Looking at a crazy Multitube shotgun microphone and trying to understand
the authors

open end tube calculations. (I wonder if it is actually open ended.) ???

> https://worldradiohistory.com/Archive-Poptronics/60s/64/Pop-1964-06.pdf

 The author says,

"To calculate tube length, firstfindwavelength
bydividingthe speedofsoundbythe frequency.  (1100 feet persecondfor
practical purposes)
Forexample,the wavelength of256cyclesequals1100 ÷256,or4.296 feet.

Tubelength, however,ishalf
this,or2.14feet,*/since/**//**/tubes/**//**/open/**//**/at/**//**/both
ends/*resonateata

Wavelengthtwice as long astheirlength."

Now my experiment;

I have 22" (.559m) tube. 1100/300Hz = 3.66 ft, but it's open ended so
divide by 2 = 1.833ft =22 inch = 0.559 meters.

With a mic setting at the open end I get resonance at 300hz. (Small,
like I'm just off the node)?

(this is close to what the author says, but far from what the
hyperphysics calculator finds.)

If I remove the tube the signal drops.

However, If I put the mic inside the pipe at the 1/2 length position I
get 10 times the signal.

If I hold the mic in place and remove the tube, the signal drops to 1/40
of what it was with the tube.

 I'm using the calculator at,

> http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/opecol.html

My measurements say I have a node at the open end and an antinode at the
center of the tube. But.

the hyperphysics calculator says /*opposite*/ about open ended tubes.

 Can anyone shed some light on this?

             Thank, Mikek

BTW, I have both an aluminum tube and PVC of the same ID, the PVC has
about 1/3 more signal at mid tube.

Not what I expected.

Bonus points!

Is the tube open at both ends, he closes it of with a funnel and
Microphone.  (see the article)

Does a closed of tube need a perfect seal?

If it is a perfect seal, do the 36 other tubes act as an open, making it
open at both ends?

It does have an opening 36* times the size of the tube all pointing away
from the mic end of the tube.

* the other 36 tubes in the assembly.

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On 17/12/2021 19:07, amdx wrote:
> Looking at a crazy Multitube shotgun microphone and trying to understand
> the authors
>
> open end tube calculations. (I wonder if it is actually open ended.) ???
>
>> https://worldradiohistory.com/Archive-Poptronics/60s/64/Pop-1964-06.pdf
>
>  The author says,
>
> "To calculate tube length, firstfindwavelength
> bydividingthe speedofsoundbythe frequency.  (1100 feet persecondfor
> practical purposes)
> Forexample,the wavelength of256cyclesequals1100 ÷256,or4.296 feet.
>
> Tubelength, however,ishalf
> this,or2.14feet,*/since/**//**/tubes/**//**/open/**//**/at/**//**/both
> ends/*resonateata
>
> Wavelengthtwice as long astheirlength."
>
> Now my experiment;
>
> I have 22" (.559m) tube. 1100/300Hz = 3.66 ft, but it's open ended so
> divide by 2 = 1.833ft =22 inch = 0.559 meters.
>
> With a mic setting at the open end I get resonance at 300hz. (Small,
> like I'm just off the node)?
>
> (this is close to what the author says, but far from what the
> hyperphysics calculator finds.)
>
> If I remove the tube the signal drops.
>
> However, If I put the mic inside the pipe at the 1/2 length position I
> get 10 times the signal.
>
> If I hold the mic in place and remove the tube, the signal drops to 1/40
> of what it was with the tube.
>
>  I'm using the calculator at,
>
>> http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/opecol.html
>
> My measurements say I have a node at the open end and an antinode at the
> center of the tube. But.
>
> the hyperphysics calculator says /*opposite*/ about open ended tubes.
>
>  Can anyone shed some light on this?
>
>              Thank, Mikek
>
> BTW, I have both an aluminum tube and PVC of the same ID, the PVC has
> about 1/3 more signal at mid tube.
>
> Not what I expected.

Simplest way is blow air across the aperture to find the resonant
frequency directly. If you have ever played a wind instrument or a
bottle it isn't too hard. But easier with the open end blocked off.

It is really easy to be out by a factor of two if you don't pay careful
attention. An open resonator is lambda/2 give or take end effects and a
closed resonator is lambda/4 with slightly more gain.

Speed of sound inside a waveguide isn't quite the same as in free space.

> Bonus points!
>
> Is the tube open at both ends, he closes it of with a funnel and
> Microphone.  (see the article)

It is imperfect and always was. If you want perfect tuning of organ
pipes you have to apply a fiddle factor for the diameter of the pipe and
boundary corrections to the speed of sound in the pipe.

> Does a closed of tube need a perfect seal?

Not really - it only affects the sharpness of the resonance.

> If it is a perfect seal, do the 36 other tubes act as an open, making it
> open at both ends?

They are likely behaving in that configuration as approximately a closed
at one end resonant tube with each tube amplifying a single frequency.
The exact frequency being determined mostly by the length of the tube.

The price you pay for this is blurring in the time domain although
probably not enough to affect inteligability for speech.

> It does have an opening 36* times the size of the tube all pointing away
> from the mic end of the tube.
>
> * the other 36 tubes in the assembly.

The other way to do a directional mike is a bunch of micorphones along a
line and some DSP. Or the compact physical implementation:

Modern equivalent is the shotgun mike.

https://www.videomaker.com/how-to/audio-how-to/everything-you-need-to-know-about-shotgun-microphones/?nowprocket=1

--
Regards,
Martin Brown

Fixed the weird text that popped up.

On 12/17/2021 1:07 PM, amdx wrote:
> Looking at a crazy Multitube shotgun microphone and trying to
> understand the authors
>
> open end tube calculations. (I wonder if it is actually open ended.) ???
>
>> https://worldradiohistory.com/Archive-Poptronics/60s/64/Pop-1964-06.pdf
>
>  The author says,
>
> "To calculate tube length, first find wavelength by dividing the speed
> of sound by the frequency.  (1100 feet persecondfor practical purposes)
> For example ,the wavelength of 256 cycles equals 1100 ÷ 256, or 4.296
> feet.
>
> Tube length, however, is half this, or 2.14 feet, tubes open at both
> ends resonate at a
>
> Wavelength twice as long as their length."
>
> Now my experiment;
>
> I have 22" (.559m) tube. 1100/300Hz = 3.66 ft, but it's open ended so
> divide by 2 = 1.833ft =22 inch = 0.559 meters.
>
> With a mic setting at the open end I get resonance at 300hz. (Small,
> like I'm just off the node)?
>
> (this is close to what the author says, but far from what the
> hyperphysics calculator finds.)
>
> If I remove the tube the signal drops.
>
> However, If I put the mic inside the pipe at the 1/2 length position I
> get 10 times the signal.
>
> If I hold the mic in place and remove the tube, the signal drops to
> 1/40 of what it was with the tube.
>
>  I'm using the calculator at,
>
>> http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/opecol.html
>
> My measurements say I have a node at the open end and an antinode at
> the center of the tube. But.
>
> the hyperphysics calculator says /*opposite*/ about open ended tubes.
>
>  Can anyone shed some light on this?
>
>              Thank, Mikek
>
> BTW, I have both an aluminum tube and PVC of the same ID, the PVC has
> about 1/3 more signal at mid tube.
>
> Not what I expected.
>
>
>
> Bonus points!
>
> Is the tube open at both ends, he closes it of with a funnel and
> Microphone.  (see the article)
>
> Does a closed of tube need a perfect seal?
>
> If it is a perfect seal, do the 36 other tubes act as an open, making
> it open at both ends?
>
> It does have an opening 36* times the size of the tube all pointing
> away from the mic end of the tube.
>
> * the other 36 tubes in the assembly.
>

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Martin Brown is all Bullshit:
====================
>
> The other way to do a directional mike is a bunch of micorphones along a
> line and some DSP. Or the compact physical implementation:
>
> Modern equivalent is the shotgun mike.
>
> https://www.videomaker.com/how-to/audio-how-to/everything-you-need-to-know-about-shotgun-microphones/?nowprocket=1
>

** Bad article to cite - all marketing BS and no facts.

Just look at a *set* of polar patterns for a typical "shotgun" mic.
They revel just how poorly the things *really* work.
The name is a terrible misnomer.

....... Phil

On 12/17/2021 4:28 PM, Phil Allison wrote:
> Martin Brown is all Bullshit:
> ====================
>> The other way to do a directional mike is a bunch of micorphones along a
>> line and some DSP. Or the compact physical implementation:
>>
>> Modern equivalent is the shotgun mike.
>>
>> https://www.videomaker.com/how-to/audio-how-to/everything-you-need-to-know-about-shotgun-microphones/?nowprocket=1
>>
> ** Bad article to cite - all marketing BS and no facts.
>
> Just look at a *set* of polar patterns for a typical "shotgun" mic.
> They revel just how poorly the things *really* work.
> The name is a terrible misnomer.
>
>
> ...... Phil
>
>
Phil, Why does my 22" opened ended tube that resonates at 300Hz have an
antinode in the center.

Everything I find says it should have antinodes at each end and a node
in the center. I get maximum

amplitude on a mic placed in the center and minimum at the ends.

                                Mikek

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amdx wrote:
==========
> On 12/17/2021 4:28 PM, Phil Allison wrote:
> > Martin Brown is all Bullshit:
> > ====================
> >
> >> Modern equivalent is the shotgun mike.
> >>
> >> https://www.videomaker.com/how-to/audio-how-to/everything-you-need-to-know-about-shotgun-microphones/?nowprocket=1
> >>
> > ** Bad article to cite - all marketing BS and no facts.
> >
> > Just look at a *set* of polar patterns for a typical "shotgun" mic.
> > They revel just how poorly the things *really* work.
> > The name is a terrible misnomer.
> >
> >
> >
> Phil, Why does my 22" opened ended tube that resonates at 300Hz have an
> antinode in the center.

** FYI:

it is * 100% smartarse* and against usenet posting rules to ASK a poster a question when they have NOT posted on the same issue.

Get it ?

...... Phil

>
> the hyperphysics calculator says /*opposite*/ about open ended tubes.
>
> Can anyone shed some light on this?

well for one thing those formulas
are the basic ones I learned in high school
physics. I have since learned resonance
is more involved, the the formulas must take
into account other factors such as tube diameter.
I take it that website is for "non scientific" types
(flutists?) & we don't want to scare them
away with too much math!
Of course the acoustic instruments, even flutes,
are complex; one does need serious insight in order to
make a professional instrument with good
intonation (accurate to the equally-tempered
scale, across its normal range).
Arthur Benade's Horns String and Harmony
comes to mind.
cheers, RS

On 12/17/2021 6:18 PM, Phil Allison wrote:
> amdx wrote:
> ==========
>> On 12/17/2021 4:28 PM, Phil Allison wrote:
>>> Martin Brown is all Bullshit:
>>> ====================
>>>
>>>> Modern equivalent is the shotgun mike.
>>>>
>>>> https://www.videomaker.com/how-to/audio-how-to/everything-you-need-to-know-about-shotgun-microphones/?nowprocket=1
>>>>
>>> ** Bad article to cite - all marketing BS and no facts.
>>>
>>> Just look at a *set* of polar patterns for a typical "shotgun" mic.
>>> They revel just how poorly the things *really* work.
>>> The name is a terrible misnomer.
>>>
>>>
>>>
>> Phil, Why does my 22" opened ended tube that resonates at 300Hz have an
>> antinode in the center.
> ** FYI:
>
> it is * 100% smartarse* and against usenet posting rules to ASK a poster a question when they have NOT posted on the same issue.
>
> Get it ?
>
>
> ..... Phil
>
>
I thought you might know the answer, I was hoping you would chime in on
the thread and when you did, I thought great,

maybe he can help. I was wrong.

                                      Mikek

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On 12/17/2021 6:49 PM, Rich S wrote:
>> the hyperphysics calculator says /*opposite*/ about open ended tubes.
>>
>> Can anyone shed some light on this?
> well for one thing those formulas
> are the basic ones I learned in high school
> physics. I have since learned resonance
> is more involved, the the formulas must take
> into account other factors such as tube diameter.
> I take it that website is for "non scientific" types
> (flutists?) & we don't want to scare them
> away with too much math!
> Of course the acoustic instruments, even flutes,
> are complex; one does need serious insight in order to
> make a professional instrument with good
> intonation (accurate to the equally-tempered
> scale, across its normal range).
> Arthur Benade's Horns String and Harmony
> comes to mind.
> cheers, RS

Your answer leaves me in the dark, I'm looking for some light.

                                                  Mikek

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amdx wrote:
=============
>
> I thought you might know the answer,
>

** Always POST such Qs to the whole NG - idiot .
Or I will post a bunch of idiotic, unanswerable Qs directed to you !.

...... Phil

fyi the technical name for a shotgun or rifle mic is "line gradient
microphone" or "interference tube" microphone (i.e. the tube
in front of the mic capsule).
Fundamental work was done by Harry Olson, RCA, in the 1940's
... in case you want to research it further...
cheers, RS

On 12/17/2021 7:14 PM, Phil Allison wrote:
> amdx wrote:
> =============
>> I thought you might know the answer,
>>
> ** Always POST such Qs to the whole NG - idiot .
>
> Or I will post a bunch of idiotic, unanswerable Qs directed to you !.
>
>
>
>
> ..... Phil
>
>
>
Phil, are you trying to teach me good social behavior?

                                       Mikek

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> Your answer leaves me in the dark, I'm looking for some light.
>
> Mikek
> --

Hi Mikek,
Let's all try to be light producing ;-)
Could you re-post your exact question, again,
if you don't mind, BUT without the formatting?
(On my computer, the post was horribly littered with a
characters, /, * My brain shuts down if I have to read
something that non-decipherable.)
regards, RS

On 12/17/2021 7:14 PM, Rich S wrote:
> fyi the technical name for a shotgun or rifle mic is "line gradient
> microphone" or "interference tube" microphone (i.e. the tube
> in front of the mic capsule).
> Fundamental work was done by Harry Olson, RCA, in the 1940's
> .. in case you want to research it further...
> cheers, RS

You didn't look at the link.

                                  Mikek

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On Saturday, December 18, 2021 at 1:51:31 AM UTC, amdx wrote:
> On 12/17/2021 7:14 PM, Rich S wrote:
> > fyi the technical name for a shotgun or rifle mic is "line gradient
> > microphone" or "interference tube" microphone (i.e. the tube
> > in front of the mic capsule).
> > Fundamental work was done by Harry Olson, RCA, in the 1940's
> > .. in case you want to research it further...
> > cheers, RS
> You didn't look at the link.
>
> Mikek
> --

you mean, did I download the PDF, search
thru it
to find a 5 page article from 1964, that related
to your question?
No I did not.
Then try to match up what you asked with
whatever is inside that article?
No I did not.
I think this is asking a lot from a typical
usenet group follower.
Hopefully those who have more free
time & love of old tech can help.

OK I downloaded the PDF.
It was nice to see Lou Garner's
name once again (the Semiconductor
Editor -- what could that mean? ;-)

I would still recommend going to
a modern website on micrphones
to get better insight.
The animation on DPA's page
I like:

https://www.dpamicrophones.com/mic-university/the-interference-tube-and-its-use-in-microphones

On 12/17/2021 7:51 PM, Rich S wrote:
>> Your answer leaves me in the dark, I'm looking for some light.
>>
>> Mikek
>> --
> Hi Mikek,
> Let's all try to be light producing ;-)
> Could you re-post your exact question, again,
> if you don't mind, BUT without the formatting?
> (On my computer, the post was horribly littered with a
> characters, /, * My brain shuts down if I have to read
> something that non-decipherable.)
> regards, RS

Sure, I copied and pasted from a pdf and it went bad.

I have a 22" long tube with open ends. ( ID is 1-3/16")

 I find a resonance at 300Hz. My understanding is a tube with both ends
open will have null (node)

in the center and antinode at both ends. I would think at a node, a mic
would pick up little sound and at the

antinode the mic would pick up maximum sound. What I find is minimum
signal amplitude from the mic at the

end (opening) and maximum signal in the center of the tube.

 For reference a (different one) see, figure 8  and note F1, it shows a
1/2 wave tube with the open end antinode then a  node in the center and
an antinode at the other open end.

http://www.ijmerr.com/uploadfile/2019/0724/20190724052507570.pdf

My question why is my testing seeing results backwards from what I see
in the literature.

             Thanks, Mikek

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On Friday, 17 December 2021 at 19:47:35 UTC-8, amdx wrote:
....
> For reference a (different one) see, figure 8 and note F1, it shows a
> 1/2 wave tube with the open end antinode then a node in the center and
> an antinode at the other open end.
>
> http://www.ijmerr.com/uploadfile/2019/0724/20190724052507570.pdf
>
> My question why is my testing seeing results backwards from what I see
> in the literature.
>
....

It depends upon whether your microphone is sensitive to pressure changes or velocity changes.

There will be maximum pressure changes (with zero velocity) at the centre and maximum velocity changes at the ends.

The open tube can be considered as being two closed-end tubes connected at the centre then removing the ends.

kw

On 2021-12-18, amdx <amdx@knology.net> wrote:
> On 12/17/2021 7:51 PM, Rich S wrote:
>>> Your answer leaves me in the dark, I'm looking for some light.
>>>
>>> Mikek
>>> --
>> Hi Mikek,
>> Let's all try to be light producing ;-)
>> Could you re-post your exact question, again,
>> if you don't mind, BUT without the formatting?
>> (On my computer, the post was horribly littered with a
>> characters, /, * My brain shuts down if I have to read
>> something that non-decipherable.)
>> regards, RS
>
> Sure, I copied and pasted from a pdf and it went bad.
>
> I have a 22" long tube with open ends. ( ID is 1-3/16")
>
>  I find a resonance at 300Hz. My understanding is a tube with both ends
> open will have null (node)
>
> in the center and antinode at both ends. I would think at a node, a mic
> would pick up little sound and at the

Because of the counter-intuitive way that open and closed are defined
in electonics, in pipes open and closed are the opposite, so an open in
a pipe (gas-accoustic transmission line) is like a short in an
electrical transmission line, so it gets you a node. (pressure
minimum, velocity maximum)

There will be an antinode (pressure maximum,velocity minumum) in the middle if it's driven at
its fundamental frequency (or some odd harmonic).

--
Jasen.

amdx wrote:
=========
>
>
> With a mic setting at the open end

** What mic are you using???

..... Phil

On 12/18/2021 12:33 AM, Phil Allison wrote:
> amdx wrote:
> =========
>>
>> With a mic setting at the open end
> ** What mic are you using???
>
>
>
>
> .... Phil

 This is what I had purchased a few years ago and will probably use
if/when I do this.

> https://www.mouser.com/datasheet/2/334/AOM-5024L-HD-R-1219369.pdf
btw, note the measurement is at 50cm, not 1 meter. So sensitivity is
probably not

useful as a comparison to other mics.

At this time,  I'm thinking

I will need to put a mic at the center point of each tube because, that
is where the

largest (at resonance) signal is. I don't understand the authors
placement at what I measure as

a null.  (I won't be surprised if I learn something and it changes)

                                       Mikek

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On 12/17/2021 10:53 PM, ke...@kjwdesigns.com wrote:
> On Friday, 17 December 2021 at 19:47:35 UTC-8, amdx wrote:
> ...
>> For reference a (different one) see, figure 8 and note F1, it shows a
>> 1/2 wave tube with the open end antinode then a node in the center and
>> an antinode at the other open end.
>>
>> http://www.ijmerr.com/uploadfile/2019/0724/20190724052507570.pdf
>>
>> My question why is my testing seeing results backwards from what I see
>> in the literature.
>>
> ...
>
> It depends upon whether your microphone is sensitive to pressure changes or velocity changes.
>
> There will be maximum pressure changes (with zero velocity) at the centre and maximum velocity changes at the ends.
>
> The open tube can be considered as being two closed-end tubes connected at the centre then removing the ends.
>
> kw

I didn't know that existed, here's the mic, can you tell what type it is?

> https://www.mouser.com/datasheet/2/334/AOM-5024L-HD-R-1219369.pdf
                                   Mikek

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On Saturday, 18 December 2021 at 13:27:15 UTC, amdx wrote:

> >> My question why is my testing seeing results backwards from what I see
> >> in the literature.
> > It depends upon whether your microphone is sensitive to pressure changes or velocity changes.
> > There will be maximum pressure changes (with zero velocity) at the centre and maximum velocity changes at the ends.
> > The open tube can be considered as being two closed-end tubes connected at the centre then removing the ends.
> > kw
> I didn't know that existed, here's the mic, can you tell what type it is?
>
> > https://www.mouser.com/datasheet/2/334/AOM-5024L-HD-R-1219369.pdf
> Mikek
That microphone responds to pressure and not velocity. Its a nice microphone
I have used a lot of them.
John

On 12/17/2021 11:51 PM, Jasen Betts wrote:
> On 2021-12-18, amdx <amdx@knology.net> wrote:
>> On 12/17/2021 7:51 PM, Rich S wrote:
>>>> Your answer leaves me in the dark, I'm looking for some light.
>>>>
>>>> Mikek
>>>> --
>>> Hi Mikek,
>>> Let's all try to be light producing ;-)
>>> Could you re-post your exact question, again,
>>> if you don't mind, BUT without the formatting?
>>> (On my computer, the post was horribly littered with a
>>> characters, /, * My brain shuts down if I have to read
>>> something that non-decipherable.)
>>> regards, RS
>> Sure, I copied and pasted from a pdf and it went bad.
>>
>> I have a 22" long tube with open ends. ( ID is 1-3/16")
>>
>>  I find a resonance at 300Hz. My understanding is a tube with both ends
>> open will have null (node)
>>
>> in the center and antinode at both ends. I would think at a node, a mic
>> would pick up little sound and at the
> Because of the counter-intuitive way that open and closed are defined
> in electonics, in pipes open and closed are the opposite, so an open in
> a pipe (gas-accoustic transmission line) is like a short in an
> electrical transmission line, so it gets you a node. (pressure
> minimum, velocity maximum)
>
> There will be an antinode (pressure maximum,velocity minumum) in the middle if it's driven at
> its fundamental frequency (or some odd harmonic).
>
 I went to pull up a couple of diagrams showing the opposite, showing
antinodes at the open ends.

The first hit was Khan academy, showing what I was looking for, BUT,
reading further, it said,

"Another way to think about standing waves in open tubes is by instead
considering how the air pressure varies

along the length of the tube. For open tubes, the air pressure at the
ends equalizes with the atmosphere.

Thus, the pressure stays constant at the open ends and they are pressure
nodes."

It goes on to show an air pressure diagram, with nulls at the open ends
and an antinode in the center.

> https://www.khanacademy.org/science/in-in-class11th-physics/in-in-11th-physics-waves/in-in-11th-physics-sound-topic/a/intro-to-sound-ap1
A couple other posts brought up the pressure/velocity idea and what type
mic I had. I hope to glean more from their responses.

                                                      Mikek

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On 12/18/2021 7:45 AM, John Walliker wrote:
> On Saturday, 18 December 2021 at 13:27:15 UTC, amdx wrote:
>
>>>> My question why is my testing seeing results backwards from what I see
>>>> in the literature.
>>> It depends upon whether your microphone is sensitive to pressure changes or velocity changes.
>>> There will be maximum pressure changes (with zero velocity) at the centre and maximum velocity changes at the ends.
>>> The open tube can be considered as being two closed-end tubes connected at the centre then removing the ends.
>>> kw
>> I didn't know that existed, here's the mic, can you tell what type it is?
>>
>>> https://www.mouser.com/datasheet/2/334/AOM-5024L-HD-R-1219369.pdf
>> Mikek
>
> That microphone responds to pressure and not velocity. Its a nice microphone
> I have used a lot of them.
> John

Great, that seems to be making sense with what I'm measuring.

I do have a question about the mic the author used, a 2-1/8" Lafeyette
PA-27 Crystal Cartridge.

Because the author mounted it at the end of a 1/2 wave open end tube, my
thinking is the crystal

cartridge is a velocity mic. What do you think?

                                    Mikek

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amdx wrote:
=========
> >>
> >> With a mic setting at the open end
> > ** What mic are you using???
> >
> .... Phil

> This is what I had purchased a few years ago and will probably use
> if/when I do this.
>
> > https://www.mouser.com/datasheet/2/334/AOM-5024L-HD-R-1219369.pdf
>

** Ok - it's a *small* pressure mic.

Not a cardiod ( aka pressure gradient ) type.
That could have invalidated all your tests.

( Nor a velocity mic either )

..... Phil