Lecture 2 (Part 1) Flashcards Preview

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Flashcards in Lecture 2 (Part 1) Deck (10):
1

What are some problems with tuning fork tests?

Problems with tuning fork tests

  • Can't control intensity 
  • Variability in thickness of skulls
  • Bone conduction componenet, so can't test one ear at a time

 

2

Describe the first audiometer. What were major developments in the US and Europe? What was the first audiometer called and who was it made by? What did it test? How was intensity controlled? How was threshold recorded (frequency, intensity, normal hearing)? 

• Major developments in US and Europe (late 19thC)

  • Telephone - receiver

• First commercial audiometer in U.S.  (1922) – Western Electric 1A (Fowler, Wegel, & Fletcher)

  •  Air conduction testing only
  • Intensity –controlled in logarithmic steps

• Recording of threshold

  •  Plotted frequency in octave intervals –abscissa (x axis)
    •  Octave intervals are:  256, 512, 1024, 2048, 4096, etc/
  • Plotted intensity along ordinate (y axis) in sound pressure
  • Top of chart –normal hearing; below it are deviations
     

3

What are the 6 types of current audiometers? Describe each

  • Screening audiometers
    • AC only
    • Frequency, hearing level in intensity
    • Type 4
  • Air and bone portable
    • Type 3
  • Clinical diagnostic
    • Type 1 or 2 
    • 2 room suite
  • Bekesy clinical diagnostic
    • automatic
      • button controls attenuation, plotter moves along
    • Continuous mode 
    • Interupted mode - on/off 200 ms
    • excursion is 10 dB. 3 dB in recruitment
    • Can tell whether tone decay is occurring
  • Automatic Audiometers
    • Good for large volume testing 
    • Interrupted mode - tone decay
  • Ultra-high fequency
    • Profound HL at low freq, good hearing at high freq
    • Need appropriate earphones
       

4

What are the required facilities for specific audiometer types?

Required facilities for specific audiometer types (ANSI S3.6, 1996, 2004, 2010) (Table 1)

• pure tone type (1, 2, 3, 4, HF)

• extended high frequency (HF)

• Speech type (A, B, C)

5

What are the components of an audiometer? 

  • On/off
  • Power supply - AC outlet
  • Signal source - Oscillator
  • Control of frequency
  • Amplifier - amplified to max. level
  • Attenuater - then attenuates max level and reduces to level you want
  • Presentation switch
  • Selection - right, left, bone

6

What were some early developments in standards and calibration of audiometers? What were they calibrated in? What is dB SPL? What strategy was used to determine normal hearing? Describe the first American standard and how is compared internationally.

• Early developments at audiometer manufacturers

  • First audiometers calibrated in SPL
  • SPL: a ratio (in dB) of the effective sound pressure of a particular tone or noise to a standard reference pressure that is the same for all frequencies.
    • sound measured on SLM
    • ratio of pressures
  • dB SPL: referent is .0002 dynes/cm2 or 20 uPa 
  • Not everyone heard 0 dB SPL at all frequencies  
  • Strategy at Western Electric for determining “normal hearing” (0 dB HL)
    • Tested 85 people
    • median value threshold at 1000 Hz - 9 dB SPL
    • became 0 dB HL
    • different for each freq.
  • But they weren't the only manufacturers - person would have different results at different places

First American Standard (ASA, 1951)

  • Didnt screen
  • Very lenient criterion for what's normal

International Standards (1955-1969) 

  • More stringent
  • Resistance to change in US

First ANSI standard in US: ANSI S3.6, 1969

Current Standard (ANSI, S3.6, 2010) 

7

Describe ANSI and the current standard.

• ANSI organization

  • non-profit organization

Current standard: ANSI S3.6 (2010)

• Definitions of ETSPLs, RETSPLs, RETFLs, etc.

  • P. 4-5 of standard
  • ETSPL: corresponds to the SPL needed at each frequency to just detect sound. SPL at threshold
  • RETSPL: is the mean ETSPL based on hearing thresholds of a large number of young normal individuals (18-30 years)
    • Reference for normal hearing
    • For 1000 Hz - 7.0 dB SPL (0 dB HL)
    • Not uniform across frequencies
    • Most sesitive to mid frequencies

See tables 5, 6, 7 and 7b from standard (RETSPLS for supra-aural, circumaural, and insert earphones, respectively)
 

8

Descrive deciBels. What is a dB? What is the equation for power? Pressure?

• dB:  a ratiobetween 2 values

  • (amount of gain or loss)

• In power:  dB = 10 (log P1/P2)

  • Ex: if P1 = 20 watts and P2 = 10 watts,  what’s the gain of P1 over P2?
  • dB = (10 log20W/10W);   dB = 10 log 2      [ log 2 = .3]
  • 10 (log 2) = 3 dB

• In pressure: dB = 20 log p1/p2

9

What is the reference for dB SPL? dB HL? dB SL?

  • dB SPL - 20 uPa
  • dB HL - RETSPL
  • dB SL - Threshold of individual

10

Describe audiometer maintenance. What are the needs for checking the audiometer? What is involved in a daily listening check? What are you checking for?

• Needs for checking audiometer

  • Verify intensity 
  • Verify frequency
  • Signal free of distortion
  • If out of calibration - inaccurate thresholds

• Daily Listening Check

  • Inspection of earphones
    • Cord, cushions, connections
  • Unwanted acoustic signals by ac
    • Cross talk
      • definition - when the signal can be heard through other side of ear phone
      •  how to check for it - disconnect each side of headphone
  • Unwanted acoustic signals by bc
    • Airborne sound level by bc must be 3dB less than sound level from same vibrator when in contact with the head
    • Measure threshold in BC and in AC - unoccluded should hear better, but shouldn't be more than 3 dB
  • Unwanted sound from audiometer
    • With audiometer HL dial set at 50 dB HL or lower
  • Check frequency and intensity of signals
  • Check linearity
    • 4000 Hz, decrease in 10 dB steps, see if gets quieter, then go up in 10 dB steps. 
      • Notice if stabilizes at any level.