Tip:
Highlight text to annotate it
X
Regarding vibrations, one of the most interesting devices that exist for tests
not only for vibrations but also for acoustics
is this structure here in which I lay my hands on
It’s the impedance pipe
It was built in concrete, together with IBM
during the development
of a semi-anechoic chamber for the IBM labs here in Rio.
What is the impedance pipe?
It is meant basically to empirically obtain
the Alfa value of the materials
that is, a sound absorbent coefficient.
Many materials were tested in it,
as a result, they found an ideal type of foam
that is to be used as a coating in the lab walls
the anechoic and semi-anechoic IBM chambers.
It is composed, basically, of this long structure here,
that we see now, it must be approximately 8 meters long
where all these equipments are on now
The end of the pipe is open, one of the ends
On the other end, a loud speaker is fitted in
which we are going to show now
Here in this wooden box, that is here
goes a loud speaker, which will generate pure tones
depending on the frequency, naturally, with a variable frequency.
And inside here goes another mobile board
with a microphone to catch this sound sent by the loudspeaker.
The normal vibration modes, the resonance frequencies,
vary exactly because of this separation of the microphone inside the pipe.
And from the composition of this normal vibration modes
knowing the acoustic power put on the loudspeaker,
we can evaluate the starting point from which the microphone receives the difference
that is, the noise absorbed by the material that is placed inside the pipe
that is, the pipe is coated with this material.