration of the eardrum to the side of the cochlea.  The fluid in the spiral of the cochlea vibrates and creates sensations into the brain.

 The nerves near the beginning see a relatively large channel and respond to longer wavelength, low frequency sound.  The nerves at the small end of the channel respond to shorter wavelength, higher-frequency sound.

Pressure of Sound Waves A sound wave is a wave of alternating high-pressure and low-pressure regions of air.

 Amplitude of sound waves is represented in unit of pressure.  Greater intensity of sound have greater compression and rarefaction.  unit of pressure are… Newton/meter 2 Pascal (Pa) Microbar 1 Newton/meter 2 = 1Pa = 10 microbar -(2)

Intensity of Sound It is defined as the amount of sound energy flows per unit area in unit time at right angle to the direction of motion.  Represented in watt/m 2 I=Q/At Wb/m 2 Intensity of sound ∞ Amplitude 2 I L =sound intensity level(db) I 0 = Ref.sound intensity= It is generally indicated in db(decibel) 1db = 10 log(P 1 /P 2 ) = 20 log(V 1 /V 2 ) - THRESOLD OF HEARING : 20*10 -6 Pa (audible sound) - THRESOLD OF PAIN/feeling : 63 Pa

LEVEL AND LOUDNESS  In order to express the wide range of sound pressure,a logarithmic metric has been universally adopted.  This metric is the decibel.  Sound pressure level (SPL) or sound level is a logarithmic measure of the effective pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level. SPL = 20 log 10 (P 0 /P ref ) db (3) The commonly used reference sound pressure in air is p ref = 20 µPa (rms),  which is usually considered the threshold of human hearing  Sound pressure inversely proportional to distance is called 1/r law or distance law.

Loudness(L):  Degree of sensation produced by the ear. (measured in dB)  Loudness depends upon the intensity of sound and sensitiveness of ear. Phon and Sone are the units of loudness. Phon:  The “Phon” is defined as equal loudness of intensity of sound in db over threshold of hearing as perceived by the ear at 1 kHz pure sound.  OR 1 phon equal to 1db SPL at 1KHz.  The frequency response of the ear is not at all uniform and it also changes with SPL.  The subjective response to level is called loudness and is measured in phons. Sone: equal loudness level of of 40 Phon. Sone is used to determine the increase in loudness. Timbre: Quality of sound is called… Pitch :  it is the characteristics of sound mainly related to frequency.  It is determine by frequency alone  When sound consist pure tone without harmonics then is called “pitch”.  Standard pitch is a sound of 440 Hz.

LOUDNESS VS SOUND INTENSITY Sr.NoLOUDNESSINTENSITY 1Degree of Sensation produced by ear Quantity of sound energy 2It is varies from listener to listener Independent to listener 3Physiological quantity Physical quantity 4Unit phon and shone Unit W/m 2

Common Sounds and their Loudness

Examples 1. Intensity increase by 20 times then what change in db? ANSANS 2. Amplitude double then what change in intensity in db. ANSANS

Frequency Response and Linearity

Linearity and Non Linearity

Audio Level Metering  The simplest (and least expensive) level meter is essentially an AC voltmeter with a logarithmic response.  As the ear is logarithmic, the deflection of the meter is roughly proportional to the perceived volume, hence the term volume unit (VU) meter.

A VU meter is often included in audio equipment to display a signal level in Volume Units;audio signal level the device is sometimes also called volume indicator (VI). it measure the RMS voltage level of electrical signal The typical VU scale is from −20 to +3. ADVANTAGES  Simplest meter design  Cheap  No more component required, it's only sound indicating meter

Root Mean Square Measurements

RMS value for sine and square wave

Reflection and Refraction

Reflection Reflection – some or all of a wave bounces back into the first medium when hitting a boundary of a second medium When all the wave energy is reflected back instead of being transmitted, it is total reflection If some energy is transmitted and some is reflected, the wave is partially reflected

The Law of Reflection Incident rays and reflected rays make equal angles with a line perpendicular to the surface. Angle of Incidence – angle made by the incident ray and the normal (i) Angle of Reflection – angle made by the reflected ray and the normal (r) Law of Reflection – the angle of incidence and the angle of reflection are equal

Diffuse Reflection Diffuse Reflection – light incident on a rough surface is reflected in many directions A surface’s roughness is dependent upon the wavelength of the wave incident upon that surface;

Reflection of Sound An echo is reflected sound Sound reflects from all surfaces of a room Acoustics is the study of the way sound reflects off of objects in a room Reverberations – Multiple reflections of sound within a room.

Reflection of Sound

Refraction Refraction – the change in direction of a wave as it crosses the boundary between two media in which the wave travels at different speeds.

Refraction

Refraction of Sound Sound waves are refracted when parts of a wave front travel at different speeds This happens in uneven winds or temperatures Sound waves tend to bend away from warm ground, since it travels faster in warmer air On a cold night, the speed of sound is slower near the ground than above, so we can hear over larger distances

Refraction of Sound

Absorption of sound Sound absorption is defined, as the incident sound that strikes a material that is not reflected back When a sound wave strikes an acoustical material the sound wave causes the fibers or particle makeup of the absorbing material to vibrate. This vibration causes tiny amounts of heat due to the friction and thus sound absorption is accomplished by way of energy to heat conversion. The more fibrous a material is the better the absorption; The sound absorbing characteristics of acoustical materials vary significantly with frequency. In general low frequency sounds are very difficult to absorb because of their long wavelength. ex,- wood,