OFF TOPIC; Resonance of open end tube and node position...

On 12/18/2021 5:38 PM, Phil Allison wrote:
amdx wrote:
=========

I do have a question about the mic the author used, a 2-1/8\" Lafeyette
PA-27 Crystal Cartridge.
** Only Crystal mics I ever came across in the 60s were all omnis.

But in truth they can be any type.


..... Phil
Click to expand...

 The author used an open 1/2 wavelength tube which has a velocity
maximum at the end, which is where the crystal mic was mounted.

 So unless the author made a huge mistake, the crystal mic should be a
velocity mic.

 I haven\'t found any info about that mic.

                           Mikek


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amdx wrote:
On 12/18/2021 12:11 PM, Phil Hobbs wrote:
amdx wrote:
On 12/18/2021 10:38 AM, Phil Hobbs wrote:
amdx 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

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.

The centre is a _velocity_ node but a _pressure_ antinode.

The ends are not exactly at the nodal points because there\'s a
mass-spring loading at the ends due to having to move ambient air
out of the way.  (This is the same physics as the Helmholtz resonance.)

The Helmholtz resonance is always the lowest mode of any cavity with
one opening.  (There\'s obviously a DC mode when both ends are open.)

Cheers

Phil Hobbs


Thanks Phil,

     I found answer that answer on a Khan Accademy website. So, with
that info I can mic the closed end of a tube and use 1/4 wavelength

tube, cutting my longest (300 Hz resonance) tube down to 11\".

Another question, what is the best approach to paralleling multiple
electret mics together for maximum amplitude from each?

Thanks, Mikek



You have to worry about the phases, of course, but I tend to be
partial to wiring that sort of stuff in series.  Phil A will of course
trash that idea. ;)



Cheers

Phil Hobbs

 I don\'t see how to wire electret mics that have internal fets in series.

Am I missing something simple?

                              Mikek
Click to expand...

With internal FETs, the series connection wouldn\'t get you anything
anyhow--it\'s about increasing the signal while not increasing the
loading or additive noise from the front end amp.

Probably a regular old audio summer, i.e. an inverting op amp stage with
a separate input resistor for each mic, will work fine. Keep the
resistor values down in order not to lose SNR to their Johnson noise,
but don\'t go so low that you load down the FETs.

I\'d guess 1-2k would work well, but they may run the FETs at super low
drain current to save power.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
amdx wrote:
===========
Another question, what is the best approach to paralleling multiple
electret mics together for maximum amplitude from each?

** Connect each mic to a small, step down transformer and wire the secondaries in series.

The signals from you mics will not be in-phase so will not add in a simple way.




I have thought about signals of different frequencies adding and
subtracting, but don\'t they do that in air also?
Click to expand...

** How many angels can dance on the head of a pin ??



...... Phil
 
On 12/18/2021 9:57 PM, Phil Allison wrote:
amdx wrote:
===========
Another question, what is the best approach to paralleling multiple
electret mics together for maximum amplitude from each?

** Connect each mic to a small, step down transformer and wire the secondaries in series.

The signals from you mics will not be in-phase so will not add in a simple way.




I have thought about signals of different frequencies adding and
subtracting, but don\'t they do that in air also?

** How many angels can dance on the head of a pin ??



..... Phil
Click to expand...
I don\'t believe in angels.
Mikek



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amdx wrote:
===========
Another question, what is the best approach to paralleling multiple
electret mics together for maximum amplitude from each?

** Connect each mic to a small, step down transformer and wire the secondaries in series.

The signals from you mics will not be in-phase so will not add in a simple way.


I have thought about signals of different frequencies adding and
subtracting, but don\'t they do that in air also?

** How many angels can dance on the head of a pin ??


I don\'t believe in angels.
Click to expand...

** Fuck off Mikek.
 
On 12/18/2021 11:13 PM, Phil Allison wrote:
amdx wrote:
===========
Another question, what is the best approach to paralleling multiple
electret mics together for maximum amplitude from each?

** Connect each mic to a small, step down transformer and wire the secondaries in series.

The signals from you mics will not be in-phase so will not add in a simple way.


I have thought about signals of different frequencies adding and
subtracting, but don\'t they do that in air also?

** How many angels can dance on the head of a pin ??


I don\'t believe in angels.
** Fuck off Mikek.
Click to expand...

I ask questions, because I don\'t know the answers, I\'m not sure why that pisses you off.
I don\'t know why you would get involved in a thread, if this is what happens.
Mikek


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On Sunday, 19 December 2021 at 09:31:32 UTC, amdx wrote:
On 12/18/2021 11:13 PM, Phil Allison wrote:
amdx wrote:
===========
Another question, what is the best approach to paralleling multiple
electret mics together for maximum amplitude from each?

** Connect each mic to a small, step down transformer and wire the secondaries in series.

The signals from you mics will not be in-phase so will not add in a simple way.


I have thought about signals of different frequencies adding and
subtracting, but don\'t they do that in air also?

** How many angels can dance on the head of a pin ??


I don\'t believe in angels.
** Fuck off Mikek.

I ask questions, because I don\'t know the answers, I\'m not sure why that pisses you off.
I don\'t know why you would get involved in a thread, if this is what happens.
Mikek


--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
Click to expand...

I may have missed it, but how many microphones do you intend to use?

John
 
On 12/19/2021 4:52 AM, John Walliker wrote:
On Sunday, 19 December 2021 at 09:31:32 UTC, amdx wrote:
On 12/18/2021 11:13 PM, Phil Allison wrote:
amdx wrote:
===========
Another question, what is the best approach to paralleling multiple
electret mics together for maximum amplitude from each?

** Connect each mic to a small, step down transformer and wire the secondaries in series.

The signals from you mics will not be in-phase so will not add in a simple way.


I have thought about signals of different frequencies adding and
subtracting, but don\'t they do that in air also?

** How many angels can dance on the head of a pin ??


I don\'t believe in angels.
** Fuck off Mikek.

I ask questions, because I don\'t know the answers, I\'m not sure why that pisses you off.
I don\'t know why you would get involved in a thread, if this is what happens.
Mikek


--
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I may have missed it, but how many microphones do you intend to use?

John
Click to expand...

 It\'s possible I could use 22, IF, I put a mic on each resonant tube
300Hz to 3000Hz.

Or I may find a way to use just one. At this time, I find I need a
velocity type microphone

to mount on a 1/2 wavelength open end tube. The only velocity type
microphone I find is a ribbon microphone,

I don\'t expect to use a ribbon microphone. This 1964 design requires a
different build because most newer mics

operate on pressure not velocity, like the mic that the design used.

                                                  Mikek
 
On 2021-12-19, amdx <amdx@knology.net> wrote:
On 12/19/2021 4:52 AM, John Walliker wrote:
On Sunday, 19 December 2021 at 09:31:32 UTC, amdx wrote:
On 12/18/2021 11:13 PM, Phil Allison wrote:
amdx wrote:
===========
Another question, what is the best approach to paralleling multiple
electret mics together for maximum amplitude from each?

** Connect each mic to a small, step down transformer and wire the secondaries in series.

The signals from you mics will not be in-phase so will not add in a simple way.


I have thought about signals of different frequencies adding and
subtracting, but don\'t they do that in air also?

** How many angels can dance on the head of a pin ??


I don\'t believe in angels.
** Fuck off Mikek.

I ask questions, because I don\'t know the answers, I\'m not sure why that pisses you off.
I don\'t know why you would get involved in a thread, if this is what happens.
Mikek


--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
I may have missed it, but how many microphones do you intend to use?

John

 It\'s possible I could use 22, IF, I put a mic on each resonant tube
300Hz to 3000Hz.

Or I may find a way to use just one. At this time, I find I need a
velocity type microphone

to mount on a 1/2 wavelength open end tube. The only velocity type
microphone I find is a ribbon microphone,

I don\'t expect to use a ribbon microphone. This 1964 design requires a
different build because most newer mics

operate on pressure not velocity, like the mic that the design used.
Click to expand...

a pressure microphome will still give a signal, but if mounted at the
closed end the signal will be stronger.

--
Jasen.
 
On Sunday, 19 December 2021 at 12:00:55 UTC, Jasen Betts wrote:
On 2021-12-19, amdx <am...@knology.net> wrote:
On 12/19/2021 4:52 AM, John Walliker wrote:
On Sunday, 19 December 2021 at 09:31:32 UTC, amdx wrote:
On 12/18/2021 11:13 PM, Phil Allison wrote:
amdx wrote:
===========
Another question, what is the best approach to paralleling multiple
electret mics together for maximum amplitude from each?

** Connect each mic to a small, step down transformer and wire the secondaries in series.

The signals from you mics will not be in-phase so will not add in a simple way.


I have thought about signals of different frequencies adding and
subtracting, but don\'t they do that in air also?

** How many angels can dance on the head of a pin ??


I don\'t believe in angels.
** Fuck off Mikek.

I ask questions, because I don\'t know the answers, I\'m not sure why that pisses you off.
I don\'t know why you would get involved in a thread, if this is what happens.
Mikek


--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
I may have missed it, but how many microphones do you intend to use?

John

It\'s possible I could use 22, IF, I put a mic on each resonant tube
300Hz to 3000Hz.

Or I may find a way to use just one. At this time, I find I need a
velocity type microphone

to mount on a 1/2 wavelength open end tube. The only velocity type
microphone I find is a ribbon microphone,

I don\'t expect to use a ribbon microphone. This 1964 design requires a
different build because most newer mics

operate on pressure not velocity, like the mic that the design used.

a pressure microphome will still give a signal, but if mounted at the
closed end the signal will be stronger.

--
Jasen.
Click to expand...

I have looked at the original article and I really struggle to understand
how it could work as intended.
The microphone is glued into a funnel which appears to be sealed at
the back. So there is no rear port. Most shotgun mics rely on
cancellation between the front and back ports to give front-back
directivity.

John
 
On 12/19/2021 7:39 AM, John Walliker wrote:
On Sunday, 19 December 2021 at 12:00:55 UTC, Jasen Betts wrote:
On 2021-12-19, amdx <am...@knology.net> wrote:
On 12/19/2021 4:52 AM, John Walliker wrote:
On Sunday, 19 December 2021 at 09:31:32 UTC, amdx wrote:
On 12/18/2021 11:13 PM, Phil Allison wrote:
amdx wrote:
===========
Another question, what is the best approach to paralleling multiple
electret mics together for maximum amplitude from each?

** Connect each mic to a small, step down transformer and wire the secondaries in series.

The signals from you mics will not be in-phase so will not add in a simple way.


I have thought about signals of different frequencies adding and
subtracting, but don\'t they do that in air also?

** How many angels can dance on the head of a pin ??


I don\'t believe in angels.
** Fuck off Mikek.

I ask questions, because I don\'t know the answers, I\'m not sure why that pisses you off.
I don\'t know why you would get involved in a thread, if this is what happens.
Mikek


--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
I may have missed it, but how many microphones do you intend to use?

John
It\'s possible I could use 22, IF, I put a mic on each resonant tube
300Hz to 3000Hz.

Or I may find a way to use just one. At this time, I find I need a
velocity type microphone

to mount on a 1/2 wavelength open end tube. The only velocity type
microphone I find is a ribbon microphone,

I don\'t expect to use a ribbon microphone. This 1964 design requires a
different build because most newer mics

operate on pressure not velocity, like the mic that the design used.

a pressure microphome will still give a signal, but if mounted at the
closed end the signal will be stronger.

--
Jasen.
I have looked at the original article and I really struggle to understand
how it could work as intended.
The microphone is glued into a funnel which appears to be sealed at
the back. So there is no rear port. Most shotgun mics rely on
cancellation between the front and back ports to give front-back
directivity.

John
Click to expand...
I question whether the 1/2 wavelength tube are actually sealed.
I don\'t think the author took great effort to seal around the funnel,
but, I think the 36 other tubes pointing to the front are an open end to
each of the other resonant tubes. (?)
If the tubes were sealed, from what I have learned about pressure and velocity,
nodes and antinodes, I also don\'t see how it would work.
Mikek
 
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