Audiometry equation —shibun-hou

[Peter Tuffley]

(cross-posted to MedEngml)

A paper I am translating concerns sudden deafness as a side-effect of
a particular medication. The text refers to a calculation method used
in a test to determine a patient's mean hearing threshold. The method
is referred to in the text as 四分法 (shibun-hou), and Japanese
Google references I have found explain it as comprising the following
equation:

mean hearing threshold in dB = (a+2b+c)/4

where:

a = pure tone hearing threshold (dB) at 500Hz

b = pure tone hearing threshold (dB) at 1,00Hz

c = pure tone hearing threshold (dB) at 2,00Hz

I am trying to track down the "official" English name (if there is
one) for this equation - so far without success. Any assistance will
be greatly
appreciated.

MTIA

Peter

[Kirill Sereda]

Perhaps you are dealing with a uniquely Japanese approach.  This calculation method may have something to do with this:

US Patent Application No. 2007/0005348 A1, Frank Klefenz:

"[0005] The outer ear forms a funnel leading the incoming sound waves to the eardrum. The auricle, the auditory canal, the form of the scull and shoulder modify the sound signal. As the auditory canal (including auricle) is open at one end and closed at the other, it is physically approximately considered as a half-open tube. Thus, in the case of resonance, i.e. when a quarter of the sound wavelength corresponds to the effective auditory canal length, a sound pressure level gain may be observed."

Kirill

[juni...@aol.com]

I couldn't have found an official English for your 四分法 (shibun-hou), yet. But
it apparently looks like a weighted average over three thereshold, a, b, and c.

I call it "weighted mean of hearing threshold" over three sound frequency ranges,
low, mid, and high.

The weighted mean of hearing threshold in dB is defined as,

 

        Σx_{i}w_{i} / Σw_{i} =(a+2b+c)/4 (dB)

where, (x_{1}, x_{2}, x_{3})= (a, b, c), and 

(w_{1}, w_{2}, w_{3}) = (1, 2, 1), respectively.

Sum Σ runs over i = 1, 2, 3, with, 

        a = pure tone hearing threshold (dB) at 500Hz

        b = pure tone hearing threshold (dB) at 1,00Hz  -> 1,000 Hz?

        c = pure tone hearing threshold (dB) at 2,00Hz  -> 2,000 Hz? 



In this mean, audibility for the mid range of sound frequencies (b) is more essential than 

higher or lower ranges (c or a).  Even now, I have question about two frequencies given 

above.  I suppose they are 1,000Hz and 2,000 Hz instead of 1,00 Hz and 2,00 Hz. 

                                                                                            Jun Iwai