System Tuning.
Live System Measurements

Blog Post #2 : Live Sound System Tuning Update # 1

I did a small indoor gig 2 days back and was on the mix for this amazing artist from Mumbai. The band was phenomenal and so energetic! It was super fun! But that’s not why we are here. This is a blog on System engineering and so let’s get started with some System Tuning.

So, luckily I got a few mins before soundcheck where I could take some measurements and make some optimisations.

Before we get into measurements and optimisation, kindly note a few things :

1)The optimisation that i’m explaining below is by no means a complete list of ‘Things to do’ to completely optimise a system.

2)The traces are with smoothing at 1/48 Octave (which is almost NO SMOOTHING).

So here we go,

System Tuning : Measuring Tops :

This is the measurement of the Tops :

System Tuning.
Tops without processing.

I looked at this trace and immediately spotted 3 zones that are drastically varying from the average curve :

1)Zone 1 :  220 Hz to 260 Hz.

2)Zone 2 : 1.3 kHz to 1.8kHz.

3)Zone 3 : 8.3 kHz to 10.9 kHz.

I did a simple voice check with a mic and heard the system and also looked at the coherences of all the three zones. I decided to first deal with Zone 2 as it seemed to be the zone very obviously affected tonally and also looking at the coherence it’s the area with maximum coherence of the three zones.

The Coherence of Zone 1 is very low and I decided to not touch that area for now.

For Zone 3 the coherence is much better than Zone 1, but I decided to deal with Zone 2 on a priority basis.

There’s a big 5 dB dip in Zone 2, (due to reasons I’ll be discussing in future posts with simulations) which I corrected using a parametric Eq and managed to get a good 4 dB back without significantly affecting the phase.

This is the the measurement of the Processesed Tops(EQ in Zone 2) :

System Tuning.
Tops with Processing.

Here’s the comparative difference in between the unprocessesed and processesed Tops :

System Tuning
Unprocessesed vs Processesed Tops.

This is all I did for the tops and I could immediately hear the tonal quality improve drastically.

System Tuning : Measuring Subs :

I took the measurement for the subs and here’s what it looks like with the processesed tops :

Unprocessesed Subs with Processesed Tops.
Unprocessesed Subs with Processesed Tops.

Looking at the measurements for Subs and the processesed tops i found the crossover zone (Zone 4) : the area extending from 103 Hz to 110 Hz.

Time Aligning the System :

It was now time to time align the Tops with the subs and so I moved on to looking at the phase trace.

The phase traces in the crossover zone aren’t overlapping but are parallel to each other, and I needed to insert some delay to align the system.

Visually from looking at design (the placement of tops and subs) i thought that a 3ms delay would work so I started with it but then it was a bit more so switched to 2 ms delay on the subs and this is what the phase trace looked like with the subs delayed by 2 ms, and I was very satisfied with the phase overlap. They seemed to be aligned at the crossover zone.

Delayed Subs with Processesed Tops
Delayed Subs with Processesed Tops

It was now time to get the Full PA running and verify our optimisations.

Optimised PA showing 6 dB gain at the crossover zone.
Optimised PA showing 6 dB gain at the crossover zone.

You can see that in The Crossover Zone (Zone 4) i got a good 6db gain, suggesting that the system is definitely aligned at the crossover. Soooo, Yaaaaay!

And at exactly this moment, the band walked in!

So this is all I did for this particular show : 

In the very limited time I had I dealt with :

1)A very important problem area 1.3 kHz to 1.8 kHz.

2)Time aligned the PA.

This System Tuning and Optimisation really made my mix sound so much, for which i would have otherwise struggled (without the optimisation).

So, that’s it for this particular Live Sound System Tuning update!

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P.S : The Part 2 to Coupling vs Comb Filtering(Part 1) will be out soon ! So Stay Tuned.


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