- #1
Sleeme
- 6
- 0
Hey everybody,
I'm trying to figure out what the vibration modes of a circular membrane would look like if we put some sound through it.
As you may know does a circular membrane with clamped edges at radius a behave according to the wave equation.
The general solution thereof has the form:
[itex]
u(r,\theta,t) = J_m(\lambda_{mn} r)\left(C\cos m \theta + D\sin m \theta\right)\left(A\cos c\lambda_{mn} t + B\sin c\lambda_{mn} t \right)
[/itex]
Therefore given a vibration mode n,m we can calculate its frequency f:
[itex]
f_{mn}= \frac{\omega}{2\pi}=\frac{c\lambda_{mn}}{2\pi} = \frac{c\alpha_{mn}}{2\pi a}
[/itex]
where alpha are the zeros of the bessel funcion
So every mode has such a eigenfrequency.
Now working the other way around: when given a soundfile, how can I determine, how the membrane would vibrate? Mostly I'm interested in solving this discretly not analyticaly.
I tried to come up with a formulation like in the discrete Fourier transform:
A*x = b where b is the sound and in A (of size t,mn I have sin(\lambda_{mn}t) where t is different in each row. But when solving this for x somehow the solution has very high frequencies. For example for a simple sinus, so I'm obviously doing something wrong here
Any Idea? Am I completely wrong how I could solve this?
Selim
I'm trying to figure out what the vibration modes of a circular membrane would look like if we put some sound through it.
As you may know does a circular membrane with clamped edges at radius a behave according to the wave equation.
The general solution thereof has the form:
[itex]
u(r,\theta,t) = J_m(\lambda_{mn} r)\left(C\cos m \theta + D\sin m \theta\right)\left(A\cos c\lambda_{mn} t + B\sin c\lambda_{mn} t \right)
[/itex]
Therefore given a vibration mode n,m we can calculate its frequency f:
[itex]
f_{mn}= \frac{\omega}{2\pi}=\frac{c\lambda_{mn}}{2\pi} = \frac{c\alpha_{mn}}{2\pi a}
[/itex]
where alpha are the zeros of the bessel funcion
So every mode has such a eigenfrequency.
Now working the other way around: when given a soundfile, how can I determine, how the membrane would vibrate? Mostly I'm interested in solving this discretly not analyticaly.
I tried to come up with a formulation like in the discrete Fourier transform:
A*x = b where b is the sound and in A (of size t,mn I have sin(\lambda_{mn}t) where t is different in each row. But when solving this for x somehow the solution has very high frequencies. For example for a simple sinus, so I'm obviously doing something wrong here
Any Idea? Am I completely wrong how I could solve this?
Selim