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PA or ? for small room with low ceilings
Old 3rd April 2018
  #31
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Quote:
Originally Posted by shufflebeat View Post
Are we approaching consensus at all?
No, improper gain-staging did not 'cause' the feedback and making that claim is incorrect and misleading...and any mention of the quality of the preamp only adds another dimension of falsehood to the overall statement.

The feedback was caused because the system was too loud and turning down the system at any stage would cut the feedback loop even if it didn't fix the gain-staging problem.
Old 3rd April 2018
  #32
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Quote:
Originally Posted by shufflebeat View Post
I've described above two distinct (experientially) types of feedback. The amp/strings feedback responds to manipulation of the strings, direct amp/pickup feedback doesn't.

The mechanics are the same but in the first the energy is mediated via the strings. It's the same for acoustic guitars except for the musicality part.
Technically, the guitar strings have nothing to do with feedback either, its the acoustic interaction between the pickup and the amp that's causing the feedback. If the amp is loud enough and the pickups are close enough to the amps just tapping the pickups or the body of the guitar will result in feedback.

You made a statement, you actually didn't describe the differences between the "two types of feedback", please stop trying to rewrite the laws of physics to suite your arguments, feedback is feedback...I can't believe we're actually having this discussion. Seriously guys?
Old 3rd April 2018
  #33
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Quote:
Originally Posted by Samc View Post
Technically, the guitar strings have nothing to do with feedback either, its the acoustic interaction between the pickup and the amp that's causing the feedback.
No, as is the case already outlined it is the whole system, not just amp/pickup.

I have a fiddle player who has a persistent resonance around his D string. It's a fiddle thing but it manifests itself when amplified (piezo). We have it generally under control but if and when it shows up at a gig he'll be the first to notice by feel. He will adjust his playing, not his position so as not to allow the resonance to get out of control, then gives me a nod so we can notch it out.

Seriously!
Old 3rd April 2018
  #34
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Quote:
Originally Posted by Samc View Post
You made a statement, you actually didn't describe the differences between the "two types of feedback",
I thought I was pretty clear on that. If I stick a mic or pickup in front of a speaker I can expect feedback, initially at the peaks of sensitivity of the system, hence the difference between the sound of dynamic vs condenser for instance. There is nothing mediating between but air.

On a guitar you can recreate the same effect by putting the pickup in front of a speaker. Whether or not there's strings on the guitar the system can be persuaded to feed back, usually on one or two notes depending on position.

In normal rock and roll circumstances there is a sweet spot before the system descends into such uncontrollable feedback where the sound coming from the speaker is setting off the strings, not the pickup, usually in my experience on the third and fifth harmonics of the note fretted. This is the same energy but now the strings have become part of the feedback.loop. I am suggesting this is a distinctly different kind of mechanical feedback than what we've been discussing earlier.

The laws of physics remain intact.
Old 3rd April 2018
  #35
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Wyllys's Avatar
 

As previously linked:

Audio feedback - Wikipedia

From the above:

"Audio feedback (also known as acoustic feedback, simply as feedback, or the Larsen effect) is a special kind of positive loop gain which occurs when a sound loop exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for example, a power amplified loudspeaker)."

N.B.

Method of transduction of/at the input makes no difference.

"Feedback is feedback is feedback."
...Grrrrtrude Steinway

Pictograph:
Attached Thumbnails
PA or ? for small room with low ceilings-image.png  

Last edited by Wyllys; 3rd April 2018 at 08:37 PM..
Old 3rd April 2018
  #36
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Quote:
Originally Posted by Wyllys View Post
As previously linked:

Audio feedback - Wikipedia

From the above:

"Audio feedback (also known as acoustic feedback, simply as feedback, or the Larsen effect) is a special kind of positive loop gain which occurs when a sound loop exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for example, a power amplified loudspeaker)."

N.B.

Method of transduction of-at the input makes no difference.

"Feedback is feedback is feedback."
...Grrrrtrude Steinway

Pictogram:
If you look back at the thread you'll notice I'm not suggesting anything different. When I said "experientially" I was suggesting a qualitative difference, not a categorical one, something like the difference between noise and music.

There is, however, a difference in that with one type you kill the strings - the feedback stops. Cause/musical significance/solution all different than the other one which does not rely on strings at all and usually has little musical value.

Of course some may like the sound of uncontrolled feedback, for most people it's reminiscent of a tom cat being adjusted with pliers as opposed to the sweet haunting wail of the end of Pretty Vacant.
Old 3rd April 2018
  #37
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Quote:
Originally Posted by shufflebeat View Post
If you look back at the thread you'll notice I'm not suggesting anything different. When I said "experientially" I was suggesting a qualitative difference, not a categorical one, something like the difference between noise and music.

Of course some may like the sound of uncontrolled feedback, for most people it's reminiscent of a tom cat being adjusted with pliers as opposed to the sweet haunting wail of the end of Pretty Vacant.
Not overlooked. It's just that sometimes you have to reiterate the basics for thread readers when the discussion gets tangential or side-tracked with special case scenarios or "what-about-ism".
Old 3rd April 2018
  #38
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Quote:
Originally Posted by Wyllys View Post
Not overlooked. It's just that sometimes you have to reiterate the basics for thread readers when the discussion gets tangential or side-tracked with special case scenarios or "what-about-ism".
Accepted.

I accidentally wandered off at a tangent due to a misreading (old age) but Sam replied to my post after I'd realised but before I'd deleted it so I was obliged to clarify.

Will read closer on phone.
Old 3rd April 2018
  #39
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thank you all for your input. I am a PA newbie so this is all good info for me! I'm also going to try using my Samson Q8X, the claim is that they are more feedback resistant than other mics, but then they all say that, don't they? I knew I had one somewhere as a backup mic and only just found it in the closet. I stopped using it when I got the AKG D5, not sure why, it's built like a tank and works well with my voice.

Thanks again, I am learning a lot!
Old 3rd April 2018
  #40
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Quote:
Originally Posted by Wyllys View Post
Not overlooked. It's just that sometimes you have to reiterate the basics for thread readers when the discussion gets tangential or side-tracked with special case scenarios or "what-about-ism".
Some of these posts can cause misunderstanding and help to spread misinformation, there is a good chance that one or more inexperienced readers may go away with all kinds of strange and false concepts about what causes feedback in a system.

For that reason alone it is important to reiterate that cheap preamps, improper gain-staging and how guitar strings are played do NOT cause feedback...you can have feedback with or without any or all of those things.
Old 3rd April 2018
  #41
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Quote:
Originally Posted by OldBlue View Post
I hope someone can help me with my quandary.

I play solo and also in a duo in some very small pubs, and some have quite low ceilings. I use a Fishman SA220 when playing solo and add a mixer and a Yamaha DBR10 speaker for the duo. Some of these places are too small to have either speaker behind me, the only space is off to one side.
Ok, this is a red flag. I understand given the layout of the room there is sometimes no choice on where to place speaker(s), but if there is a choice, you never want to place the speaker behind you, particularly if you have a soft voice, as the microphone will be pointed at the speaker and could well pick up the speaker output which leads to a feedback loop. Always set up the speaker in front of you if this is possible.
Old 3rd April 2018
  #42
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Quote:
Originally Posted by blue439 View Post
Ok, this is a red flag. I understand given the layout of the room there is sometimes no choice on where to place speaker(s), but if there is a choice, you never want to place the speaker behind you, particularly if you have a soft voice, as the microphone will be pointed at the speaker and could well pick up the speaker output which leads to a feedback loop. Always set up the speaker in front of you if this is possible.

Never say never. There are ways to make it work behind you as noted earlier in the thread...before the protracted excursion into feedback.
Old 3rd April 2018
  #43
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Quote:
Originally Posted by blue439 View Post
Ok, this is a red flag. I understand given the layout of the room there is sometimes no choice on where to place speaker(s), but if there is a choice, you never want to place the speaker behind you, particularly if you have a soft voice, as the microphone will be pointed at the speaker and could well pick up the speaker output which leads to a feedback loop. Always set up the speaker in front of you if this is possible.
Thank you! With the SA220, it is recommended to have the speaker behind you and off to one side so it also works as a monitor, similar to the Bose L1 and LD Maui systems. For the most part, this worked very well and I only struggled with feedback if the ceiling was low or the room was oddly shaped. I wouldn't set up the Yamaha speaker(s) in the same way. I have just had a deposit put on the the SA220 tonight, so I won't be using it again.
Old 4th April 2018
  #44
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There's no dispersion information on the Fishman manual, but it's likely similar to the L1 which is an extremely wide 180 degrees. (If your sound goes everywhere, it's going to hit a lot more surfaces in the room.) Given this, it's no surprise that room layout can affect feedback given such a wide dispersion. The manufacturer likely realizes that, since they've seen fit to include an anti-feedback device on it. The manufacturer suggests placing the Fishman behind you, therefore eliminating the need for a separate monitor, because it is being sold as a do-everything portable unit for the solo performer. They probably assume the volume will not be exceedingly high so as not to start feedback and have included the anti-feedback unit in case it does, but advantages usually come with disadvantages.
Old 4th April 2018
  #45
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Quote:
Originally Posted by blue439 View Post
There's no dispersion information on the Fishman manual, but it's likely similar to the L1 which is an extremely wide 180 degrees. (If your sound goes everywhere, it's going to hit a lot more surfaces in the room.) Given this, it's no surprise that room layout can affect feedback given such a wide dispersion. The manufacturer likely realizes that, since they've seen fit to include an anti-feedback device on it. The manufacturer suggests placing the Fishman behind you, therefore eliminating the need for a separate monitor, because it is being sold as a do-everything portable unit for the solo performer. They probably assume the volume will not be exceedingly high so as not to start feedback and have included the anti-feedback unit in case it does, but advantages usually come with disadvantages.
This is sensible reasoning in my opinion, a loudspeaker in front of the mic cannot reasonably be expected to operate well at high volume or in every acoustic situation. This system and setup has serious limitations that can't and probably won't be easily overcome.

The people who designed and built the system understood this, hence the inclusion of the anti feedback devise.
Old 4th April 2018
  #46
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The Fishman manual makes several recommendations regarding placement, operation and SAFETY. They actually recommend wearing hearing protection when using the unit. Maybe the legal department felt it necessary to put into the manual...
Old 4th April 2018
  #47
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Quote:
Originally Posted by Wyllys View Post
The Fishman manual makes several recommendations regarding placement, operation and SAFETY. They actually recommend wearing hearing protection when using the unit. Maybe the legal department felt it necessary to put into the manual...
Apparently they expect a lot of feedback...
Old 4th April 2018
  #48
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Quote:
Originally Posted by Samc View Post
For that reason alone it is important to reiterate that cheap preamps, improper gain-staging and how guitar strings are played do NOT cause feedback...you can have feedback with or without any or all of those things.
Sam, I can see you are keen to promote clarity but by misrepresemting posts you are at risk of doing the opposite.

You've outlined the physics, no-one is questioning that reality. What you haven't addressed is the behaviour that leads to bad outcomes by use/misuse of systems.

Inappropriate gain staging, leading to clipping will exacerbate feedback. An ovedriven distorted guitar can be coaxed I to feedback at very low volume, perfectly in line with conventional principles.

We are talking about two different aspect of the same situation, to disregard either is to mislead.
Old 4th April 2018
  #49
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Quote:
Originally Posted by Samc View Post
This system and setup has serious limitations that can't and probably won't be easily overcome. The people who designed and built the system understood this, hence the inclusion of the anti feedback devise.
This is a Fishman device. It's promoted to acoustic guitar players who often have to deal with feedback issues due to body and string resonances as discussed earlier but dismissed by yourself.

Their other hardware, not aimed at microphone users, employs the same feature for the same reason.
Old 4th April 2018
  #50
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Quote:
Originally Posted by shufflebeat View Post
Sam, I can see you are keen to promote clarity but by misrepresemting posts you are at risk of doing the opposite.

You've outlined the physics, no-one is questioning that reality. What you haven't addressed is the behaviour that leads to bad outcomes by use/misuse of systems.

Inappropriate gain staging, leading to clipping will exacerbate feedback. An ovedriven distorted guitar can be coaxed I to feedback at very low volume, perfectly in line with conventional principles.

We are talking about two different aspect of the same situation, to disregard either is to mislead.
The physics does not change regardless of how we initiate or bend and twist feedback...feedback is feedback. The only thing that matters is that a loop is created between an input and output devise. Trying to split hairs by adding other, irrelevant criteria to the equation is muddying the water and will only confuse and mislead.

The specific claims that were made by both you and AnthonyG (including the two above) are false and misleading.
Old 4th April 2018
  #51
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Quote:
Originally Posted by Samc View Post
The physics does not change regardless of how we initiate or bend and twist feedback...
Correct. That feedback exists at all is what you are describing.

Quote:
feedback is feedback. The only thing that matters is that a loop is created between an input and output devise.
(my emphasis)

Incorrect

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.)

Quote:
Trying to split hairs by adding other, irrelevant criteria to the equation is muddying the water and will only confuse and mislead.
Discussing this as though we are operating in a lab, while technically not incorrect, is telling only half the story. Any universal theory must explain every potential state of every element. The laws of physics do that, your incomplete broad statement of principle doesn't.

Quote:
The specific claims that were made by both you and AnthonyG (including the two above) are false and misleading.
Incorrect, as most people will know from their own experience and I think you do too.
Old 4th April 2018
  #52
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While Wyllys and SamC are far more experienced that I, I do wonder if either of them have run a small budget mixer badly to see what happens.

If poor gain staging isn't incompetence that leads to feedback then I'd like to know what is?

I'm going to have to run some experiments.
Old 4th April 2018
  #53
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i'd like to comment on three things:

'gain staging' does have to do with feedback: bring down the channel gain but raise the level of the vca/dca/subgroup/aux/master/matrix: you get the same overall gain/level, but the system is less prone to feedback.

(we had this discussion before, but the other way round with more sensitive mics - we agreed not to agree in our findings...)

'more feedback' is possible: feedback can start to occur at additional frequencies once an initial feedback started and you are making no attempts to stop it.

'column design loudspeakers' can be driven at pretty high levels even if they are positioned behind the musicians: the quasi line array characteristics (the combined output of multiple small speakers/the directivity) come into place in the far field (away from the column) while at the mic position (close to the column), the rather low output speakers produce not much directivity/a more diffuse soundfield.

although i haven't been a big fan of those systems (for various reasons), i have come across quite a few recently that were more than just okay; they were capable of delivering a rather uniform soundfield across a wide area that would have taken a much bigger effort to achieve with more convential 2-way hornloaded speakers (hk audio, ld systems, now even l'acoustics come to mind)!
Old 4th April 2018
  #54
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Quote:
Originally Posted by deedeeyeah View Post

'gain staging' does have to do with feedback: bring down the channel gain but raise the level of the vca/dca/subgroup/aux/master/matrix: you get the same overall gain/level, but the system is less prone to feedback.
If you can show accurate measurements of the voltage output of the desk they will show that the onset of feedback occurs at the identical voltage. Working without measurements by simply raising and lowering faders and noting their physical positions relative to scalar markings or digital readouts tells you nothing about the actual levels in terms of physics, merely the reference measurements for that stage.

Physical or virtual positioning of faders or knobs must be verified by actual measurement of voltage for any test or comparison to be valid. Q.E.D.
Old 4th April 2018
  #55
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Quote:
Originally Posted by deedeeyeah View Post
i'd like to comment on three things:

'gain staging' does have to do with feedback: bring down the channel gain but raise the level of the vca/dca/subgroup/aux/master/matrix: you get the same overall gain/level, but the system is less prone to feedback.
This is FALSE, as long as the overall SPL of the output (and all the other elements of the equation) remains the same, the feedback loop will exist. If you do not change the angle or distance of the mic in relation to the output devise, you will still have feedback

This is very simple and easy to test, we do not need to speculate or guess about it.
Old 4th April 2018
  #56
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Quote:
Originally Posted by AnthonyG View Post

If poor gain staging isn't incompetence that leads to feedback then I'd like to know what is?
Incompetence.

Or more politely, inexperience.
Old 4th April 2018
  #57
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Quote:
Originally Posted by Wyllys View Post
If you can show accurate measurements of the voltage output of the desk they will show that the onset of feedback occurs at the identical voltage. Working without measurements by simply raising and lowering faders and noting their physical positions relative to scalar markings or digital readouts tells you nothing about the actual levels in terms of physics, merely the reference measurements for that stage.

Physical or virtual positioning of faders or knobs must be verified by actual measurement of voltage for any test or comparison to be valid. Q.E.D.

who tells you that i'm not measuring?! (i was just illustrating the underlying process in simple words in my previous post...)
Old 4th April 2018
  #58
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Quote:
Originally Posted by Samc View Post
This is very simple and easy to test, we do not need to speculate or guess about it.
told you that we agreed not to agree - i guess it's been too long since you worked with in small club with inadequate equipment...
Old 4th April 2018
  #59
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Quote:
Originally Posted by AnthonyG View Post
While Wyllys and SamC are far more experienced that I, I do wonder if either of them have run a small budget mixer badly to see what happens.

If poor gain staging isn't incompetence that leads to feedback then I'd like to know what is?

I'm going to have to run some experiments.
Please go read what the reference books and articles have to say, constantly repeating the same falsehoods over and over is not helping.

I have a lot of experience doing experiments on low-end equipment...some old Yamaha, Mackie, and Soundcraft boards can attest to that. If you can link to a paper, article or reference book which explain why low-cost preamp are more prone to feedback I'd appreciate it.

Does anyone else here actually believe this?

Last edited by Samc; 4th April 2018 at 01:43 PM..
Old 4th April 2018
  #60
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Quote:
Originally Posted by deedeeyeah View Post
told you that we agreed not to agree - i guess it's been too long since you worked with in small club with inadequate equipment...
Please explain the science behind your claim(s), we don't need to argue endlessly about this.

You might be surprised if you knew some of the things I do on a regular basis and why some people hire me for certain gigs. You cannot be good at the big, well equipped gigs if you can't perform well in the smaller less equipped situations, only people who don't have a broad experience at both ends constantly make these stupid reflections.

Throw me into a small venue/bar with a few bits and pieces and you'll see what I can do with it...I just had that experience in a small bar in a backwater third world country.
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