Just moozing

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Sound and volume

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Having been to a festival recently and using my ear plugs, I started thinking about volume and how it affect the ears.

Most things makes a sound. Loud sounds can be supported for short periods of time and lower intensity sounds for longer periods. We normally measure sound volume in decibels.Wikipedia includes a list of examples of “acoustic decibels” like 30-60 for normal speech.

It is a logarithmic value based on the actual sound pressure. The decibel ratings are commonly calculated using A-weighting (dBA), and protective gear’s rating is commonly using C-weighting. The C-weighting (dBC) include more weight on the lower frequencies, so dBC values are expected to be higher. These weightings are to reflect how well humans hear different frequencies (some background information).

There are rules and regulations for noise levels at the work place, and some standard values for exposure.

85 dB over 8 hours per day seems to be the international norm for work environments – and then halve it for every extra 3 dB, leading to max 15 minutes in 100 dB. The 85 dB threshold is way lower for ambient noise.

The values are also lower for children. I found this from WHO, some statistics and comments from Center for hearing and communication.

 

Protection

One option is to be further away from the source. It follows the inverse square law, so doubling the distance, results in a factor of 4 reduction in intensity (ie. -6 dB). The opposite is also true, so reducing the distance by a factor of two, increases the level by 6 dB.

Personal hearing protection devices have a Noise reduction rating (NRR) or a single number rating (SNR). The previous decibel values were calculated using A-weighting, while NRR and SNR are calculated using A- or C-weights.

3M makes a lot of hearing protections devices, and they have a datasheet with lots of information.

  • At the festival I used these, which the Oticon Foundation had sponsored a lot of. They have an SNR of 30 dB.
  • At home, I use these. With an NRR of 23 dB, these are probably a safe choice for lawn mower work (at 85 dB).

So the earplugs, that you can pick up for DKK 10 at the festival is noise reducing that is better than most ear muffs. Very cool and thank you Oticon foundation.

 

Concerts

I had a talk with a sound engineer, and he said that the concert never exceeded 103 dB. This is measured in the some where next to engineering in the middle of the tent – and it is an average value with peaks going very high at some concerts.

Standing halfway between engineering and the loud-speaker, would increase the sound level to 109 dB, which might be ok for around 2 minutes – so don’t do that. Using the earplugs, you get 109 dB – 30 dB = 79 dB (following the math laid out in the background link above), which according to health and safety is ok for more than the duration of the concert.

If you don’t want to use good ear plugs, you need to be more than 4 times further away that the engineering booth. That is way out of the tent (provided no repeater loud speakers), and if the concert is indoor, outside the building.

In conclusion, doing multiple concert per day will give you an issue with the sound level of most concerts. So use ear protection, since you probably cannot be far enough away from the sound source(s).

 

Bonus: I located the sound policy document (in Danish and unknown year).

 

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Written by moozing

July 17, 2017 at 09:00

Posted in Tech, Uncategorized

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