Welch Allyn TM286 Auto Tymp - User Manual - Manual (Page 50)

46 Routine Maintenance Welch Allyn TM286 Auto Tymp
Pre-Test Audiometric Checks
Noise recovery period
Exposure to high levels of sound (e.g., unmuffled lawn mowers, loud music, gunfire)
tends to create a temporary threshold shift (TTS) which diminishes with time after
exposure. Any subject/patient tested soon after such exposure may exhibit a hearing loss
that does not reflect his or her normal hearing threshold. It is, therefore, important that
the testing procedure prescribe some time interval - usually at least 16 hours- between
the last exposure to high-level sounds and the administration of any hearing test.
Elimination of ambient noise
Excessive noise in the test environment during audiometric testing such as that produced
by conversation, typewriters, public address systems reduces test validity as it tends to
mask the test signals, particularly at the lower frequencies where earphone cushions
provide less effective attenuation. An acoustically treated room may be required if
ambient noise reaches objectionable levels (i.e., sufficient to cause apparent hearing loss
at the low frequencies). Also, Audiocups are available from Welch Allyn as an optional
accessory. If the person being tested is in the same room as the audiometer, it is
recommended that he/she be seated about three feet (1 meter) away from the
instrument.
Maximum permissible noise levels are specified by the American National Standards -
Criteria for Permissible Background Noise during Audiometric Testing, ears covered with
earphones (S3.1 1991 revised). The table below,
“Maximum Permissible Backround Noise
Levels” shows the maximum background levels that can be present inside the room
while a valid hearing test is being conducted. For more comprehensive information about
hearing testing and hearing conservation see the
“Bibliography” on page 67.
Table 2. Maximum Permissible Backround Noise Levels
Biological Check
For Tympanometry and Reflex tests, the best way to determine that the instrument is
operating properly is to perform a daily check on a normal ear - the operator's ear if
possible. This allows the operator to listen for the probe tone and the stimulus tone
Frequency (Hz) Test Room
Maximum dB SPL in 1/3 Octave Band
125 29.0
250 17.5
500 14.5
750 16.5
1000 21.5
1500 21.5
2000 23.0
3000 28.5
4000 29.5
6000 33.0
8000 38.5