Help with formula - Maximizing Performance from Loudspeaker Ports?
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eqjive
diyAudio Member

Join Date: Jan 2013
Help with formula - Maximizing Performance from Loudspeaker Ports?

Can anyone clarify this formula from the AES paper 'Maximizing Performance from Loudspeaker Ports'? (see attached screen shot). I'm looking to create a spreadsheet (as the paper suggests possible) to determine tuning frequency of heavily flared ports (NFR .5 - 1).

It is formula number 11, page 14 of the paper 'Maximizing Performance from Loudspeaker Ports' or page 32 of the J. Audio Eng. Soc., Vol. 50, No.1/2, 2002 January/February

I'm having some trouble figuring this one out... what are the units to be used if speed of sound is given in meters, what should throught area, diameter, volume etc be?

Can anyone give an example using the formula so I can understand where I am getting confused?

Thank you!!

EqJive
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 16th September 2013, 10:48 AM #2 sreten   R.I.P.   Join Date: Nov 2003 Location: Brighton UK Hi, I'd uses cm, cm/s, cm squared and cm cubed for calculations. Convert C to cm/s and Litres to cm cubed. Really doesn't matter as long as your consistent. What you uses to input parameters can be converted in the calculations, so use whatever input format you like like C in m/s and Vb in litres. Note that big ports will reduce the actual Vb. rgds, sreten. If its going to end up part of something more complex standardise on m, m/s, m squared and m cubed for all calculations and convert the input / output format. Last edited by sreten; 16th September 2013 at 10:58 AM.
 16th September 2013, 10:49 AM #3 AndrewT   diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders I get the impression that everything is in metres. __________________ regards Andrew T.
 17th September 2013, 02:11 AM #4 OscarS   diyAudio Member   Join Date: Jan 2011 As reten said, so long as you're consistent you can use different units. The main idea is to realize that since c is in units of "distance/time", and frequency is "1/time", you need to cancel out the "distance" unit in the numerator that "c" contributes. That means that the outcome of the square root function has to simplify down to "1/distance". Sure enough, Aeff= distance˛, and the product of Leff*Vb = distance^4. Distance˛/distance^4 reduces to 1/distance˛, the square root of which leads to "1/distance". So as long as the units for distance are consistent, the formula will churn out the correct numbers. __________________ ____________ http://www.diyaudio.com/forums/swap-...fers-sale.html
 17th September 2013, 01:50 PM #5 eqjive   diyAudio Member   Join Date: Jan 2013 Thank you!!! With your help, I figured it out. - EqJive

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