Many microphones driving one amplifier. How do I do it?

[Qmavam]

I did a little experimenting, I built a 1/2 wave tube that is resonant at 1000Hz. While working with it, I found I had 10 time more signal if I put the mic in the center, instead of at the end, like the Pop sci author did. Google to the rescue and I discovered there are velocity waves and pressure waves. and they are opposite each other in a resonannt tube. The electret mic I have is a pressure mic, apparently the authors Crystal Cartridge mic was a velocity mic so his 1/2 wave tubes worked. Then I figured a 1/4 wave closed end tube has it's pressure an antinode at the closed end. so I built a 1/4 wave tube with the mic mounted in the closed end. The 1/4 wave closed end tube with the mic at the end had the same output level as a 1/2 wave tube with the mic mounted at the middle of the tube. The problem, each tube will need it's own mic.
I do have a few questions: Is a 1/4 wave closed end resonant tube as directional as an open 1/2 wave tube? Does tube diameter make any difference in amplitude? I don't think so, but, I'm not sure.

 

[Qmavam]

Unfortunately, the guy who wrote the article had it all wrong with the theory.

I'd like to hear what you think he got wrong. I chased my tail for a while not understanding velocity and pressure. And I never had anyone confirm the Crystal Cartridge mic used by the author was a velocity type microphone, In fact a was told just the opposite, if that was true, the mic is placed at or very near a pressure node.
Connected a 1000Hz 1/4 tube with end mic on my 2500 gain preamp tonight. The preamp need a high impedance at least 5kΩ headphones, I tried some old crystal radio headphones, they worked but I had way to much feedback. Then I remembered a matching transformer I had, I matched the amp to my 64 ohm Sennheiser over the ear headphones this was better, but still had to be in the right position to prevent feedback. We have a clock that ticks very loud and I could pick speaker playing a1000Hz tone 20 ft away that I couldn't hear without the amp and headphones. So, it was promising, I'll start getting it packaged so I can get outside and do some longer distance tests. Also get it battery operated, I had a little hum, hope that goes away.

 

[abbey road d enfer]

I did a little experimenting, I built a 1/2 wave tube that is resonant at 1000Hz. While working with it, I found I had 10 time more signal if I put the mic in the center, instead of at the end, like the Pop sci author did.

Do you want to record only 1kHz? If that is your goal, do it. But what most people want to achieve is a reasonably flat response, which is what you get at the end of the tube.

The electret mic I have is a pressure mic, apparently the authors Crystal Cartridge mic was a velocity mic so his 1/2 wave tubes worked.

A crystal mic is pressure mic.

Then I figured a 1/4 wave closed end tube has it's pressure an antinode at the closed end. so I built a 1/4 wave tube with the mic mounted in the closed end. The 1/4 wave closed end tube with the mic at the end had the same output level as a 1/2 wave tube with the mic mounted at the middle of the tube. The problem, each tube will need it's own mic.

Why? If the tubes end up in a common enclosure, the sound pressures will add-up acoustically.

I do have a few questions: Is a 1/4 wave closed end resonant tube as directional as an open 1/2 wave tube?

The tubes themselves are not directional. It's the combination of different length tubes that makes the system directional.

 

[Garagescience]

Reminds me of that classic film "The Conversation" with Gene Hackman where they use a microphone 'invented' to capture, from a distance, a young couple's conversation. They 'used' 3 microphones, including a parabolic, to produce 3 tapes that Gene 'mixes down'(!) It looked like a gun:
View attachment 87533View attachment 87534

One of my favorite movies ever!

 

[Qmavam]

Do you want to record only 1kHz? If that is your goal, do it.

I'm shooting for voice intelligibility, Bell Labs say 300Hz to 3000 Hz. btw, I'm here to learn, if I sound argumentative, I'm not, just looking for information.

But what most people want to achieve is a reasonably flat response, which is what you get at the end of the tube.

I'm assuming you mean the mic'ed end of the tube. A 6", 1/2 wave open ended tube is resonant at 1000Hz, you get a peak in amplitude at 1000Hz, it is not a flat response. However, the peak pressure is in the center and that is the position where the mic has maximum amplitude.

A crystal mic is pressure mic.

If that is the case and it mostly likely is, Why did the author put the pressure mic at the end of an open ended pipe? This is where the pressure node is.
(a pressure, null)

Why? If the tubes end up in a common enclosure, the sound pressures will add-up acoustically.

Ya, I'm little unsure of this, but I could make an air tight seal at the end of all the tubes in a common enclosure, but every tube is still open to the world at the other end of all the other tubes.

The tubes themselves are not directional. It's the combination of different length tubes that makes the system directional.

I have no understanding how the other tubes affect the directionality of a single tube. Can you enlighten me?

 

[abbey road d enfer]

I'm assuming you mean the mic'ed end of the tube. A 6", 1/2 wave open ended tube is resonant at 1000Hz, you get a peak in amplitude at 1000Hz, it is not a flat response.

This is the respônse of ONE tube. Now the whole contraption has 3 dozens of tubes, each resonating at a different frequency. When they are mixed together (acoustically), the resposne is somewhat linear.

However, the peak pressure is in the center and that is the position where the mic has maximum amplitude.

The idea is not to capture the response of a single tube. And remeber that each tube has several resonances.

If that is the case and it mostly likely is, Why did the author put the pressure mic at the end of an open ended pipe? This is where the pressure node is.
(a pressure, null)

Because he does not look specifically for capturing the resonance.

I have no understanding how the other tubes affect the directionality of a single tube. Can you enlighten me?

You have to understand phase cancellation. Knowledge comes in layers. If you try to bypass some layer, you just lose connection.

 

[Qmavam]

This is the respônse of ONE tube. Now the whole contraption has 3 dozens of tubes, each resonating at a different frequency. When they are mixed together (acoustically), the response is somewhat linear.

Yes, I tested one tube, I wabnted to get an understanding before I bought tube and cut it all to length.

The idea is not to capture the response of a single tube. And remember that each tube has several resonances.

You have become fixated on my testing of one tube, I realize for fidelity I need to cover a range. It was a good experience I learned a lot doing it, I also tested several other length tubes at other resonant frequencies, at both 1/4 wave closed end and 1/2 wave open end.

You have to understand phase cancellation. Knowledge comes in layers. If you try to bypass some layer, you just lose connection.

Yes, I understand path length will change the phase and can be additive or subtractive.

 

[abbey road d enfer]

You have become fixated on my testing of one tube, I realize for fidelity I need to cover a range. It was a good experience I learned a lot doing it, I also tested several other length tubes at other resonant frequencies, at both 1/4 wave closed end and 1/2 wave open end.

You have a multitrack recording, you listen to all the tracks individually, you get an idea of the song, but it's only when you have the mix that you have the full result.