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Can you tune a PA with a 31 band and iPhone?

Tahoebrian5

Fractal Fanatic
Just wondering if you guys can give me some tips on how to tune a PA to kill feedback freqs. In the studio we don’t have a bunch of fancy gear, just a basic mackie board, but we do have a 31 band that could be used. Can someone school me on whether or not I could use maybe an iPhone app to find the feedback freqs to pull out?
 

Muad'zin

Forum Addict
I was taught to place a mic on a stand near a monitor speaker, then slowly increase volume on that speaker until feedback starts, then start fiddling with the EQ faders until you find the fader that will eliminate the feedback. Slide that back a notch until the feedback stops. Then increase volume again until feedback starts again, rinse and repeat until you can really turn the volume really up on that speaker until even a mic cupping singer with hearing problems will be satisfied. Chances are you will experience feedback all over the spectrum, but most of it in the middle. A good sound engineer can do this fairly quickly. And even tell which frequencies are causing feedback from hearing alone. The only frequency I recognize is 1K, as that used to be the one you'd hear on TV when there was nothing on, except that test image. So at least I could eliminate half of the frequencies when looking for the culprit.

As for the app, don't use it. You got to learn how to identify feedback frequencies yourself before using (and making yourself reliant on) an app. Practice, practice, practice!
 

KevinP

Inspired
The above method will work for pure volume but likely still needs some tone shaping applied, and you need to make sure you are setting gain correctly for the microphone - that's a critical part of the equation.

As far as apps to detect frequencies, you can absolutely use a RTA (Real Time Analyzer) app as a learning tool or you can use it permanently and either are fine. I could identify feedback very easily by ear, but I still have an RTA running on our mixers Left and Right out to quickly allow me visuals during shows (the board has it built in). When I was first learning to do sound 20 years ago Peavey came out with an EQ that had small lights at the top of each band. Being a new sound guy that saved me a ton of time and I got to the point of not even needing to look after a pretty short while - partly through self discipline which was just me listening and guessing the frequency in my own mind before I looked at the EQ. I don't know about iPhone but there are definitely apps for this on Android (and I would assume I phone as well). Is it good to learn the frequencies yes - but there are so many other things to work on if you have a reliable piece of technology to help your ears I think you should do it.
 

GiRa

Forum Addict
I'd actually work on mic and speaker placement.

Exploit the pickup pattern of your mics and try to place them in a way so they cannot "hear" the speakers.

Another thing that helps is cutting the stuff you don't need for each channel. For example, vocals probably don't need a lot of low frequencies.
About the mixer: cutting stuff you don't want is better than boosting the stuff you want from a feedback point of view.
 

biskitboy

Veteran
In addition to the above, I would boost each frequency on your 31 band individually until you find the offender(s). When you do, you'll cut those 6db+. Do this for each band you have. This is much easier to do with PEQ's, but you don't have those. I typically "ring out" the mics this way and apply this to the vocal group. The individual vocal channels will then get their own individual tone sculpting which feed into the group.
 

BBN

Fractal Fanatic
In addition to the above, I would boost each frequency on your 31 band individually until you find the offender(s). When you do, you'll cut those 6db+. Do this for each band you have. This is much easier to do with PEQ's, but you don't have those. I typically "ring out" the mics this way and apply this to the vocal group. The individual vocal channels will then get their own individual tone sculpting which feed into the group.
I would try this first.

Bring that 31 band unit out in front of the speakers, run some music that you know really well and listen for offending frequencies when you push up each slider individually.
 
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