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Old 29th October 2002, 05:32 PM   #1
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Default radiation pattern math question

Hello all,

I am moddeling my speaker to be in Software.
Reading material is :
1. Loudspeaker and HeadPhone handbook by Borwick
2. Acoustics by Beranek
3. My old physics book
4. my old Telecom syllaby/text book (transmission lines and antennas)

So far i have been able to program 1 simple and 2 simple point sources and let it produce quite nicely a polar plot.

The problem is the plane piston source.
I do not know how to translate the formula into a nice piece of c-code !

Can any one help ?

For those who have the books
It is about formula 1.18 of [1]
or
formula 4.17 of [2]


best regards,


Simon
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Old 29th October 2002, 09:40 PM   #2
f4ier is offline f4ier  Australia
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I take it you're having problems with the directivity term. The Numerical Recipes Home Page might interest you

Good luck!

Isaac
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Old 30th October 2002, 05:14 PM   #3
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Default good direction

thanks for the link.

Did not really find what i was looking for (except after paying for the code). But th e direction / hint was more than fine.

I was able to code the formula and except for some minor multiplication factor i got the pictures i was after.

Thanks


grtz

Simon
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Old 30th October 2002, 05:21 PM   #4
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Default Re: good direction

This little appendix might provide some clues as well.

dave
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Old 31st October 2002, 04:24 PM   #5
MJK is offline MJK  United States
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Blu-Line,

If you go to my website, look in the TL Theory Section, open the Calculation Algorithm article, then find Figure 4.6, it shows a series expansion that calculates the acoustic impedance for a piston in an infinite baffle. I think that is what you are looking for, an expansion for the Bessel function to calculate the radiation pattern for a piston in an infinite baffle. You just need to extract the series expansion term and change the equation appropriately.

Hope that helps,

Martin
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Old 31st October 2002, 04:58 PM   #6
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Default pressure instead of impedance

Thanks for the link.

I have scanned it quickly (thorough read later), but see you work with the acoustic impedance. Why not pressure ??

(They are related anyway !)


grtz

Simon
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Old 31st October 2002, 05:04 PM   #7
MJK is offline MJK  United States
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Hi Simon,

The acoustic impedance is used as a boundary condition for my method. I do calculate the driver's volume velocity and the pressure to get the SPL which is plotted in my results.

Hope that helps,

Martin
www.quarter-wave.com
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