Plotting simple sound source

[jellicorse]

I've been trying to plot the behaviour of a simple sound source (harmonically oscillating piston) as the driving frequency passes through the resonant frequency.

However, the graph I obtain doesn't look like what I am expecting: i.e. a sharp rise in Sound Pressure Level towards a peak at resonance and a decrease thereafter, and I can't see why not...

I was wondering if anyone could take a quick look at this and see if there's anything obviously wrong:


%--------------------------------------------------------------------------
%
% Parameters
%
%--------------------------------------------------------------------------

mt=0.07; % mass of radiator

At=0.0430; % area of radiator

Rt=3.0; % damping coefficient, t

Kt=68000; % equivalent t stiffness

c2=340^2; % speed of sound squared
rho=1.205; % density of air
V = 0.015; %Vol of box

pref=50;

kappa=c2*rho/V;

%--------------------------------------------------------------------------
%
% Uncoupled natural frequency
%
%--------------------------------------------------------------------------

omt=sqrt( (Kt + kappa*At^2)/mt);


%--------------------------------------------------------------------------
%
% frequency, angular frequency
%
%--------------------------------------------------------------------------

f=(0:0.5:500);

om=2*pi*f;


%--------------------------------------------------------------------------
%
% Velocity
%
%--------------------------------------------------------------------------
>> F=0.4;
>> gamt=Rt/mt;
>> ut = F*i*om./(mt*(omt^2-om.^2) + i*gamt*om);
>> Atut=At.*ut; %Source Strength

%--------------------------------------------------------------------------
>> %Pressure
%
%--------------------------------------------------------------------------
>> r=1;
>> p=-i.*om*rho/(4*pi*r).*Atut;
>> dB=20*log (abs(p)/pref);


%--------------------------------------------------------------------------
%plot results

%--------------------------------------------------------------------------
>> plot(f,dB)

 

[jellicorse]

I've just solved the problem.... (I had neglected to change the damping)