V_SOUNDSPEED gives the speed of sound, density of air and acoustic impedance as a function of temp & pressure [V,D,Z]=(T,P,M,G) Inputs: T air temperature in Celsius [20 deg C] P air pressure [1 atm] M average molecular weight of air [0.0289644 kg/mol] G adiabatic constant for air [1.4] Outputs: V is the speed of sound in m/s D density of air in kg/m^3 Z characteristic impedance of air Pa.s/m

0001 function [v,d,z]=v_soundspeed(t,p,m,g) 0002 %V_SOUNDSPEED gives the speed of sound, density of air and acoustic impedance as a function of temp & pressure [V,D,Z]=(T,P,M,G) 0003 % 0004 % Inputs: T air temperature in Celsius [20 deg C] 0005 % P air pressure [1 atm] 0006 % M average molecular weight of air [0.0289644 kg/mol] 0007 % G adiabatic constant for air [1.4] 0008 % 0009 % Outputs: V is the speed of sound in m/s 0010 % D density of air in kg/m^3 0011 % Z characteristic impedance of air Pa.s/m 0012 0013 % Notes: (1) Sound pressure is often measured in dB (SPL) relative to 20uPa [20*log10(p/p0)] 0014 % Sound pressure is inversely proportional to distance. 0015 % (2) Sound intensity is often measured indB relative to pW/m^2,[10*log10(J*10^12)] 0016 % Intensity is inversely proportional to distance squared. 0017 % (3) Intensity * impedance = pressure^2, so with the default values, 1 pW/m^2 = sqrt(Z) = 20.33 uPa 0018 % So: X dB (SPL) = X-93.98 dB (Pa) = X-0.14 dB (pW/m^2) = X-120.14 dB (W/m^2) 0019 % where 93.98=20*log10(50000), 0.14=10*log10(Z/400), 120.14=10*log10(1e12*z/400) 0020 % (4) The default air pressure (which does not affect sound speed) in various units is: 0021 % 1 atm = 101325 Pa = 1.01325 bar = 1.0332 at = 760 torr = 14.696 psi 0022 0023 % Copyright (C) Mike Brookes 2006 0024 % Version: $Id: v_soundspeed.m 10865 2018-09-21 17:22:45Z dmb $ 0025 % 0026 % VOICEBOX is a MATLAB toolbox for speech processing. 0027 % Home page: http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html 0028 % 0029 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 0030 % This program is free software; you can redistribute it and/or modify 0031 % it under the terms of the GNU General Public License as published by 0032 % the Free Software Foundation; either version 2 of the License, or 0033 % (at your option) any later version. 0034 % 0035 % This program is distributed in the hope that it will be useful, 0036 % but WITHOUT ANY WARRANTY; without even the implied warranty of 0037 % MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 0038 % GNU General Public License for more details. 0039 % 0040 % You can obtain a copy of the GNU General Public License from 0041 % http://www.gnu.org/copyleft/gpl.html or by writing to 0042 % Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA. 0043 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 0044 0045 if nargin<4 0046 g=1.4; 0047 if nargin<3 0048 m=0.0289644; % gm/mol 0049 if nargin<2 0050 p=1; 0051 if nargin<1 0052 t=20; 0053 end 0054 end 0055 end 0056 end 0057 p=p*101325; % convert pressure: atm to pascal 0058 k=t+273.15; % absolute temperature 0059 r=8.3144; % J/(mol K) universal gas constant 0060 d=p*m/(r*k); 0061 v=sqrt(g*r*k/m); 0062 z=v*d;

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