Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
SimpleP48 -- Polarity
|
I have drawn this out showing the basics of the? mic preamp with the two 6.8K resistors. If you want to maintain the phase relationship of the incoming audio you actually want the "+" terminal of the capsule going?to Pin3 of the XLR. The circuit will work connecting pin 2 or 3.? Best Regards, Jules Ryckebusch 214 399 0931 |
|
Jules, I don't think this is the case for polarity.? This is what I say in the latest version of simpleP48.pdf
POLARITY SimpleP48basic
The usual electret with FET has the capsule capacitance between Source & Gate. When the air pressure rises, the capacitance increases, Vgs & FET current goes down, Vds increases¡. so the Drain goes up and the Source, down. We connect FET Drain (usually marked + on the capsule) to XLR p2. C1 connects the Source (usually the case on a 2-wire capsule) to XLR p3. p2 goes +ve wrt to p3 with a pressure increase ¡ which is the AES standard for balanced lines and microphones.
SimpleP48RCA
Here the capsule capacitance is between Gate & Drain. Increasing air pressure makes the capacitance increase, current increases and Vds goes down. The Drain goes down and Source, up. We connect Drain to XLR p3 and the Source, via C1 to XLR p2
My latest ravings put me in-line with Henry Spragens & Rick Wilkinson.? Any other gurus want to join in? |
¿ªÔÆÌåÓýHmmm. ¡°When the air pressure rises, the capacitance increases, Vgs & FET current goes down¡±?My understanding is that when air pressure rise capacitance goes up and that as the charge on the capacitor can not change instantaneously the voltage goes up. ? Thus voltage across the Drain and Source goes down as it conducts more. ?Love some insight on this here if I am looking at this incorrectly.?Best Regards, Jules Ryckebusch? On Dec 16, 2023, at 19:28, Richard Lee <ricardo@...> wrote:
|
¿ªÔÆÌåÓýThink it over.
Le 17/12/2023 ¨¤ 03:51, Jules Ryckebusch
a ¨¦crit?:
Hmmm. ¡°When the air pressure rises, the capacitance increases, Vgs & FET current goes down¡±?My understanding is that when air pressure rise capacitance goes up and that as the charge on the capacitor can not change instantaneously the voltage goes up. ? Thus voltage across the Drain and Source goes down as it conducts more. ?Love some insight on this here if I am looking at this incorrectly.? |
|
Wow, lightbulb moment?for me on this one. You are correct. Now my conundrum. I have? multiple mics out there wired with "+" to Pin 3. It works but the absolute phase is?obviously reversed. Hmmmm....?? Jules On Sat, Dec 16, 2023 at 10:07?PM Jerry Lee Marcel <jerryleemarcel@...> wrote:
--
Best Regards, Jules Ryckebusch 214 399 0931 |
|
Jules Ryckebusch:
> It works but the absolute phase is obviously reversed. Hmmmm.... ? https://musicproductionglossary.com/what-is-absolute-phase/ More correctly termed absolute polarity, What is Polarity?Polarity is a term used in the field of electronics to describe the relationship between two points that have opposing electric potentials, with one point having a positive electric potential and the other having a negative electric potential. It is important to clarify that polarity is not the same as phase, which refers to a relationship that is based on time.? Although engineers, consoles, and preamps may refer to the switch as a ¡°phase¡± switch, in reality, it is a switch that inverts the polarity of the signal. ------------- Best regards, Goran Finnberg The Mastering Room AB Goteborg Sweden E-mail: mastering@... Learn from the mistakes of others, you can never live long enough to make them all yourself.??? -?? John Luther (\__/) (='.'=) (")_(") Pyret, Ranglet, Aron, VovVov, Nero, Smurfen & Pussin:RIP |
|
I just do what I always do when finishing a mic. Hold it next to a ¡°store-bought¡± expensive mic, and check phase. Then I figure out why it works as it does if I was wrong, or congratulate myself if I got it right for once. Reminder to self: ¡°store-bought" mics from China are mostly wired backwards.
So, looking at our little electret, the backplate has the electret film with a bunch of extra captured electrons in it. Those electrons repel electrons on the diaphragm, so the diaphragm is positively charged with respect to the backplate. When the diaphragm approaches the backplate, more electrons exit to ground, and the ¡°voltage" across the capsule capacitor goes up. The diaphragm is grounded, so the backplate goes negative. Now looking at the JFET, more electrons on the gate which is wired to the capsule backplate narrows the conduction channel, causing source-to-drain current to decrease. Drain goes up, source goes down, etc. Or just look at keeping C x V constant, like Richard says. The confusing thing is polarity of the capsule. Voltage increases, but the + side of the capsule is grounded, and signal comes off the ¡ª side. Electrets are weird in other ways because the charge is trapped and can¡¯t flow from place to place like in most circuits. For instance, the capsule acts as if there is a voltage between diaphragm and backplate, but if you connect the two, no current flows. |
|
Henry Spragens:
Hold it next to a ¡°store-bought¡± expensive mic, and check phase."Check polarity" Is Polarity a Phase? It¡¯s important to keep the concepts of ¡°phase¡± and ¡°polarity¡± separate from one another. The terms ¡°phase¡± and ¡°polarity¡± describe changes to an audio system, with ¡°phase¡± referring to a shift in time relative to a reference point and ¡°polarity¡± indicating a switch in the positive and negative connections. --------- Best regards, Goran Finnberg The Mastering Room AB Goteborg Sweden E-mail: mastering@... Learn from the mistakes of others, you can never live long enough to make them all yourself.??? -?? John Luther (\__/) (='.'=) (")_(") Pyret, Ranglet, Aron, VovVov, Nero, Smurfen & Pussin:RIP |
|
So what happens if I have a mic with polarity reversed?
Usually, nothing. If the mic is not paired with another one, for instance a soloist or individual drum mic, acoustic phasing is more or less random and varies with frequency (wavelength) in a way too complicated to figure out. If you have a ¡°PHASE¡± switch on your mic preamp, try it both ways. Chances are neither setting is vastly better. If the mic is paired with another one, for instance ORTF or Decca tree style, chances are you built both the same way, and they match. Way back when I started out, stereo was brand new, and my second channel didn¡¯t match my original mono channel. Phase was one of the few things I could afford to check and match, so I did. I still do. |
|
Henry Spragens,
So what happens if I have a mic with polarity reversed?If I were to believe in the above gospel then there should not be any standard at all as regards polarity and stereo as we know it today would sound very weird indeed. Henry Spragens: So what happens if I have a mic with polarity reversed?Polarity, if hot is pin 2 or 3, you check by putting one reference mic from any reputable manufacturer, Neumann, AKG, Schoeps, R?de, etc as CLOSE AS POSSIBLE TOGETHER such as to remove the ACOUSTIC TIME DELAYS between capsules then and only then you use the mono button while listening over headphones and/or looking at a VU meter. The right polarity comes when the audio is as full sounding, in polarity, compared to the thin sounding version, out of polarity sounding when pushing the mono button over HEADPHONES. As soon as you moves mic apart THEN and ONLY THEN, do I agree with your version above Henry Spragens but as this is WAVELENGHT dependent then even the 16 feet pipe on the church organ can be heard to diminish as the mics in a two mic recording is monitored in mono as mics are moved apart. YOU decide if that matters to you. POLARITY do matter as soon as you use any INTENSITY recording techniques also called XY, that excludes timing differences among microphone PAIRS. Timing differences occur due to path length differences that is minimized in XY or Stereo microphone techniques. WHERE POLARITY REALLY MATTERS: Using any of the INTENSITY Stereo recording methods that DO excists: Schoeps CMC301/501, Neumann SM69 etc etc etc. No wonder that in the age of CD that the old button on Neumann cutters could be switched to mono everything below 70 Hz, 150 Hz & 300 Hz by rolling off the difference channel using an inductor between the stereo feed and series resistors in each leg. The above to avoid having the cutting head sapphire not lift out of the lacquer. so as the final LP disc unplayable. ------------- Best regards, Goran Finnberg The Mastering Room AB Goteborg Sweden E-mail: mastering@... Learn from the mistakes of others, you can never live long enough to make them all yourself.??? -?? John Luther (\__/) (='.'=) (")_(") Pyret, Ranglet, Aron, VovVov, Nero, Smurfen & Pussin:RIP |
|
I just recorded a stereo file of my voice into the following two mics held close together - L is a TOA K4 cardioid true condenser stick mic, absolute stock, and R is a TSB140 electret cardioid mic wired exactly as per Jules' diagram in this thread. Playing back in Audacity (stereo split into two mono tracks, trim to balance relative levels, then both panned to center) - I hear a reasonably bassy mono sound; if I invert one track, i get a thinner sound. Zooming in on a long vowel sound, the two tracks look to be in phase (and obviously out if I invert one side). So I conclude that Jules' polarity assignment (capsule hot to pin 3) matches the polarity of the TOA mic.
[edit - yes the TOA mic is XLR pin 2 hot - goes positive for positive air pressure] This was just a quickie test, but pretty obvious. |
Henry Spragens,Google this:So what happens if I have a mic with polarity reversed? "what is the 3 to 1 rule when dealing with microphones" The book by one of the founders of Electro-Voice, Inc "Lou Burroughs" Microphones: Design and Application Sagamore Publishing Company ISBN0-914130-00-5 Chapters 9+10 are very illuminated Note "Lou Burroughs" always use "Out of Phase" which is more properly called "Out of Polarity which is today the proper use when pin 2 & 3 is swapped or the so called Phase switch is in use which is a Polarity switch as anyone can see by looking at the mixer schematic and what happens is that a simple inverting opamp is switched in circuit and how that can produce any phase change is completely beyond me. An inverting -amp = polarity switch is -180¡ã for ALL FREQUENCIES, while phase differences is ALWAYS RELATIVE to something, input, that is held constant then compared to the, output. And thus when putting up mics it is the distance in meter or feet that sets the relationship between one mic to another mic that gives rise to acoustic phase cancellation and the 3:1 rule avoids this as shown by Mr Burroughs. That book is very good and was published in 1975 when polarity versus out of phase was known but much better to make absolutely sure that the correct expression is used to avoid so many false misconception that seems to never ever die completely. ------------ Best regards, Goran Finnberg. The Mastering Room AB Goteborg Sweden E-mail: mastering@... Learn from the mistakes of others, you can never live long enough to make them all yourself.??? -?? John Luther (\__/) (='.'=) (")_(") Pyret, Ranglet, Aron, VovVov, Nero, Smurfen & Pussin:RIP |
¿ªÔÆÌåÓýI'm a little confused, myself... all the SP48 mics I've ever made have capsule + to XLR pin 3. A few years ago I went through all of my microphones (commercial and DIY), and all of my devices and preamps and 1/8" jacks and cameras and such, to confirm polarity on everything... I do a lot of stereo recording, mid/side, etc, so I needed to be sure, in order to avoid confusion and delays when mixing. The only things that tested "wrong" were some PiP inputs (e.g.
Zoom H4N PiP inputs are "inverted" polarity), an EV666 dynamic, my
dbx RTA-M measurement mic, the 12AX7 stages on a tube amp project,
and a few other minor things. All the SP48 mics tested as normal
(i.e. matched all the commercial mics), which if I'm understanding
this thread correctly should not be the case... ? I just tested a SP48 mic again (against an AKG C-535-EB) and it seemed to be of correct polarity. Looking back through all my old project schematics, it's always pin 3 to +... (with one exception, which is the RCA mod SP48, but my understanding is that that circuit is supposed to be reversed from normal.) When testing polarity, I hold two mics right next to each other,
make a deep "p" pop sound, and in the DAW confirm that the
wavefront excursion for both mics is in the same direction. Jules -- have you confirmed anything recently one way or the
other? -Casey On 12/17/23 05:52, Jules Ryckebusch
wrote:
|
|
I just checked my Pin 3 SimpleP48 against my U87 and more scientifically, looked at the waveform from an impulse. Both show that Pin 3 for the "+"of the capsule provides the signal swinging positive upon sound wave moving the diaphragm?in.? My thoughts here are that the polarity?of the electret film is such that its increase in voltage as the capacitance?goose?down results is opposite that of the bias voltage on the gate of the FET. I believe?Henry mentioned this.? Jules On Sun, Dec 17, 2023 at 4:23?PM Casey via <mbuilders=[email protected]> wrote:
--
Best Regards, Jules Ryckebusch 214 399 0931 |
|
Jules Ryckebusch:
>I just checked my Pin 3 SimpleP48 against my U87 and more scientifically, >swinging positive upon sound wave moving the diaphragm in. What is + on a prepolarized condenser capsule ? Is it where the resistor going to the positive supply + should be connected ? Or is it the positive pressure applied to the diaphragm ? coming out on capsule + ? Jules Ryckebusch sent a schematic that proves that + goes to pin 3 but that is inverse? polarity according to said .png schematic due to the actual 1 cycle sinus input to the diaphragm which IS a positive pressure increase before the diaphragm and that is in? polarity with what comes out on pin 2 exactly as the standard predicts. Positive pressure on diaphragm should give positive rise on pin 2 XLR. Schematic is correct. So I would hazard to claim that the + sign should indicate to be connected via a resistor? to a positive + voltage and has nothing to do with polarity. ? --------------- Best regards, Goran Finnberg The Mastering Room AB Goteborg Sweden E-mail: mastering@... Learn from the mistakes of others, you can never live long enough to make them all yourself.??? -?? John Luther (\__/) (='.'=) (")_(") Pyret, Ranglet, Aron, VovVov, Nero, Smurfen & Pussin:RIP |
|
On Sun, Dec 17, 2023 at 03:12 PM, Goran Finnberg wrote:
On a two-terminal electret capsule, + means hot (ie: not ground), and is usually the drain of the included FET. And as you say, it's connected to a resistor from the positive bias voltage. From my test, and Jules' test with an impulse, I'm satisfied that Jules' diagram at the top of this thread results in a mic that follows AES convention (positive air pressure -> positive voltage on XLR pin 2) |
|
I would think the upper and lower heads of a snare drum would be? pretty good test but with the opposite expectation. The summed sound would be thicker if the two mics have opposite polarity.
toggle quoted message
Show quoted text
Regards, John Thaden
|
|
Goran: Appologies for using phase and polarity interchangeably. That is the way engineers I know carelessly use the terms.
"So I would hazard to claim that the + sign should indicate to be connected via a resistor to a positive + voltage and has nothing to do with polarity.¡± I agree. Nonetheless, the + teminal of the capsule goes positive, and connects to pin 2 of the XLR for the basic Simple P48 mic. The resistor to pin 1 and the capacitor to pin 3 connect to the ¡ª terminal of the capsule. ¡°Linkwitz¡¯d¡± capsules and other circuits may differ. I didn¡¯t emphasize enough that if you are using stereo pair mic techniques, then polarity match matters. Very much so. That would be X-Y, ORTF, crossed Fig-8s, Decca Tree, drum overheads, etc. However, if the polarity of BOTH mics is ¡°wrong¡±, they will work OK. As long as your pairs of mics match, absolute polarity doesn¡¯t matter. The positive signal on pin 2 with rising air pressure standard ensures that mics from Neumann, AKG, Shure, and others work together. For a single mic located away from the main pair, or isolated in a studio setting, switching polarity can be heard, but usually neither way sounds especially better. Bleed from other mics makes for complex comb filter effects, and switching polarity makes dips into peaks and vice-versa, rather like moving the mic around a few inches. |
|
On Mon, Dec 18, 2023 at 07:11 AM, Henry Spragens wrote:
For a single mic located away from the main pair, or isolated in a studio setting, switching polarity can be heard, but usually neither way sounds especially better.There have been a number of studies regarding teh audibility of phase and polarity. Regarding phase audibility, it's been shown that phase distorion could be heard when it changed significantly the crest factor of a complex signal. Regarding polarity, I witnessed myself a case where two sound engineers diagnosed polarity reversal in loudspeakers, listening to a kick drum. They said "it sucks air, instead of pushing air". Thet were right, when correct polarity was restablished, the sound was better. I never had the possibility to investigate the issue. |
John Thaden
to navigate to use esc to dismiss