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Blumlein overheads and polarity/phase problems
Old 2 weeks ago
  #1
Gear Nut
 

Blumlein overheads and polarity/phase problems

Today I was experimenting with using a Cascade X-15 (with Lundahl transformers) as a stereo drum overhead mic, specifically as the stereo ribbon pattern should result in good imaging and phase correlation. But, either my expectations/understanding with a Blumlein array are completely off or one of the mic channels is out of phase with the other one!?

Taking a look at the waveforms, I can see that polarity between the two channels seems to be opposite (more importantly, I can hear it).




Additionally, it just seems to sound better when I flip the polarity on one of the channels, but this is surprising to me as I expected better phase coherence right out of the gate.

I did try rotating the microphone in 45 degree increments to see if that improved matters - some positions sounded better than others but still showed opposite polarity between the channels. Currently the mic is right above the kick pedal about 48" above the top of the kick drum, or six feet off the ground or so. I have tried moving it closer and further from the kit and also tried rotating it along its other axis, to no avail.

Attaching some files so you can see what I mean - one stereo file, hard panned, straight in, and another with the polarity flipped on the Left channel in my DAW - each new pattern after spinning the mic another 45 degrees. I have tried different stereo cables and preamps as well. What am I missing? Since it seems to sound better with one channel flipped, am I potentially causing unforeseen problems by doing that?
Attached Files

Blumlein OH LR.mp3 (2.35 MB, 287 views)

Blumlein OH LR Polarity Flipped L.mp3 (2.35 MB, 290 views)


Last edited by Dokterrock; 2 weeks ago at 06:19 AM.. Reason: additional question
Old 2 weeks ago
  #2
have you 100% checked the polarity of your cables? You're right in that it *should* be in phase; but I wouldn't be surprised if something else in the chain is causing the issue.

Or maybe one capsule is wired out of phase on your mic. But cables are more likely. You say you've tried different stereo cables, but have you used a cable or continuity tester and checked there's not a pin 2/3 mixup somewhere along the line? or possibly going from preamp to interface (if that's the setup).
Old 2 weeks ago
  #3
Gear Nut
 

Quote:
Originally Posted by psycho_monkey View Post
have you 100% checked the polarity of your cables? You're right in that it *should* be in phase; but I wouldn't be surprised if something else in the chain is causing the issue.

Or maybe one capsule is wired out of phase on your mic. But cables are more likely. You say you've tried different stereo cables, but have you used a cable or continuity tester and checked there's not a pin 2/3 mixup somewhere along the line? or possibly going from preamp to interface (if that's the setup).
I don't have a cable tester but have tried the following:

Different stereo cables (I only have two to test)
Different XLR cables coming out of the stereo cables (both stereo cables are 10')
Plugged into preamp
Plugged into interface

I can definitely try more XLR cables or even buy yet another stereo cable. What's really strange is that I've been using this mic as a drum room mic about 6' from the kit and THOSE tracks are not all out of whack, which is why I'm trying to make sure I'm getting the expected results.
Old 2 weeks ago
  #4
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Poopypants's Avatar
 

A question, more for my own sake than anyone else's:

Isn't the top example a timing issue and not a phase issue, whereas the bottom example is a phase (or polarity) issue?
Old 2 weeks ago
  #5
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Quote:
Originally Posted by Poopypants View Post
A question, more for my own sake than anyone else's:

Isn't the top example a timing issue and not a phase issue, whereas the bottom example is a phase (or polarity) issue?
Looks like the top example has a polarity issue, to me it looks like something happened on one side (not sure which is left vs. right) that doesn’t get picked up as well on the opposite side. The initial waveform does go negative but, it’s smaller in amplitude.

To the OP:
I definitely recommend getting a polarity checker. If you’re serious about recording it’s a great $100 to invest. I’ve come across tons of unexpected polarity issues. Finding mics wired in reverse, cables, guitar cabs, outboard and in one case a studios monitors. A great way to make sure everything is coming in correctly and an easy way to troubleshoot.
Old 2 weeks ago
  #6
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Yes the first first segment of the first file, one side is polarity inverted. (The remainder of these 'rotated segments just confuses the situation.
'Flipping polarity on one side of my playback rig the two files swap which is 'centered and coherent stereo vs vague out of polarity stereo.
Old 2 weeks ago
  #7
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Quote:
Originally Posted by Poopypants View Post
A question, more for my own sake than anyone else's:

Isn't the top example a timing issue and not a phase issue, whereas the bottom example is a phase (or polarity) issue?
I 'looked first as well, then all was clear when I read closer and he was also apparently 'rotating the mic. Playing the (later) examples one could think 'center shift via arrival time. But the very first segments -in the two, cleared that up.
Old 2 weeks ago
  #8
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Quote:
Originally Posted by Dokterrock View Post
..I can definitely try more XLR cables or even buy yet another stereo cable. What's really strange is that I've been using this mic as a drum room mic about 6' from the kit and THOSE tracks are not all out of whack, which is why I'm trying to make sure I'm getting the expected results.
Is that to say it was when extending their five pin XLR x dual XLR Y with a longer pair the issue began? If so there you go. :>)
Old 2 weeks ago
  #9
Gear Nut
 

Quote:
Originally Posted by Wayne View Post
Is that to say it was when extending their five pin XLR x dual XLR Y with a longer pair the issue began? If so there you go. :>)
Nah, I've tried a totally different five pin cable.
Old 2 weeks ago
  #10
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Quote:
Originally Posted by Dokterrock View Post
Nah, I've tried a totally different five pin cable.
..but with out the extensions? (just to be clear, but I guess you must have gone back/tried the earlier config..?
Old 2 weeks ago
  #11
Gear Nut
 

Quote:
Originally Posted by Wayne View Post
..but with out the extensions? (just to be clear, but I guess you must have gone back/tried the earlier config..?
Yes, and well, yes. The only difference with the earlier config is the distance between the microphone and the drum kit. Which is why this whole thing is so strange and why I initially thought it was a positioning issue and wanted to make sure I wasn't expecting the wrong results. Seems very unlikely (impossible, even) that one of the capsules would reverse its polarity.
Old 2 weeks ago
  #12
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Got ya. All I can think of is wondering how the more distant image actually fared. (as in more diffuse' and just wasn't as obvious?
Old 2 weeks ago
  #13
Gear Nut
 

Quote:
Originally Posted by phanlon View Post
To the OP:
I definitely recommend getting a polarity checker. If you’re serious about recording it’s a great $100 to invest. I’ve come across tons of unexpected polarity issues. Finding mics wired in reverse, cables, guitar cabs, outboard and in one case a studios monitors. A great way to make sure everything is coming in correctly and an easy way to troubleshoot.
Thanks! So I was trying to find the right thing for this yesterday and couldn't seem to find one that does 5-pin. Also I'm definitely missing something about how it works with a microphone - how do you close the loop?
Old 2 weeks ago
  #14
Gear Nut
 

Quote:
Originally Posted by Wayne View Post
Got ya. All I can think of is wondering how the more distant image actually fared. (as in more diffuse' and just wasn't as obvious?
I thought so too, but I did the same test where I flipped the polarity of one channel and it was DEFINITELY out of phase, so... process of elimination leads me back to cables (even though I'm using the same ones!) or the mic itself. It's weird!
Old 1 week ago
  #15
Quote:
Originally Posted by Dokterrock View Post
Thanks! So I was trying to find the right thing for this yesterday and couldn't seem to find one that does 5-pin. Also I'm definitely missing something about how it works with a microphone - how do you close the loop?
You can use a multimeter for non standard connections, you just have to check one pin at a time.

A cable tester doesn’t need to see a mic - you just plug both ends of the cable into the tester.

As for empirical tests, set it up, and clap or snap your fingers at the centre point of the array. That should tell you polarity. If that’s not in phase, neither is your mic!
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