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Old 24th September 2007, 07:06 AM   #1
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Default Formula for pipe Q

Hi All,

I had read somewhere that there's a formula which relates pipe length to circumference and cross sectional area for determining the Q of a pipe. Can anyone provide the formula or point me to a link? I tried to Google this, but was unsuccessful.

I'm evaluating a design for a Hegeman style subwoofer, but need to adjust the pipe dimensions to better fit a larger driver. I'd like to find out if there are any constraints I'll need to contend with.
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Old 24th September 2007, 04:37 PM   #2
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Greets!

The basic material Q I'm familiar with is = (SQRT SoS)/net po, so a 1 m long pipe with a 0.1 m dia = (SQRT~342)/((1*(0.1^2*pi/4)*1.21) = ~1946. Then there's a pipe cut-off Q = Fc/F as discussed here: http://mmd.foxtail.com/Archives/Dige....11.05.03.html

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Old 24th September 2007, 05:11 PM   #3
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Quote:
The basic material Q I'm familiar with is = (SQRT SoS)/net po, so a 1 m long pipe with a 0.1 m dia = (SQRT~342)/((1*(0.1^2*pi/4)*1.21) = ~1946. Then there's a pipe cut-off Q = Fc/F as discussed here: http://mmd.foxtail.com/Archives/Dig...9.11.05.03.html
Thanks for your reply, but could you help with defining the terms in the formula?

SoS?
net po?
where does 1.21 come from?

And is the above formula for the resonant frequency or the cutoff frequency?
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Old 24th September 2007, 07:02 PM   #4
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Speed of Sound and depending on who you ask/read, it will vary a bit, but FWIW in case you want to use MJK's TL simming program: 342 m/sec, the one I used in the example

po = weight of air, which varies with temp and humidity, which MJK uses 1.21 kg/m^3

Neither, it's the quality factor of the air mass 'slug', which is what you asked for by description, but I doubt it's what you think you need to accomplish your task. Not knowing the design details of the sub I can't help further beyond saying that scaling rarely works well without knowing how to scale everything, including the driver's specs.
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