Feedback Issues!!!

Posted: Tue Mar 07, 2006 7:55 pm

Hello,
I have a question regarding a feedback. I have been doing sound for no longer than a couple of weeks and one of the problems I have been running into is that when micing a person who speeking at a podium the mic is constantly feedingback. I can barely get the gain up at all and yet the mic keeps feeding back. The set up is as followed:

The mic is a Sennheiser E835 that sits about a foot away from the speakers mouth. That is going directly into a Mackie SR-32 VLZ Pro, which is linked to an Alesis M-EQ32. The speakers that are used are Mackie SRM450s. The mic is neither in front or behind the speakers kind of centered between them, and no monitors. The speeches are done in a middle school gymnasium--so you can imagine it is a very LIVE room.

Yeah, I don't what else to say. The speaker imoves constantly from right to left and that is why I chose the E835 over the SM57 or 58.

Please, any help is greatly appreciated.
sincerely,
NoviceAtBest

Posted: Tue Mar 07, 2006 9:22 pm

Hi, what I would do is change it for a Beta 58A or get you're self a 31 band Eq and try eliminating the frequencies that are doing the feedback in the stage, after that I don't know what else to say I never had this problem with the Beta's, good luck. Smile

Zoro.

Posted: Wed Mar 08, 2006 12:33 am

Are you sure that you have a grip on gain structure? If you are not in the line of fire of the speakers, you shouldn't have that many issues.

If you are in a gym, then you are going to have issues no matter what you use. The issues are just going to vary in frequency and intensity.

You can have electronic feedback and/or acoustic feedback.

What you need is a great multi-band, parametric EQ. You are not going to dial in a mic in a live room like that with the EQ of a Mackie. The bell is too big.

Forget the Alesis as well. What do you think the chances are of having the exact frequency landing on one of those filters in that EQ? Not likely. You need a parametric, a frequency analyser, or a great guitar tuner and a knowledge of notes = frequency.

A dynamic might not be a bad idea if you cannot get a grasp of the room and EQ.

Posted: Wed Mar 08, 2006 9:17 pm

[You need a parametric, a frequency analyser, or a great guitar tuner and a knowledge of notes = frequency.]

Excuse me for my ignorance, but what exactly will these do? Like I mentioned, I am extremely new to this teritory. I got some books ("Live Sound Reinforcemnet") a couple of weeks ago and have been plowing through them; but, I have been playing music piano, guitar, etc. for over 18 years so I definitely understande notes. How do apply this knowledge to, for example, using a guitar tuner to analyze and minimize feedback? Thanks again gentlemen.
sincerely,
NoviceAtBest[/quote]

Posted: Wed Mar 08, 2006 10:14 pm

If you do not have or can't afford a good spectrum analyser, a high end guitar tuner will help you find the notes that are causing problems. You can use one of those books to cross reference the exact frequencies that are giving you fits. You need a parametric, because graphic EQs are too vague. You may have a 30dB boost at 7kHz. Your graphic (if it has ISO centered frequencies will have 6.3kHz, then 8kHz. How are you gonna notch it? You will have to get close. A parametric will allow you to dial in the exact frequencies, then adjust the bandwidth, Q, and then boost.cut.

Posted: Thu Mar 09, 2006 3:15 am

I agree with sheet that a parametric is technically the most appropriate tool for the job, but I think what you really may need is some practise.

The situation you are in by the sounds of it is you have some ok gear, sure it's not the top gear out there, but it's not junk. and for one mic in a Gym, it's more than adequate.

What I would suggest is set up your system when you have a bit of time, and when there's nobody else around to annoy, Gradually bring the volume up until it just begins to feed back - then back it off about 3db.

Now go through with the eq lifting each fader and returning it to the 0dB mark until you find which ones cause it to feedback. Then back these ones down as far as you had to lift them.

Repeat all of this a few times, you will hit a point where you get several different freq's at the same time - this is about the liit of volume you have.

After a bit of time, you will start to learn what the frequencies all sound like. And you'll head to the right place on the eq faster.

If it's the Alesis eq I'm thinking of, it has little pinch sliders - so I'd suggest some earplugs too, things can squeal pretty bad till you get the slider back down.

Once you have sorted how to get the most out of your current gear, then you will be in a good position to know what to buy to improve it more.

I'd say a parametric won't be to much use until you have a good feel for what frequencies sound like, and I wouldn't get a RTA or SpecAn for a while, they are too easy to rely on too much and you can forget to listen.

Hope this helps you.

Al Wink

BTW- Great that your reading stuff, Yamaha did a great book on it all if you can track it down.

Posted: Thu Mar 09, 2006 7:54 am

Thanks to all of you for your help. I trully appreciate. And I agree, AltheGatman, I do need some serious practice. I'll be printing out your responses and will be cross-referencing them immediately. Take care.
sincerely,
NoviceAtBest

Posted: Fri Mar 10, 2006 8:53 am

Maybe this is too late, but...
That suggestion to use the guitar tuner is a very good one. In fact, the tuner technology that Sabine developed and licensed out to others is the basis for their anti-feedback processors.
As for the issue of using a parametric, they are actually a LOT easier to use than given credit for. Simply rolling the Frequency control ("sweep") with the band (s) set for a fairly narrow notch (say, a 1/4-oct, 6-dB cut)
will make tuning out the offending resonance node(s) a snap. Especially with a single mic. Been there, done that. And there are always a few parametrics on e-bay at decent prices. Symmetrix, Ashley, Orban, and others can be found at bargain prices. Perfect for a "second life" in the rack of an up-and-coming sound engineer.

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