>Hello guys,
>
>I'm having problems with understanding what I have read from an SAE
>international paper.
>
>There they did an measurement called : Acoustic response test of an open
>cavity, where they evaluate the acoustic response of a cavity with small
>orifice by a transfer function of the system.
>
>The measurement consists of two steps. In the first step, white noise is
>emmitted by a loudspeaker while the cavity is opened. A primary signal G1
>inside the cavity and a reference signal F1 outside cavity are recorded.
>Then a transfer function of the open cavity is obtained by H1= G1(f)/F1(f)

>with  G1(f) and F1(f) being the Fourier transforms of each signal
>respectively.
>
>In the second step, the cavity is closed during the excitation. Two
signals
>G2 and F2 both outside the cavity are recorded. And agian the transfer
>function of the closed system was given by H2= G2(f)/F2(f). 
>
>After those two step, the transfer function of the acoustic response H is
>the ratio of the transfer function of step1 and step2: H=H1/H2. The plot
of
>the magnitude of H versus frequency is larger than that of H1.
>And it said that the second step is necessary to account for the
scattered
>pressure field being generated near the orifice,and using this method the
>incident pressure can be isolated. Another saying is that the second step
>is used to compensate for transfer losses of sound from the peaker toward
>the cavity region.
>
>The first question is what does the magnitude of the transfer function
tell
>about the cavity system. I would interpret it like that, it gives us the
>amount of gain from a certain input signal. So with the transfer function
>and a input signal(at the same location as F1) given, we could directly
>obtain a response of the output. How would  you interpret? 
>
>Anothe question is why do we need the step2 to compensate the transfer
>loss. Im not sure how to interpret this.
>
>Any ideas and comments are very welcome.
>Thanks a lot.
>
>Eva
> 
>any ideas ? 

Hello guys,

I'm having problems with understanding what I have read from an SAE
international paper.

There they did an measurement called : Acoustic response test of an open
cavity, where they evaluate the acoustic response of a cavity with small
orifice by a transfer function of the system.

The measurement consists of two steps. In the first step, white noise is
emmitted by a loudspeaker while the cavity is opened. A primary signal G1
inside the cavity and a reference signal F1 outside cavity are recorded.
Then a transfer function of the open cavity is obtained by H1= G1(f)/F1(f) 
with  G1(f) and F1(f) being the Fourier transforms of each signal
respectively.

In the second step, the cavity is closed during the excitation. Two signals
G2 and F2 both outside the cavity are recorded. And agian the transfer
function of the closed system was given by H2= G2(f)/F2(f). 

After those two step, the transfer function of the acoustic response H is
the ratio of the transfer function of step1 and step2: H=H1/H2. The plot of
the magnitude of H versus frequency is larger than that of H1.
And it said that the second step is necessary to account for the scattered
pressure field being generated near the orifice,and using this method the
incident pressure can be isolated. Another saying is that the second step
is used to compensate for transfer losses of sound from the peaker toward
the cavity region.

The first question is what does the magnitude of the transfer function tell
about the cavity system. I would interpret it like that, it gives us the
amount of gain from a certain input signal. So with the transfer function
and a input signal(at the same location as F1) given, we could directly
obtain a response of the output. How would  you interpret? 

Anothe question is why do we need the step2 to compensate the transfer
loss. Im not sure how to interpret this.

Any ideas and comments are very welcome.
Thanks a lot.

Eva