Welch Allyn TM 262 Auto Tymp - User Manual - Manual (Page 33)

Revised 4/11/08 2-15
Installation
Pre-Test Audiometric Checks (Models with
Audiometer only)
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 because 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). Table 3 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 the user is referred to the Bibliography.
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