On Tue, Sep 28, 2010 at 8:14 AM, Torben Poulsen <tp@xxxxxxxxxxxxxx>
Thanks to Al for a clear explanation and 'calm down' statement.
I can add to things
1) In the audiometry standard ISO 8253-1 'Basic pure tone audiometry' an example is given for the uncertainty: "The expanded measurement uncertainty is evaluated for the determination of the hearing threshold level of a test subject using air conduction audiometry at a frequency below 4 kHz without masking and assuming that the requirements on ambient noise are met and that no further uncertainty contribution arises from any other
sources. The uncertainty budget then has a form as presented in Table A.2.
---I omit the table ---. The result is: Combined standard uncertainty: u = 4,9 dB.
Expanded measurement uncertainty for 95 % coverage probability, rounded to the nearest full decibel: U = 10 dB."
In other words there is a 10 dB uncertainty in the measurements itself - for frequencies below 4 kHz. The uncertainty will increase at higher frequencies (e.g. 4, 6, and 8 kHz)
2) It is well known that a fake hearing loss is often seen at 6 kHz when thesholds are determined with a Telephonics THD39 or THD49 earphone. This 'hearing loss' is about 5 dB and is possibly caused by an error in the reference value for audiometer calibration (for this specific earphone). This is mentioned as one of the conclusions in the Schlauch & Carney paper that the UMNews refer to.