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Date: Sun, 30 May 2021 15:23:18 -0400
From: "Don" <dgpolvani@gmail.com>
To: <Phys-L@Phys-L.org>
Subject: Re: [Phys-L] rms / conic / arithmetic / geometric averages
Message-ID: <000801d75589$3f2c0910$bd841b30$@gmail.com>
Content-Type: text/plain; charset="utf-8"
Thanks again to David Bowman for his (5/29/21) clear, detailed, and helpful comments on my 5/29/21 post regarding the flared horn paraboloid and spherical segment equivalent cylindrical radii.
1) Flared Horn
David is quite right. I neglected the minus sign option when taking the square root and ended up mistakenly revolving the outer side of the parabola about the y-axis (which produces a bulbous horn) instead of the inner side (which produces a flared horn). Again, a plot of my expression for x as a function of y would have shown this error (I did plot y vs x but not my chosen x vs y) I agree with his results for the equivalent cylindrical radius (R) for the flared horn formed by the inner side of my chosen parabola. (See David's response below for my notation and more expressions)
R = sqrt((R_1^2 + 2*R_1*R_2 + 3*R_2^2)/6)
2) Spherical Segment with Two Bases
I'm glad that we have reached consensus that my results of 5/24/21 are correct despite the ambiguities of the English language.
Finally, I have not been able to find a mathematical expression for the shape of the flared bell of a trumpet. I have found internet articles for bell sizes, bore sizes, and how trumpets are made but no mathematical expression for the shape of a trumpet bell. If any of you know of such an expression, I would be most appreciative if you would send it to me.
Don Polvani
-----Original Message-----
From: Phys-l <phys-l-bounces@mail.phys-l.org> On Behalf Of David Bowman
Sent: Saturday, May 29, 2021 10:23 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] rms / conic / arithmetic / geometric averages
Regarding Don P's 'average' radius calculation for his new updated paraboloid
of revolution:
1) My results for a "proper" flared (parabolic) horn (similar to a
trumpet bell) are as follows:
Parabola : y = a*(x - c)^2
a = h/(R_1 - R_2)^2
c = R_1
V = pi*h*((17*R_1^2 - 14*R_1*R_2 + 3*R_2^2)/6)
R = sqr((17*R_1^2 - 14*R_1*R_2 + 3*R_2^2)/6)
Where: h = vertical height between bottom and top of the paraboloid
of revolution
R_1 = radius (larger) of bottom base
R_2 = radius (smaller) of top base
V= volume of paraboloid of revolution
R = radius of equivalent cylinder with same
height and same volume
As a high school trumpet player (long, long ago!), I am curious if
anyone on the list knows the exact mathematical shape of a trumpet
bell?