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Old July 31st, 2005, 01:31 PM   #1
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Can a mic be damaged by feedback?

I loaned a Rode stereo condenser to a choir to mic a live performance through a pa, since it seerned pretty optimal for what they are trying to do. We live off pa feeds routinely for our video, so seemed like a good idea to return the favor across disciplines, so to speak.

I forewarned about feedback, thinking a condenser would be more sensitive than a dynamic, and would be more susceptible. Sure enough, it did feedback some, but they rode the level down, and there were only a couple of instances.

Question, can feedback damage a condenser (or any mic)? And is there some other mic that would be optimal for micing a choir through a pa?

Thanks.
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Old August 1st, 2005, 11:20 AM   #2
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Chiors are usually miced with a large-diaphram condenser mic of some kind, so no problem there.

Things you can do to reduce feedback:

- set the mics' pickup pattern to cardiod, and aim them at the chior
- make sure the mics are behind the house speakers
- Use a spectrum analyzer and a 1/3 octave EQ to pull back any resonant frequencies on the stage

Finally, look for any unusual objects that could contribute to feedback. Someone mentioned that singers wearing cowboy hats can reflect stage noise into the singer's mic and cause feedback that wouldn't be present with a bareheaded singer. Podiums and music stands are also potential culprits if they are too close to the mics.

-Troy
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Old August 1st, 2005, 07:19 PM   #3
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Quote:
Originally Posted by Eddie Vaughn
...Question, can feedback damage a condenser (or any mic)?...
No. Remember, it's all just sound to the mic. There's nothing special happening electrically to it during a feedback squeal. And in terms of sound, good mics are spec'd to not only withstand sound pressures well above the threshold of pain, but to operate normally at those levels. Theoretically, an exception could be feedback at the natural mechanical resonant frequency of the diaphram. But that frequency necessarily has to be above the audible range, and the fequency response of the PA system drops off above that range.

For the PA speakers themselves, feedback levels can be another story.
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Old August 1st, 2005, 10:48 PM   #4
 
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Quote:
Originally Posted by Fred Retread
No. Remember, it's all just sound to the mic. There's nothing special happening electrically to it during a feedback squeal. And in terms of sound, good mics are spec'd to not only withstand sound pressures well above the threshold of pain, but to operate normally at those levels. Theoretically, an exception could be feedback at the natural mechanical resonant frequency of the diaphram.
Actually, to argue just a bit :-)....a ribbon mic can easily be killed by feedback. One of the most expensive lessons I ever had in my youth was putting a Beyer (i think it was a 380) in front of a kick drum, and promptly destroyed it at first kick. It was embarrassing, and boy...did I never do that again. Feedback can set some ribbon mics into a roll that will spit or break the ribbon. But it's very rare you'd have a ribbon mic on any stage, anyway.
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Old August 2nd, 2005, 08:49 AM   #5
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No argument, Doug, thanks for the correction. I should have known better than to give a flat "no," or to imply that all good mics have high max SPLs

I guess that would have been a mic with a low max SPL, which I now see is historically characterisitic of the ribbon designs. From what I just read, some could be blown in front of a kick drum even without PA or amp feedback. The Beyers and Coles currently offered at B&H--not cheap mics--have max SPL listed as "not specified by manufacturer." We know what that means.

By contrast, btw, some new Royer ribbon designs (R-121, 122, etc.) boast max SPLs not achievable before the advent of rare earth magnets. They start at just under $2000. Have you heard any of them? The claim is a degree of flatness in response that you can't get with other mic types, resulting more naturalness and immediacy of sound than you can get with other types.
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Old August 3rd, 2005, 06:12 AM   #6
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Quote:
Originally Posted by Troy Tiscareno
Chiors are usually miced with a large-diaphram condenser mic of some kind, so no problem there.

Things you can do to reduce feedback:

- set the mics' pickup pattern to cardiod, and aim them at the chior
- make sure the mics are behind the house speakers
- Use a spectrum analyzer and a 1/3 octave EQ to pull back any resonant frequencies on the stage

Finally, look for any unusual objects that could contribute to feedback. Someone mentioned that singers wearing cowboy hats can reflect stage noise into the singer's mic and cause feedback that wouldn't be present with a bareheaded singer. Podiums and music stands are also potential culprits if they are too close to the mics.

-Troy

In most churches I've been, choirs are miced by small diameter lav like "choir mics" hung over the choir.

You do have to be careful about where the mics are and where the speakers are to avoid feedback. There are times when the location of the choir is disharmonious to proper micing and PA.

As for the Rode stereo condenser, the issue was more likely the increased sensitivity of the Rode mic. Being more sensitive, just plugging it in would be like turning up the existing mic a whole lot.

My experiences with worship audio is that it's all over the road. Some installs are incredibly well-engineered, others are put together with little or no idea of what's required.

The cowboy hat scenario is quite possible. A good tip.

Many churches turn mics on at the pulpit and other places and leave them on because they can't afford anyone to mix the service (bring down mics that are not in use) or can't find a willing volunteer. All those open mics raise the possibility of feedback significantly.

Regards,

Ty Ford
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Old August 3rd, 2005, 09:17 AM   #7
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Good advice, thanks all.
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Old August 6th, 2005, 03:21 PM   #8
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Quote:
Originally Posted by Ty Ford
In most churches I've been, choirs are miced by small diameter lav like "choir mics" hung over the choir.
I should have clarified that to say "in the studio." Oops.

-Troy
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