Proximity effect: explanation?

[Jay Kadis]

I've been doing a lot of reading about proximity effect and still fall short of
exactly understanding its root cause. I read the Josephson AES pre-print and
its citation of the Olson work in "Acoustical Engineering" (1957), but our
library has sent that book into storage.

The issue of pressure gradient across a directional mic element is clear
enough, but I fail to understand what causes the difference between front and
back pressure to increase at low frequencies. As I understand it, the
curvature of the wavefront from nearby point source excitation causes an
increased pressure difference across the transducer relative to a plane wave of
distant origin. But the frequency-dependent nature of this phenomenon is still
confusing. (If I were better at math I might get more out of the equation
cited by Josephson.)

Thanks if you can make this clear!

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ----x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Don Pearce]

On Wed, 8 Oct 2003 19:15:55 +0000 (UTC), (Jay
Kadis) wrote:

>I've been doing a lot of reading about proximity effect and still fall short of
>exactly understanding its root cause. I read the Josephson AES pre-print and
>its citation of the Olson work in "Acoustical Engineering" (1957), but our
>library has sent that book into storage.
>
>The issue of pressure gradient across a directional mic element is clear
>enough, but I fail to understand what causes the difference between front and
>back pressure to increase at low frequencies. As I understand it, the
>curvature of the wavefront from nearby point source excitation causes an
>increased pressure difference across the transducer relative to a plane wave of
>distant origin. But the frequency-dependent nature of this phenomenon is still
>confusing. (If I were better at math I might get more out of the equation
>cited by Josephson.)
>
>Thanks if you can make this clear!
>
>-Jay

It is not the pressure, but the velocity. Close to a point source the
velocity of the air particles obeys a law higher than inverse square -
and this gets worse the lower the frequency. Because of this any
microphone that uses the velocity component (anything other than a
pure omni) will suffer from bass lift. Figure 8 mics will be the worst
because they are pure velocity. Cardioids use a mix of velocity and
pressure, so suffer to a lesser extent.

d

_____________________________

http://www.pearce.uk.com

[Don Pearce]

On Wed, 8 Oct 2003 19:15:55 +0000 (UTC), (Jay
Kadis) wrote:

>I've been doing a lot of reading about proximity effect and still fall short of
>exactly understanding its root cause. I read the Josephson AES pre-print and
>its citation of the Olson work in "Acoustical Engineering" (1957), but our
>library has sent that book into storage.
>
>The issue of pressure gradient across a directional mic element is clear
>enough, but I fail to understand what causes the difference between front and
>back pressure to increase at low frequencies. As I understand it, the
>curvature of the wavefront from nearby point source excitation causes an
>increased pressure difference across the transducer relative to a plane wave of
>distant origin. But the frequency-dependent nature of this phenomenon is still
>confusing. (If I were better at math I might get more out of the equation
>cited by Josephson.)
>
>Thanks if you can make this clear!
>
>-Jay

It is not the pressure, but the velocity. Close to a point source the
velocity of the air particles obeys a law higher than inverse square -
and this gets worse the lower the frequency. Because of this any
microphone that uses the velocity component (anything other than a
pure omni) will suffer from bass lift. Figure 8 mics will be the worst
because they are pure velocity. Cardioids use a mix of velocity and
pressure, so suffer to a lesser extent.

d

_____________________________

http://www.pearce.uk.com

[Jay Kadis]

In article > Don Pearce
> writes:
[snip]
>
> It is not the pressure, but the velocity. Close to a point source the
> velocity of the air particles obeys a law higher than inverse square -
> and this gets worse the lower the frequency.
[snip]
>
> http://www.pearce.uk.com

Why do low frequencies deviate more from inverse-square than higher
frequencies? I've seen some pretty inventive explanations of this phenomenon.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ----x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Jay Kadis]

In article > Don Pearce
> writes:
[snip]
>
> It is not the pressure, but the velocity. Close to a point source the
> velocity of the air particles obeys a law higher than inverse square -
> and this gets worse the lower the frequency.
[snip]
>
> http://www.pearce.uk.com

Why do low frequencies deviate more from inverse-square than higher
frequencies? I've seen some pretty inventive explanations of this phenomenon.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ----x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Don Pearce]

On Wed, 8 Oct 2003 19:43:15 +0000 (UTC), (Jay
Kadis) wrote:

>In article > Don Pearce
> writes:
>[snip]
>>
>> It is not the pressure, but the velocity. Close to a point source the
>> velocity of the air particles obeys a law higher than inverse square -
>> and this gets worse the lower the frequency.
>[snip]
>>
>> http://www.pearce.uk.com
>
>Why do low frequencies deviate more from inverse-square than higher
>frequencies? I've seen some pretty inventive explanations of this phenomenon.
>
>-Jay

Not sure I can say why, but the situation is that the ratio of
pressure to velocity is considered unity for a plane wave - this is
the far field condition. At distances closer than about a wavelength,
the ratio changes, decreasing so that about a tenth of a wavelength,
the relative velocity is twice as great as the pressure. In addition,
the phase relationship between them changes - about ten degrees apart
at one wavelength, and getting close to 90 degrees at about a
hundredth of a wavelength (about an inch at 100Hz).

I will try and write a paper on this for my website soon - it'll help
me understand it.

d

_____________________________

http://www.pearce.uk.com

[Don Pearce]

On Wed, 8 Oct 2003 19:43:15 +0000 (UTC), (Jay
Kadis) wrote:

>In article > Don Pearce
> writes:
>[snip]
>>
>> It is not the pressure, but the velocity. Close to a point source the
>> velocity of the air particles obeys a law higher than inverse square -
>> and this gets worse the lower the frequency.
>[snip]
>>
>> http://www.pearce.uk.com
>
>Why do low frequencies deviate more from inverse-square than higher
>frequencies? I've seen some pretty inventive explanations of this phenomenon.
>
>-Jay

Not sure I can say why, but the situation is that the ratio of
pressure to velocity is considered unity for a plane wave - this is
the far field condition. At distances closer than about a wavelength,
the ratio changes, decreasing so that about a tenth of a wavelength,
the relative velocity is twice as great as the pressure. In addition,
the phase relationship between them changes - about ten degrees apart
at one wavelength, and getting close to 90 degrees at about a
hundredth of a wavelength (about an inch at 100Hz).

I will try and write a paper on this for my website soon - it'll help
me understand it.

d

_____________________________

http://www.pearce.uk.com

[Jay Kadis]

In article >,
Don Pearce > wrote:

> On Wed, 8 Oct 2003 19:43:15 +0000 (UTC), (Jay
> Kadis) wrote:
>
> >In article > Don Pearce
> > writes:
> >[snip]
> >>
> >> It is not the pressure, but the velocity. Close to a point source the
> >> velocity of the air particles obeys a law higher than inverse square -
> >> and this gets worse the lower the frequency.
> >[snip]
> >>
> >> http://www.pearce.uk.com
> >
> >Why do low frequencies deviate more from inverse-square than higher
> >frequencies? I've seen some pretty inventive explanations of this
> >phenomenon.
> >
> >-Jay
>
> Not sure I can say why, but the situation is that the ratio of
> pressure to velocity is considered unity for a plane wave - this is
> the far field condition. At distances closer than about a wavelength,
> the ratio changes, decreasing so that about a tenth of a wavelength,
> the relative velocity is twice as great as the pressure. In addition,
> the phase relationship between them changes - about ten degrees apart
> at one wavelength, and getting close to 90 degrees at about a
> hundredth of a wavelength (about an inch at 100Hz).
>
> I will try and write a paper on this for my website soon - it'll help
> me understand it.
>
> d
>
> _____________________________
>
> http://www.pearce.uk.com


Thanks. I think the wavelength effect is the answer I was looking for and it is
a term in the Olson equation. I'm trying to explain this to my class and not
make it sound like hand-waving. This helps a lot. I will have my wife help me
work through the physics/math once I get ahold of the Olson book.


-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Jay Kadis]

In article >,
Don Pearce > wrote:

> On Wed, 8 Oct 2003 19:43:15 +0000 (UTC), (Jay
> Kadis) wrote:
>
> >In article > Don Pearce
> > writes:
> >[snip]
> >>
> >> It is not the pressure, but the velocity. Close to a point source the
> >> velocity of the air particles obeys a law higher than inverse square -
> >> and this gets worse the lower the frequency.
> >[snip]
> >>
> >> http://www.pearce.uk.com
> >
> >Why do low frequencies deviate more from inverse-square than higher
> >frequencies? I've seen some pretty inventive explanations of this
> >phenomenon.
> >
> >-Jay
>
> Not sure I can say why, but the situation is that the ratio of
> pressure to velocity is considered unity for a plane wave - this is
> the far field condition. At distances closer than about a wavelength,
> the ratio changes, decreasing so that about a tenth of a wavelength,
> the relative velocity is twice as great as the pressure. In addition,
> the phase relationship between them changes - about ten degrees apart
> at one wavelength, and getting close to 90 degrees at about a
> hundredth of a wavelength (about an inch at 100Hz).
>
> I will try and write a paper on this for my website soon - it'll help
> me understand it.
>
> d
>
> _____________________________
>
> http://www.pearce.uk.com


Thanks. I think the wavelength effect is the answer I was looking for and it is
a term in the Olson equation. I'm trying to explain this to my class and not
make it sound like hand-waving. This helps a lot. I will have my wife help me
work through the physics/math once I get ahold of the Olson book.


-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Don Pearce]

On Wed, 08 Oct 2003 13:27:08 -0700, Jay Kadis >
wrote:

>In article >,
> Don Pearce > wrote:
>
>> On Wed, 8 Oct 2003 19:43:15 +0000 (UTC), (Jay
>> Kadis) wrote:
>>
>> >In article > Don Pearce
>> > writes:
>> >[snip]
>> >>
>> >> It is not the pressure, but the velocity. Close to a point source the
>> >> velocity of the air particles obeys a law higher than inverse square -
>> >> and this gets worse the lower the frequency.
>> >[snip]
>> >>
>> >> http://www.pearce.uk.com
>> >
>> >Why do low frequencies deviate more from inverse-square than higher
>> >frequencies? I've seen some pretty inventive explanations of this
>> >phenomenon.
>> >
>> >-Jay
>>
>> Not sure I can say why, but the situation is that the ratio of
>> pressure to velocity is considered unity for a plane wave - this is
>> the far field condition. At distances closer than about a wavelength,
>> the ratio changes, decreasing so that about a tenth of a wavelength,
>> the relative velocity is twice as great as the pressure. In addition,
>> the phase relationship between them changes - about ten degrees apart
>> at one wavelength, and getting close to 90 degrees at about a
>> hundredth of a wavelength (about an inch at 100Hz).
>>
>> I will try and write a paper on this for my website soon - it'll help
>> me understand it.
>>
>> d
>>
>> _____________________________
>>
>> http://www.pearce.uk.com
>
>
>Thanks. I think the wavelength effect is the answer I was looking for and it is
>a term in the Olson equation. I'm trying to explain this to my class and not
>make it sound like hand-waving. This helps a lot. I will have my wife help me
>work through the physics/math once I get ahold of the Olson book.
>
>
>-Jay

Ha! Students see through hand-waving in a second - and they pounce
like rabid dogs.

d

_____________________________

http://www.pearce.uk.com

[Don Pearce]

On Wed, 08 Oct 2003 13:27:08 -0700, Jay Kadis >
wrote:

>In article >,
> Don Pearce > wrote:
>
>> On Wed, 8 Oct 2003 19:43:15 +0000 (UTC), (Jay
>> Kadis) wrote:
>>
>> >In article > Don Pearce
>> > writes:
>> >[snip]
>> >>
>> >> It is not the pressure, but the velocity. Close to a point source the
>> >> velocity of the air particles obeys a law higher than inverse square -
>> >> and this gets worse the lower the frequency.
>> >[snip]
>> >>
>> >> http://www.pearce.uk.com
>> >
>> >Why do low frequencies deviate more from inverse-square than higher
>> >frequencies? I've seen some pretty inventive explanations of this
>> >phenomenon.
>> >
>> >-Jay
>>
>> Not sure I can say why, but the situation is that the ratio of
>> pressure to velocity is considered unity for a plane wave - this is
>> the far field condition. At distances closer than about a wavelength,
>> the ratio changes, decreasing so that about a tenth of a wavelength,
>> the relative velocity is twice as great as the pressure. In addition,
>> the phase relationship between them changes - about ten degrees apart
>> at one wavelength, and getting close to 90 degrees at about a
>> hundredth of a wavelength (about an inch at 100Hz).
>>
>> I will try and write a paper on this for my website soon - it'll help
>> me understand it.
>>
>> d
>>
>> _____________________________
>>
>> http://www.pearce.uk.com
>
>
>Thanks. I think the wavelength effect is the answer I was looking for and it is
>a term in the Olson equation. I'm trying to explain this to my class and not
>make it sound like hand-waving. This helps a lot. I will have my wife help me
>work through the physics/math once I get ahold of the Olson book.
>
>
>-Jay

Ha! Students see through hand-waving in a second - and they pounce
like rabid dogs.

d

_____________________________

http://www.pearce.uk.com

[Jay Kadis]

In article > Don Pearce
> writes:
[snip]
>
> Ha! Students see through hand-waving in a second - and they pounce
> like rabid dogs.
>
> d
>
> _____________________________
>
> http://www.pearce.uk.com

Especially EE graduate students! They're better at physics than I am, but I
still know more about mic technique than they do, so they pay attention.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ----x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Jay Kadis]

In article > Don Pearce
> writes:
[snip]
>
> Ha! Students see through hand-waving in a second - and they pounce
> like rabid dogs.
>
> d
>
> _____________________________
>
> http://www.pearce.uk.com

Especially EE graduate students! They're better at physics than I am, but I
still know more about mic technique than they do, so they pay attention.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ----x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Ron Capik]

Jay Kadis wrote:

> < ...snip.. >
>
> Especially EE graduate students! They're better at physics than I am, but I
> still know more about mic technique than they do, so they pay attention.
>
> -Jay
> --

Out of curiosity, what class are you teaching?

I taught a senior level physics lab last semester
and the students didn't seem to know much of
anything with respect to the real world...

Ron Capik
NJ Pinelands Cultural Society
< www.AlbertHall.org >
--

[Ron Capik]

Jay Kadis wrote:

> < ...snip.. >
>
> Especially EE graduate students! They're better at physics than I am, but I
> still know more about mic technique than they do, so they pay attention.
>
> -Jay
> --

Out of curiosity, what class are you teaching?

I taught a senior level physics lab last semester
and the students didn't seem to know much of
anything with respect to the real world...

Ron Capik
NJ Pinelands Cultural Society
< www.AlbertHall.org >
--

[Jay Kadis]

In article > writes:
> Jay Kadis wrote:
>
> > < ...snip.. >
> >
> > Especially EE graduate students! They're better at physics than I am, but
I
> > still know more about mic technique than they do, so they pay attention.
> >
> > -Jay
> > --
>
> Out of curiosity, what class are you teaching?
>
> I taught a senior level physics lab last semester
> and the students didn't seem to know much of
> anything with respect to the real world...
>
> Ron Capik
> NJ Pinelands Cultural Society
> < www.AlbertHall.org >
> --
>
It's an undergraduate/graduate course on audio recording for music, science,
and technology students called "Theory and practice of audio recording". Our
grad students do a lot of physical modeling and DSP programming and DO know
quite a bit about the physical world.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ----x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Jay Kadis]

In article > writes:
> Jay Kadis wrote:
>
> > < ...snip.. >
> >
> > Especially EE graduate students! They're better at physics than I am, but
I
> > still know more about mic technique than they do, so they pay attention.
> >
> > -Jay
> > --
>
> Out of curiosity, what class are you teaching?
>
> I taught a senior level physics lab last semester
> and the students didn't seem to know much of
> anything with respect to the real world...
>
> Ron Capik
> NJ Pinelands Cultural Society
> < www.AlbertHall.org >
> --
>
It's an undergraduate/graduate course on audio recording for music, science,
and technology students called "Theory and practice of audio recording". Our
grad students do a lot of physical modeling and DSP programming and DO know
quite a bit about the physical world.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ----x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Chris Hornbeck]

On Wed, 8 Oct 2003 19:15:55 +0000 (UTC), (Jay
Kadis) wrote:

>I've been doing a lot of reading about proximity effect and still fall short of
>exactly understanding its root cause. I read the Josephson AES pre-print and
>its citation of the Olson work in "Acoustical Engineering" (1957), but our
>library has sent that book into storage.

Hi Jay,
I have a spare copy of the Olson. Email me a street address.

Chris Hornbeck
new email address

[Chris Hornbeck]

On Wed, 8 Oct 2003 19:15:55 +0000 (UTC), (Jay
Kadis) wrote:

>I've been doing a lot of reading about proximity effect and still fall short of
>exactly understanding its root cause. I read the Josephson AES pre-print and
>its citation of the Olson work in "Acoustical Engineering" (1957), but our
>library has sent that book into storage.

Hi Jay,
I have a spare copy of the Olson. Email me a street address.

Chris Hornbeck
new email address

[Ron Capik]

Jay Kadis wrote:

> I've been doing a lot of reading about proximity effect and still fall short of
> exactly understanding its root cause. I read the Josephson AES pre-print and
> its citation of the Olson work in "Acoustical Engineering" (1957), but our
> library has sent that book into storage.
> < ...snip.. >

Maybe this will help:
I did a quick search on Josephson and proximity effect and found lots
of papers on those superconducting junctions that I worked with
back in the 80's. Then I found this nice (mostly) graphic presentation on
microphone proximity effect:

< http://arts.ucsc.edu/EMS/Music/tech_background/TE-20/Proximity_Effect.html >

Later...

Ron Capik
--

[Ron Capik]

Jay Kadis wrote:

> I've been doing a lot of reading about proximity effect and still fall short of
> exactly understanding its root cause. I read the Josephson AES pre-print and
> its citation of the Olson work in "Acoustical Engineering" (1957), but our
> library has sent that book into storage.
> < ...snip.. >

Maybe this will help:
I did a quick search on Josephson and proximity effect and found lots
of papers on those superconducting junctions that I worked with
back in the 80's. Then I found this nice (mostly) graphic presentation on
microphone proximity effect:

< http://arts.ucsc.edu/EMS/Music/tech_background/TE-20/Proximity_Effect.html >

Later...

Ron Capik
--

[Don Pearce]

On Thu, 09 Oct 2003 00:20:57 GMT, Ron Capik >
wrote:

>Jay Kadis wrote:
>
>> I've been doing a lot of reading about proximity effect and still fall short of
>> exactly understanding its root cause. I read the Josephson AES pre-print and
>> its citation of the Olson work in "Acoustical Engineering" (1957), but our
>> library has sent that book into storage.
>> < ...snip.. >
>
>Maybe this will help:
>I did a quick search on Josephson and proximity effect and found lots
>of papers on those superconducting junctions that I worked with
>back in the 80's. Then I found this nice (mostly) graphic presentation on
>microphone proximity effect:
>
>< http://arts.ucsc.edu/EMS/Music/tech_background/TE-20/Proximity_Effect.html >
>
>Later...
>
>Ron Capik

Unfortunately that article is totally wrong in its treatment of
spherical wavefronts.

d

_____________________________

http://www.pearce.uk.com

[Don Pearce]

On Thu, 09 Oct 2003 00:20:57 GMT, Ron Capik >
wrote:

>Jay Kadis wrote:
>
>> I've been doing a lot of reading about proximity effect and still fall short of
>> exactly understanding its root cause. I read the Josephson AES pre-print and
>> its citation of the Olson work in "Acoustical Engineering" (1957), but our
>> library has sent that book into storage.
>> < ...snip.. >
>
>Maybe this will help:
>I did a quick search on Josephson and proximity effect and found lots
>of papers on those superconducting junctions that I worked with
>back in the 80's. Then I found this nice (mostly) graphic presentation on
>microphone proximity effect:
>
>< http://arts.ucsc.edu/EMS/Music/tech_background/TE-20/Proximity_Effect.html >
>
>Later...
>
>Ron Capik

Unfortunately that article is totally wrong in its treatment of
spherical wavefronts.

d

_____________________________

http://www.pearce.uk.com

[Arny Krueger]

"Don Pearce" > wrote in message

> On Thu, 09 Oct 2003 00:20:57 GMT, Ron Capik >
> wrote:
>
>> Jay Kadis wrote:
>>
>>> I've been doing a lot of reading about proximity effect and still
>>> fall short of exactly understanding its root cause. I read the
>>> Josephson AES pre-print and its citation of the Olson work in
>>> "Acoustical Engineering" (1957), but our library has sent that book
>>> into storage. < ...snip.. >
>>
>> Maybe this will help:
>> I did a quick search on Josephson and proximity effect and found lots
>> of papers on those superconducting junctions that I worked with
>> back in the 80's. Then I found this nice (mostly) graphic
>> presentation on microphone proximity effect:
>>
>> <
>>
http://arts.ucsc.edu/EMS/Music/tech_background/TE-20/Proximity_Effect.html >
>>
>> Later...
>>
>> Ron Capik
>
> Unfortunately that article is totally wrong in its treatment of
> spherical wavefronts.

....not to mention the hand-waving.

I'm looking forward to seeing your treatment, as the rest of the stuff on
your web site is FWIW IMO very good.

[Arny Krueger]

"Don Pearce" > wrote in message

> On Thu, 09 Oct 2003 00:20:57 GMT, Ron Capik >
> wrote:
>
>> Jay Kadis wrote:
>>
>>> I've been doing a lot of reading about proximity effect and still
>>> fall short of exactly understanding its root cause. I read the
>>> Josephson AES pre-print and its citation of the Olson work in
>>> "Acoustical Engineering" (1957), but our library has sent that book
>>> into storage. < ...snip.. >
>>
>> Maybe this will help:
>> I did a quick search on Josephson and proximity effect and found lots
>> of papers on those superconducting junctions that I worked with
>> back in the 80's. Then I found this nice (mostly) graphic
>> presentation on microphone proximity effect:
>>
>> <
>>
http://arts.ucsc.edu/EMS/Music/tech_background/TE-20/Proximity_Effect.html >
>>
>> Later...
>>
>> Ron Capik
>
> Unfortunately that article is totally wrong in its treatment of
> spherical wavefronts.

....not to mention the hand-waving.

I'm looking forward to seeing your treatment, as the rest of the stuff on
your web site is FWIW IMO very good.

[Jay Kadis]

In article > writes:
> Jay Kadis wrote:
>
> > I've been doing a lot of reading about proximity effect and still fall
short of
> > exactly understanding its root cause. I read the Josephson AES pre-print
and
> > its citation of the Olson work in "Acoustical Engineering" (1957), but our
> > library has sent that book into storage.
> > < ...snip.. >
>
> Maybe this will help:
> I did a quick search on Josephson and proximity effect and found lots
> of papers on those superconducting junctions that I worked with
> back in the 80's. Then I found this nice (mostly) graphic presentation on
> microphone proximity effect:
>
> < http://arts.ucsc.edu/EMS/Music/tech_background/TE-20/Proximity_Effect.html
>
>
> Later...
>
> Ron Capik
> --
>

Yeah, I saw that one, but it's more of a hand-waving exercise than a true
physical explanation, although it seems to be on the right track about
spherical versus plane waves. There seems to be a lot of misunderstanding
about this topic. Most of the text books mention the effect but don't have a
clear explanation of the reason for it. I'm beginning to see why: the
explanation is not simple.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ----x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Jay Kadis]

In article > writes:
> Jay Kadis wrote:
>
> > I've been doing a lot of reading about proximity effect and still fall
short of
> > exactly understanding its root cause. I read the Josephson AES pre-print
and
> > its citation of the Olson work in "Acoustical Engineering" (1957), but our
> > library has sent that book into storage.
> > < ...snip.. >
>
> Maybe this will help:
> I did a quick search on Josephson and proximity effect and found lots
> of papers on those superconducting junctions that I worked with
> back in the 80's. Then I found this nice (mostly) graphic presentation on
> microphone proximity effect:
>
> < http://arts.ucsc.edu/EMS/Music/tech_background/TE-20/Proximity_Effect.html
>
>
> Later...
>
> Ron Capik
> --
>

Yeah, I saw that one, but it's more of a hand-waving exercise than a true
physical explanation, although it seems to be on the right track about
spherical versus plane waves. There seems to be a lot of misunderstanding
about this topic. Most of the text books mention the effect but don't have a
clear explanation of the reason for it. I'm beginning to see why: the
explanation is not simple.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ----x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Don Pearce]

OK, Jay,

Here is my explanation of the proximity effect in terms that I hope
are easy to understand, and picture in the real world. I will base me
paper on this.

You remember I said that the reason was the velocity of the air
particles affecting microphones that use velocity - figure 8s,
cardioids etc.

OK, sound pressure decreases in an inverse square law. To cause those
pressure changes air has to be moved in and out of the peaks and
troughs. The volume of air represented by a peak or trough is that
contained between two concentric spheres, and that volume increases as
the cube of the distance from a point source. So to keep that
increasing volume filled, the air must move correspondingly faster.
When the size of the sphere is large compared to the wavelength, that
change in volume between the compression region and the rarefaction
region isn't big - and that is the far field case. When you are down
at around a wavelength from the source, the cube vs square law problem
exists virtually undiluted, and the velocity is consequently much
increased.

How does that sound - make any kind of sense? I am sure I can explain
it better with pictures.

d

_____________________________

http://www.pearce.uk.com

[Don Pearce]

OK, Jay,

Here is my explanation of the proximity effect in terms that I hope
are easy to understand, and picture in the real world. I will base me
paper on this.

You remember I said that the reason was the velocity of the air
particles affecting microphones that use velocity - figure 8s,
cardioids etc.

OK, sound pressure decreases in an inverse square law. To cause those
pressure changes air has to be moved in and out of the peaks and
troughs. The volume of air represented by a peak or trough is that
contained between two concentric spheres, and that volume increases as
the cube of the distance from a point source. So to keep that
increasing volume filled, the air must move correspondingly faster.
When the size of the sphere is large compared to the wavelength, that
change in volume between the compression region and the rarefaction
region isn't big - and that is the far field case. When you are down
at around a wavelength from the source, the cube vs square law problem
exists virtually undiluted, and the velocity is consequently much
increased.

How does that sound - make any kind of sense? I am sure I can explain
it better with pictures.

d

_____________________________

http://www.pearce.uk.com

[Jay Kadis]

In article >,
Don Pearce > wrote:

> OK, Jay,
>
> Here is my explanation of the proximity effect in terms that I hope
> are easy to understand, and picture in the real world. I will base me
> paper on this.
>
> You remember I said that the reason was the velocity of the air
> particles affecting microphones that use velocity - figure 8s,
> cardioids etc.
>
> OK, sound pressure decreases in an inverse square law. To cause those
> pressure changes air has to be moved in and out of the peaks and
> troughs. The volume of air represented by a peak or trough is that
> contained between two concentric spheres, and that volume increases as
> the cube of the distance from a point source. So to keep that
> increasing volume filled, the air must move correspondingly faster.
> When the size of the sphere is large compared to the wavelength, that
> change in volume between the compression region and the rarefaction
> region isn't big - and that is the far field case. When you are down
> at around a wavelength from the source, the cube vs square law problem
> exists virtually undiluted, and the velocity is consequently much
> increased.
>
> How does that sound - make any kind of sense? I am sure I can explain
> it better with pictures.
>
> d
>
> _____________________________
>
> http://www.pearce.uk.com


Yes, that does a good job of explaining the situation. I'm still going to go
through the math with my in-house mathematician (wife), but this is a clear
description of the situation. Thanks.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

[Jay Kadis]

In article >,
Don Pearce > wrote:

> OK, Jay,
>
> Here is my explanation of the proximity effect in terms that I hope
> are easy to understand, and picture in the real world. I will base me
> paper on this.
>
> You remember I said that the reason was the velocity of the air
> particles affecting microphones that use velocity - figure 8s,
> cardioids etc.
>
> OK, sound pressure decreases in an inverse square law. To cause those
> pressure changes air has to be moved in and out of the peaks and
> troughs. The volume of air represented by a peak or trough is that
> contained between two concentric spheres, and that volume increases as
> the cube of the distance from a point source. So to keep that
> increasing volume filled, the air must move correspondingly faster.
> When the size of the sphere is large compared to the wavelength, that
> change in volume between the compression region and the rarefaction
> region isn't big - and that is the far field case. When you are down
> at around a wavelength from the source, the cube vs square law problem
> exists virtually undiluted, and the velocity is consequently much
> increased.
>
> How does that sound - make any kind of sense? I am sure I can explain
> it better with pictures.
>
> d
>
> _____________________________
>
> http://www.pearce.uk.com


Yes, that does a good job of explaining the situation. I'm still going to go
through the math with my in-house mathematician (wife), but this is a clear
description of the situation. Thanks.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x