I am trying to learn the membrane backed by air cavity in the following paper, figure 2. My code result does not match the paper result. can somebody point out the error?
I Have used equation no 3, 4, 5, and 9 to obtain figure 2 (a)
Tension is 76.53 N, density of membrane(T) is 0.265, air cavity (D) is 100 mm, radius of tube (a) is 50mm
Article Membrane sound absorber with a granular activated carbon infill
clc
clear all;
f= (100:2:1600);
omega= 2*pi*f;
rho_s=0.265; T=76.53*(1+1j*0.005); D=0.1; a=0.05; % Fig 2 a
c=343; rho_0=1.213; Z_0 = rho_0*c;
k0=omega/c;
km=omega.*sqrt(rho_s/T);
%% Impedance of membrane with air cavity only
Z_m = (1j*omega*rho_s)./(1-((2./km*a).*(besselj(1, km*a)./besselj(0,km*a))));
Z_w = -1j*Z_0*cot(k0*D);
Z_s = Z_m + Z_w
Z_s =Z_s/Z_0;
R = (Z_s - 1)./(Z_s + 1);
alpha_1 = 1 - ((abs(R)).^2);
figure(1)
set(gca,'FontSize',16)
plot(f,alpha_1);
xlabel('Frequency (Hz)')
ylabel('Sound absorption coefficient')
grid on
grid minor
ylim([0 1])
set(gca, 'XScale', 'log')
set(gca, 'YScale', 'log')
Hi! I suggest that you simply re write the original article equation in here, so readers outside institututions with acess to the journals does not need to pay for access to the paper journal in other to help you.
Thanks! Now, it is more interesting, in my opinion, to get a model that works in real rooms. Usually the data one can get out of a tube test like this will not give the same result as in a diffuse soundfield, in general. All too much of the literature care about measurements that are almost irrelevant. However, its easier to get nice results from tube measurements than in real rooms. Good luck with the work!
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