There seems to be some confusion here.

 

The H&SE publication "Contolling noise at work" published in 2005, refers to EN 26189:1991 for guidance on how quiet the environment should be before test results are affected.

 

What matters of course is what the ear hears, and the ear is protected from environmental noise by the earphone cushion plus perhaps an audiocup, plus perhaps a booth.

 

Table 2, provided in EN 26189 (see below), gives guidance on the maximum level (of octive band sound pressure) allowed in the test environment near to the head, assuming:-

 

1) the Beyer DT48 or TDH39 earphone fitted with the MX 41/AR cushions are used and

 

2) you don't want to measure accurately thresholds below 0dB

 

If you add audiocups or a booth then you can allow higher levels of background noise, but if you are dealing with new starts and want to accurately measure baseline audiograms, you will want to test and look for thresholds well below 0 dB, and will therefore need a much better test environment.

 

An accurate assessment of what constitutes a valid test environment therefore needs to take into account:-

 

1) the background noise measured in 1/3 octave band frequencies

2) the background noise supression provided by earphone cushion, audiocup and booth

3) the lowest level you need to measure to

 

The background noise at each of the relevant frequencies, can be determined with a good sound level meter.

The supplier of your equipment should be able to give you a table of attenuation values provided by the setup you have (earphone cushion, audiocup and booth etc).

You should probably assume that you want to measure to at least -15 dB to cover every situation which might arise.

 

Please remember that the table below is only relevant under the very restricted conditions detailed above.

 

 

Regards

 

Eric Greig

 

Freq		Lmax
500		18
1000		20
2000		27
4000		38
8000		36