Two lavs, one with the phase flipped?

[podgorny]

Most of MJ's vocals were NOT done with an SM7. One was used on Thriller. Bruce Swedien has talked about this on multiple occasions. I cannot speak for his reasoning behind choosing one over say, a C12, but I suspect it had something to do with performance, attitude, and handling noise because these are the reasons why I have chosen an SM7 over other microphones myself.

 

Same goes for Bono's famous use of a Beta 58.  In all cases (just as it should be), performance and attitude trump sonics.

[jrd456]

I worked at Wally Heider recording,which was one of the top studios of that time [late 60's,early 70's] and the mic. we had the most of was the SM57,after that it was the U87.------you can almost anything with these two mics.

JD

[podgorny]

Dynamic mics (not the ribbon kind) are popular for live applications partly because they are a lot less susceptible to feedback

None of this has got anything to do with polar pattern.

This is my attempt at an explanation.

 

 

This is purely a function of polar pattern. What you are describing is greatly-varying sensitivity across a range of SPLs, and I've never experienced that with any microphone. Assuming gain, frequency response and polar patterns are equal, you will not see condensers exhibit more susceptibility to feedback than another transducer type.

[studiomprd]

Constantin has it mostly spot on, but

" For a moving-coil dynamic mic to sound good you need to get it pretty close to the source. So close that the preamp doesn't need to amp so much and the noise will appear quieter. But if you were to use a condenser at the same distance, I'd bet it's the same scenario. "

actually, in most designs, there is a fixed backplate and a movable front plate, fixed a specific distance apart and an electrical charge is applied. As sound hits the movable plate, it flexes or vibrates. This creates a tiny change in the capacitance, which can be turned into an electrical signal. However, this actual output of the condenser element is

extremely small and needs some amplification before it is suitable for connection to audio equipment. Consequently, condenser microphones require a fair amount of electronic circuitry to produce usable audio. Thus Condenser mic's typically have higher output because there is a pre-preamp built into the mic.

" Dynamic mics ...are popular for live applications partly because they are a lot less susceptible to feedback  None of this has got anything to do with polar pattern. "

feedback suppression has everything to do with polar (pick-up) pattern

Edited June 26, 2013 by studiomprd

[podgorny]

Yes, you have shifted the phase of all the frequencies present by 180 degrees. Also you have inverted the signal. And yes, you have "switched the polarity". All mean the same.

Best,

Larry F

Lectro

 

 

 

Except, you are not shifting the phase, but inverting it, turning it upside down. That doesn't delay it.

 

 

I purposely echoed Soundwill's choice of words. "Shifting" phase IS a function of delay. From a technical perspective, this is DIFFERENT from inverting polarity.

 

"Flipping phase" may have come to mean the same thing as "inverting polarity", so this is purely a semantic discussion. But seeing as this is a technical field, it doesn't hurt to be specific.

[podgorny]

I worked at Wally Heider recording,which was one of the top studios of that time [late 60's,early 70's] and the mic. we had the most of was the SM57,after that it was the U87.------you can almost anything with these two mics.

JD

 

 

Nothing has changed (except that engineers are afraid to put vintage U87s on toms now).

 

[podgorny]

In response to the OP...

 

 

You could tape two cardioid microphones together, facing opposite directions from each-other (so that one is facing the talent and the other has the talent in the null), and invert the polarity of either. With their gains matched, this will effectively create a figure-of-eight microphone, which potentially could minimize some amount of ambient noise, but depending on what the second capsule is pointed at, may also introduce other problems.

 

If you can record these on discrete tracks, you could choose the pattern (omni, cardioid, hypercardioid or figure of eight) in post to suit each situation.

 

If schedule or track count limitations are forcing you to commit to a particular pattern, it's probably better to use a hypercardioid mic placed as close to the talent as permitted and just go with it.

 

Can you bring gobos?

[Scott Smith]

About the only implementation of the reverse-phase mic technique I've ever seen work with any degree of success was the dual-mic technique used in the '70's for vocals on the elaborate Grateful Dead sound system. I don't recall right off hand who came up with the idea (I think it was either Bear or Ron Wickersham from Alembic Audio, but I could be wrong).

 

It worked reasonably well if the vocalist was careful to sing into one mic only at close proximity. Typically, the concert would start out fairly well in this respect, but as the evening went on and a few controlled substances were involved...well, you get the idea....

 

On the other hand, I have had quite a bit of success using mics such as the U-87 in figure-8 pattern, which will cause cancellation at low frequencies, while not affecting the dialog range too much. Try it, you'll like it! Boom op's hate 'em though...

 

-S

 

 

 

Jerry Garcia-Grateful Dead

[podgorny]

From Wikipedia:

The Wall of Sound was designed to act as its own monitor system, and it was therefore assembled behind the band so the members could hear exactly what their audience was hearing. Because of this, a special microphone system had to be designed to prevent feedback. The Dead used matched pairs of condenser microphones spaced 60 mm apart and run out-of-phase. The vocalist sang into the top microphone, and the lower mic picked up whatever other sound was present in the stage environment. The signals were summed, the sound that was common to both mics (the sound from the Wall) was cancelled, and only the vocals were amplified.

 

 

 

 

It makes sense, but I think there is a reason why this experiment never really took off.
(By most accounts, the phase-cancelling microphone array simply sounded bad.)

[old school]

One of the main reasons was the system was a beast and took to long to set up and then tear down and move. I've read other reasons as well. 

CrewC

[Soundwil]

 

 

 

 

 

 

I purposely echoed Soundwill's choice of words. "Shifting" phase IS a function of delay. From a technical perspective, this is DIFFERENT from inverting polarity.

 

"Flipping phase" may have come to mean the same thing as "inverting polarity", so this is purely a semantic discussion. But seeing as this is a technical field, it doesn't hurt to be specific.

 

Yep. The use of "shifting" was misleading. 

[Constantin]

Constantin has it mostly spot on, but

" For a moving-coil dynamic mic to sound good you need to get it pretty close to the source. So close that the preamp doesn't need to amp so much and the noise will appear quieter. But if you were to use a condenser at the same distance, I'd bet it's the same scenario. "

actually, in most designs, there is a fixed backplate and a movable front plate, fixed a specific distance apart and an electrical charge is applied. As sound hits the movable plate, it flexes or vibrates. This creates a tiny change in the capacitance, which can be turned into an electrical signal. However, this actual output of the condenser element is

extremely small and needs some amplification before it is suitable for connection to audio equipment. Consequently, condenser microphones require a fair amount of electronic circuitry to produce usable audio. Thus Condenser mic's typically have higher output because there is a pre-preamp built into the mic.

" Dynamic mics ...are popular for live applications partly because they are a lot less susceptible to feedback None of this has got anything to do with polar pattern. "

feedback suppression has everything to do with polar (pick-up) pattern

I didn't say that no amplification takes place. I meant the pre-amp in the (e.g.) recorder doesn't need to be turned up as much, because the source is so close to the mic.

My polar pattern comment slipped down. I had originally meant that as a comment about the dynamic mics. Sorry about that. Nonetheless, polar pattern is one aspect of feedback suppression it is not everything. If you have a cardioid condenser and a cardioid dynamic (non-ribbon) which one is more likely to produce a feedback?

[podgorny]

If you have a cardioid condenser and a cardioid dynamic (non-ribbon) which one is more likely to produce a feedback?

 

 

If the polar patterns and frequency responses are equal, and if gain is matched, neither is more likely to produce feedback.

 

You're acting as if there is some unquantifiable aspect of microphones which makes one behave differently from another. In fact, we can measure these aspects, and use the data to make informed decisions about which tools we will choose for a particular application.

[Constantin]

If the polar patterns and frequency responses are equal, and if gain is matched, neither is more likely to produce feedback.

You're acting as if there is some unquantifiable aspect of microphones which makes one behave differently from another. In fact, we can measure these aspects, and use the data to make informed decisions about which tools we will choose for a particular application.

I am not "acting" like that at all. I am not doing live sound...

But it is not an unquantifiable aspect of mics, in fact I wrote a lengthy post earlier outlining aspects of dynamic mics. Their most fundamental working principle is somewhat different than that of condensers. So they are behaving differently. It is audible, measurable and quantifiable. And, among various other aspects, it makes them less susceptible to feedback. You yourself named a reason for that

[studiomprd]

" If you have a cardioid condenser and a cardioid dynamic (non-ribbon) which one is more likely to produce a feedback? "

it depends

 

" among various other aspects, it makes them less susceptible to feedback. "

whichever "them" you mean, that is incorrect.

 

" About the only implementation of the reverse-phase mic technique I've ever seen work with any degree of success was the dual-mic technique used in the '70's for vocals on the elaborate Grateful Dead sound system. "

this is how "noise cancelling" microphones work (Coles Lip Mic)... this is also the basis for "noise cancelling headphones".

Edited June 27, 2013 by studiomprd

[Constantin]

" among various other aspects, it makes them less susceptible to feedback. "

whichever "them" you mean, that is incorrect.

Both. Or the other one

[Constantin]

" If you have a cardioid condenser and a cardioid dynamic (non-ribbon) which one is more likely to produce a feedback? "

it depends

On what?

[studiomprd]

" Both. Or the other one "

either Dynamic or Condenser

that characteristic of a mic does not make it any more, or less, susceptible to feed-back...

 

" On what?   "

on the specific situation, and on all of the usual factors involved in each individual mic's being likely to have feed-back

 

Dynamic mic's compared to Condenser mic's ?? Google is your friend

[Constantin]

Dynamic mic's compared to Condenser mic's ?? Google is your friend

That's true, how did you know? Not exactly one of my best friends, but a friend nevertheless.

I do know the differences between dynamic mics and condenser mics. I do not work much with dynamic mics nowadays, except maybe for explosions and such like, but usually in combination with a condenser. Also, like I said before, I don't do live (amplified) sound work. But: when I learned about these things at school, as well as when reading various books, the gist was always (really, invariably) that dynamic moving-coil mics are less prone to feedback. This was a few years ago. Now there seems to be a new paradigm and now the claim is that both types are equally prone to feedback, always with the added qualifier "with proper gain staging" or something similar. So without that...

[studiomprd]

" the claim is that both types are equally prone to feedback, "

or equally resistent to feedback...depending!

Edited June 28, 2013 by studiomprd

[Constantin]

" the claim is that both types are equally prone to feedback, "

or equally immune...depending!

Immune? Interesting. I'm surprised we even have a term for this feedback thing, when we've got all these feedback-immune mics.

[Bill Kole]

My suggestion of the dynamic lav is solely based on it being less sensitive than powered lavalieres.  In a loud environment, the talent would likely be raising their voice to be heard. A dynamic lav would be less likely to distort from voice or background.  It'll be next to impossible to entirely remove the entire background, but a dynamic lav in (relatively) close proximity might provide a better chance than a more sensitive mic to have seperation between the voice and the background without crushing the front end of a wireless (or two).  Results may vary, but I've had luck with recording "shout talking" in a busy music club environment with the Shure SM-11: http://www.shure.com/americas/products/microphones/sm/sm11-lavalier-microphone.  I suggested this as an alternative to phase cancellation as phase cancelling the background noise in a dynamically changing, uncontrolled environment would be difficult for even the most seasoned of veterans.  If its okay for the background to be there (laughter, general talking vs. music without clearances) the dynamic lav technique should keep the background from pumping in and out better than an auto mixer or fixed limiter might.  There is, of course, no correct answer for all situations.

[studiomprd]

" equally immune. "

edited to read equally resistent to

[podgorny]

One of the main reasons was the system was a beast and took to long to set up and then tear down and move. I've read other reasons as well. 

CrewC

 

Considering the elaborate stage and sound systems used by touring groups every day, I'd say this is a fallacy. The problem with the Wall of Sound is that it simply didn't work well (which is why Bob Heil took over with one of his systems).

 

 

 

 

phase cancelling the background noise in a dynamically changing, uncontrolled environment would be difficult for even the most seasoned of veterans

 

Since the array would not be changing, it's really a set-and-forget scenario. The problem is that using two mics pointed at the same thing with one's polarity inverted is a recipe for comb-filtered nastiness - which is to say, it doesn't work (and that include's the Grateful Dead's ill-fated attempt). The idea of using two cardioid capsules facing away from each-other to create new polar patterns is of course, a time-tested technique that is used every day (probably by people who don't even realize it).

[Jay Rose]

 

Due to low output and inherent self-noise, dynamics are generally less desirable for applications requiring lots of gain.

 

 

I made the mistake of not checking this thread for a few days, and there's been a lot of misinformation thrown about. Most was caught by our more knowledgable members, but this one...?

 

Dynamics don't have any self-noise, unless you're talking thermal noise through the resistance of the coil itself. And that's way below the noise floor of 24-bit recording. They're completely passive devices, converting mechanical energy into electrical. They don't - and can't - generate any energy of their own.

 

An unshielded transformer in a dynamic mic could pick up some induced noise, but that's environmental... not self-noise. And it goes away in other environments. 

 

The electrets used in every lav do have self-noise, from the necessary impedance-converting FET. Better lavs manage to push the noise down to where it's not a problem at normal dialog distances.

 

---

 

Now, dynamics do have lower output voltages than electrets, and the output loading is much more critical than an electret or any other condenser. Perhaps the poster was thinking of the self-noise you get from low gain preamps, or the comparative extra preamp noise when the dynamic's voltage is being sucked down by too little input impedance, or - with some mics - the HF lift from the internal transformer when they're seeing too high an impedance. But that's something else entirely.

 

With both dynamics and ribbons, choosing a proper preamp is critical.