Frequency Range of Hearing (question) (fwd)

dybala at utdallas.edu dybala at utdallas.edu
Thu Jan 25 13:37:32 EST 1996


Tony Woolf (tony at howl.demon.co.uk) wrote:
> In article <199601211903.NAA14491 at moe.cc.utexas.edu>
>            sirianni at UTS.CC.UTEXAS.EDU "Jeffrey G. Sirianni" writes:

> > I don't think we've ever discussed the practice of high-frequency
> > audiometry in this group.

> I'm not an audiologist but I do know one who is testing above 10kHz.
> Also an organisation which is testing above 10kHz when screening its
> new staff.

> However I understand that there are no proper standards for
> audiometric earphones at these frequencies so it is only possible to
> compare between people tested with the same equipment.

> Am I right in this?
>  
> -- 
> Tony Woolf


The problem with testing in the higher frequencies has to do with
calibration of the intensity of the stimulus.

As the cps are increased the wavelength of the stimulus
becomes shorter and shorter.  Due to the length of the ear canal
being longer than the wavelengths of frequencies higher than 10kHz,
the problem of standing waves occur.  In that, if a standing
wave was to occur, a node could possibly occur at the eardrum.
Therefore, sound would not be percieved by the patient 
and your test results would be innacurate. 

This standing wave problem is also affected
by the difference in ear canal lengths and sizes of pinnas
changing the distance of the earphone to the eardrum.

It sounds like the company who is doing the testing above 10 kHz
is basing "normal" by a biological calibration done on normal hearing 
persons. If that is true, I don't know if the biological calibration
would be accurate due to the standing wave problem and also ~there are 
no norms for those hf!~ aka no HL levels for normals. 

Warble tones are used in the sound field for the same
reason of problems with standing waves.
Possibly if someone used warbled hf tones in 
the earcanal this problem would not occur.  I don't know, just a guess.

Audiologists (in general) do not use hf (above 8-10kHz) while testing
the hearing of patients because we are worried about how well
persons can understand ~speech~ and, how well a patient  uses that perceived 
information to communicate. Speech information (in general) lies btw 
500-4000 Hz.

Sometimes hf audiometry is used for monitoring persons on
ototoxic drugs because the dammage usually occurs first in
the hf (above 10 kHZ). Therefore, most of the literature
on hf audiometry is on ototoxic monitoring.

-- 
Thank you for your support,
Paul Dybala
dybala at utdallas.edu
http://wwwpub.utdallas.edu/~dybala/kelly.htm



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