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high pass filter and feedback

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Bryan Tucker
high pass filter and feedback
on Feb 23, 2009 at 3:24:13 am

I'm a soundman at our church, and we just moved into our new building with a professionally installed soundsystem. We have noticed everything sounds very trebley (my descripion) or tinny. It's as if someone has turned up the higher bands on a graphic equalizer too high. The audio installers insist, however, that the equalization of the system is set for the room. We are locked out from the processor to change this at this time. We are having frequent feedback problems when choirs sing, and "ringing" when our pastor speaks. All this feedback and ringing is very high end.
My question is: Would having a 80 hz high-pass filter turned "on" on our mixer cause our equalization to be boosted to the higher end, and thus contribute to feedback?.

Bryan Tucker


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Greg Curda
Re: high pass filter and feedback
on Feb 23, 2009 at 4:42:41 am

Hi Bryan,

The hi-pass does not actually increase high freq, but cuts lows, giving the perception of more highs, as compared to lows. I don't think that would have anything to do with increased feedback, but also doesn't sound like you need it in. Sounds more like some disparity between speaker and mic placement, or room acoustics and EQ.

I never like being locked out of EQ control and would insist that the installation company come back and experience the problem... I would ask for the room (Church) to be "pinked", which is a way to measure frequency response of a room from various positions.

Also check that there are no omni mics in play, and all mics are behind speaker placement. At least get control of your EQ till you get it the way you want it and then lock it down...

Just thoughts.

Greg



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JC Boulay
Re: high pass filter and feedback
on Feb 23, 2009 at 4:12:53 pm

Most definitely get your install guys back in. And you should not be charged for this. Their setup should work in actual usage conditions.



JC Boulay
Audio Z
Montreal, Canada
http://www.audioz.com


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Bryan Tucker
Re: high pass filter and feedback
on Feb 25, 2009 at 2:44:20 am

Thanks Greg. Our acoustics are being evaluated, and all of us feel that the room is e.q.ed too high. Mic placement is definetally an issue because our installers assumed that all our singing would be on our stage. They "forgot" that our 50+ person choir would be standing on the steps in front of the stage.
We are working with them. But until they fix things, I'm trying to think of anything else I can do to help.
Also, as somebody else noted, I am not professionally trained (like alot of Church sound guys.) That's why I'm doing research, and some of it pointed to this sight. I'll be sure to visit it often.
Thanks again!
Bryan

Bryan Tucker


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Jordan Wolf
Re: high pass filter and feedback
on Feb 25, 2009 at 6:44:02 am

Bryan,

I would greatly recommend you buy the Yamaha Sound Reinforcement Handbook (Second Edition, or whichever is the newest). It covers much of the basics of audio. A lot of answers to "why does this do that" can be found there.

I come here for audio-for-video type answers/insight and it has been a great help in that area. But I would recommend joining a forum that deals primarily with live sound/sound reinforcement. The ProSoundWeb Sound Reinforcement forum(s) are a great choice; many industry professionals frequent the site. You would want to post in the "LAB Lounge" so you can work on your chops.

Feel free to contact me via my e-mail in my profile. (If it's not there, let me know).


Best of luck and keep on experimenting!

Wolf
<><


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Jordan Wolf
Re: high pass filter and feedback
on Feb 24, 2009 at 12:10:18 am

80Hz is where a lot of the rumble and stage noise tends to be at; a high-pass (aka low cut) filter would not make a system sound tinny NOR would it make it more prone to feedback, especially at higher frequencies.

If I were a betting man - and I'm not - I would say that your main feedback problems are between 1kHz and 6kHz. High-mid frequency feedback (1kHz to 8kHz-ish) sounds like somebody stuck a pig with a pitchfork (squealing). High frequency feedback (8kHz-ish to 20kHz) sounds more like a television is on.

What is the system processor? It sounds like it's a dbx Driverack that someone used the AutoRTA* function on. Since it's an RTA, it is time-blind and can only identify differing amplitudes of frequencies; it cannot tell you whether "x" frequency is due to comb filtering, a reflection, etc.



* - WARNING: NEVER use that feature; your ears are much better judges.

Wolf
<><


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Jordan Wolf
Re: high pass filter and feedback
on Feb 24, 2009 at 12:13:25 am

Oh, and it sounds like you should really read up on your audio.

Try here (scroll down the page a bit) and also here.

That should do you for starters.

Wolf
<><


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Greg Curda
Re: high pass filter and feedback
on Feb 24, 2009 at 5:12:40 pm

Great resources, Wolf!
Always pays to keep reading...

G



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