Calculation of insertion loss in ducts after Piening

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Calculation of insertion loss in ducts after Piening

Postby interface » Wed Jul 13, 2005 7:34 pm

This Excel file may be interesting for you.
Would appreciate your comments.

interface

p.s. Analysis ToolPak needs to be activated
Last edited by interface on Tue Aug 30, 2005 8:50 pm, edited 1 time in total.
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Postby Robert2004 » Wed Jul 13, 2005 11:01 pm

Very slick interface. I don't know what the Analysis ToolPak is, and didn't knowingly activate it, but I was able to change the width of the duct and the graph updated. When I changed the absorption thickness to 0, the graph zero-ed out  (as likely would be expected), but when I undid the change (back to the default value), the graph didn't update, and all the insertion loss values get " #NAME?".

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Postby Eric.Desart » Wed Jul 13, 2005 11:40 pm

Robert,

That's a logical error if
1) Analysis Toolpak isn't installed, or installed but not activated
2) For people with other language Excel editions they will always get this error (in their own language), Analysis Toolpak installed and activated or not, when an analysis toolpak function from another language edition is used.

Check via Tools > Add-Ins > Analysis Toolpak that checkbox should be checked.
If the name Analysis Toolpak isn't there it means it isn't installed (it's standard on your office CD, and standard installed if you choosed complete installation)

Or search Excel help for Analysis Toolpak

try this formula (in English Excel edition):
=RANDBETWEEN(1,1)
the result should be 1
if an error shows then your analysis toolpak isn't installed, or installed but not activated.  This then means that > 90 Excel functions are not available to you.
Last edited by Eric.Desart on Thu Jul 14, 2005 9:58 am, edited 2 times in total.
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Postby Robert2004 » Thu Jul 14, 2005 3:48 am

OK, that worked perfectly (Mac OS X, Excel 2004).

No complaints here, a fantastic interface -- but what would it take to add round duct?  And does the gauge of steel (thickness) of the ductwork matter, or is that pretty much irrelvant? Any insertion data on turning vanes?

So far the air handling design and custom ductwork has been the (relatively) highest cost factor of my studio.

Robert
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Postby Eric.Desart » Thu Jul 14, 2005 9:12 am

Robert,

Round duct by definition will give significant higher insulation in the low frequencies than rectangular duct for the same guage thickness of the iron. or alu they are made of.

Rectangular ducts are noisier to the outside world, but will give higher low frequent absorption.
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Postby interface » Thu Jul 14, 2005 1:41 pm

Hi Robert,

The thickness of the steel matters but in a certain way it is also irrelevant, the absorption is calculated by the damping of the absorber and the transmission through the wall impedance (steel wall).
Therefore I added a very massive wall to get only the damping results of the porous absorber.
There is an interrelationship between absorption and transmission.
Have a look at this second excel file.
The insertion losses of turning vanes or curves are always higher than for straight ducts.
But it is also important to keep the pressure loss and velocity of flow in mind.
As a genaral rule the velocity of flow in ducts or silencers shouldn’t exceed 3m/s (but these needs to be calculated more in detail).

interface
Last edited by interface on Tue Aug 30, 2005 8:51 pm, edited 1 time in total.
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Postby Andrew Steel » Thu Jul 14, 2005 9:26 pm

Hi Interface,

You mention a relationship between absorptoin and transmission - do you have any explanation?

Andrew
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Postby interface » Thu Jul 14, 2005 9:55 pm

Hi Andrew,

Absorption is the opposite of reflection.
If there is maximum absorption you don’t get any or less energy (reflection) back.
If a wall is very light (foil or similar) there is a strong transmission especially in the lower frequencies (effect of a tent). That means you don’t get any energy back as well.
But this is not absorption and the effect is the same.
If you enter a low value for the mass in the second excel sheet, you would get the effect of higher absorption, which is actually a transmission.
This also means that you have to shield your ducts as good as possible.

Interface
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