Sound Transducers

WHAT IS SOUND?

A physical phenomenon consisting of a series of disturbances formed by the vibration or movement of air.

WHAT IS SOUND AS A PSYCHOLOGICAL PHENOMENON?

Sound is an auditory experience—the act of hearing.

WHAT IS SOUND PHYSICALLY?

Sound is really tiny fluctuations of air pressure.

HOW IS SOUND CARRIED THROUGH AIR?

Sound is carried through air as compressions and rarefactions in air pressure, which form waves.

WHAT IS AN ACOUSTIC SIGNAL?

Sound; sound can also be referred to as an acoustic signal.

WHAT TYPE OF WAVE IS SOUND?

Sound is a longitudinal wave.

WHAT IS A LONGITUDINAL WAVE?

A wave in which the motion of particles is along the direction of propagation.

WHAT IS A TRANSVERSE WAVE?

A wave in which the motion of particles is perpendicular to the direction of propagation.

WHAT ARE EXAMPLES OF TRANSVERSE WAVES?

Water waves and light.

WHAT ARE THE TWO IMPORTANT CHARACTERISTICS OF A SOUND WAVE?

Frequency and intensity.

WHAT IS FREQUENCY?

How often or how frequently a wave repeats itself in one second.

WHAT DOES FREQUENCY MEASURE?

The number of cycles a wave completes per second.

WHAT IS THE UNIT FOR FREQUENCY?

Hertz (Hz).

WHAT HAPPENS TO WAVELENGTH AS FREQUENCY INCREASES?

High-frequency sounds have shorter wavelengths.

WHAT IS THE HUMAN EAR'S APPROXIMATE FREQUENCY RANGE?

Approximately 20 Hz to 20,000 Hz.

WHAT IS A PURE TONE?

A sinusoidal wave consisting of a single frequency.

WHAT IS A COMPLEX SIGNAL?

A sound containing more than one frequency; speech is an example.

WHAT FREQUENCY INFORMATION FROM VOWELS IS NEEDED FOR SPEECH INTELLIGIBILITY?

Approximately 200–2400 Hz.

WHAT DO CONSONANTS DO IN ENGLISH?

Consonants carry the meaning of words in English.

WHAT FREQUENCY INFORMATION FROM CONSONANTS IS NEEDED FOR SPEECH INTELLIGIBILITY?

Approximately 500–6000 Hz.

WHAT IS INTENSITY?

Intensity is related to wave amplitude and is described as volume.

WHAT IS THE ABSOLUTE UNIT OF SOUND PRESSURE/INTENSITY?

Pascals (Pa) or microPascals (μPa).

WHAT IS THE RELATIVE UNIT OF SOUND LEVEL?

Decibel (dB), which is typically used in clinical applications.

WHAT IS THE LOWEST SOUND PRESSURE WE CAN HEAR IN ABSOLUTE UNITS?

Approximately 0.00002 Pa.

WHAT IS THE DISCOMFORT/PAIN LEVEL IN ABSOLUTE SOUND PRESSURE?

Approximately 200 Pa.

WHY ARE ABSOLUTE PRESSURE UNITS COMPLICATED FOR DAY-TO-DAY CLINICAL USE?

The range of sound pressures is extremely large, making absolute pressure values cumbersome to use clinically and when incorporating them into an audiogram.

WHAT IS SOUND PRESSURE LEVEL (SPL)?

SPL is the term used to measure the magnitude of sound.

WHAT IS THE FORMULA FOR dB SPL?

dB SPL = 20 log(p/pref).

WHAT DOES p REPRESENT IN THE dB SPL FORMULA?

p represents the known sound pressure.

WHAT DOES pref REPRESENT IN THE dB SPL FORMULA?

pref represents the reference sound pressure.

WHAT IS THE TYPICAL REFERENCE SOUND PRESSURE FOR dB SPL?

20 μPa, or 0.0002 dynes/cm², which represents the lowest level of human hearing.

WHAT KIND OF UNIT IS dB SPL?

A relative unit.

WHAT DOES dB SPL INVOLVE?

A ratio between a known sound pressure and a reference sound pressure.

WHAT MATHEMATICAL FUNCTION IS USED IN dB SPL?

A logarithm.

IS dB SPL LINEAR OR NON-LINEAR?

dB SPL is non-linear.

WHAT DOES dB SPL USE AS A REFERENCE?

It is expressed in terms of various reference levels.

WHAT HAPPENS WHEN TWO EQUAL SOUND LEVELS ARE COMBINED?

Two equal levels result in a 3 dB increase in the overall level.

WHAT IS 60 dB + 60 dB?

63 dB SPL.

HOW DO YOU ADD dB SPL VALUES?

First convert the dB values back to absolute pressure using an antilog, add the absolute pressures, and then use the formula 20 log(p/pref) to convert the combined pressure back to dB SPL.

WHY CAN'T YOU SIMPLY ADD TWO dB VALUES?

Decibels are relative, logarithmic, and non-linear rather than absolute linear pressure units.

WHAT IS HEARING LEVEL (HL)?

HL is a measured value of an individual's threshold of hearing, expressed in dB.

HOW IS HEARING LEVEL WRITTEN ON AN AUDIOGRAM?

dB HL.

WHAT IS THE RANGE OF SOUND INTENSITIES TO WHICH THE HUMAN EAR RESPONDS?

The human ear responds to a very large range of sound intensities.

WHAT DOES 0 dB HL REPRESENT?

The lowest sound level humans can hear.

WHAT DOES 130–135 dB HL REPRESENT?

The threshold of pain.

WHAT DOES dB HL MEASURE?

It represents an individual's hearing threshold relative to the appropriate reference level.

WHY IS dB HL USED ON AN AUDIOGRAM?

It provides a standardized way to represent an individual's hearing threshold.

WHY IS dB SPL DIFFERENT FROM dB HL?

SPL and HL use different reference points.

WHY IS CONVERTING dB HL TO dB SPL CUMBERSOME?

The conversion is cumbersome because SPL and HL have different reference points, and the relationship varies by frequency and transducer.

DOES dB HL HAVE THE SAME dB SPL EQUIVALENT AT EVERY FREQUENCY?

No. dB HL varies by frequency and by the transducer used.

WHAT IS THE 500-HZ CONVERSION FROM 0 dB HL TO dB SPL?

0 dB HL at 500 Hz corresponds to 5 dB SPL.

WHAT IS THE 500-HZ CONVERSION FROM 25 dB HL TO dB SPL?

25 dB HL at 500 Hz corresponds to 39 dB SPL.

WHAT IS THE 500-HZ CONVERSION FROM 60 dB HL TO dB SPL?

60 dB HL at 500 Hz corresponds to 65 dB SPL.

WHAT IS THE 1000-HZ CONVERSION FROM 0 dB HL TO dB SPL?

0 dB HL at 1000 Hz corresponds to 7 dB SPL.

WHAT IS THE 1000-HZ CONVERSION FROM 40 dB HL TO dB SPL?

40 dB HL at 1000 Hz corresponds to 47 dB SPL.

WHAT IS THE 1000-HZ CONVERSION FROM 75 dB HL TO dB SPL?

75 dB HL at 1000 Hz corresponds to 82 dB SPL.

WHAT IS THE 1000-HZ CONVERSION FROM 110 dB HL TO dB SPL?

110 dB HL at 1000 Hz corresponds to 117 dB SPL.

WHAT IS HEARING THRESHOLD?

The level at which a sound is audible only 50% of the time it is presented.

WHERE IS HEARING THRESHOLD MARKED ON AN AUDIOGRAM?

Threshold is marked in dB HL on the audiogram.

WHAT IS THE EXAMPLE RIGHT-EAR THRESHOLD AT 250 HZ SHOWN ON THE AUDIOGRAM?

25 dB HL.

WHAT IS SENSATION LEVEL (SL)?

The number of decibels of a sound above a person's hearing threshold.

WHAT DOES dB SL MEASURE?

How far above the person's hearing threshold a target signal is presented.

WHAT IS THE FORMULA FOR dB SL?

dB SL = level of target signal − level of threshold.

WHAT IS THE DIFFERENCE BETWEEN HL AND SL?

HL represents a person's measured hearing threshold, while SL represents how many decibels above that person's threshold a sound is presented.

WHAT DOES 0 dB HL MEAN?

It represents the lowest sound level humans can hear; it does not mean there is no sound.

WHAT IS THE RANGE FROM 0 dB HL TO THE THRESHOLD OF PAIN?

Approximately 0 dB HL to 130–135 dB HL.

WHAT DOES dB HL STAND FOR?

Decibels Hearing Level.

WHAT DOES dB SPL STAND FOR?

Decibels Sound Pressure Level.

WHAT DOES dB SL STAND FOR?

Decibels Sensation Level.

WHAT IS THE DIFFERENCE BETWEEN dB SPL AND dB HL?

dB SPL describes sound pressure relative to a physical reference pressure, while dB HL represents an individual's hearing threshold relative to standardized hearing-level references.

WHAT IS VELOCITY?

The speed with which sound travels from the source to another point.

WHAT DOES THE VELOCITY OF SOUND DEPEND ON?

It depends on the density of the medium through which the sound travels.

WHAT IS THE SPEED OF SOUND IN AIR?

Approximately 343 meters per second.

WHAT IS THE SPEED OF SOUND IN WATER?

Approximately 1497 meters per second.

WHAT IS THE SPEED OF SOUND IN GLASS?

Approximately 5100 meters per second.

WHAT IS THE SPEED OF SOUND IN STEEL?

Approximately 5790 meters per second.

WHAT IS THE SPEED OF SOUND IN ALUMINUM?

Approximately 6420 meters per second.

WHICH LIST CORRECTLY ORDERS THE SOUND SPEEDS FROM SLOWEST TO FASTEST?

Air (343 m/s) → water (1497 m/s) → glass (5100 m/s) → steel (5790 m/s) → aluminum (6420 m/s).

WHAT IS A TRANSDUCER?

A device that changes one form of energy into another form of energy.

WHAT DO WE WANT A TRANSDUCER TO DO WHEN TESTING HEARING?

Change mechanical or electrical energy into acoustic energy.

WHY DO WE SELECT AN APPROPRIATE TRANSDUCER WHEN TESTING HEARING?

The appropriate transducer is selected based on the part of the hearing system being tested.

WHAT ARE THE MAIN TRANSDUCERS DISCUSSED IN THE SLIDES?

Air-conduction headphones, bone oscillators/bone-conduction vibrators, and speakers.

WHAT IS AIR CONDUCTION (AC)?

A method in which sound travels through the outer and middle ear before arriving at the inner ear.

WHAT ARE THE THREE COMMON TYPES OF AIR-CONDUCTION EARPHONES/HEADPHONES?

Insert earphones, supra-aural headphones, and circum-aural headphones.

WHAT ARE INSERT EARPHONES?

Air-conduction transducers that deliver sound through an ear-specific insert.

WHAT ARE SUPRA-AURAL HEADPHONES?

Air-conduction headphones that sit on or over the outer ear rather than surrounding the entire ear.

WHAT ARE CIRCUM-AURAL HEADPHONES?

Air-conduction headphones that surround the outer ear.

WHAT DOES IT MEAN THAT AIR-CONDUCTION TRANSDUCERS ARE EAR-SPECIFIC?

The transducer is used to present sound to a particular ear.

WHAT PATH DOES SOUND TAKE DURING AIR-CONDUCTION TESTING?

Sound travels through the outer ear and middle ear before reaching the inner ear.

WHAT IS A BONE OSCILLATOR/BONE-CONDUCTION VIBRATOR?

A transducer that produces calibrated mechanical vibrations to stimulate the hearing system through the skull.

WHAT TYPE OF ENERGY DOES A BONE OSCILLATOR USE?

Electrical, calibrated mechanical vibrations.

HOW IS A BONE OSCILLATOR PLACED?

It is pressed tightly against the head to vibrate the entire skull at once.

WHERE CAN A BONE OSCILLATOR BE PLACED?

It can be placed behind the ear on the mastoid or on the forehead.

WHAT PART OF THE HEARING SYSTEM DOES BONE CONDUCTION BYPASS?

It bypasses the outer and middle ear.

WHAT DOES BONE CONDUCTION DIRECTLY STIMULATE?

It directly stimulates the inner ear, specifically the cochlea.

WHAT DOES "BETTER EAR RESPONDS" MEAN FOR BONE CONDUCTION?

The better ear responds to the bone-conduction stimulus.

HOW DOES BONE CONDUCTION DIFFER FROM AIR CONDUCTION?

Bone conduction bypasses the outer and middle ear and stimulates the cochlea through skull vibration, whereas air conduction sends sound through the outer and middle ear before reaching the inner ear.

WHAT ARE SPEAKERS USED FOR IN HEARING TESTING?

Speakers are used for hearing device benefit evaluations.

WHAT FACTOR ABOUT SPEAKERS MATTERS DURING TESTING?

The distance of the speakers from the patient matters.

WHAT DOES "BETTER EAR RESPONDS" MEAN FOR SPEAKER PRESENTATION?

The better ear responds to the sound presented by the speaker.