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 Post subject: Speaker cone math
PostPosted: Mar Wed 07, 2018 3:01 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1890
Location: Mesa, AZ, USA
I am trying to make a replacement speaker cone.

I found an article with a mathematical formula, but can't seem to get it to work.
http://www.hrsasa.asn.au/docs/recone%20speakers.PDF

The article says calculate the angle of the cone using angle=tan-1( h(D1-D2)/2)*pi/180
Tried this on the given sample data of D1=10 D2=1.75 h=2.75, but do not come up with the given angle of 34.8 degrees.

in Excel I am using: =DEGREES(ATAN((F3/(F1-F2)/2)))*(3.1415/180)

Is the formula given at that web site correct?


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 Post subject: Re: Speaker cone math
PostPosted: Mar Wed 07, 2018 3:24 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 12000
Location: S. Dartmouth MA 02748-1225 USA
ASUMike wrote:
I am trying to make a replacement speaker cone.
I found an article with a mathematical formula, but can't seem to get it to work.
http://www.hrsasa.asn.au/docs/recone%20speakers.PDF
The article says calculate the angle of the cone using angle=tan-1( h(D1-D2)/2)*pi/180
Tried this on the given sample data of D1=10 D2=1.75 h=2.75, but do not come up with the given angle of 34.8 degrees.
in Excel I am using: =DEGREES(ATAN((F3/(F1-F2)/2)))*(3.1415/180)
Is the formula given at that web site correct?
I have used the formula at Nostalgia air, old school...

http://www.nostalgiaair.org/References/ ... lash03.htm

There is a notation in the article about using radians instead of degrees. It is how the calculator works, maybe applicable to excel too.

"Be aware that if you do the above calculations with a scientific calculator you may need to account for the angle in radians rather than in degrees .... "

YMMV

Chas


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 Post subject: Re: Speaker cone math
PostPosted: Mar Wed 07, 2018 3:46 pm 
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Joined: Feb Fri 19, 2016 1:57 am
Posts: 95
Location: Boyertown, PA
=DEGREES(ATAN(F3/((F1-F2)/2)))
or
=ATAN(F3/((F1-F2)/2))*(180/PI())


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 Post subject: Re: Speaker cone math
PostPosted: Mar Wed 07, 2018 6:20 pm 
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Joined: Dec Wed 25, 2013 7:57 am
Posts: 2184
Location: USA
I prefer seeing math formulas written out with full notation so there's less chance of confusion. I also like seeing formulas derived in steps so the reader can see how it works.

In this case, the author made a mistake. The "π/180" term converts "degree" into "radian", there's no reason for it to be there. I don't know how he got "34.8" degrees.

To keep it simple, you can just measure "h" and "w" then use the calculator to get ARCTAN.

As always, please check my math (drawing is not to scale)
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 Post subject: Re: Speaker cone math
PostPosted: Mar Thu 08, 2018 5:20 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1890
Location: Mesa, AZ, USA
Thanks! That was most helpful.


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