The Daily Decibel

Decibel Meters (Sound Level Meters) and What They Measure

What are decibels? Who uses them?

The decibel is a scientific unit to measure sound. Generally, the higher the decibel level, the louder the sound.

The decibel is sometimes abbreviated dB or dBA. It is not the same type of unit as the Volt (V), the Watt (W), or the meter (m). Instead, the decibel is a logarithmic unit for ratios used in math and science. For example, the pH (level of acidity) for hydrogen ion concentrations in liquids and the Richter scale for earthquake event energy both use a logarithmic ratio.

Physicists and mathematicians often need to use decibels and logarithms in their research.

In the United States, many high school students begin learning logarithms in their math classes as early as the 11th grade.

If you'd like to measure decibels with a decibel meter, you can get one for about 30 to 50 dollars. See the decibel meters below.

These can be useful for a science project involving sound and noise. We have seen a decibel meter on sale at Radio Shack, for $30. (The regular price was $40.)

A decibel meter from SMART SENSOR

a CASELLA sound meter

Extech.com - LCD Digital Sound Level Meter

A sound level meter from Radio Shack

The above photos are examples of decibel meters.

Decibel meters are also called sound level meters.

You can probably find several brands at Amazon.com. or Google Shopping or Yahoo Shopping. Just visit the site and type in:

"decibel meter"

or....

"sound level meter"

Aha!! But must your decibel meter be OSHA-compliant? OSHA stands for the Occupational Safety and Health Administration of the United States. In the workplace -- retail sites, industrial sites, etc. -- you need to be OSHA-compliant if you are testing the environment. Here is the OSHA compliance page on instrumentation. For example, if you are using a sound level meter, OSHA will want you to adhere by these standards.

The History of The Decibel

Sound was originally measured in a unit named after Alexander Graham Bell. The unit was called the Bel. Alexander Graham Bell (1847-1922), born in Edinburgh, Scotland, was a pioneer in the field of telecommunications.

   Electrical engineers came to require better precision, however. And the Bel was considered too large a unit for them. In 1929, the decibel was introduced. It is one-tenth (deci) of a Bel, just as a decimeter is one-tenth of a meter.

   Soon afterwards, the decibel (dB or dBA) was adopted worldwide.

   The decibel is also expressed in mathematical terms of 10 to a given power. This is done simply by dividing the given dB level by 10.

   The dBA is a weighted scale that should only be used up to approximately 60 dB. Upwards, dBB should be used for decibel levels 60 - 80. And dBC should be used for decibel levels 80 and higher. But, for some reason, dBB and dBC are not used much. Normally, engineers simply use the scale dBA.

   The decibel is also known as dB SPL, referenced to the nominal threshold of human hearing.

Noise

Noise has been defined differently by different persons or groups.

At The Daily Decibel, we consider noise to be repeated, unwelcome sound.

How Loud is Too Loud?

From Our Friends At The Center for Hearing And Communication

Experts agree that continued exposure to noise above 85 dBA over time, will cause hearing loss. To know if a sound is loud enough to damage your ears, it is important to know both the loudness level (measured in decibels, dBA) and the length of exposure to the sound.

In general, the louder the noise, the less time required before hearing loss will occur. According to the National Institute for Occupational Safety and Health (1998), the maximum exposure time at 85 dBA is 8 hours. At 110 dBA, the maximum exposure time is one minute and 29 seconds. If you must be exposed to noise, you should limit the exposure time and/or wear hearing protection.

Measure Up and Turn it Down: Decibel Levels Around Us

The following are decibel levels of common noise sources around us. These are typical levels, however, actual noise levels may vary depending on the particular item. Remember: noise levels above 85 dBA will harm hearing over time. Noise levels above 140 dBA can cause damage to hearing after just one exposure!

Points of Reference *measured in dBA or decibels

0 The softest sound a person can hear with normal hearing
10 normal breathing
20 whispering at 5 feet
30 soft whisper
50 rainfall
60 normal conversation
110 shouting in ear
120 thunder

Home	Work	Recreation
50 refrigerator 50 - 60 electric toothbrush 50 - 75 washing machine 50 - 75 air conditioner 50 - 80 electric shaver 55 coffee percolator 55 - 70 dishwasher 60 sewing machine 60 - 85 vacuum cleaner 60 - 95 hair dryer 65 - 80 alarm clock 70 TV audio 70 - 80 coffee grinder 70 - 95 garbage disposal 75 - 85 flush toilet 80 pop-up toaster 80 doorbell 80 ringing telephone 80 whistling kettle 80 - 90 food mixer or processor 80 - 90 blender 80 - 95 garbage disposal 110 baby crying 110 squeaky toy held close to the ear 135 noisy squeeze toys	40 quiet office, library 50 large office 65 - 95 power lawn mower 80 manual machine, tools 85 handsaw 90 tractor 90 - 115 subway 95 electric drill 100 factory machinery 100 woodworking class 105 snow blower 110 power saw 110 leafblower 120 chain saw, hammer on nail 120 pneumatic drills, heavy machine 120 jet plane (at ramp) 120 ambulance siren 125 chain saw 130 jackhammer, power drill 130 air raid 130 percussion section at symphony 140 airplane taking off 150 jet engine taking off 150 artillery fire at 500 feet 180 rocket launching from pad	40 quiet residential area 70 freeway traffic 85 heavy traffic, noisy restaurant 90 truck, shouted conversation 95 - 110 motorcycle 100 snowmobile 100 school dance, boom box 110 disco 110 busy video arcade 110 symphony concert 110 car horn 110 -120 rock concert 112 personal cassette player on high 117 football game (stadium) 120 band concert 125 auto stereo (factory installed) 130 stock car races 143 bicycle horn 150 firecracker 156 capgun 157 balloon pop 162 fireworks (at 3 feet) 163 rifle 166 handgun 170 shotgun

Lesson Plans -- Sound, Noise, and How You Can Protect Your Hearing!

Lesson Plans For Science Teachers And Health Education Teachers

The National Institutes of Health (NIH) has provided five (5) lesson plans for teachers who wish to teach sound, hearing, measurement of sound, and hearing protection. They are linked here for anyone who wishes to use them or just browse through them. Surely, more lesson plans on sound, hearing, measurement, and protection are out there on the internet and in educational catalogs and manuals. You might check with your local school district to determine what -- and how -- they are teaching sound and hearing to children.

Lesson Plan 1
Getting The Message
Science-education.nih.gov/supplements/nih3/Hearing/guide/lesson1.htm

Lesson Plan 2
Sound Communication
Science-education.nih.gov/supplements/nih3/Hearing/guide/lesson2.htm

Lesson Plan 3
Do you hear what I hear?
Science-education.nih.gov/supplements/nih3/Hearing/guide/lesson3.htm

Lesson 4
A Black Box Problem: How Do I Hear?
Science-education.nih.gov/supplements/nih3/Hearing/guide/lesson4.htm

Lesson 5
Too Loud, Too Close, Too Long
Science-education.nih.gov/supplements/nih3/Hearing/guide/lesson5.htm

For More Information!