SLPA 456 Exam 3

Electricity

Energy produced when charged particles (electrons) flow directionally from atom to atom

Example of electricity occurring naturally

Lightning

Name the 4 Measures/units of electricity

Voltage (volts)

Current (ampere)

resistance (ohms)

power (watts)

Voltage:

Drive for electrons to move or flow - based on a difference in electrical charge between two points

Electromotive force (EMF)

basis of voltage - difference in electric potential causes tendency to move towards equilibrium

What does the # of volts represent?

diference in electric potential between two points

Electric Current

rate at which electrons are flowing in a particular direction

Amperage:

the # of electrons moving past a fixed point in 1 second

Electric Power

the rate at which energy is being supplied or consumed over a period of time

Power equation

W = V\*I

Power = voltage \* current

What is power proportional to?

Voltage squared

What are electric adapters charging boxes) used for?

converting power from one level to another → an adapter with output at the wrong level can ruin the device

Resistance:

tendency of a material to resist the flow (current) of a charge

Purpose of resistance

allow electrical energy to be converted into other forms

* eg. the wires that glow in light bulbs and produce heat in ovens

Ohm’s Law equation:

V = I\*R

Voltage = Current \* Resistance

Direct Current (DC)

unidirectional and steady flow from high potential difference to lower potential difference

Direct current flower in ______ direction(s)

ONE

Use of DC:

Supply power to electrical devices and also to charge batteries

What uses DC power

everything that runs on a battery and uses an adapter while plugging into a wall or uses a USB cable

Alternating Current:

flower of electrons keeps switching directions periodically - forward and backward

What uses AC power:

controlled by power plants that carry flow through power lines to home/school/offices

Circuit:

A closed path capable of being followed by an electrical current

A current starts and stops at _____ place.

the same

Short Circuit:

direct connection between the positive and negative sides of your power supply (unhelpful and dangerous)

Open Circuit:

the loop isn’t fully connected (power switch off, loose wire, broken connection)

Serial Circuit / connections

all circuit components are connected end-to-end along a single path

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In a serial circuit, current is the ____ throughout the entire circuit.

SAME

Example and disadvantage of serial circuits:

Christmas lights - if one element stops work, everything downstream stops working

Parallel circuit/connections:

multiple routes for current to flow with sets of electrically common points

in a parallel circuit, current ___ __and__ ____ off at electrically common points.

varies; splits

Total current within a parallel circuit:

the sum of currents across each parallel connection

Components of Circuits

Transducers and Transformers

Types of Transducers:

Resistors, Capacitors, Inductors

Transducers:

a circuit component that converts electrical energy into non-electrical energy

Dynamic Range (characteristic of transducers)

Smallest to largest amplitude signal it can effectively translate

Noise (characteristic of transducers)

amount of random disruption to circuit flow as a result of transduction (loss of energy)

Repeatability (characteristic of transducers)

the consistency with which it can produce an identical output from the same input

Resistors: (type of transducer)

components that offer a specified “resistance” to reduce current within a circuit

Fixed type of resistors provide a ___ amount of resistance

constnat

examples of fixed type resistors:

cell phone charger, toaster, lightbulb

Variable resistors provide an ______ amount of resistance

adjustable

Examples of variable type resistors

dimmer switch, volume dial, electronic high/low pass filters, thermostat, streetlights

Capacitors: (type of transducer)

components that, when electrons flow through them, store energy in an electric field

* provide small boosts of power to a circuit by releasing stored energy at specific moments

Examples of capacitors:

fuel sensor in car, touchscreens (and virtually any other electronic circuit), condensor microphones

Inductors: (type of transducer)

components that, when electrons flow through them, store energy in a magnetic field

* include a coil which increases the electromotive force (voltage) within the inductor

Examples of inductors:

radio tuning circuits to find your favorite station, transmission-disabling devices (blocking cell phones at a concert), some types of microphones, modern cochlea implant

Transformers:

components that transfers electrical energy from one circuit to another

main use of transformers

shift AC voltage levels up or down (to ensure that voltage level is safe for the particular circuit/device/application)

Analog Signals:

can have any possible amplitude value depending on the desired specificity of the measure (continuous)

Digital Signal:

amplitude data is captured only at predetermined times and include only a fixed set of values (discrete)

Steps of analog → digital conversion (A/D)

1. Incoming waveform is sampled at specified times
2. Amplitude of each sample is saved as the closest available value
3. The # of different value steps is determined by the “bits” available

Steps of digital → analog conversion (D/A)

1. performed at the frequency of the original sampling rate
2. stored digital values are converted into voltage levels
3. the voltage is converted by a transducer into analog output

\*\* algorithm brings it back!

Sound Booths

create an ideal circumstance to record sounds as close to their original frequency/amplitude relationship as possible

examples of less-than-ideal recording environments

classrooms, bedside, in-home visit

Environmental Considerations of Recording environment

background noise, acoustics of recording space,

Environmental noise (ambient noise, background noise)

any noise that can contaminate the quality of the recording

Common sources of environmental noise:

electrical noise from the lights, room cooling/heating systems, wind, emergency sirens, traffic sounds, conversations in adjacent spaces, and side convos

Transmission:

amount of the original energy that is present after sound has passed from one propagation medium through some interface to a second medium (ie across walls in adjacent rooms)

Recommended environmental specifications for quality recordings:

Ambient noise level: at least 10 dB

Signal to noise ratio =/> 30 dB (>42 dB is ideal)

Signal to noise ratio: (SNR)

common measure of amplitude of targeted signals as compared to surrounding noise

How to calculate SNR:

Take signal amplitude - background noise = SNR

How to measure environmental background noise:

Sound level meters can be used to measure the intensity of any sound

Components of a SML:

Microphone, digital signal processer (DSP), display

SLM reads and measures the sound intensity in terms of _________ scales

weighted

Types of audio weighted scales:

dB(A), dB(B), dB(C), (dB(Z)

dB(A) weighted scale (sound level):

matches the hearing sensitivity of human ear

* most clinical recording using A scale

dB(B) weighted scale (sound level)

limited utility

dB(C) weighted scale (sound level)

matches hearing sensitivity of human ear

* used for industrial noise recording and *high impulse noises*
* AuD. routinely screen for occupation related hearing loss in industries

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Noise dosimeter:

SLM that measures noise over longer durations used to monitor ambient noise in industries

dB(Z) weighted scale (sound level)

used for very high impulse sounds - aircraft taking off, bomb blast intensities, etc.

Reverberation:

the persistence of sound, even after the source has stopped vibrating

Possible sources of reverberation:

ceiling, floor, and other hard surfaces

disadvantages of reverberation:

significant consequences for functional communication

* reduces speech intelligibility
* persons with hearing loss may struggle to hear in reverberant settings
* adds another layer of noisiness to recordings

Free Field:

no points that sound bounces and reverberates off of

Near Field:

region close to a sound source

\*\* 1/4 the length of the longest wave-length of the source

\*\* drastic fluctuations in levels as much as 10 dBA for small changes in distance from the source

What is typically done in Near Fields (for a clinical purpose)

testing hearing aids - most relatable to typical conversations

Far Field:

sound field beyond the near field limits

\*\* sound Pressure level drops off at the theoretical rate of 6 dB for every doubling of distance from the source

\*\* called the inverse square law

Diffuse Field:

so many reflections contributing to the total sound field that sound levels measured virtually anywhere in the sound field are the same

\*\* usually indoor environments

Absorption Coefficient: (Sabine)

number between 0-1 that indicates the proportion of sound which is absorbed by the surface compared to the proportion which is reflected back to the room

* closer to 0 = extremely reflective
* closer to 1 = no reflections/extremely absorptive

desired coefficient for recording rooms

0\.6-0.8 (mostly absorptive, less reverberation)

Absorption:

sound equivalent of friction - sound energy being converted to heat

Sampling Rate

frequency of taking amplitude samples to convert into digital form

Nyquist theorem

explains that sampling rate should be 2X the number of the highest frequency involved in the analog sample

Quantization

how many “steps” are available to capture changes (amplitude bits)

3 types of microphones:

Dynamic Microphones

Condenser Microphones

Electret Microphones

Dynamic Microphones work on the principle of _______ __using__ ______

electromagnetic induction; magnets

3 parts of a dynamic mic:

Diaphragm, wire coil (ribbon), Permanent magnet

Working of the dynamic microphone:

sound vibration → move diaphragm → more electric coil → generates electricity in form of electromagnetic induction

\*\* pressure signals are converted to electrical signals

Dynamic Microphone Utility

Professional recordings, high quality signal recordings

Advantages of Dynamic Microphones:

Relatively high quality transduction

Minimal loss of signal

Disadvantages of Dynamic Microphones:

expensive

Bulky instrumentation

Condenser Microphones work on the principle of ______ __using__ ________.

Capacitance; capacitor plates

4 parts of a condensor mic:

diaphragm

capacitor plates

resistor

external power source

function of capacitor plates:

measures difference in initial charge to post-signal change in capacitance

Working the condenser microphone:

sound wave vibrates the diaphragm → diaphragm moves charged capacitance plate → changes electrical resistance → electrical current

\*\* pressure signals converted to electrical signals

Utility of condenser mic:

most modern day recording devices

phones, computers etc.

Advantages of condenser mic:

less bulky

relatively inexpensive

Disadvantages of condenser mic:

less reliable recording quality

Electrical noise from the internal power supply

Electret Microphones work on the principle of _____ __using__ ______.

Capacitance; Pizo electric material (permanently polarized magnets)

Fiberoptic microphone:

used for specialized application such as magnetic resonance imaging

\-- acoustic signal converted into modulated light intensity