How to EQ and Tune a PA Sound System Using an iPad App




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If you want to tune a PA system properly, you are going to either have to call in a professional to do it or buy some expensive equipment. But I am going to show you how to do it adequately on the cheap using an iPad as a spectrum analyzer and a mobile phone to produce pink noise.

Well, a number of things can affect the frequency response of a live sound system. a) the interaction between the loudspeakers b) the interaction between the loudspeakers and the walls, surfaces, and furniture in the room c) the positioning of the speakers relative to the congregation. d) the interaction of mics and monitor speakers e) gain structure set up and dynamic range of sound sources

Setting up the system EQ will help you to balance out the sound and get rid of some unwanted frequencies. One way of describing it is tuning your PA to the surroundings. You shouldn’t confuse this with individual channel EQ on your mixing desk, but what we are talking about here is using an EQ unit for your entire system. What we want to achieve is a flat frequency response from the system running live in the sanctuary or worship space, to begin with. Once you have that, then you can adjust the bass and treble response to your taste.

If all you have at the moment is a mixer, power amp, and/ or passive speakers or powered speakers, you are going to need some extra kit.

What you will need

First, you will need a stereo graphic EQ unit. A half-decent graphic equalizer will have at least 15 bands on each channel. I wouldn’t go for any less than that but would recommend a 31-band graphic EQ unit if you can afford it. Also, most professional units come with a 19″ rack mount kit, but I would guess if you have a power amp and wireless mic receivers you will already have them in a 19″ rack.

You will also need an extra couple of 1/4″ jack cables, long enough to reach from your mixing desk to your EQ unit. Some folks might have a compressor, which I would recommend putting in line before the mixer, in which case you will only need a couple of short 1/4″ jack cables if your compressor is installed in the rack.

You will require a stereo mini jack to 1/4″ jack cable or stereo mini jack to phono cable to take the audio from your phone to the mixing desk.

Speaker Tuning App

You will also need a couple of iPads or one iPad and one iPhone. You could technically do this with two iPhones, but I think it would be difficult to see the frequency data on the screen. I haven’t tested this on Android as I only use Apple, but if the same app isn’t available, there may be some equivalents out there. If you do know the answer to this, please let me know.

The app I use is called Spectrum Analyzer by ONYX Apps. You can download it from the iTunes app store or get here. It is quite expensive for an app, but I have found that this one works and for me is the best speaker tuning app for iPad.

I have a great resource I think you will find useful on 101 Ideas for Church Sound Systems. You can find it here.

Setting it all up

To set this up, take the left and right main outputs from your desk and wire them up to the L and R inputs on the EQ unit(adapt accordingly if using a compressor). Then connect up your power amp to the L and R outputs of the equalizer. If using powered speakers, then you just connect the L and R speaker cables to the outputs of the graphic equalizer unit.

When you install the app on your phone and iPad, it will ask for permission to use the microphone. It’s important that you enable this. Plug the phone into a channel on the mixing console and play some music to test that you are getting audio through the system. You want are fairly high volume for this to start with.  Now switch to the app and turn on pink noise and you should hear it coming through your live sound system. It can be a bit irritating at first but you will just need to hang with it until you have completed the test. If you are building a system for your church, you should check out my list of 15 Best Products for Church Sound Systems. Follow this link to read more.

Graphic equalizer settings for church – aiming for a flat frequency response

Now set all the bands across the frequency range on your EQ unit to 0dB, so it should be flat(no smiley faces!). And on the channel you are running the iPhone into, you should set all the EQs to their midpoints.

Turn on the app on the iPad and switch to FFT and bar chart. The app will display a frequency spectrum response which is the result of the sound waves bouncing around the sanctuary. You will now be able to see easily where all the peaks and nulls are across the frequency bands. You can mess around with the bit rate to see what display is most helpful to you. (If you are interested in the science behind FFT analysis, you may be interested in this article here)

Now if you see a peak on the iPad that is above the average, you can read off the frequency and then adjust the band control on the EQ unit. If a peak is too high, turn down the matching frequency band on the equalizer. I would try the left and right channels independently. In the same way, if there is a drop-off response at the low frequencies or high frequencies, you may want to give them a boost, until you have a nice flat response readout on the iPad app.

To begin with, I would run the test from the sound booth where your mixing console is situated. Then it may be an idea to monitor frequencies at different places in the church sanctuary. If you have a digital mixer with a detachable control panel, this can give you an extra advantage in being able to tweak things as you go.

When doing the test, remember to have your monitor speakers turned on and their volume levels set at where they normally would be. Also, it’s not absolutely necessary, but I would try doing the test with your stage vocal microphones turned on at typical volume levels. Remember to set it up for an optimum gain structure, so that you won’t find later on that once you crank up the volume you start getting unwanted frequencies.  All of these things can affect your overall sound.

Once you have a nice flat response across the frequency range, try out a few music tracks through the iPhone and see how they sound. Most EQ units have on/off effect buttons, so you will be able to see how the system sounds when it is tuned and untuned to make a comparison.

Now, I am fully aware that for professional audio engineers, there’s a lot more to tuning a PA system than what I have described, but if you follow the steps above and it helps you to get a flat frequency response, it will go a long way to making your whole church audio experience a significantly better. Once you have that flat response, you can then make adjustments at low and high frequencies to suit what you want. If you use a digital mixer it is worth saving your settings, so if you need to tune again, you don’t need to start from scratch.

Of course, if you want something more precise than using an iPad, there is some gear you can buy, which I will add to this post at a later date, along with some graphic EQ units I could recommend.

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