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Old 26th December 2008, 11:17 AM   #1
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Default stage monitor question

something crossed my mind and i need advice .....

lets suppose you have a small stage with 2 main pa speakers located left and right of the stage just a bit in front of the microphone where the singer is located ....

then ofcourse you have one monitor looking towards the singer

so the voice and the microphone of the singer are almost in phase with the PA speakers ..... but the monitor has a diference of 180 since is located against the pa speakers and the vocalist ...

the question :
if the polarity of the monitor is reversed and actually is "tuned " more in phase compaired to the voice and the PA system

will this have any effect on feedback cancelation ???? will actually create more ???? or less ???? feedback .....

and then again if you have no feedbak issues will the vocalist hear better if the monitors are more in phase with the pa and the voice ????... or not ????

( keep in mind that we talk about a small stage ... in a small club for 150 pax ....meaning that the vocalist will hear from the monitors but also he has a sense from the PA also since its located quiet close to him ...)

all input is very welcome .... thank u very much
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Old 26th December 2008, 11:51 AM   #2
HK26147 is offline HK26147  United States
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Quote:
will this have any effect on feedback cancelation ???? will actually create more ???? or less ???? feedback .....
Yes, and possibly... And that is the reason that many PA systems include a polarity reverse switch, so each mic line can be inverted.
Because each stage is different and the spacing between mics and other mics and sound sources ( including virtual ones from reflections ) can create "interesting" sonic situations, that call for interesting solutions.

Although 2 sources will be 180 degrees out at a particular frequency, at a given distance, they will have other phase relationships ( constructive and destructive ) at other frequencies and spacing.

Syd
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Old 26th December 2008, 01:26 PM   #3
HK26147 is offline HK26147  United States
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Google this phrase:
microphone "polarity reversal"
and you will get a lot of detail on this.
Including:
The Sound Reinforcement Handbook
By Gary Davis, Ralph Jones, Yamaha International Corporation
* available as a limited Google book preview.
see page 186 - Polarity ( Phase ) Reversal

IMO This book is a must have/1st book reference.

Syd
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Old 26th December 2008, 08:31 PM   #4
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Use hypercardioid stage mics...

some people like the DSP based "feedback destroyers".

yes the relationship between the mics and the ambient sources of high level sound will effect feedback.

Better to also do something acoustically (not urethane foam) to control the reverberation levels in your room and on ur stage as well... most "club" rooms are awful acoustically for amplified music...

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Old 27th December 2008, 07:31 AM   #5
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Default GUYS COME ON !!!!!!!

this is not a question about feedback cancelation .....

also there is no question of reversing pahse in the microphone ....

in a given situation ..... 2 pa speakers left and right just a bit in front of the mike and one monitor towards the vocalist ....

Question remains ::::

will reversing the polarity of the monitor improove the listening conditions of the vovalist ????

the creation or cancelation of more or less feedback is a very secondary issue ....

thanks you ...
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Old 27th December 2008, 11:55 AM   #6
HK26147 is offline HK26147  United States
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You are not seeing ALL the elements that make up the scenario.
You can flip the polarity of a microphone OR a monitor.
Quote:
will reversing the polarity of the monitor improove the listening conditions of the vovalist ????
Possibly, and again,
This is one of the reasons why the polarity flip option is provided on monitors and mics: to allow for a possible fix.
Quote:
the creation or cancelation of more or less feedback is a very secondary issue ....
On the contrary: In a small venue with the real source ( the vocalist ) on a small stage, room acoustics are a huge factor.
Original source ( the vocalist ) + electrically amplified and modified source ( the microphone to monitor chain ) and a small venue with nearby walls, floor, and ceiling surfaces of varying qualities of sound absorption and reflectivity guarantee that the vocalist is going to hear a lot of reflection.
Running simulations of the interactions of 2 sound sources in an enclosed environment ( these allow for the simulation of a polarity flip BTW ), you will observe that it is NOT a panacea.
Polarity flip is just one technique. Subtle adjustment of placement of monitor, vocalist, and microphone can have a large effect on the overall sound, and what the vocalist hears in a small room.
See the above reference for comb filtering: The vocalist gets to hear the sum of direct sound production, an amplified analogue ( ie the monitor ) and the reflections from the surrounding surfaces.
It's a sonic soup and how the monitor interfaces with the room and mic obviously is going to effect what the vocalist hears.
Practically speaking I have better success with placement and EQ vs polarity reversal at any point in the mic to monitor chain.
I found feedback destroyers to be too coarse in their action and ultimately left the sound "dull".

* BTW: Bob McCarthy details the subject of polarity flip in his online work.

** Shouldn't this thread be moved?
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Old 27th December 2008, 12:37 PM   #7
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Default ok start to get it

like this doesnt get somewhere ...

this is all too theoretical ....it should be a yes or no thing by someone who tested this or not ....

the thing is that in a small setup like that where only onesound engineer exists and most of the time is spended in fron of the PA and in front of monitors ....then i think that only real life extented tests will show results .....

thanks though
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Old 27th December 2008, 12:46 PM   #8
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Quote:
it should be a yes or no thing by someone who tested this or not
I have and found it necessary ONLY with multiple monitors placed close together, and not necessary or effective for other circumstances.

See this article:
http://mixonline.com/live/applicatio...tanding_phase/

section PHASE AND POLARITY
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Old 27th December 2008, 12:59 PM   #9
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Default thanks

your answer is a basis i will start to make also real life test

thanks for the usefull link
thank u
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Old 27th December 2008, 01:08 PM   #10
HK26147 is offline HK26147  United States
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You are quite welcome.
When it comes to live sound you have to be willing to improvise and experiment, because every room is different.

Bob McCarthy approach is less math intensive, and very helpful
These articles may also help:

http://mixonline.com/live/applicatio...ualizing_room/
http://mixonline.com/live/applicatio...ity/index.html

He has some very helpful videos online and books as well.
http://www.youtube.com/watch?v=5Ig_oRpz3_k
http://www.youtube.com/watch?v=A9098KMP_Q8
http://www.youtube.com/watch?v=C2PGZq5PEe8&

Google also allows for preview of Bob McCarthy's book

http://books.google.com/books?id=w9B...sec=frontcover
Best of Luck
Syd
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