PA System Tuning 101

Posted on August 30th, 2010. Written by Barry Jackson

Tuning a PA System

It never ceases to amaze me just how many engineers out there don’t understand the basic principles of tuning a PA. Twice this year already I have seen an engineer walk into a gig & destroy my afternoon’s work by drastically changing the graphic EQ settings before even taking a moment to listen. They think “hey mate, this is a JBL rig… JBL speakers should always be EQ’d like this…” Not necessarily.

Inevitably, their set is plagued with feedback & odd hums going off left, right & center. Yes, JBL Speakers do have a certain frequency response like any other brand, but that combined with the mics on stage, the shape/size of the outdoor arena, my speaker management, cross-over points, etc.. all contribute to the unique sound on any given day. I would like to remedy this by explaining how I go about manually EQing my rig…

Practical Use of a Graphic EQ.

So let’s say you’ve got your rig setup the way you like it, and there are 8 microphones on stage. Bring up your Master fader to zero & give the first touch of graphic EQ relevant to the sound of your well listened reference CD… Nice. Apply the Channel EQ to each mic according to its relevant instrument or voice sound check.

Feedback Frequencies

Next we need to find the feedback frequency hot-spots & eliminate them. One by one, bring each microphone level to zero to the point just before the microphone feeds back. We now end up with 8 open microphones that are really hot. Now go to the Graphic EQ and one by one test each frequency slider for feedback by slowly boosting to 100% & listening carefully. Some frequencies will feedback as soon as you move that slider a millimeter. If that is the case then cut that frequency 100%. Some frequencies will take up to a few seconds before you can hear the feedback creeping in, in which case only slight reduction is required. Some frequencies won’t feedback at all, so leave the relevant filter at zero. Basically, judge how much to cut a frequency by how quickly you can hear feedback creep in when a given frequency is boosted on the Graphic EQ.

Now go back to the reference CD. Sound like crap? Don’t panic yet. If you have found yourself with a pretty drastic graphic EQ setting then it is probably time go back to the individual microphone channels & find any hotspots using the parametric EQ. Using the same principle as before, open only the first microphone & push the high EQ knob to max. Hear any feedback creeping in? If so, cut accordingly with the Channel EQ. Now boost the mid filter and gradually sweep the frequency until you find any hotspots & again cut accordingly using the same EQ. Repeat with the lower mid & bass frequencies. Repeat this process on each microphone until they are all tuned accordingly. Now open all the microphone channels & go back to the overall Graphic EQ, testing each individual frequency again by boosting as before, and cutting accordingly.

The Curve

You should now have a less drastic looking set of curves, and shouldn’t need to tweak too much more to get that reference track sounding near perfect. You should also find it difficult to get those microphones to feedback on stage, even if you do get excited and push that guitar solo a bit hotter than you should. You can now enjoy the mix with piece of mind. That is until the next bands mix engineer comes in and carves a smiley face into your Graphic EQ…

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Barry Jackson

Audio Engineer, Multi-instrumentalist, DJ & producer. I have extensive touring experience as a musician & sound techy. Extensive label credits on over 30 records to date. Currently based in Wellington, New Zealand. Owner of Glasgow record label Refo Recordings & Ex-member of the underground UK band Sound Development Agency. My worldwide gig experience including prestigious venues such as Glastonbury Festival 2005 (UK), Subclub (UK), Engine Rooms (UK), Green Ant (Aus), Sandwiches (NZ), Southpaw (AUS), King Tuts Wah Wah Hut (UK), Liquid Lounge (UK) & Home (UK) www.reforecordings.co.uk & www.myspace.com/refo

http://google.com/profiles/coppinger7 Randy Coppinger

I ran a PA recently but did not have a graphic EQ, only a four band parametric. Your post got me to thinking… what if you started ringing out the room with the parametric and used it to cut the most significant feedback, especially if you had a Q setting more narrow than 1/3 octave? That could be more surgical, doing less damage overall. Then you could run through the graphic EQ to touch up the smaller issues. Just a thought.
- Enoch
  
  pls i need help with live mix.
- San
  
  You need graphic EQ to tune your room acoustic,every PA FOH needs
  It to control feedback
http://www.weiss-sound.com Matthew Weiss

Nice article Barry. I come from the alternative perspective – to eq the individual sources and leave the graphic eq alone unless the space is just overwhelming in particular frequency bands. Those graphic eqs can do a lot of damage, especially the cheap ones, but they can really save the day too.
http://www.reforecordings.co.uk Barry

I find when I use the approach of just EQing each source, I end up taking the same 2 or 3 frequencies out of every single channel.

I do agree that graphic EQ applied incorrectly, like many things can be destructive to your overall sound, especially with bad graphics. You really want a unit that cuts the chosen frequency with a very high Q (or narrow band) Personally I use Klark Technics & JBL DBX Graphics units more than any other, because they have that presicion & cut that can really shape the sound with.
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Dave

Interesting method Barry and I guess similar to the one I have been using with the exception that I give the system only a brief listen to check components and then set up a mix in headphones while the artist is having monitors set.
Once I have a nice cans mix and the act is happy with their stage sound I turn up the house and neutralise any instability and negative System / mic interaction.

This allows me to make accurate assessment of the mix in my cans even if the mix position is not representative of the majority of the audience (like a festival mix tower or beneath a mezzanine).

If I find myself eq-ing channels in unfamiliar ways I know that the system is poorly tuned.

All the best
Bill

Engineers should always listen to the in-house settings on the graphic EQ as most venues/engineers should know the PA/Space/Room better than anyone. We all know that this is not always the case but a quick listen to a CD through the PA will help identify any important issues that need sorting right away.

Once you’re happy I think most of the work should be done on the desk. I use a full parametric Midas Verona 40ch at the moment so obviously you can do whatever needs doing EQ wise using the channels alone.

With smaller rigs it will probably come more down to the settings on the graphic.

I do not agree that you should get the settings right through headphones before you begin on the FOH / Monitors. That cannot give you any real indication of the true sound of the FOH or the room and I would never even dream of doing such a thing. Cans come more into use when your getting down to mixing the band for FXs etc.

Everyone is different. But sometimes it winds me up when you have a PA/Room sounding great and a touring engineer just comes in, wipes everyone without even listening and then ends up struggling later on.

Take the time to listen to the in house settings, then adjust accordingly.
- Dave
  
  Bill! I couldnt agree more with your comment re wiping a tune before cranking a bit of pink noise through it.
  The house engineer is very often a walk in guy’s most valuable resource and their tune is likely a perfect starting spot when yr in a small room.
  
  As regards system EQ, I’m sure that you also find when operating in larger rooms that the system is smaarted to perfection and that the 31 band is just a grab eq (security blanket!) as the system response will be neutral. A perfect blank canvas.
  
  The method of mix referencing which I originally described is one which was recommended to me by the chief FOH rigger on one of my first tours involving spaces that were 5000+.
  I learnt a lot on that tour but I really held onto his comment that it was his job to ensure that the system was focused and tuned so that what came out of the desk was the same as what the entire audience was hearing.
  He was awesome! Constantly monitoring and adjusting the response around the venue to take into crowd shifts, temperature changes etc. a dedicated pro who took great pride in the sound of the system.
  
  I do find however that my channels always look basically the same so my cans mix is always the same and that means any desk recordings are the same.
  This is true for me in all rooms regardless of the size. 100, 1000, 10000.
  
  It stands to reason that if the output of the desk is consistent from show to show then one has a consistant reference point for the performance of the system.
  
  As for setting the mix in cans and then fine tuning the PA, it may not be your cup of tea but I know that the whole world is happier with one less guy tuning to their voice or forcing a pa to feed.
  It really isn’t that different to your method of turning up the vocal mics and ringing the system out except I have all of the mics open and only touch sliders that come up hot in the spectrum.
  Often, if the house tune is complementary with the artist in question I don’t touch the GEQ. Most often the adjustment of component levels at the processor will produce superior results.
  All systems sound different and I am happy to hear the tonal differences presented by different speaker manufacturers so if I have kf750s I’m not going to try and eq it to sound like a J-line.
  
  One point re ringing a PA out for those beginners that are reading these comments…
  Feedback is a function of physical positioning as well as dB SPL.
  I have found that sometimes it’s better to move speakers wider or further forward (or move the frontline upstage) or simply turn it down rather than chopping up the system EQ. A moderate mix that is clean and clear is always nicer than a loud mix that is full of phase anomalies. It is a good idea to have a calibrated SPL meter to ensure that you are not making it all harder than it has to be.
  
  PAs are fun!