Volume 8 Issue 3 (pdf) - Andrew John Publishing Inc
Volume 8 Issue 3 (pdf) - Andrew John Publishing Inc
Volume 8 Issue 3 (pdf) - Andrew John Publishing Inc
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CLiniCaL Questions |<br />
Q: We are trying to relate sound<br />
pressure levels (SPL) in the ear canal<br />
to damage risk criteria for hearing<br />
loss ... it seems most of the standards<br />
use dBA not dB SPL. Are there any<br />
standards based on SPL in humans or<br />
of a way to convert SPL to dBA<br />
A: The SPL in the ear canal versus<br />
Damage Risk Criteria (DRC) came up<br />
immediately in the early 2000s when I<br />
was doing my dissertation on<br />
headphones and risk for hearing loss.<br />
Several authors before and since have<br />
With Brian J. Fligor, ScD Board Certified in<br />
Audiology with a Specialty Certification in<br />
Pediatric Audiology, Director of Diagnostic<br />
Audiology, Boston Children's Hospital; Instructor<br />
in Otology and Laryngology, Harvard Medical<br />
School.<br />
forgotten that the DRC were developed<br />
with microphones in the diffuse field,<br />
and not in a coupler (e.g., a 2 cc<br />
coupler, or in an ear canal – which is of<br />
course also a coupler). Coupler-todiffuse-field<br />
transfer functions are even<br />
more variable than dB SPL (flat) to A-<br />
weighted dB SPL – unless all your<br />
energy is above 1000 Hz where there<br />
are minimal SPL-dBA differences.<br />
One of the problems in this area is<br />
terminology. Some researchers use the<br />
phrase “Transfer Function of the Open<br />
Ear” (TFOE) and others (especially<br />
audiologists) use “Real Ear Unaided<br />
Gain” (REUG). For the purposes of this<br />
question, the two acronyms are<br />
equivalent.<br />
For broadband noise, the TFOE<br />
essentially gives about 7 dB higher level<br />
at the eardrum/ear canal than you get at<br />
the shoulder/diffuse field. This means a<br />
DRC that is 85-dBA for 8-hr TWA with<br />
3 dB exchange rate would be 92-dBA<br />
for 8-hr TWA with 3 dB exchange rate<br />
if the location of measurement was the<br />
ear canal rather than diffuse field. A<br />
“correction factor” can then be<br />
subtracted from the ear canal (probe<br />
tube microphone) measure to change<br />
the results to equivalent diffuse field<br />
results for a valid estimation of DRC.<br />
The real ear to diffuse correction factor<br />
can be used but only if the exact nature<br />
of the spectrum is known.<br />
Canadian Hearing Report 2013;8(3):9.<br />
CANADIAN ACADEMY OF AUDIOLOGY<br />
PO Box 62117 777 Guelph Line, Burlington ON, L7R 4K2 T: 905-633-7114/1-800-264-5106 F: 905-633-9113 E: caa@canadianaudiology.ca<br />
BOARDOFDIRECTORS / CONSEIL DE DIRECTION<br />
Steve Aiken<br />
President/Présidente<br />
Dalhousie University<br />
Halifax, NS<br />
Rex Banks<br />
Director/Directeur<br />
Canadian Hearing Society<br />
Toronto, ON<br />
Salima Jiwani<br />
Director/Directeur<br />
University of Toronto<br />
Toronto, ON<br />
Maxine Armstrong<br />
Director/Directeur<br />
Toronto General Hospital<br />
Toronto, ON<br />
Susan Nelson-Oxford<br />
President-Elect /Présidente-Désignée<br />
Vancouver Island Health Authority<br />
Victoria, BC<br />
MJ Desousa<br />
Director/Directeur<br />
Connect Hearing<br />
Toronto, ON<br />
Gurjit singh<br />
Director/Directeur<br />
University of Toronto<br />
Toronto, ON<br />
Victoria Lee<br />
Past President/Présidente-Sortant<br />
Auditory Outreach Provincial<br />
Program Burnaby, BC<br />
Susan English-Thompson<br />
Director/Directeur<br />
Sackville Hearing Centre<br />
Sackville, NS<br />
Glynnis Tidball<br />
Director/Directeur<br />
St. Paul’s Hospital<br />
Vancouver, BC<br />
Petra Smith<br />
Treasurer/Trésorière<br />
Hastings Hearing Centres<br />
Steinbach, MB<br />
Joy Gauvreau<br />
Director/Directeur<br />
Costco<br />
Saskatoon, SK<br />
Erica Wong<br />
Director/Directeur<br />
Mount Sinai Hospital<br />
Toronto, ON<br />
REVUE CANADIENNE D’AUDITION | CANADIAN HEARING REPORT 9
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