Vibrating Molecules That Moves Energy From

8/14/2019 Vibrating Molecules That Moves Energy From

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Read through Making the Connection and take notes (in your blog) on the basic principles of sound,sound terms, basic sound equipment, and acoustical rules of speaker placement and sound behavior.

Basic principles of sound its a wave of vibrating molecules that moves energy from the collisions sound is our perception of the vibration of molecules in the air which pass on energy

sound waves can only travel through matter anything sound moves through have elasticity and inertia elasticity means that the molecules can be compressed inertia means the tendency of matter to remain stationary if already stationary, and if

moving, to keep moving toward a place of rest. Movement

Moves forward with a compression and then back with a rarefaction. This process from beginning to end is called one cycle of a sound wave.

Cycles per second, or how often this cycle moves through the air, is called frequency and isexpressed in hertz abbreviated as Hz the higher the frequency, the higher the pitch

Periods are expressed in seconds per cycle period = 1/freq.

Wavelength is the actualy physical distance covered by one complete cycle of a given soundas it passes through the air. It is based on the speed of sound wavelength = speed of sound / frequency sound waves travel through the air at approximately 1130 feet/second at sea level @ 59

degrees F Amplitude the height and depth of a sound wave (how much air is actually moved)

sounds of higher amplitude are louder, compressing and rarefying the air molecules to agreater extent than do lower amplitude, softer, sounds

Adding Sine Waves Phase

refers to the relative position of one sound wave to another and is expressed in degrees two waves which are started at the same time having the same amplitude and frequency

will produce a new wave with the same frequency but twice the amplitude...these twowaves are said to be in phase

if two waves start moving in opposite directions (one positive, one negative), the waveswill be 180 degrees or out of phase which results in them canceling each other out see examples on page 18

Harmonics waves that have frequencies that are related by whole numbers are called harmonics the sine wave frequency that can be heard as the note is the fundamental and it is usually

the loudest (highest amplitude) of the set of sine waves that make up the sound's waveform above fundamental are the other sine waves whose frequencies are multiples of the

fundamental or more harmonics. if the fundamental =500 Hz then the harmonics will occur at 1000, 1500, 2000

Hz..etc Non Harmonics

when sounds are not multiples of the fundamental Humans' range of hearing is from 20 20,000 Hz

humans speak roughly 100 Hz 6 kHz


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The Electrical Representation of Sound An audio signal is an electrical representation of a sound, in the form of a fluctuating

current. Within the limits of the audio equipment, the signal voltage, or current, fluctuates at exactly

the same rate as the acoustical energy that it represents, and the amplitude of the audiosignal- the signal level is proportionate to the amplitude of the original sound wave.

Properties of Electricity voltage, current, resistance, and power Voltage

is electrical pressure it is the force which causes current to flow through an electronic circuit measured in volts

Current when electrons jump from one atom to another insulators have their electrons way more tightly bound so they don't pass current too

easy rated in amps Direct Current

electrons flow in one resolute direction from negative to positive batteries have direct current

Alternating Current AC switches back and forth from positive to negative several times a second if AC flows in one direction it creates a voltage peak with alternates with a voltage

drop this up and down behavior of AC resembles the up and down nature of the

alternating compression and rarefaction in a sound wave Power

voltage and current together, voltage multiplied by current, create power, measured inwatts so the watt is a measurement of work done or the amount of energy expended

Resistance/Impedance resistance allows us to use electrical current offensive line in football is like the resistance as the frequency of an audio signal changes, the reactance and hence the impedance

changes with it both measured in ohms

Ohms Law the amount of current in Amps (I), is equal to the electrical potential in Volts (E),

divided by the resistance in ohms (R I = E / R

R = E/I E=I*R These can be re-wrtieen using impedance

I = E/Z Z=E/I E=I*Z Impedance differs from resistance, in that it takes into account a frequency based factor

known as reactance the value of a specific impedance, and consequently the flow of current, will change

as the frequency of the signal changes More equations...

I = E/Z P=E^2/Z Z=R + Cr (capacitive reactance) + Ir (inductive reactance) Power Calculations


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Power in watts = E (electrical potential in volts) * I (current in amps) E= I*Z P = I 2 * Z or R see table on page 28 if I need more variations of these equations

Decibels used in audio calculation to describe both the electrical and acoustical values a dB is 1/10 th of a el, and a Bel is the logarithm of a power ratio

to express the relationship of two power values, P1 to P2 in Bels: Bel =log(P1/P2) Since a decibel is 1/10 of a bel it can be mathematically expressed as:

dB = 10log(P1/P2) 5^2 = 25

base = 5 log = 2 antilog = 25

here is a 1/3 octave graphic equalizer that uses logs

dBm is a measurement of electrical power. It is referenced to 1 milliwat (o dBm= 1 milliwatt)

dBu is a voltage measurement. .775 volts is the zero reference for dBu dBV and dBv

dBV = 1 volt rms dBv = .775 v olts

dBW = 1 watt 0 dBW = 1 watt, 10 dBW = 10 watt, 20 dBW = 100 watt


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Mic Level includes microphones, record cartridges, and tape heads no signal to -20 dBu

Line Level -20 dBu to +30 dBu (24.5 volts). It includes outputs, preamp outputs, mixing board

outputs, and amplifier inputs Speaker Level

all levels above +30 dBu, mostly the speaker outputs of power amplifiers How these levels work together...


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Perception of Sound Measurement of Sound Sound Pressure

A source which vibrates the air is transferring energy to the air which is then radiated inthe form of sound waves. In other words a sound source radiates acoustical energy.

the measurement for power is the acoustical watt and there is a huge difference in

loudness from the lowest acoustical watt we can hear to the highest Relative vs. Absolute Levels there are many factors affecting how loud a sound is and it's hard to measure for example doubling power at a sound source doesn't double the sound it actually

creates a barely perceptible shift in the sound pressure level (approx 3 dB) because of all the factors, our common measurement of loudness is SPL, and it measures

the difference between two values, rather than measuring the values themselves it is a ratio value and is expressed by the decibel

Sound Pressure Level (SPL) dB SPL

SPL is treated as the same way as voltage calculations in Ohm's Law dB SPL = 20log(P1/P2)

the doubling of 10log to 20log in the calculation reflects the resistancecomponent in dB SPL

3 dB an increase of 3 dB represents the smallest perceptible change most ppl can hear in order to get this change you need to double your power

6 dB an increase or decrease of 6 dB SPL reflects a 2 to 1 ratio in SPL, yet it

represents only the first noticeable change in the perception of sound 10 dB

if you increase 10 dB most people perceive this as doubling loudness but to do this....you need to increase power 10 times

So if I have a 100 watt amp with an SPL of 95 dB, I would need a 1000 wattamp to double my loudness

dB PWL db PWL is the value referenced to 1 watt of acoustic power and follows the same 10

log conversion scale as dBW The Three amigos

Volume power level, loudness, or sound intensity

Level the ratio of a quantity's magnitude to an arbitrarily selected magnitude for examples SPL is expressed in dB relative to .0002 dynes/sq. cm

Gain gain is the increase in power or voltage of an audio signal the opposite of gain or a decrease in signal level is called attenuation

Loudness Most people use this to refer to volume or SPL but it is actually much more complicated Fletcher Munson

developed a set of equal loudness contours based on the perception of sound @ 1kHz, and a system of evaluation known as phons

the curve these men developed flattens out @ higher sound pressure levels


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A, B, C weighted scales we use different scales on our sound level meters to accomplish reading sound

the way we actually hear sound A weighted scale reflect the ears sensitivity at low listening levels

the meter measures SPL levels along the 40 phon curve and reflects the

lower frequencies that the ear experiences at this sound pressure level B and C weighted these scales reflect the flattening of the FM curves @higher sound pressure levels we use these for higher SPL events such as rock concerts

Dynamic Range and Headroom-range is the difference refers to both the software and the hardware.

Acoustic Dynamic Range-noise floor-peaks=total dB

Electrical Dynamic Range-peak level-noise floor=dynamic range

Headroom-difference between the nominal and the peak levels in the headrom

The speed of sound.. and light-1130 fps


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Sound outdoors-weather affects the speed of sound

temperature-temperature affects the speed of sound

Humidity-affect the speed of sound

wind speed-make it appear to come from somewhere else

Wind changes-can bend the sound, oh yea

The inverse square law-double the distance and the dB decreases by 6 and the area covered quadruples-power needed also quadruples to compensate

Sound indoors-inside is much harder that the outside

Boundaries-walls bounce things

The absorption coefficient-rating between one and zero for how much the material absorbs

Reflection Reverberation-the intensity of the reflected sound is equal all over the room

Critical distance-maximize this distance to enhance the direct sound and not the reverberated sound

Standing waves-Interacting waves

The ear -hears sound

Outer ear -catches the sound

Middle-transducer

Inner -cochlea


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Basic types of equipment-transducers

-input tranducers-ait pressure and velocity mics-contact pickups-magnetic pickups

-phono pickups-laser pickups-optical pickups

output transducers

signal processors

Mixers, mixing board, and consoles

Power amplifiers

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Vibrating Molecules That Moves Energy From