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PA or ? for small room with low ceilings
Old 4th April 2018
  #61
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Quote:
Originally Posted by shufflebeat View Post
Correct. That feedback exists at all is what you are describing.
Yes, the cause does not change regardless of the circumstance...I'm discussing the scientific cause of feedback and you are discussing how feedback can be manipulated which are two different things.

Quote:
Within the confines of your statement above, in any given instance there will be circumstances that give rise to feedback, incorrect placement of speakers/mics, a small powered wedge monitor pushed beyond it's capacity so that the overdriven preamp results in a clipped signal which, in accordance with the physics, feeds back at predictable points. I think this was the kind of scenario AntG was referring to although I wouldn't want to speak for him.

Amplified "acoustic" instruments introduce their own stress points because they are, by definition, not designed for the job, this must be addressed, for instance by one or more notch filters or a physical solution like soundhole plug (feedback buster, clue's in the name).

The science behind this is so robust and predictable that it can be relied on to be used creatively (Hendrix, J.)
Here we go again:

Feedback is caused when there is a loop between the input and the output, how you create the loop is beside the fact. We can affect feedback by manipulating one or more elements of the equation...the SPL of the output, the sensitivity of the input devise, the frequency response of both the input and output, the distance between the input and output and the angle of pickup and dispersion of the input and output respectively.

Everything you've described above is just a manipulation of one or more of these elements, the stories you use and the improper explanations only serve to muddy the water.
Old 4th April 2018
  #62
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it's indeed interesting how various people (all with a broad level of experience) come to different conclusions on a specific issue - i'm actually tempted to do a small video to provide evidence by means of an spl and/or volt meter and a recorder...

meanwhile (to all heretics): keep the gain low!
Old 4th April 2018
  #63
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The science is very clear and does not need translation, none of the text I've ever read on the matter deviates from the fact and nobody has of yet offered a serious argument to support the claims that have been made.

Improper gain-staging and low quality preamps do not 'cause' feedback...

I wish you would make a video showing the relevant measurements.
Old 4th April 2018
  #64
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Quote:
Originally Posted by Samc View Post
Improper gain-staging and low quality preamps do not 'cause' feedback...
Is it fair to suggest improper gain staging (overdriving an underpowered monitor beyond the point where it's producing any more actual SPL) and feedback will often coincide?
Old 4th April 2018
  #65
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I got the Yamaha speaker out from the box in the closet. I've been using the SA220 over the last 12 months and we used my old duo partner's PA for the two gigs we had last year. I was a bit shocked at how big the Yamaha was, I remembered it being about half the size that it is. It also is a bit awkward to put on a high speaker stand, I must have lost some strength in the time that's passed since I last used it. It does sound nice though - at least in our front room.

When/if I get another speaker, would the 8" version be a viable choice or should I have a "matching pair" of 10"? In any case I may invest in one of those K&M crank speaker stands...
Old 4th April 2018
  #66
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Quote:
Originally Posted by shufflebeat View Post
Is it fair to suggest improper gain staging (overdriving an underpowered monitor beyond the point where it's producing any more actual SPL) and feedback will often coincide?
If there is a loop between a microphone and the monitor there will be feedback, but if all the criteria for creating the loop are not met you will not have a loop or feedback. The cost of the preamp won't matter either.
Old 4th April 2018
  #67
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Quote:
Originally Posted by OldBlue View Post
When/if I get another speaker, would the 8" version be a viable choice or should I have a "matching pair" of 10"? In any case I may invest in one of those K&M crank speaker stands...
Stay with a matching pair of either version.
Old 4th April 2018
  #68
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Quote:
Originally Posted by Samc View Post
The science is very clear and does not need translation, none of the text I've ever read on the matter deviates from the fact and nobody has of yet offered a serious argument to support the claims that have been made.

Improper gain-staging and low quality preamps do not 'cause' feedback...

I wish you would make a video showing the relevant measurements.
you seem to be stuck with what you got from the theory...

try this: bring the gain of a mic close to feedback and measure the output level of the wedge with an spl meter (just before the onset of feedback).

then bring down the gain and compensate for the loss of level with pushing the output fader until you measure the same level on the spl meter - no feedback.

the price? maybe some more noise when working analog.

maybe you could even do a video (showing it doesn't work) before me...


p.s. i didn't say it's got to do with low quality preamps (it doesn't). i was referring to situations when the overall system has poor headroom/low spl capacity and one needs to fight for every db. the above mentioned simple procedere allows you to successfully do so.
Old 4th April 2018
  #69
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To any interested readers who favor science over opinion in re gain staging : feedback, there's an easy way to ascertain when any two different stages are passing signal at identical voltage (reference "channel fader down/group fader up")...

1. Set and forget channel input gain.

2. Route channel to mains via a group.

3. Set channel fader and group fader anywhere you wish.

4. Raise masters until to the onset of feedback.

5. Lower your channel fader until feedback ceases.

6. Raise group fader until feedback returns.

You have now established that the channel decrease and the group increase have changed by exactly the same voltage. Physical distance of movement, fader scale markings, digital # readout and LED signal lights are REFERENCE ONLY and have no precise value, merely a "ballpark" indication.

If anyone cares to cling to the popular audio myths, you are welcome. Whatever works for you. Those wishing to understand exactly why and how things work based on demonstrable physics and math are also welcome.

You're welcome...
Old 4th April 2018
  #70
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Quote:
Originally Posted by Samc View Post
If there is a loop between a microphone and the monitor there will be feedback, but if all the criteria for creating the loop are not met you will not have a loop or feedback. The cost of the preamp won't matter either.
Excellent, so my 15w practice amp and tube screamer combination is wailing and sustaining like bagpipes without bothering the neighbours while my big, clean Roland jc120 can't be coaxed into anything like feedback despite the serious SPLs.

What am I missing?
Old 4th April 2018
  #71
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Quote:
Originally Posted by shufflebeat View Post
Excellent, so my 15w practice amp and tube screamer combination is wailing and sustaining like bagpipes without bothering the neighbours while my big, clean Roland jc120 can't be coaxed into anything like feedback despite the serious SPLs.

What am I missing?
Laboratory conditions and exact, repeatable measured tests?
Old 4th April 2018
  #72
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Quote:
Originally Posted by deedeeyeah View Post
you seem to be stuck with what you got from the theory...

try this: bring the gain of a mic close to feedback and measure the output level of the wedge with an spl meter (just before the onset of feedback).

then bring down the gain and compensate for the loss of level with pushing the output fader until you measure the same level on the spl meter - no feedback.

the price? maybe some more noise when working analog.

maybe you could even do a video (showing it doesn't work) before me...


p.s. i didn't say it's got to do with low quality preamps (it doesn't). i was referring to situations when the overall system has poor headroom/low spl capacity and one needs to fight for every db. the above mentioned simple procedere allows you to successfully do so.
You make it sound like being stuck on the scientific theory is a bad thing...you should know that Ive been at this for a long time and have a lot of practical experience that supports the theory.

scientific theory tells me that gain is gain, if you get it at the mic pre, the channel fader or at the master output fader the feedback will not care. Therefore, if nothing else changes and the output is reset as before, the system status will remain the same.

If this was not the case when you tried this little test then something was wrong with the test, gain is gain!!! Maybe you guys should spend more time understanding the theory and you would be better off understanding what's really happening.

AnthonyG made the claim that the quality of the preamp in the console was a factor, in fact he made the claim several times, stating that cheap preamps would cause feedback if you drove them hard. I just noticed that some people were sidestepping those claims like dog droppings on the sidewalk.
Old 4th April 2018
  #73
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Quote:
Originally Posted by shufflebeat View Post
Excellent, so my 15w practice amp and tube screamer combination is wailing and sustaining like bagpipes without bothering the neighbours while my big, clean Roland jc120 can't be coaxed into anything like feedback despite the serious SPLs.

What am I missing?
Apart from the amp is everything else in the system EXACTLY the same? Are you using the same guitar with the same pickups and with no adjustment to the tone or gain knobs? Is the relationship between the guitar amp and the guitar pickup EXACTLY the same and is the tone/frequency the same? Can you explain the science behind the cause of this phenomenon...because I'm about ready to call BULL****...!
Old 4th April 2018
  #74
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Quote:
Originally Posted by Wyllys View Post
To any interested readers who favor science over opinion in re gain staging : feedback, there's an easy way to ascertain when any two different stages are passing signal at identical voltage (reference "channel fader down/group fader up")...

1. Set and forget channel input gain.

2. Route channel to mains via a group.

3. Set channel fader and group fader anywhere you wish.

4. Raise masters until to the onset of feedback.

5. Lower your channel fader until feedback ceases.

6. Raise group fader until feedback returns.

You have now established that the channel decrease and the group increase have changed by exactly the same voltage. Physical distance of movement, fader scale markings, digital # readout and LED signal lights are REFERENCE ONLY and have no precise value, merely a "ballpark" indication.

If anyone cares to cling to the popular audio myths, you are welcome. Whatever works for you. Those wishing to understand exactly why and how things work based on demonstrable physics and math are also welcome.

You're welcome...
Well put.

So now

1) I compress my signal (no idea why but go with it) and I can't hear my voice any more so I add some make up gain to compensate, taking me back into feedback in accordance with what you have just suggested. I can't hear what I'm singing because the compression has killed all dynamic range but the system is in feedback.

Alternatively

2) When I overload my mic input there comes a point where my headroom is all eaten up and not getting any louder/clearer no matter how hard I push into the red (idiot), a bit like a compressor/limiter but with added distortion. I bring up my main outs in a vain attempt to... etc.

Does the physics add up here?
Old 4th April 2018
  #75
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Wyllys's Avatar
 

Quote:
Originally Posted by shufflebeat View Post
Well put.

So now

1) I compress my signal (no idea why but go with it) and I can't hear my voice any more so I add some make up gain to compensate, taking me back into feedback in accordance with what you have just suggested. I can't hear what I'm singing because the compression has killed all dynamic range but the system is in feedback.

Alternatively

2) When I overload my mic input there comes a point where my headroom is all eaten up and not getting any louder/clearer no matter how hard I push into the red (idiot), a bit like a compressor/limiter but with added distortion. I bring up my main outs in a vain attempt to... etc.

Does the physics add up here?
What physics? Try giving actual numbers and measurements instead of vague hypotheticals. Physics is neither the analysis of appearances nor of subjective opinions and conjecture

Last edited by Wyllys; 4th April 2018 at 08:50 PM..
Old 4th April 2018
  #76
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Quote:
Originally Posted by Wyllys View Post
What physics? Try giving actual numbers and measurements instead of vague hypotheticals. Physics is not the analysis of appearances.
Exactly...instead of a bunch of meaningless, vague and imaginary scenarios in an attempt at gotcha, we should be getting serious scientific arguments to support the (false) claims being made.
Old 4th April 2018
  #77
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Quote:
Originally Posted by Samc View Post
Exactly...instead of a bunch of meaningless, vague and imaginary scenarios in an attempt at gotcha, we should be getting serious scientific arguments to support the (false) claims being made.
Once again - I am not disputing the science behind feedback loops. I am suggesting that a simple mic/amp/speaker in the lab does not represent the kind of real life situations faced by many, including myself. Real life is muddy.

We usually tend to avoid compression on monitors for the reasons I've described. On my Mackie desk the Aux sends default to pre-fade/post DSP. That means some people are probably operating with compression on their monitors. If your answer to feedback is "turn something down' then you've given bad advice.

My point, and my only point, is that your simplistic headline statement is not enough to cover the various situations that myself and AntG have suggested and other folks come across all the time. If you want to cover all those you'll have to go into more depth and account for the changing dynamics of real life.
Old 4th April 2018
  #78
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Quote:
Originally Posted by Samc View Post
Apart from the amp is everything else in the system EXACTLY the same? Are you using the same guitar with the same pickups and with no adjustment to the tone or gain knobs? Is the relationship between the guitar amp and the guitar pickup EXACTLY the same and is the tone/frequency the same? Can you explain the science behind the cause of this phenomenon...because I'm about ready to call BULL****...!
Of course not. It's a jc120. That's my point. It's not all about one measurement.
Old 4th April 2018
  #79
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Wyllys's Avatar
 

Quote:
Originally Posted by shufflebeat View Post
Once again - I am not disputing the science behind feedback loops. I am suggesting that a simple mic/amp/speaker in the lab does not represent the kind of real life situations faced by many, including myself. Real life is muddy.

It's not all about one measurement.

We usually tend to avoid compression on monitors for the reasons I've described. On my Mackie desk the Aux sends default to pre-fade/post DSP. That means some people are probably operating with compression on their monitors. If your answer to feedback is "turn something down' then you've given bad advice.

My point, and my only point, is that your simplistic headline statement is not enough to cover the various situations that myself and AntG have suggested and other folks come across all the time. If you want to cover all those you'll have to go into more depth and account for the changing dynamics of real life.
But it IS about one (basic underlying) principle.

If you understand this...or merely accept it as a given...you can apply it to EVERY situation in which you find yourself. Without understanding the one single basic principle, you're attempting to re-invent the wheel every time you encounter a different occasion/set-up/problem. You'll save a lot of time and grief by actually studying rather than imagining, learning HOW and WHY the principle applies.

It also helps to be able to think logically...

Last edited by Wyllys; 4th April 2018 at 09:42 PM..
Old 4th April 2018
  #80
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Just for fun, here's a story my Grandpa told me:

A Tale of Two Farmers

Two farmers had horse pastures on either side of the fence dividing their properties.
The problem they had was that the horses would break through the fence and get mixed up. The farmers tried all sorts of solutions to tell which horse was theirs.

First they tried cutting the tail off of one, but it grew back. Second, they tried trimming the mane. Same fail...it grew back. Finally they tried measuring them and found that the black one was 4 inches taller than the white one.

Last edited by Wyllys; 4th April 2018 at 10:20 PM..
Old 4th April 2018
  #81
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Quote:
Originally Posted by Wyllys View Post
But it IS about one (basic underlying) principle.

If you understand this...or merely accept it as a given...you can apply it to EVERY situation in which you find yourself. Without understanding the one single basic principle, you're attempting to re-invent the wheel every time you encounter a different occasion/set-up/problem. You'll save a lot of time and grief by actually studying rather than imagining, learning HOW and WHY the principle applies.

It also helps to be able to think logically...
And this is exactly why knowing and understanding the theory is so important...when you understand that the equation is always the same and all that’s happening is that it’s only the values that keep changing it becomes easier to get the end result you want.
Old 4th April 2018
  #82
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Quote:
Originally Posted by shufflebeat View Post
Of course not. It's a jc120. That's my point. It's not all about one measurement.
If you change the values in the equation how do you expect to get the same result...?
Old 4th April 2018
  #83
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Quote:
Originally Posted by shufflebeat View Post
Once again - I am not disputing the science behind feedback loops. I am suggesting that a simple mic/amp/speaker in the lab does not represent the kind of real life situations faced by many, including myself. Real life is muddy.

We usually tend to avoid compression on monitors for the reasons I've described. On my Mackie desk the Aux sends default to pre-fade/post DSP. That means some people are probably operating with compression on their monitors. If your answer to feedback is "turn something down' then you've given bad advice.

My point, and my only point, is that your simplistic headline statement is not enough to cover the various situations that myself and AntG have suggested and other folks come across all the time. If you want to cover all those you'll have to go into more depth and account for the changing dynamics of real life.
You don’t do over 200 gigs per year all around the world in all kinds of circumstances and not have feedback problems if you don’t know what you’re doing. Just thought I’d throw that out there.

And yes, if you have feedback you either turn something down or move something, how you turn it down is irrelevant...notching out frequencies is turning it down too by the way.
Old 4th April 2018
  #84
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Quote:
Originally Posted by Wyllys View Post
But it IS about one (basic underlying) principle.
Agreed, 100%

Now, why does compression in a monitor mix eat up headroom before feedback?

(That was a Dave Allen joke, it was funnier first time).
Old 4th April 2018
  #85
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Quote:
Originally Posted by Wyllys View Post
To any interested readers who favor science over opinion in re gain staging : feedback, there's an easy way to ascertain when any two different stages are passing signal at identical voltage (reference "channel fader down/group fader up")...

1. Set and forget channel input gain.
I'm not doubting your experience here Wyllys yet improper setting of the input gain is precisely what I'm talking about.

No set and forget.

So are you guys saying that the input gain can be maxed out and this won't cause feedback earlier than if the input gain had been set properly?
Old 4th April 2018
  #86
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Quote:
Originally Posted by Samc View Post
I'm discussing the scientific cause of feedback and you are discussing how feedback can be manipulated which are two different things.
Sorry, missed this bit.

I agree we are talking about two different things, direct feedback via the pickup/amp loop which is not dependant on strings being present and a separate system in which the strings are physically driven by the sound energy which can be manipulated.

Thank you.
Old 5th April 2018
  #87
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Quote:
Originally Posted by AnthonyG View Post
I'm not doubting your experience here Wyllys yet improper setting of the input gain is precisely what I'm talking about.
Got it

Quote:

So are you guys saying that the input gain can be maxed out and this won't cause feedback earlier than if the input gain had been set properly?
It won't cause feedback, the cause is exactly as W and S describe. What it will do is make it more likely that you'll turn something up later in the chain (beyong f/b threshold) because your dynamic range is limited so you can't hear anything, usually the cause for pushing up your channel input gain in the first place.
Old 5th April 2018
  #88
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Quote:
Originally Posted by AnthonyG View Post
I'm not doubting your experience here Wyllys yet improper setting of the input gain is precisely what I'm talking about.

No set and forget.

So are you guys saying that the input gain can be maxed out and this won't cause feedback earlier than if the input gain had been set properly?
You really don't seem to have a clue despite the deluge of information from responders whom you admit to be experienced sound professionals. AND...

You've taken the "set and forget" out of my context (how to test for even gain staging) and interpolated it into your context (voodoo audio). And, yes, we are saying the feedback won't occur "earlier" although I'm not exactly sure what your concept of "earlier" might be...
Old 5th April 2018
  #89
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Quote:
Originally Posted by shufflebeat View Post
Got it.

It won't cause feedback, the cause is exactly as W and S describe. What it will do is make it more likely that you'll turn something up later in the chain (beyong f/b threshold) because your dynamic range is limited so you can't hear anything, usually the cause for pushing up your channel input gain in the first place.
Please do not think that your acknowledgement of the veracity of our posts somehow validates the meaningless post hoc assertions you then make.
Old 5th April 2018
  #90
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Quote:
Originally Posted by Wyllys View Post
You really don't seem to have a clue despite the deluge of information from responders whom you admit to be experienced sound professionals. AND...

You've taken the "set and forget" out of my context (how to test for even gain staging) and interpolated it into your context (voodoo audio). And, yes, we are saying the feedback won't occur "earlier" although I'm not exactly sure what your concept of "earlier" might be...

Your condescension isn't helping.

See I'm not sure if the "professionals" here really do understand just how badly a mixer can be run.

Me? I'll solo the channel and set input gain with the meter every time.
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