# Feedback busters / Spectrum Analyzers



## Milkman (Feb 2, 2006)

Hey Pa guys,

Back in the 80s we used to use Spectrum anayzers to set the main graphs. It was a bit clumsy as you had to set up a special mic and pump white noise through the mains and then read the device (rack mounted unit). You would then set the graph based on this information.

I know that there are some more modern devices out there now. I would be interested in trying one as long as it doesn't automatically make corrections.

Can anyone recommend such a device?

I'm fine without it, but anything that can save a few minutes during set up is worth considering.


thanks,


Mike


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## Hamm Guitars (Jan 12, 2007)

There are allot of feed back eliminators that are built into graphic EQs that will locate feedback but not actually do anything about it. Behringer and Peavey are two that I have run accross that I have used that had this feature. They have led's above the bands on the graph that can be put into 'show' mode. I can get you the behringer model if you want to try it out, as we don't use it.

However, I've never used a feedback eliminator that I liked. It is kind of like having someone hacking at your graph when you are trying to mix and they seem to detect warmth as being feedback. I always disable them when I run across them, but I usually turn them on at some point for a bit to give them another chance, but they've allways left a bad taste in my mouth.

The DBX drive rack also has a feedback filter, but they are in the amp racks so I rarely have a chance to play with them when I am mixing. I'll have a look at it tonight and let you know if it can display but not actually do anything to the signal.

As for the spectrum analyzer, I have used one that was PC based. It was connected to the PA with a seperate splitter/mixer (there were two of them actually) that allowed the signal to be tapped from the PA before and after the drive rack, had an input for the PFL and also had a mic input. It was a novel idea, but the patching was a little complex. I used it a couple of times, and then the novelty wore off.

Originally, I was going to use two of these:
http://www.rane.com/sm26s.html

But these were actually more versatile and did the job:

http://www.altoproaudio.com/html/details.php?ID=28&

I still have one of these if you want to test out something similar.

I did this as I couldn't find something on the market that would do the same thing. The Alto splitter/mixers were cheap as well and I just used one of my laptops to run the analyzer.


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## Milkman (Feb 2, 2006)

Thanks for the feedback (sic) guys.

Two things.

My system is stereo so I'd need a dual 31 or two individual 31s.


I absolutely don't want a device that takes charge. I want one that gives advice.

I'm quite used to ringing out the system the old way, but things change during the course of a show, including the simple but significant impact of more bodies in the room. I like the idea of a quick and dirty indicator of which frequencies are squawking, particularly when I'm on stage and my soundman is running things.


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## Milkman (Feb 2, 2006)

Paul said:


> I hear you....What I like about the graphic EQ's with feedback indication is that a red light goes on above the slider(s) where the hot frequency is. The sound guy can then grab it and pull it back. It's very tactile and there is active integration between sound dude and system. The disadvantage is that it is a fairly wide Q, (1/3 octave), and this is sometimes noticable. You will pull out more than just the offending freq.
> 
> The thing I like about the automatic ones is that I can ring out the system with the 4 or 5 "hot" freq's, and lock them in. Those freq's will stay notched out, with a much much narrower "Q" than a 1/3 octave graphic. The remaining bands will monitor the situation and jump on any hot spots as they occur. The notches are less noticable, and you can get a bit more performance out of your system. It's a tool to be used wisely and judiciously. Don't treat it like a mallet or a sledge, it's more a tack hammer.



I like the idea of the Peavey and Behringer graphs with the LED idiot lights but I would prefer a better quality graph.

A dual 31 with such indicators would be ducky for me.

I'm just not into automatic stuff in this application.


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## Hamm Guitars (Jan 12, 2007)

The Behringer we have kicking around is this model:

http://www.behringer.com/DEQ1024/index.cfm?lang=eng

It is stereo, and it does have a feedback 'show' mode (there are LEDs on the faders). We have/had a dual 15 analog only graph as well with the same function.

I looked at the drive rack tonight and it won't really work all that well as the screen is too small even if it would tell you what it wanted to notch out.


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## Robboman (Oct 14, 2006)

*Peavey VSX26, DBX Driverack... others?*



Milkman said:


> Back in the 80s we used to use Spectrum anayzers to set the main graphs. It was a bit clumsy as you had to set up a special mic and pump white noise through the mains and then read the device (rack mounted unit). You would then set the graph based on this information.


I'm still manually tweaking 31 band graphs but I read up on this tech a while back. I like the concept but haven't yet tried it myself. 

From what I've read the Peavey VSX 26 does a good job of this. First you put your calibrated RTA mic in front of your PA, just like the old days. Then you push a button and the rest is automatic and FAST; Pink-noise blasts out for two or three seconds, then the EQ is automatically set. Then your new EQ curve shows up on the LCD. Now you can manually tweak, A/B against your previous settings, undo or re-run the pink noise as many times as you like and automatically average the results. When you're done you can save the preset so you don't have to do it all over again next time your band sets up in that room.

Of course these units also function as 2 or 3 way crossovers, comp-limiters, realtime feedback-killers, parametric EQ, time delay etc. They're reasonably cheap and only 1U so I don't see why you couldn't use one for only part of it's full functionality.


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