Looking for Nearfield formula definitions - esp from engineering/math folks

JMB · 8th December 2005, 02:55 PM

Keele describes the need to measure at less than 0.55*De (effective diameter). NDT resource center (referring to ultrasonics) defines the transition point as N=D^2/(4*Lambda) where N is the transition point and D is the effective diameter of the transducer. I have also read that using the multiplier of 10 rather than 4 in the denominator may be a better way to estimate.

Would love some input, especially from engineering types.

Thanks,

Jay

MJK · 8th December 2005, 08:12 PM

I don't understand what you are looking for, if you could ask your question in a simplified and more detailed methodical way I might have an answer. Sorry, I am just not sharp enough to understand your opening paragraph.

Ron E · 8th December 2005, 11:09 PM

Methinks Jay wants to know the maximum distance that can be used in a nearfield cone measurement. I'm not really sure why, though.

DanWiggins · 9th December 2005, 05:04 AM

Always used d^2/lambda in the SONAR world... Always seemed to be fairly accurate.

Dan Wiggins
Adire Audio®

JMB · 9th December 2005, 12:39 PM

To Clarify,

As I am finishing up the Speaker Workshop Manual 2nd Edition, I came upon some conflicting information regarding Nearfield. I understand that it is a region in which there is considerable phase interference from shorter wavelength signals so that there is an effective upper frequency that one can use. I also understand that the distance (transition point) is defined by frequency so that that maximum usable upper frequency would define the transition distance if one is to do a nearfield measurement. It is that maximum measurement distance that I am looking for.

My sense is that Keele in defining the maximum measurement distance (0.55*De) was taking the transition point and then defining some point within that region to safely eliminate environmental influences. I am trying to clearly define the transition point so that people can determine their own safety margin for nearfield measurements. I also recognize that the closer to the cone, the better, but it is always nice to have an understanding of some of the theory involved.

Thanks,

Jay

8th December 2005, 02:55 PM	#1
JMB diyAudio Member Join Date: Apr 2004 Location: Texas	Looking for Nearfield formula definitions - esp from engineering/math folks Keele describes the need to measure at less than 0.55De (effective diameter). NDT resource center (referring to ultrasonics) defines the transition point as N=D^2/(4Lambda) where N is the transition point and D is the effective diameter of the transducer. I have also read that using the multiplier of 10 rather than 4 in the denominator may be a better way to estimate. Would love some input, especially from engineering types. Thanks, Jay

8th December 2005, 11:09 PM	#3
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	Methinks Jay wants to know the maximum distance that can be used in a nearfield cone measurement. I'm not really sure why, though. __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan

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8th December 2005, 08:12 PM	#2
MJK Account disabled at member's request Join Date: Feb 2002 Location: Clifton Park, NY	I don't understand what you are looking for, if you could ask your question in a simplified and more detailed methodical way I might have an answer. Sorry, I am just not sharp enough to understand your opening paragraph.

9th December 2005, 05:04 AM	#4
DanWiggins diyAudio Member Join Date: Aug 2002 Location: Seattle or Shanghai	Always used d^2/lambda in the SONAR world... Always seemed to be fairly accurate. Dan Wiggins Adire Audio®

9th December 2005, 12:39 PM	#5
JMB diyAudio Member Join Date: Apr 2004 Location: Texas	To Clarify, As I am finishing up the Speaker Workshop Manual 2nd Edition, I came upon some conflicting information regarding Nearfield. I understand that it is a region in which there is considerable phase interference from shorter wavelength signals so that there is an effective upper frequency that one can use. I also understand that the distance (transition point) is defined by frequency so that that maximum usable upper frequency would define the transition distance if one is to do a nearfield measurement. It is that maximum measurement distance that I am looking for. My sense is that Keele in defining the maximum measurement distance (0.55*De) was taking the transition point and then defining some point within that region to safely eliminate environmental influences. I am trying to clearly define the transition point so that people can determine their own safety margin for nearfield measurements. I also recognize that the closer to the cone, the better, but it is always nice to have an understanding of some of the theory involved. Thanks, Jay

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