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MECA Electronics

Absorption and Velocity of Sound in Still Air
Sound is a vibration that travels through an elastic medium as a wave. The speed of sound describes how much distance such a wave travels in a certain amount of time. In dry air at 20 °C (68 °F), the speed of sound is 343 meters per second (1,125 ft/s). This equates to 1,236 kilometers per hour (768 mph) or about one mile in five seconds. This figure for air (or any given gas) increases with gas temperature, but is nearly independent of pressure or density for a given gas. For different gases, the speed of sound is dependent on the mean molecular weight of the gas, and to a lesser extent upon the ways in which the molecules of the gas can store heat energy from compression (since sound in gases is a type of compression).

Although "the speed of sound" is commonly used to refer specifically to the speed of sound waves in air, the speed of sound can be measured in virtually any substance. Sound travels faster in liquids and non-porous solids than it does in air, traveling about 4.4 times faster in water than air. Additionally, in solids, there occurs the possibility of two different types of sound waves: one type is associated with compression (the same as usual sound waves in fluids) and the other is associated with shear-stresses, which cannot occur in fluids. These two types of waves have different speeds, and (for example in an earthquake) may thus be initiated at the same time but arrive at distant points at appreciably different times. The speed of compression-type waves in all media is set by the medium's compressibility and density, and the speed of shear-waves in solids is set by the material's rigidity and density. - Wikipedia

     Speed of Sound = (Coefficient of Stiffness / Material Density )

The tables of data below refer only to the temperature 20°C (68°F). Values are provided for relative humidities of 0%, 30%, 50%, 70% 90%, and 100%.
 
Frequency
(Hz)		 Absorption
(dB/1000 ft)		 Absorption
(dB/km)		 Absorption
(dB/s)		 Velocity
(1000 ft/s)
Relative Humidity = 0%
         
20 0.154 0.51 0.174 1.126892
40 0.327 1.07 0.368 1.127013
50 0.384 1.26 0.433 1.127050
63 0.436 1.43 0.491 1.127085
100 0.509 1.67 0.573 1.127131
200 0.560 1.84 0.631 1.127161
400 0.596 1.96 0.672 1.127169
630 0.645 2.11 0.727 1.127171
800 0.692 2.27 0.780 1.127172
1250 0.861 2.82 0.970 1.127172
2000 1.262 4.14 1.423 1.127173
4000 2.696 8.84 3.030 1.127178
6300 4.541 14.89 5.118 1.127182
10000 8.013 26.28 9.032 1.127184
12500 10.918 35.81 12.306 1.127186
16000 15.901 52.15 17.923 1.127187
20000 22.978 75.37 25.901 1.127187
40000 81.405 267.01 91.759 1.127188
63000 196.544 644.66 221.542 1.127188
80000 314.677 1032.14 354.700 1.127188

Frequency
(Hz)		 Absorption
(dB/1000 ft)		 Absorption
(dB/Km)		 Absorption
(dB/s)		 Velocity
(1000 ft/s
Relative Humidity = 30%
         
20 0.009 0.03 0.010 1.127976
40 0.034 0.11 0.038 1.127980
50 0.051 0.17 0.057 1.127984
63 0.075 0.25 0.085 1.127987
100 0.151 0.50 0.170 1.127999
200 0.309 1.01 0.349 1.128023
400 0.484 1.59 0.546 1.128037
630 0.682 2.24 0.770 1.128041
800 0.868 2.85 0.979 1.128044
1250 1.552 5.09 1.751 1.128045
2000 3.333 10.93 3.760 1.128047
4000 11.856 38.89 13.374 1.128056
6300 27.626 90.61 31.164 1.128072
10000 62.493 204.98 70.498 1.128105
12500 89.659 294.08 101.148 1.128131
16000 128.814 422.51 145.324 1.128166
20000 171.847 563.66 193.879 1.128204
40000 338.710 1110.97 382.172 1.128316
63000 499.838 1639.47 563.998 1.128361
80000 635.085 2083.08 716.614 1.128375

Frequency
(Hz)		 Absorption
(dB/1000 ft)		 Absorption
(dB/Km)		 Absorption
(dB/s)		 Velocity
(1000 ft/s
Relative Humidity = 50%
         
20 0.006 0.02 0.006 1.128795
40 0.022 0.07 0.025 1.128797
50 0.034 0.11 0.038 1.128798
63 0.052 0.17 0.058 1.128800
100 0.117 0.38 0.132 1.128807
200 0.313 1.03 0.353 1.128826
400 0.563 1.85 0.636 1.128849
630 0.734 2.41 0.828 1.128858
800 0.851 2.79 0.961 1.128860
1250 1.231 4.04 1.390 1.128862
2000 2.176 7.14 2.457 1.128865
4000 6.752 22.15 7.622 1.128867
6300 15.643 51.31 17.659 1.128871
10000 37.521 123.07 42.357 1.128881
12500 57.009 186.99 64.357 1.128890
16000 89.594 293.87 101.143 1.128903
20000 132.719 435.32 149.830 1.128922
40000 382.722 1255.33 432.101 1.129020
63000 654.606 2147.11 739.115 1.129099
80000 844.024 2768.40 953.016 1.129133

Frequency
(Hz)		 Absorption
(dB/1000 ft)		 Absorption
(dB/Km)		 Absorption
(dB/s)		 Velocity
(1000 ft/s
Relative Humidity = 70%
         
20 0.004 0.01 0.005 1.129618
40 0.016 0.05 0.018 1.129619
50 0.025 0.08 0.028 1.129619
63 0.039 0.13 0.044 1.129620
100 0.092 0.30 0.104 1.129623
200 0.284 0.93 0.321 1.129638
400 0.611 2.01 0.691 1.129662
630 0.829 2.72 0.937 1.129673
800 0.947 3.11 1.070 1.129678
1250 1.250 4.10 1.412 1.129683
2000 1.915 6.28 2.163 1.129685
4000 5.056 16.58 5.712 1.129687
6300 11.197 36.73 12.649 1.129689
10000 26.624 87.33 30.077 1.129693
12500 40.758 133.69 46.044 1.129697
16000 65.246 214.01 73.708 1.129704
20000 99.365 325.92 112.254 1.129712
40000 339.153 1112.42 383.165 1.129770
63000 673.667 2209.63 761.137 1.129842
80000 924.481 3032.30 1044.556 1.129884

Frequency
(Hz)		 Absorption
(dB/1000 ft)		 Absorption
(dB/Km)		 Absorption
(dB/s)		 Velocity
(1000 ft/s
Relative Humidity = 90%
         
20 0.003 0.01 0.004 1.130443
40 0.013 0.04 0.014 1.130443
50 0.019 0.06 0.022 1.130444
63 0.031 0.10 0.035 1.130444
100 0.074 0.24 0.084 1.130446
200 0.250 0.82 0.283 1.130457
400 0.621 2.04 0.702 1.130478
630 0.903 2.96 1.021 1.130493
800 1.045 3.43 1.182 1.130498
1250 1.344 4.41 1.520 1.130505
2000 1.892 6.21 2.139 1.130508
4000 4.337 14.22 4.903 1.130511
6300 9.099 29.84 10.286 1.130512
10000 21.133 69.32 23.891 1.130514
12500 32.258 105.81 36.468 1.130516
16000 51.762 169.78 58.518 1.130520
20000 79.424 260.51 89.791 1.130526
40000 290.117 951.58 327.995 1.130561
63000 629.701 2065.42 711.948 1.130612
80000 911.286 2989.02 1030.346 1.130651

Frequency
(Hz)		 Absorption
(dB/1000 ft)		 Absorption
(dB/Km)		 Absorption
(dB/s)		 Velocity
(1000 ft/s
Relative Humidity = 100%
         
20 0.003 0.01 0.003 1.130856
40 0.011 0.04 0.013 1.130856
50 0.018 0.06 0.020 1.130857
63 0.028 0.09 0.031 1.130857
100 0.068 0.22 0.076 1.130858
200 0.234 0.77 0.265 1.130868
400 0.616 2.02 0.696 1.130888
630 0.928 3.05 1.050 1.130902
800 1.087 3.57 1.230 1.130909
1250 1.399 4.59 1.582 1.130917
2000 1.917 6.29 2.168 1.130921
4000 4.140 13.58 4.682 1.130924
6300 8.451 27.72 9.557 1.130925
10000 19.357 63.49 21.891 1.130926
12500 29.461 96.63 33.318 1.130929
16000 47.227 154.90 53.410 1.130931
20000 72.538 237.93 82.036 1.130935
40000 269.598 884.28 304.905 1.130963
63000 601.714 1973.62 680.543 1.131007
80000 888.113 2913.01 1004.492 1.131042



Information from CRC Handbook of Chemistry and Physics, 7first Edition, 1990-1991, David R. Lide
Minor corrections made 8/17/2005 - thanks to Andy H.
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