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About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024

Webmaster:

    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

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Sound Level Chart

Location Min Max
(dBA)
Inside Home 25 45
Inside Office 35 50
Inside Airplane Cabin 75 85
Inside Factory 65 100
Talking @ 3 ft 55 65
Shouting @ 3 ft 75 85
Clothes Dryer @ 3 ft 55 65
Vacuum @ 3 ft 65 80
Chain Saw @ 3 ft 100 120
Clothes Washer @ 3 ft 55 75
Car @ 25 ft @ 65 mph 70 80
Airplane @ 1000 ft 95 110
Traffic @ 300 ft 40 60
Rural Ambient 25 35

Sound powers for the following equation in dBA units are referenced to a picowatt (10-12 W).

Sound Power Formula - RF Cafe

Where: W1, W2 = sound power in similar units of watts

The threshold of pain for the human ear is usually taken to be around 120 dBA.

One of the best compilation of noise power level data can be accessed in Chapter 5 of the Occupational Safety and Health Administration's OSHA Technical Manual website.

Loudness is the subjective human response to sound. It depends primarily on sound pressure but is also influenced by frequency. Three different internationally standardized characteristics are used for sound measurement: weighting networks A, C, and Z (or "zero" weighting). The A and C weighting networks are the sound level meter's means of responding to some frequencies more than others. The very low frequencies are discriminated against (attenuated) quite severely by the A-network and hardly attenuated at all by the C-network. Sound levels (dB) measured using these weighting scales are designated by the appropriate letter (i.e., dBA or dBC). The A-weighted sound level measurement is thought to provide a rating of industrial noise that indicates the injurious effects such noise has on human hearing and has been adopted by OSHA in its noise standards (OTM/Driscoll). In contrast, the Z-weighted measurement is an unweighted scale (introduced as an international standard in 2003), which provides a flat response across the entire frequency spectrum from 10 Hz to 20,000 Hz. The C-weighted scale is used as an alternative to the Z-weighted measurement (on older sound level meters on which Z-weighting is not an option), particularly for characterizing low-frequency sounds capable of inducing vibrations in buildings or other structures. A previous B-weighted scale is no longer used.

The following tables present examples of some common noise sources.

Noise Source

(at Given Distance)

Distance

(ft)

Noise Environment A−Weighted

Sound Level

(dBA)

Relative to 70 dBA

Reference

Military Jet @ Takeoff w/Afterburner 50 Carrier Flight Deck 140 128x
Civil Defense Siren 100   130 64x
Commercial Jet @ Take-off 200   120 32x

Threshold of Pain

Pile Driver 50 Rock Music Concert

Inside NY Subway

110 16x
Ambulance Siren

Newspaper Press

Gas Lawn Mower

100

5

3

  100 8x

Very Loud

Food Blender

Prop Plane Flyover

Diesel Truck

3

1,000

150

Boiler Room

Printing Press Plant

90 4x
Garbage Disposal 3 Higher Limit of Urban Ambient Sound 80 2x
Passenger Car, 65 mph

Living Room Stereo

Vacuum Cleaner

25

15

10

  70 0x

(reference)

Normal Conversation

Air Conditioning Unit

5

100

Data Processing Center

Department Store

60 1/2x
Light Traffic   Large Business Office

Quiet Urban Daytime

50 1/4x
Bird Calls (distant)   Quiet Urban Nighttime 40 1/8x
Soft Whisper 5 Library and Bedroom at Night

Quiet Rural Nighttime

30 1/16x
    Broadcast and Recording Studio 20 1/32x

Just audible

      10 1/64x
    Picowatt (10-12 W) power level 0 1/128x

Threshold of hearing

Source: Compiled by Kimley-Horn and Associates, Inc., for the San Diego County government

The networks evolved from experiments designed to determine the response of the human ear to sound, reported in 1933 by a pair of investigators named Fletcher and Munson. Their study presented a 1,000-Hz reference tone and a test tone alternately to the test subjects (young men), who were asked to adjust the level of the test tone until it sounded as loud as the reference tone. The results of these experiments yielded the frequently cited Fletcher-Munson, or "equal-loudness," contours shown in the chart below.

Fletcher-Munson Contours, Sound Pressure Level Chart (OSHA) - RF Cafe

Fletcher-Munson Contours, OSHA

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