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Loudness is measured in decibels (dB). A decibel is one tenth of a bel, a seldom-used unit named in honor of Alexander Graham Bell.
It is a logarithmic (base 10) scale so 20 dB has 100 times the power as 10 dB. 30 dB has 1,000 times.
A-weighted decibels, abbreviated dBA, or dBa, or dB(a), are an expression of the relative loudness of sounds in air as perceived by the human ear.
The human ear is more sensitive to sound in the frequency range 1 kHz to 4 kHz than to sound at very low or high frequencies. dBa adjusts sound level down at low and high frequencies to compensate for this.
See: Decibel A, B and C at EngineeringToolbox.com
Sounds with a loudness of 120 dB or more can cause pain and damage to the human ear.

LOUDNESS OF SOME SOUNDS

Sound Decibels (dB)
jet engine 170
rock concert 100-125
thunderstorm 90-110
vacuum cleaner 75-80
conversation 60-70
refrigerator 40
classroom 35
whispering 10-20
near total silence 0
See:
Acceptable Noise - dBA - Levels

The speed of a sound wave depends upon the medium the wave is moving through. Sound moves faster through dense materials such as wood or metal because the molecules are close together. Sound also moves faster through warmer materials because the molecules of a warm substance are colliding more often than the molecules of a cold substance.

Medium Speed of Sound (m/sec)
air (0° C./32° F.)
(sea level)
331 (740 MPH)
air (20° C./68° F.) 344 (770 MPH)
cork 500
alcohol 1,240
water 1,500
wood (oak) 3,850
brick 3,650
glass 4,540
aluminum 5,000
iron 5,103
steel 5,200
I've seen Mach 1 (the speed of sound) listed as 761.5 and 770 MPH.

FREQUENCY RANGE OF SOME SOUND

Source of Sound Frequency Range (Hz)
Porpoise 7,000-120,000
Bat 10,000-120,000
Stereo 15-30,000
Dog whistle 20,000-24,000
Frog 50-8,000
Piano 30-4,100
Dog 450-1,800
Human 85-1,100
Vocal, Bass 40 to 900
Vocal, Tenor 130 to 1300
Vocal, Alto 175 to 1760
Vocal, Soprano 220 to 2100
Human Voice
Professional singers usually have a range of 3+ octives. Julie Andrews has a range of 4 octaves, from C3 below middle C to C7 above high C (some credit her with 5 octaves).
Source of Sound Frequency Range (Hz)
Acoustic Guitar 82 to 880
Bass Guitar 41 to 300
Bass, Standup 41 to 261
Bass Guitar, 5 String, with Low B String 32 to 300
Bassoon 62 to 525
Clarinet 160 to 1750
Electric Guitar 82 to 1050
Flute 260 to 2600
French Horn 82 to 1000
Oboe 260 to 2600
Piccolo 525 to 4200
Pipe Organ 27 to 4200
Trumpet 160 to 1000
Tuba 45 to 240
Violin 200 to 3100
Middle C (C4), Hi-C (C6)261.63, 1046.52 Hz
Octave around middle C (A3 - G4)220-415.4
Piano A0 - C8 27.5-4186
Sound Examples
Note 1: Note numbering starts at C. e.g. C4 follows B3. A piano keyboard goes A0, B0, B0, C1, C1, D1, ...
Note 2: Concert pitch with A4 set to 440hz is modern. In other times and other places concert pitch may have been a different frequency, and usually a bit lower. The pitch of A440 has remained since 1939; pitches have risen a little, particularly in Eastern European countries, which often wish pianos to be tuned to A 444 or even a bit above.
Note 3: Each octave represents a doubling of frequencies.

RANGES OF HEARING

Organism Frequency (Hz)
Dolphin 150-150,000
Bat 1,000-120,000
Cat 60-70,000
Dog 15-50,000
Human 20-20,000

ULTRASOUND

Ultrasound refers to sound waves that travel at very high frequencies. Doctors use ultrasound to look at soft tissues inside the human body without having to perform surgery. Ultrasonic waves reflect off soft tissue and the reflected waves can be converted into a picture, called a sonogram.

Ultrasound can also be used to find tumors, break up kidney or gall stones, clean teeth, and treat muscle spasms and sprains. Ultrasonic vibrations are used to clean small metal items, such as jewelry, electronic components, and machine parts.

Brief History of Recording

From: AUDIO AND HI-FI at www.diarama.cwc.net
The earliest attempts at sound recording is credited to Alexander Graham Bell with his invention of the "Phonograph" in 1877. Sound waves from the subject to be recorded were "captured" by a horn and focused onto a metal diaphragm. The diaphragm was connected to a stylus that traced a groove onto a wax cylinder.

Around 1915 Berliner invented of the Gramophone Disc. Similar in concept to the Cylinder but made from a 10 inch Shellac (an early form of plastic similar to Bakalite) disc rotating at 78 rpm.

1920 Bell System pioneers electrical recording, improved frequency response, lower distortion, the orthophonic phonograph, and the long-playing record.

1933: Stereophonic sound: Bell Labs transmits first stereo sound, a symphony concert, over phone lines from Philadelphia to Washington.
LP and stereo records Prior to 1931, most phonograph records were produced by laterally cutting vibrations into wax discs. Bell Labs developed a technique that used vertical cutting, which resulted in better stylus tracking and lower harmonic distortion. It also made possible closer groove spacing for longer playing time. The record "album" was born.

In 1978 digital recording was developed by Philips in Germany. Two years later, Sony of Japan joined Philips to perfect a commercially viable format that was to become known as the "Compact Disc". It was launched in Japan in 1982 and eventually launched in Europe in 1983. The sound signal was represented as "pits" and "troughs" on a protected part of the disc and was "read" by a low powered laser.

Some General Principles

At one time, the range of human hearing was considered to be from 50 Hz to 15 kHz (original definiton of high-fidelity [hi-fi]), and so recordings and playback equipment had to be able to reproduce that range of frequencies. As technical progress continued, the range was redefined as 20 Hz to 20 kHz.

Digital sampling theory requires you sample at twice the maximum frequency you want to record, so CDs record a 16-bit (levels of audio) sample at a rate of 44kHz. See Digital Recording Basics.

While the human ear can't hear pure tones above about 20kHz, the presence (or absence) of upper partial tones far above this frequency is clearly audible because these ultrasonic components affect the resultant waveform that the ear receives.

Sony and Philips, the co-inventors of the compact disc, have publicly acknowledged the inadequacies of the 16-bit/44kHz digital format. They have a new product called the Super Audio Compact Disc (SACD) that uses a new digital recording process called Direct Stream Digital (DSD). The DSD process extends bandwidth and dynamic range far beyond the inadequate limits of compact disc. Sony's literature says the new product is "more like analog."

Sound can be heard from further away in very dry air than in humid air. Water or humidity in the air absorbs much of the sound, thus reducing how far it will travel and still be heard. Wind can also reduce the distance. On a cold, dry winter day you should be able to hear sounds from greater distances than on a day before it will snow.

The density of the air actually only affects the speed of the sound and not the distance it travels.

last updated 17 Nov 2002