4x EM272Z1 electrets in parallel (off-grid). Extra power needed for a USB soundcard?

[YvesD]

Hello everyone,

I am looking for some good advice or good help. I am working on a bio-acoustics project that involves 4x EM 272Z1 electret capsules. Ideally, all four of these need to be connected in parallel to a single microphone input. (USB Soundblaster Play! 3)

Now, standard USB sound cards have enough bias voltage to power two of these EM 272Z1 capsules, but since my project requires four, I am wondering if I need to provide some kind of "extra power supply" of 5 volts so that all capsules definitely receive enough voltage and current to function properly.
Furthermore, everything needs to be set up outdoors in a nature reserve, so there will be no mains power available.

I have already inquired here and there, but didn't get a truly satisfactory answer anywhere.

I have seen such a setup before, but I didn't have the opportunity to look at the components.
Is there anyone who happens to be able to help me guide this with a simple schematic and the necessary components? There are USB power banks available on site.
I am actually a bit desperate, and that is why I am coming to this forum with this question, because I have received great help several times in the past that really worked very well.

To the moderator: if this is inappropriate, it may be removed.

Regards,
Yves

 

[cebersp]

Hi,
Perhaps you also could live with 3 in parallel?
I would do DC voltage measurements with 1, 2 , 3 and 4 microphones in parallel. Or just try it.
The datasheet does not say much about dc consumption.
Christof

 

[AaronD]

I'm curious why you're putting mics in parallel in the first place. I assume it's an array, which has its own acoustic behavior that I assume is useful for you. But just mashing sources together with no explicit mixing design, is a pretty strong indicator of either poor electronic understanding, or excellent electronic understanding that tells you that you can get away with it despite the usual problems (beyond just powering all of them), and thus minimize cost for mass production.

Doesn't sound like you're mass producing these things, so I would strongly recommend a separate power supply (could be a second USB port), a dedicated preamp for each capsule, an explicit mixer after the separate preamps, and then the soundcard. Or, a multiple-input sound card or just multiple sound cards, to run each capsule separately into the computer and then process them there.

Then each capsule actually does perform per the datasheet (or at least has a chance to, factory quality notwithstanding), and they're not "dragged down" because they're all acting as potentially wacky loads on each other.

 

[YvesD]

Hi,
Perhaps you also could live with 3 in parallel?
I would do DC voltage measurements with 1, 2 , 3 and 4 microphones in parallel. Or just try it.
The datasheet does not say much about dc consumption.
Christof

No not really, i do need the four winddirections for this. :-(

I'm curious why you're putting mics in parallel in the first place. I assume it's an array, which has its own acoustic behavior that I assume is useful for you. But just mashing sources together with no explicit mixing design, is a pretty strong indicator of either poor electronic understanding, or excellent electronic understanding that tells you that you can get away with it despite the usual problems (beyond just powering all of them), and thus minimize cost for mass production.

Doesn't sound like you're mass producing these things, so I would strongly recommend a separate power supply (could be a second USB port), a dedicated preamp for each capsule, an explicit mixer after the separate preamps, and then the soundcard. Or, a multiple-input sound card or just multiple sound cards, to run each capsule separately into the computer and then process them there.

Then each capsule actually does perform per the datasheet (or at least has a chance to, factory quality notwithstanding), and they're not "dragged down" because they're all acting as potentially wacky loads on each other.

The mixing is done by Birdnet-GO itself to mono, needed to plot the spectrograms.
This is also not a mass-production setup, it's very specialized to capture bird vocals during migration.
The biggest problem is that it's a off-grid setup (nature reserve). I can provide 5V USB power a much as needed, but can not provide mains power on-site.
The choosen soundcard is a Soundblaster Play! 3 type (because we have this already)
Mixing can be done by a Teensy 4.1 or by the end-station Raspberry Pi 4B.
That is not the real problem, the problem is that the software only allows 1 soundcard for streaming, and we need the 4 electrets EM272Z1's (winddirections).
Some guy told me (but i have indeed not enough insights in electronics itself) that those capsules should best get some (5V !) phanthom from a battery or USB port. Once i know for sure this would work, i can collect and assemble this on a breadboard PCB for testing. But calculating or finding out what is needed is to far off for my understanding....

I just lack the knowledge what components would be needed to achieve this goal.
All those capsules have a TRS male connections (15cm cable) on them.
Anyway, thanks already for your time just looking at my post !!!

Grtz,
Yves

 

[YvesD]

New approach ... ordered a Rode AI dual mic soundcard ... could help me along.
I´ll inform you guys on the progress asap.

 

[DD4WH]

Yves, the EM272 is omnidirectional.
You only need ONE mic for all wind directions.
I have been using EM272 and AOM5024 with BirdNET-Pi and also BirdNET-Go for several years now at different sites. They work very well with one mic. There is no advantage of using more than one mic in parallel in this setup (except for a slight increase in SNR, but the EM272 already has 80dB, which is more than enough for BirdNET-Go).

You asked a similar question a while ago, and got a similar answer, BTW.

https://forum.pjrc.com/index.php?threads/help-in-making-a-birdvocals-recognition-system.77550/post-364233

 

[AaronD]

No not really, i do need the four winddirections for this. :-(

The mixing is done by Birdnet-GO itself to mono, needed to plot the spectrograms.
...
That is not the real problem, the problem is that the software only allows 1 soundcard for streaming, and we need the 4 electrets EM272Z1's (winddirections).

It doesn't matter if your signal processing is acoustic, analog, or digital. The mathematical rules and limitations are the same regardless, but different domains make some operations easier and others harder.
(Digital makes it far easier to just brute-force things! It's not that digital has any sort of special tricks - it doesn't - it's just that it can do so MUCH in a small space, that makes it appear special when it really isn't.)

What I'm getting at, is that it doesn't matter if you mix your directions acoustically (1 omnidirectional mic) or electrically (analog mix of multiple mics that collectively cover every direction evenly) or in software. The result is practically the same, except for some non-idealities in the mics' coverage patterns and the electronic circuitry.

If you want to distinguish different directions, then you have to keep the signals separate all the way into your distinguisher, whatever and wherever that is. One of the fundamental universal rules is, "You can't unmix." Unless you preserve the original, pre-mixed signals, you can't know anymore, what direction anything came from.

The biggest problem is that it's a off-grid setup (nature reserve). I can provide 5V USB power a much as needed, but can not provide mains power on-site.

5V is plenty. As long as you keep your analog signals within the range of your supply, you're fine.

Actually, most circuitry can't go *all* the way to the supply rails - they have some internal functions that operate at some offset to make the signal correct, and that offset also needs to stay within the supply - but I think you get the idea. Read the datasheet for each chip that you want to use: it'll tell you directly what the signal range is for both input and output.

Professional analog audio uses 15-0-15V (total 30V, centered on ground), but a lot of consumer devices run on 5V total or even 3.3V. So there are lots of chips designed for that too.

Some guy told me (but i have indeed not enough insights in electronics itself) that those capsules should best get some (5V !) phanthom from a battery or USB port.

That's exactly the schematic on the right, in the datasheet that you posted. *That's* phantom power...in a more general sense than what the pro-audio industry means by that term.

Specifically, pro-audio phantom uses a 3-pin XLR connector with the signal appearing as a difference between two of those pins (2-3) while the third pin (1) is ground. Both signal pins get a 6.8k resistor to a shared +48V DC supply.
Remove one of the signal wires and its resistor, and reduce the resistor value to partially compensate for a lower supply voltage, and you get the schematic in your datasheet. So yes, you already have phantom in the more general sense.

And, a headset jack (single 4-pin TRRS connector) already has that. No need to add your own. In fact, if you do add your own, the two of them will interact and might give you some unexpected results.
A dedicated mic jack (3-pin TRS) *probably* also has that on its dedicated power pin, but I wouldn't guarantee it. It could also be a "stiff" supply, with a current limit to handle a dynamic mic (literally a speaker operating in reverse) on a 2-pin TS connector that doesn't need power and shorts it out instead.

For an electret mic, I'd recommend a headset TRRS, just to be sure. USB to that is cheap: I bought 12 of them at once last week, to try an idea for a different project. Only use the mic connections, and ignore the two on the end of the plug. Do that for each electret individually, so they each end up with their own dedicated USB connectors and no circuitry of your own, and see where that gets you...once you figure out which <identical_name.number> is which mic, because identical products on the same operating system do that.

 

[AaronD]

TL;DR:
Use a USB to headset adapter for each electret mic individually, directly connected with no circuitry in between. They're literally designed for each other. Signal to Sleeve, Ground to the first Ring. Done!

If you have multiple mics, connect them all like this, each to its own dedicated USB to headset adapter. Then figure out how the operating system identifies each one, and whether each startup assigns those labels differently (if you care). Then mix them in software if you need that.