Conclusion, questions, discussion

You can see the results of this comparison using the links above.
Both tables labeled Z show the differences between the ISO and the ANSI standards. We can say that for ears covered there are not any big differences. It is interesting that for ears not covered (which was my main interest) ANSI standard allows higher background noise than ISO standard. There is just one value, at 8000 Hz, which is 3 dB lower but we can say that the ANSI values are, on average, 5 dB higher.
At some frequencies it is very similar to column D, where the values are increased by 8 dB. I've added that comparison as well. Click here to see the table (D - values from ISO 8253-2 + 8 dB, C - values form the new ANSI S3.1-1999 standard).
Here are some questions and topics for discussion. Please, use the text field below each question for your answer. If you want you can fill in your name and e-mail address beneath this text and I will send you an e-mail when there is a new contribution. Thank you very much.
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Question 1:
The ISO stardard states that if we use values given in the table, we can measure with a maximum uncertainty of +2 dB due to ambient noise. If we accept the maximal uncertainty of +5 dB we can increase those values by 8 dB. We have learnt that corrected ISO values are very similar to the ANSI 1999 values.
What is the maximum uncertainty if I measure according to the ANSI standard (due to ambient noise)?
Question 2:
Is there a practical example of using increased (+8dB) background noise levels?
Multi - question 3:
The uncertainty estimation.

In the ISO standards we can read that the maximum uncertainty is +2 dB or +5 dB due to ambient noise but these are just a part of the overall uncertainty (uncertainty of calibration of audiometer, uncertainty of hearing testing!!! etc)

Do users of audiometers calculate and use the uncertainties in practice? What is, for example, the overall uncertainty of measurement of threshold audiometry by means of earphones?
Question 4:
What is the reason to have 1/1 octave band values in the ANSI standard if there are also 1/3 octave bands values?
Question 5:
Tables in the ANSI standard include the values which can be measured by means of octave or one-third octave filters. But for one-third octave bands there are just centre frequencies in one octave steps. This example explains the meaning (the numbers in bold are included in the ANSI standard):
Octave band [Hz] - 125, 250, 500, 1000, 2000, 4000, 8000
1/3 octave band [Hz] - 125, 160, 200, 250, 315, 400, 500, 630, 800, 1k, 1.25k, 1.6k, 2k etc.
Why isn't the background noise measured at the frequencies between one octave steps as well?
Question 6:
The ISO standard includes the table for maximum permissible ambient sound pressure levels in one-third octave bands for bone conduction audiometry. These values are 3dB higher than values for ears not covered.
Does any ANSI standard deal with this problem with the bone conduction measurement?
Multi - question 7:
During my searching on Internet I've found this table:
Audiometric test rooms - 1910.95AppD
Standard number: 1910.95AppD
Standard Title: Audiometric test rooms
SubPart Number: G
SubPart Title: Occupational Health and Environmental Control
Table D-1 - Maximum allowable octave-band pressure levels for audiometric test rooms
Octave-band center frequency (Hz)
Sound pressure level (dB)
Does anyone know more about this table? Where is it used?
Question 8:
In the ISO 8253-2 are also defined: free sound field, diffuse sound field and quasi-free sound field. (for practical purposes the quasi-free sound field is the best solution). It means that it is not just a question of background noise levels but also a question of reverberation, sound reflection etc.
Is it also mention in the ANSI or AS standards?
Question 9:
Both the ANSI and the AS standards include maximum permissible ambient sound pressure levels for the insert earphones. It would be useful to have such values in the ISO standard.
Are these insert earphones often used in clinical practice in your country?
Question 10:
The last question (but not the least) is about high frequency audiometry.
Does there exist any research/recommendation for maximum permissible ambient noise levels for high frequency audiometry?