Sound Education

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Sound Education

Sound Education - Understanding the basics of sound pressure and reduction.

The deciBel system, (a numerical system based on the unit of ten or deci), used to measure sound
pressure was created by Alexander Graham Bell. The letter B is always capitalized in deciBel or the
abbreviation dB. as a tribute to Mr. Bell.

Sound pressure is the amount of energy produced by a sound wave(s). The greater the energy produced,
by a sound wave, the greater the sound pressure it creates. The greater the sound pressure, the louder
the sound and the farther it will travel, as it plows though air molecules until dissipating.

Using sounds that you are familiar with and can easily relate to, see "The dB. Equals Chart", below, it
will give you a good understanding of deciBels/dB. By the way, pitch/frequency is not going to be covered,
as it is not necessary for understanding the dB./deciBel system or NRR./Noise Reduction Ratings, at a basic
understanding level.

It is important to note that the deciBel system is log rhythmic and as such the sound pressure, as it
correlates to the number of dB., increases exponentially by doubling in pressure with every three dB.
increase. In other words, 120 dB. is considerably more than twice the sound pressure of 60 dB. and will
sound much louder than twice as loud. You'll see.

The dB. Equals Chart

0 dB. = The lowest sound audible to the human ear. The person who can hear this has
                    excellent hearing. In this case zero does not mean "nothing", it is just a base from
                    which to measure sound, as it relates to the hearing of humans.

30 dB. = Quiet Library, soft whisper.

40 dB. = Quiet Office.

50 dB. = Refrigerator, light traffic at a distance.

60 dB. = Conversation.

70 dB. = Busy traffic, noisy restaurant.

                Entering The Hazardous Zone. From 80 dB. on... over exposure can cause
                    permanent hearing loss. Use hearing protection from here on.

  80 dB. = Subway, heavy city traffic - 80 dB. is dangerous, when exposed, for over 8 hours.

90 dB. = Factory, shop tools, lawn mower - 90 dB. is dangerous after 4 hours.

100 dB. = Chain saw, jack hammer, motorcycle - 100 dB. is dangerous at 2 hours exposure
                    and with each 5 dB. increase, safe exposure time is cut in half.

120 dB. = Sand blasting, loud concert in front of the speakers - 120 dB. is immediately
                    harmful to your hearing.

140 dB. = Gun shot blast, jet engine - at a 140 dB. instant hearing loss is assured without
                    hearing protection.

180 dB. = Rocket launching pad. WHAT?

It is advisable and OSHA, (Occupational Safety and Health Administration), mandates that hearing protection be worn by those exposed to 80 dB. average or higher for 8 hours, or more. Generally speaking, you should wear hearing protection at the point at which sound is uncomfortably loud and certainly when your reflexive impulse is to plug your ears with your fingers.

When Sound is either unwanted or uncomfortably loud it becomes noise pollution and should be avoided, as it certainly can be harmful to your hearing and your health in general.

When exposure to noise pollution can not be avoided, hearing protection is the only solution to reducing noise pollution.

All legitimate hearing protection is assigned a number with a dB. NRR. next to it, that indicates how effective the hearing protection is at reducing noise, when used properly. That number is the noise reduction rating or abbreviated NRR.

Hearing Protection ~ NRR. Noise Reduction Rating

If you have ever had your smoke detector go off, you know that even when you plug your ears, with your fingers, you can still hear it. The reason is because the sound is still being conducted to your cochlear through what is known as bone conduction.

No matter how well your ears are pluged, covered or blocked, because of bone conduction, if a sound is loud enough, you will still hear it, only it will be quieter and muffled. This is true, even with low volume sounds, especially low frequency/base, rumble sounds.

After 17 years, in the field of hearing conservation, I have seen a lot of hearing protection and the highest NRR./noise reduction rating, that I've ever seen was 34 dB. NRR. but... because of bone conduction, I must assert that, realistically 30 to 31 dB. NRR. is the highest amount of actual protection that can be obtained.

Hearing protection rated between 12 to 20 dB. NRR. is fine for most needs, such as lawn mowing, working with shop tools, light construction, manufacturing, etc.

For loud industrial environments, medium construction, outdoor shooting, etc., 21 to 25 dB. NRR. is good.

For heavy construction, flight deck operations, etc., 26 to 31 dB. NRR. is good.,

For indoor shooting, 28 to 31 dB. NRR. is good and both earplugs and earmuffs, worn together, are strongly recommended.

-Kevin Wolf

For more information on hearing conservation, click Noise and Hearing Conservation.

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