Green Bullet Harmonica Mic Help

[NYMorningstar]

...The reason it works is because of *where* the turn ups and turn downs are happening. Think about it for a minute (but not too hard ); the volume at the speakers remains the same, but the volume at the mic is lower. That means that the overall volume thru the loop is lower.

It's no different in effect than swapping that mic for the cardioid; both will have the effect of reducing the bleed volume coming out of the mic. The only difference is the reason in one case is because you're changing polar patterns in order to decrease the bleed volume, and in the other you're turning a knob to reduce the bleed volume.
G.

Thanks for sticking with me on this Glen. I gave it a minute but it still not working.

I get what your saying about reducing the volume at the mic but your are also increasing it in the mix so i see that in simple terms of -1 +1 = 0 change to the loop.

I also see swapping the polar patterns as different because tranducer mics are directional and less sensitive at different angles thus the sound usually off to the sides from the speaker is not going back into the mic at the same volume.

 

[SouthSIDE Glen]

I get what your saying about reducing the volume at the mic but your are also increasing it in the mix so i see that in simple terms of -1 +1 = 0 change to the loop.

Think of it this way instead; the volume at the speakers is not changing, that's where your zero sum is happening, yes. But you still have the -1 at the microphone. So its more like 0 + -1 = -1 as the pseudo math for the *loop*.

I also see swapping the polar patterns as different because tranducer mics are directional and less sensitive at different angles thus the sound usually off to the sides from the speaker is not going back into the mic at the same volume.

Technically the mechanisms are different, but the effect of the volume of it coming out of the mic being less is the similar. That's the key. Whether it's because the mic is not picking it up because of the way the mic is facing, or whether it's because the mic is attenuating it's output is not a difference that the feedback monster can appreciate.

G.

 

[Yammie072]

NYM, maybe this will help. Not a perfect analogy, but a useful one:

Think of like a poorly shielded tele and a super-modern gain machine. The higher the gain is set on the amplifier, the easier it is to feed it back. This does not mean, however, that you cannot achieve the same volume from the amplifier with a lower gain setting. By, i'm assuming everybody's, personal experience, we know that running an amp clean at high volumes is much less likely to lead to microphonic pickup feedback.

This isn't exactly the same thing thats happening, but its close enough for a basic understanding.

 

[NYMorningstar]

Thx for chiming in Yammie. I've not had problems with guitars and feedback but what you're saying does seem to make sense regarding distortion. I've had guitar that have resonance problems and had to attenuate certain frequencies.

I guess I'm just being dense and I'll have to try this out in the real world to show myself.

 

[NYMorningstar]

Think of it this way instead; the volume at the speakers is not changing, that's where your zero sum is happening, yes. But you still have the -1 at the microphone. So its more like 0 + -1 = -1 as the pseudo math for the *loop*...G.

Your equation drops the +1 you are adding back.

I've been researching this and found the following from Shure but basically I find exactly the same from every resource I've found so far:
To eliminate feedback, you need to interrupt the feedback loop.

Here are some suggestions:
• Change the position of the microphone and/or speaker so that the speaker output isn't feeding directly into the mic. Keep speakers further forward (i.e. closer to the audience) than microphones.
• Use a directional microphone.
• Speak or sing close to the microphone.
• Turn microphones off when not in use.
• Equalize the signal, lowering the frequencies causing the feedback.
• Lower the speaker output, so the mic doesn't pick it up.
• Avoid aiming speakers directly at reflective surfaces such as walls.
• Use personal monitors instead of speaker monitors.

Not a one of them have said to turn down the mic and add back the same amount further down the line in the mix as a way of eliminating feedback. Your technique so far is unique as far as I can determine and you may be onto something if it actually works. I can't test it until the end of this week but if it pans out it will be nice to have another tool to use in a pinch.

 

[SouthSIDE Glen]

Your equation drops the +1 you are adding back.

No, no, no. The zero sum you perceive is at the speakers. The volume of the speakers is the same. That's where the zero sum is. Not in the loop but just at the speakers. But the volume of the bleed going through the microphone is lower, which cuts down on the chance for feedback. That's the -1. So it's 0 + -1 = -1. There is no +1. Yeah the gain is boosted at the mixer, but the *result*, the *effect* of that is not a +1, it's a 0, because all it's doing is putting the volume at the speakers back to where it was.

Not a one of them have said to turn down the mic and add back the same amount further down the line in the mix as a way of eliminating feedback. Your technique so far is unique as far as I can determine and you may be onto something if it actually works. I can't test it until the end of this week but if it pans out it will be nice to have another tool to use in a pinch.

OMG, I am not "on to" anything. You act like I discovered some new revolutionary approach. Not even close; this is basic, basic stuff. People do it every day, all the time. If you decrease the volume of the bleed that the microphone delivers, you decrease the chances for feedback. That's all it is.

Just because you haven't found it on the Internet means nothing. Have you ever heard, "absence of evidence is not evidence of absence"?

Oh, and BTW, you have found it on the internet. Right here. From both me and Acidrock.

G.

 

[NYMorningstar]

No, no, no. The zero sum you perceive is at the speakers. The volume of the speakers is the same. That's where the zero sum is. Not in the loop but just at the speakers. But the volume of the bleed going through the microphone is lower, which cuts down on the chance for feedback. That's the -1. So it's 0 + -1 = -1. There is no +1. Yeah the gain is boosted at the mixer, but the *result*, the *effect* of that is not a +1, it's a 0, because all it's doing is putting the volume at the speakers back to where it was.OMG, I am not "on to" anything. You act like I discovered some new revolutionary approach. Not even close; this is basic, basic stuff. People do it every day, all the time. If you decrease the volume of the bleed that the microphone delivers, you decrease the chances for feedback. That's all it is.

Just because you haven't found it on the Internet means nothing. Have you ever heard, "absence of evidence is not evidence of absence"?

Oh, and BTW, you have found it on the internet. Right here. From both me and Acidrock.

G.

The zero sum I'm perceiving is the max volume level before feedback occurs in the loop. Once you cross that you will have positive feedback. I see where turning down the mic reduces the chance of feedback if that's all you do. It's adding the voltage/db's (however you want to measure it) back into the system (the loop) that befuddling me.

It's not that I'm not finding information on this both on the net or in my books, I'm not finding anything that supports what you are saying. Can you give me source that backs it?

 

[brother rat]

Can you give me source that backs it?

I'll be a source that backs it. Albeit a newbish source.

I'm no expert, but I have dealt with similar situations in live performances (as have many, many other performers).
Here's a way to think about it.
Think about using a guitar amp where you can control the gain of the pre-amp and the power amp. You would be more likely to get feedback if you had the pre cranked and the power amp gain turned down. Now, if you turn down the pre and boost the gain in the power section, you can achieve the same speaker volume with less chance of feedback. In the first situation, we were trying to use the pre-amp to do the heavy lifting, which it is not designed to do. That's what the power amp is for.
Applying this to the bullet mic situation, the mic gain is not designed to do any heavy lifting, the PA amp is. By feeding the PA amp a "less hot" signal (i.e. turning down the mic gain), we let the PA amp do what it is designed to do.
The idea is to keep each piece of equipment operating where it is comfortable and not in its maximum range.

 

[SouthSIDE Glen]

I see where turning down the mic reduces the chance of feedback if that's all you do. It's adding the voltage/db's (however you want to measure it) back into the system (the loop) that befuddling me.

OK, try this; the key part of the loop is the acoustic link between the loudspeakers (the source of the bleed) and the microphone (the pickup of the bleed.) That is where the feedback loop actually exists; the feedback does not originate in the board or in the wires or anywhere else in the signal path; the real source is the dynamic between the speakers and the microphone.

So what we have in that dynamic is that on one side the volume out of the source does not change; the gain boost on the board is not boosting the overall volume coming out of the speaker, it remains the same. On the other side of the acoustic dynamic, the volume out of the pickup goes down, because the gain built into the mic goes down. The combiination of the same volume out of the speakers and the effective decreased sensitivity of the mic is a net decrease in the potential for feedback.

What's happening on the board beyond that is irrelevant to that key dynamic - other than the fact that is the gain settings on the board that ensure that the volume at the speakers remains constant.

It's no different than if we reversed the situation; if the gain/sensitivity on the mic did not change, but the volume out of the speakers were lowered, the chances for feedback would reduce equally. Feedback is not an intelligent being; it doesn't know the difference between a lower volume at the speaker and a lower volume at the mic, it only "knows" whether *the combination of the two* is enough to cause it.

Once again, it doesn't know whether the decreased volume out of the mic is because of a change in the mic's intrinsic gain on an omni with a gain control, or whether it's because of a cardioid being turned away from the speaker, or whether its because the volume out of the speakerhas been turned down. The end result in all three situations is the same; it's a decrease in the volume of the bleed going through the microphone, regardless of the cause of that decrease.

It's not that I'm not finding information on this both on the net or in my books, I'm not finding anything that supports what you are saying. Can you give me source that backs it?

My source that backs it is my 11+ years owning and using the exact microphone in question and using it on stage as well as in the studio, combined with my 31 years or so of education and experience in this field with microphones and recording in general.

I didn't have to read it in any source; it's basic common sense stuff. The only reason you're having a problem with it is because you don't like me as a source. Apparently if you read it from someone else, you'll believe it, but if you read it from me, you wont believe it.

G.

 

[NYMorningstar]

I didn't have to read it in any source; it's basic common sense stuff. The only reason you're having a problem with it is because you don't like me as a source. Apparently if you read it from someone else, you'll believe it, but if you read it from me, you wont believe it.

G.

I assure you it's got nothing to do with you but I have to admit sometimes you make it hard not to make it that way.

The list of handling feedback that I posted is pretty common ways of handling feedback but the way you suggest is totally new to me. I'm just trying to understand it is all.

For me feedback is anything but common sense. It's about electrical engineering, room acoustics and resonance, electrical, positive and negative feedback loops. When you have parasitic oscillation in an amp there is alot of things to consider. Is trimming the gain of your mic and then adding back the gain causing some sort of EQ change? The initial voltage from your mic is from a magnetic coil right? Is it moving less and generating less voltage when you turn the mic's output down making it less sensitive as you say or is the SPL the same and the mechanical movement the same and all the sensitivity you raise electrical?

I totally get a guitar amp using channel gain for distortion but that's not what this is about. Doesn't the amp still distort when you turn down the guitar pickups? (Yes, you are still clipping the main). You might get less feedback when turning up the amps main to get back the volume after that because turning down the pickups will act as an EQ but it's minimal and I don't see that happening in the mic scenario.

 

[SouthSIDE Glen]

The list of handling feedback that I posted is pretty common ways of handling feedback but the way you suggest is totally new to me. I'm just trying to understand it is all.

No, its not new to you at all. You've already said - and even suggested - that he switch to a cardioid mic. OK, let's do that for a second and look at it. The reason that would work as a potential help is because you can change the mic's sensitivity in picking up the bleed from the speakers just by changing the direction that the mic is facing. The volume from the speakers isn't changing, it's just the amount of it bleeding back into the loop that's changing because of a decrease in efficiency of the mic due to a change in it's directionality.

OK so far, right? You seem to already understand that. Okay, now imagine you can effect a similar change in the amount of bleed coming from the speakers not from rotating a directional mic, but instead from turning down the sensitivity of an onmi mic. No polar pattern change, no frequency response change, nothing esoteric or even new. It's exactly the same reason as the situation with the cardioid; we're doing something to the mic to lessen the amount of bleed it's getting from the speaker and sending back through the loop to the speaker again.

There's no difference in effect there between the two situations as far as feedback is concerned. It's just the mechanism, turning a mic around to reduce it's sensitivity versus turning a mic down with a knob to reduce it's sensitivity, that's changed.

G.

 

[NYMorningstar]

No, its not new to you at all. You've already said - and even suggested - that he switch to a cardioid mic. OK, let's do that for a second and look at it. The reason that would work as a potential help is because you can change the mic's sensitivity in picking up the bleed from the speakers just by changing the direction that the mic is facing. The volume from the speakers isn't changing, it's just the amount of it bleeding back into the loop that's changing because of a decrease in efficiency of the mic due to a change in it's directionality.

OK so far, right? You seem to already understand that. Okay, now imagine you can effect a similar change in the amount of bleed coming from the speakers not from rotating a directional mic, but instead from turning down the sensitivity of an onmi mic. No polar pattern change, no frequency response change, nothing esoteric or even new. It's exactly the same reason as the situation with the cardioid; we're doing something to the mic to lessen the amount of bleed it's getting from the speaker and sending back through the loop to the speaker again.

There's no difference in effect there between the two situations as far as feedback is concerned. It's just the mechanism, turning a mic around to reduce it's sensitivity versus turning a mic down with a knob to reduce it's sensitivity, that's changed.

G.

I agree with that 100% but what happened to:

At the same time, the OP increases the gain on the mic channel on the PA mixer, so that the actual PA volume of the vocal channel is not decreased but stays the same.

That's the part I am having a struggle with.

 

[SouthSIDE Glen]

All that does is ensure that the volume coming out of the speakers remains the same as it was before the mic was turned down. It's not part of the feedback "solution", so to speak. The "solution" is in the mic sensitivity change. It's just making sure that the "solution" does not mess up the rest of it.

The increase in the gain at the board is only to make sure that the decrease in the mic gain does not decrease the enjoyment of the audience due to the vocals not coming out of the speakers as loud. It "makes up" for the loss in mic gain by returning the speaker volume to where it was before the gain change, not louder than it was before the gain change.

So, once again, the resulting situation is that the volume of the speakers remains the same as before. But the sensitivity of the mic is reduced, so the volume of the bleed from the speakers thru the mic is also reduced. The -1 +1 = 0 result is the result at the speaker volume.Yet there is still a reduction in thhe amount of bleed going thru the mic. So you have 0 change at the speakers, but still have the -1 in level of bleed going back into the loop at the mic.

Again, it's the same as a rotation of a cardioid. 0 change at the speaker, but -1 gain at the mic.

G.

 

[NYMorningstar]

Let me ask this another way. You have a situation where your bullet mic is feeding back and you turn the trim down -2db and the feedback stops. How much gain can you add back further down the line before it will cause feedback again?

 

[acidrock]

Why don't you just try it out?
I don't know how a computer works,but I know it works and that's good enough for me.

 

[SouthSIDE Glen]

Let me ask this another way. You have a situation where your bullet mic is feeding back and you turn the trim down -2db and the feedback stops. How much gain can you add back further down the line before it will cause feedback again?

You know how feedback is; you gotta go what you gotta do, and that often means a compromise of compound actions. Just like sometimes with a regular mic when sometimes you have to do a little treble cut *and* a little volume cut because if you cut the volume only, you have to cut it too low, or if you cut the treble only, you have to cut it so far that it sounds like crap, so you have to do a little of each. Other times you get lucky and only a little of one or the other is all you need.

It's no different here. Sometimes maybe you can just recover that 2dB on the board and you're OK. Other times it might require a little of both the gain change and the treble cut before you can recover everything. It all depends on the situation.

Nothing personal meant, but I can't help but keep thinking, based upon your questions, that you're tripping yourself up on this issue by trying to over-think it. If you've done any live sound at all, and have had to deal with feedback, you know everything you need to know about feedback and about this situation:

To combat feedback, you simply have to figure the best way of keeping the high frequencies from the speakers from being picked up too loudly by the microphone. That's all each of those items in that list of solutions is meant to do in it's own way. And that's what that little black knob on the bottom of a GB DX helps you do. That's it in a nutshell. End of story.

I really am running out of both ways and will to explain it further than that. There's only so many ways one can explain "See Spot run". I think you're getting hung up on whether Spot is a beagle or a terrier.

G.

 

[Goldilox]

As a harmonica player and owner of multiple bullet mics (though not a green bullet) I can attest that what SouthSIDE Glen says is correct about controlling feedback. I must admit to being bewildered as to why NYMorningstar is finding it hard to grasp, given that reducing gain in the early stages of the chain and increasing the master volume is pretty much a standard response to feedback, whether it's coming from a guitar amp, a PA or anything else.

In reference to the OP what are you plugging your Green Bullet into? These mics are really designed to go into a guitar amp, putting them into a PA they just sound sort of boxy and middley and depending on the PA can lead to impedance issues. If you are going direct into a PA (and aren't interested in going through an amp and micing up) I might suggest using some kind of amp sim, like the Boss fender pedals or a POD to get the tone you were wanting.

 

[NYMorningstar]

As a harmonica player and owner of multiple bullet mics (though not a green bullet) I can attest that what SouthSIDE Glen says is correct about controlling feedback. I must admit to being bewildered as to why NYMorningstar is finding it hard to grasp, given that reducing gain in the early stages of the chain and increasing the master volume is pretty much a standard response to feedback, whether it's coming from a guitar amp, a PA or anything else.

We weren't talking about reducing gain, at least I wasn't. We were talking about triming the initial output of the mic(prior to an amp) and adding gain from the channel preamp to make up for it. The master volume would not be changing. To me that's just adding noise from your preamp which arguably could be better.

We're talking about reducing feedback not distortion. Adding back your volume to where it was is not changing your positive feedback loop problem. Getting rid of feedback should be so easy. Ever hear of negative feedback amps or phase shifting to control feedback?

Sure there's a simple solution, turn down the overall volume or sweep the mic and EQ or better yet use an appropriate mic (what I suggest). You are right about using one through a PA, they sound terrible. That's why you run them through guitar amps instead. They were built to distort and for vocals you'd be better off using $20 cardioid mic instead.

 

[SouthSIDE Glen]

We've been talking about mic gain all along, I don't know which thread you've been reading.

Green bullets were not built to distort.They were built for radio communication. The newer DX mics are actually far cleaner than the older models used to be, and cleaner than most harp players would like them to be, which is why they are actually NOT a favorite amongst hardcore harp players.

One runs bullet mics through an amp not because the mics distort, but because they don't distort enough. And because one needs amplification to compete on stage or to busk on a streetcorner.

And you wonder why I get so irritated about people not knowing what they're talking about posting misguided answers on forums like this.

G.

 

[NYMorningstar]

We've been talking about mic gain all along, I don't know which thread you've been reading...
And you wonder why I get so irritated about people not knowing what they're talking about posting misguided answers on forums like this.

G.

Glen, go sit in the corner until you can behave. You're in time out until you grow up.