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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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