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Background :

My blower in one of the experiments is generating noise due the a short airflow path to atmosphere. The reason is due to a sudden change in pressure (high to low) the high noise is generated. I am not sure if the blower is noisier or the movement of air is creating the noise. Below is one of my design that I think should reduce the noise by allowing more volumetric area for the air to move out and thus reducing the noise.

Any comments ?Based on my understanding Sound 2 should be lesser than Sound 1

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    $\begingroup$ Nice exponential horn you got there. The second may actually be louder than the first. It's not the change in pressure that generates the noise but it's the turbulence, which already develops inside the pipe. $\endgroup$ – CuriousOne Mar 23 '16 at 7:41
  • $\begingroup$ Consider using an internal helix inside the tube to force air passing through to spin as it exits effectively reducing turbulence. $\endgroup$ – Neil Mar 23 '16 at 7:45
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    $\begingroup$ @CuriousOne - Up late, eh? :-) $\endgroup$ – DIYser Mar 23 '16 at 7:48
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    $\begingroup$ There's turbulence generated inside the pipe, and there's the question of impedance-matching at the interface between the end of the pipe and the open atmosphere. So if you've got back-pressure inside the pipe, you need a wider pipe from end to end. For impedance matching, take a look at any brass musical instrument's bell. $\endgroup$ – Carl Witthoft Mar 23 '16 at 14:05

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