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

[Qmavam]

I'm looking at building a multitube shotgun microphone, 22 resonant tubes from 300Hz to 3000Hz.
I want to mic each tube. I'll probably want a low noise preamp on each mic.

My question is, what is the best way to combine 22 mics (preamps) to drive one amplifier?

Original Project Source, pg 51.
https://worldradiohistory.com/Archive-Poptronics/60s/64/Pop-1964-06.pdf
Thanks Mikek

 

[rock soderstrom]

Hi Mikek!

You want a audio mixer with a minimum of 22 mic preamps. You can buy them used already from 100 bucks. Look for YAMAHA MC 2404, Behringers or similar. That would be the simplest and probably cheapest solution.

Thanks for linking this cool magazine!

"The shotgun sound snooper" ROFL

 

[Qmavam]

Hi Rock, Your recommended type of mixers don't fit the profile I need. Let me tell you the things I have run up on. The author uses 1/2 Wavelength tubes mic'ed at an open end. The open end of a 1/2 wave tube is a velocity antinode, but a pressure node point, and the electret mic I'm using is a pressure mic. The Antinode is in the center of a resonant tube which would require mounting the mic in the center. The only thing I can think of, is the Crystal Cartridge the author used is velocity mic, which would work fine at the velocity anti node or, the author got it all wrong. I'm experimenting with the use of 1/4wave tubes that have the pressure antinode at the closed end. This has the advantage of reducing the length by half. But this does require a mic on each tube and then mixing. Do you have any other to mix 22 preamps, specifically this preamp. Low Noise Microphone Preamp
OK, hard to understand context, but your emojis make me think you don't like this design, could you elaborate?
Thanks, Mikek

 

[musipol]

Just a comment. A friend of mine built something similar to this(multiple tube mic thing) back in the early 70's. He was hoping for good directional performance. In that respect it performed poorly. He later built a parabolic reflector for a single mic which worked well.

 

[rock soderstrom]

Hi Rock, Your recommended type of mixers don't fit the profile I need.

Why? You need a lot of microphone preamplifiers with plenty of gain for this arrangement, completely independent of the microphone position and type. A mixable summing amplifier, the built-in equalizers and the additional outputs plus headphone amplifier are also helpful. A mixer offers all this quite compactly and affordably in one device. (The quality is far above the rudimentary basic circuits linked before by you).

An upgrade would be a digital 24 channel audio interface with built in mic preamps and plenty of software. That will cost more money.

I'm not an expert on such things. No idea if this setup is any good. I would probably try it with a parabolic reflector microphone first.

What I do know is that I would be careful setting up such a thing in public where people are. It looks very dangerous. Google a gattling gun, it's pretty similar. That's why the smileys.

If you're unlucky, someone will feel threatened and call the police or shoot at you. That is not funny.

 

[pinchemotherloaf]

I'm looking at building a multitube shotgun microphone, 22 resonant tubes from 300Hz to 3000Hz.
I want to mic each tube. I'll probably want a low noise preamp on each mic.

My question is, what is the best way to combine 22 mics (preamps) to drive one amplifier?

Original Project Source, pg 51.
https://worldradiohistory.com/Archive-Poptronics/60s/64/Pop-1964-06.pdf
Thanks Mikek

Hi Mikek, you might look into producing a summing amplifier using op amps (or just buy one.) Used in broadcast extensively: Summing Amplifier or Op Amp Adder | Electrical4U

 

[emrr]

Not knowing the performance goal, it’s hard to imagine any one path. All the early multi-tube mics like this used a single large omni capsule like a Western Electric 618 or 633. I have a home made vintage tube array intended for such.

 

[mjrippe]

Seems like RCA's version used a "broad cardioid"...

 

[NOON]

Does this count as a 'tube mic'? I saw one of these RCA beasts recently. I've been helping a guy clear out his Dad''s workshop, he was a broadcast engineer for many decades. In a huge wooden box in the back room was the tubes section of one of these mics. Unfortunately no sign of the capsule or any other parts.

 

[abbey road d enfer]

Before any attempt at DIYing one, it is important to understand the principle behind it.
The Popular Electronics article fails miserably in this respect.

check pages 89 & 90 there
https://books.google.fr/books?id=Ir...=onepage&q=varidirectional microphone&f=false
There are very few references to these as they have been replaced with "interference tubes", that operate on a similar principle and are easier to make.
The principles are as similar (or as different) as cardioid mics using a dual capsule (condenser mics) and those using the rear acoustic filter (similar to the ubiquitous SM58).
In one case, the path difference is created geometrically, in the other it is simulated by an acoustic All Pass Filter.

 

[NOON]

More of a thought experiment than a practical solution, wonder what would happen with a series - parallel array of dynamic capsules, wired like you do with e.g. a 4 x 12 speaker cabinet to arrive back at the nominal impedance of one capsule.

 

[Qmavam]

Seems like RCA's version used a "broad cardioid"...

That's interesting I haven't seen it, I'm confused by the length, it says 6". A 1/2 wave resonant tube would need to be 16.5".

 

[Qmavam]

Just a comment. A friend of mine built something similar to this(multiple tube mic thing) back in the early 70's. He was hoping for good directional performance. In that respect it performed poorly. He later built a parabolic reflector for a single mic which worked well.

Ya, I'm kicking myself I had 3 dishTV type satellite dishes and during a cleanup, threw them all away. I'm on the look out for one.

 

[abbey road d enfer]

That's interesting I haven't seen it, I'm confused by the length, it says 6". A 1/2 wave resonant tube would need to be 16.5".

6" is just the mic itself; the "ultra directional attachment" is much longer than that, about 32".

 

[igloo701]

Sorry Guys,

The initial principle was developed by Western Electric in 1937 - WE 618A + D-99098. It's exactly the same principle as usual interference microphones like the Sennheiser MKH816. It just requires one microphone. And later by RCA (MI-10006 in 1960) and Electro-Voice (between 1960 and 63 with three models 642, 643, 644). None of them has survived.

Not based on resonance but on various individual delays and lateral comb filtering...

As it's described in the Pop Electronics magazine, with one microphone.... and originally with pressure microphones (omnidirectional)

 

[abbey road d enfer]

The initial principle was developed by Western Electric in 1937 - WE 618A + D-99098. It's exactly the same principle as usual interference microphones like the Sennheiser MKH816. It just requires one microphone. And later by RCA (MI-10006 in 1960) and Electro-Voice (between 1960 and 63 with three models 642, 643, 644). None of them has survived.

It's frustrating there's so little reference available, compared to the more common multi-hole interference tube.

Not based on resonance but on various individual delays and lateral comb filtering...

Speaker designers are more adept at understanding the principles, because it's what governs the "end-fire arrays" that are not commonly used in big PA systems, particularly for subwoofers.

As it's described in the Pop Electronics magazine, with one microphone.... and originally with pressure microphones (omnidirectional)

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

 

[abbey road d enfer]

Just a comment. A friend of mine built something similar to this(multiple tube mic thing) back in the early 70's. He was hoping for good directional performance. In that respect it performed poorly. He later built a parabolic reflector for a single mic which worked well.

It must be understood that a parabolic reflector, in addition to tightening the directivity pattern, also concentrates the acoustic energy, and thus increases enormously the sensitivity. That's probably what creates the perception of better directivity, but a well-designed multi-tube rifle mic is capable of excellent directivity control.
Poor DIY implementation is probably what has given it bad rep.
One must admit that, for similar results, an interference tube mic is much more practical. It's quite difficult to put 34 tubes in a 19mm (3/4") circle.

 

[pinchemotherloaf]

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:

 

[emrr]

It's frustrating there's so little reference available, compared to the more common multi-hole interference tube.

The RCA and the Electro-Voice were both patented in the US.

The EV 642 won an Oscar. I have a pair of 642's.

On closer inspection, the homemade version I have has to be from that same article, 37 tubes from 1" to 36".

 

[abbey road d enfer]

The RCA and the Electro-Voice were both patented in the US.

The EV642 is a single interference tube design.
I couldn't find any reference to the RCA patent.