I'm in the process of designing & building a MicPre for testing various sound equipment etc. The mic capsule is a very good & flat response electret type, that i managed to obtain.
It occured to me that, the way they are usually internally connected, as shown, is a two wire one. In which case, i'm not 100% sure if the output is therefore Inverted. Is this correct ? If so i'll make the Preamp inverted to compensate. If it is so, then a Lot of electret measurement microphones sold, are in need of taking this into account !
It occured to me that, the way they are usually internally connected, as shown, is a two wire one. In which case, i'm not 100% sure if the output is therefore Inverted. Is this correct ? If so i'll make the Preamp inverted to compensate. If it is so, then a Lot of electret measurement microphones sold, are in need of taking this into account !
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You'll have to check with a scope to see if the output polarity of the circuit is positive,
with a positive going air pressure sound, like from saying "p".
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Phase is a relative term, polarity is absolute.
Example in use, integration and tuning of an electronic crossover multi amp multi way loudspeaker system.
My first test is an impulse test of each amp channel and driver. This tells me the channel is at least operational and the output polarity of the driver and more.
I know not everyone cares about polarity but I do. Leaving the which side of the drum the mic was on for others to argue, if I have a recording of an explosion like fireworks, I want a unified positive pressure initial wave front from my speaker system. Simple as that.
Barry.
Dayton UMM-6 is inverted.
MiniDSP UMIK-1 is not.
It all shows up easily the moment you do a sweep in REW and look at sign of impulse function. In which case, click the "invert mic" radio button.
Assuming you have a known positive polarity amp and test your full range speaker with a 1.5v battery to make sure cone moves out when +be applied to red lead. I say full range because a multiway with xo - all bets are off unless you know the design well.
MiniDSP UMIK-1 is not.
It all shows up easily the moment you do a sweep in REW and look at sign of impulse function. In which case, click the "invert mic" radio button.
Assuming you have a known positive polarity amp and test your full range speaker with a 1.5v battery to make sure cone moves out when +be applied to red lead. I say full range because a multiway with xo - all bets are off unless you know the design well.
Yes, that's what i thought, & the reason for my thread, so people can now be aware, if they weren't before.
Good to know for people. I download all the PDF's i could find on their www, but couldn't see any mention of this. Can you provide a link please ?
Yes for one reason.
And also some people might be alarmed to discover that drivers/tweeters etc are sometimes produced with their magnets reversed ! It's happened to me & others i know & have heard of. Which means they are the opposite polarity expected. = unless you test them first, the total acoustic output will be incorrect.
Good advice
Good to know for people.
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So far, we already have several Confirmed reports of reversed polerity.
I take your point. I thought too late after my post that I should have put 180 degrees out of phase, which was the point I meant to make.
Anyway, I believe you are right about the wave front of an explosion portrayal, however I still don't see how the polarity of a measurement mic fits in here?
From the CLIO v4 printed manual, page 26:
"...the output of the power amplifier is connected to the loudspeaker with an inversion in cables polarity, this compensates the fact that Audiomatica microphones are phase inverting..."
Knowing the polarity of measurement mic might be important under some circumstances, I'd be interested to know what they are. Is it that it's important when doing certain tests using certain software?
I have the MiniDSP UMIK-1 and I think it has inverted polarity. At least that's what I see on my step response measurements. The official documentation doesn't say anything about that though.
A quick search shows that other people have the same issue - UCI Sound Design: The MiniDSP UMIK-1 USB Measurement Mic
A quick search shows that other people have the same issue - UCI Sound Design: The MiniDSP UMIK-1 USB Measurement Mic
Scott,
Without confirming the polarity of the test system, the test system can't be used to determine polarity of the unit under test. It is a simple thing to use a battery and observe the direction of a cone driver, but in the case of a sealed high frequency driver, one can't observe the movement. Each amplifier stage introduces a potential polarity swap, and every pole of a crossover induces a 90 degree phase shift.
In the case of a "Tapped Horn", polarity is a bit counter intuitive- in a "normal" driver positive voltage to the positive terminal will push the cone away from the magnet structure, "forward". In the TH the driver is generally mounted with the magnet outward "forward" , my initial thought was to reverse polarity on the driver, wrong choice- most of the output exits through the "Horn".
In my initial TH testing, the polarity vs phase issue was further compounded by a plate amplifier which had a swapped polarity between the exterior panel Speakon connector and the rear snap connector to pigtail, an ambiguously labeled polarity switch, and a test microphone that was wired counter to the usual leading portion of the wave front at the front of the microphone resulting in a positive voltage on pin 2 and negative voltage on pin 3.
The serial combinations resulted in hours of fun determining the problems- I now have a pin 2/3 swap polarity reverse cord attached to the RTA 420 microphone, as the circuit board XLR connection would make an internal "correction" near impossible.
The suggestion of comparing the test mic to a dynamic mic is made a bit more difficult in that although the usual leading portion of the wave front at the front of the microphone should result in a positive voltage on pin 2 and negative voltage on pin 3, there are many exceptions, and a dynamic mic output lags in phase response compared to a condenser or back electret mic.
Cheers,
Art
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