EQ’ing a system   5 comments

Most of the time (not always!) i see people watching there analyser screen during system tuning looking at spikes and dips and then hacking away with a 31-band graphic eq or if they’re lucky with a parametric eq.

Same happens with regards to what most people call “time alignment” which for me is doing delay’s in/out-fills or a flown main system to a sub array. X-over alignment to me is a “phase alignment” which if you only have delay as a means of getting a system aligned comes down to time alignment but with most modern day processors you get some additional filters like All-pass 1st and 2nd order or elliptic which will give you the possibility of doing a real phase alignment.

I do a lot of system tuning on loudspeakers that have no pre-sets what so ever so i have to start from scratch with most of the time only hints with regards to what the manufacturer thinks the recommended x-over frequency should be. The rest is up to me.

So how do I eq and align a system?

First let me give a small description of the system i used during this tuning of a 12”coax 2 way loudspeaker. Within my rack there are 5 Smaart i/o’s and for the rest i used SMAART7.4 and 2 mic’s (DPA4007 and a ISEMcon emx-7150) for this post.

I could use for instance a Roland octa-capture or a 8 channel pre fro MOTU but there’s 1 thing lacking with these unit’s which is gain tracking. If i use the smaart i/o’s i can adjust gain without the spl read-out changing if i do due to gain tracking. For tunings this is not really a issue but come show-time it’s a rather nice feature since the local government down here in the Netherlands can and will give you a fine if you exceed the levels set by them as max SPL dBa or c or both (about 10.000 euro open air Amsterdam city centre).

Set-up.

So first i do a measurement configuration for SMAART. The mic channel is pretty standard (mic vs reference in transfer mode) but i also want to measure the output of the processor.

0001Measurement config inv. processor

If i set the TF measurement on the processor i also tell smaart to invert the trace(plot is set to 1 below that you can invert the trace).

0002Measurement config inv. processor

So now i can start with working on that system. First i eq the low driver to be “flat”.

The first screen shot is the “raw driver” response (black) which i keep visible all trough the eq procedure. The pinkish trace is the inverted trace of the output from the processor channel for that driver.

You might also look at the live IR (the small top window which will change with every eq point i apply). 

001 strt low eq

First eq point on the low driver @422Hz Q:2 –7.5dB. The purple trace is the response of the eq-ed driver. You can also see the impulse response changed because of the eq point.

002 low eq1

I like a bit of “body” in a system so i put in a Low-shelf eq at 100Hz of i think 6dB. By doing this at about 160Hz the purple trace shows a rise in level so gotta take care of that on the next eq point.

003 low eq2

Turned out i needed a –3dB dip @ 185Hz Q:3 to get it towards the 0db line again and as expected the purple trace (the eq-ed driver response) goes to the target (the 0db line again).

004 low eq3

The 500Hz to 800Hz range still needed to come down a bit so the next eq point took care of that 600Hz Q:8 –3dB.

005 low eq4

The next 2 eq points might seem small but they are in the x-over area which is around 1200Hz so i tried to flatten them a bit.

1110Hz Q:8 3db up

006 low eq5

Low eq6: 1220Hz Q:8 –2db.

007 low eq6

And now the High-pass and Low-pass filters and then move on to the high driver.

008 lr4hp 100H

009 low lr4hp100Hz Lr4lp@1200H

As you can see by inverting the processor trace (pinkish) and getting it to about the same as the raw driver response (black) you can flatten the response of a driver(purple).

Move on to the high driver.

It’s the same procedure as on the low driver. Black again is the raw driver response pinkish again the processor output and blue will be the eq-ed driver response.

010 High eq1011 high eq2 shelf012 High eq3013 High eq4014 High eq5

As far as i can remember the manufacturer’s spec with regards to the x-over point was somewhere around 700/800Hz but i choose to go a little higher @1200Hz. (has to do with some of the other products of this manufacturer).

015 high lr4hp 1200Hz

And now the “phase alignment” still has to be done. If i sum both drivers together you see a dip in the frequency response from about 600Hz up to 1K6 which is the x-over area.

In the phase trace you also see a hump a clear sign of both drivers not being properly aligned. To see the problem i need to get solo traces of both drivers and fix this.

016A Sum High low no alignment

Here you see the sum of both and the trace from the low and high driver. Phase takes the middle road since it’s the sum of level and degrees on a frequency basis (no idea if this is correct English sorry i’m Dutch).

016B Sum High low no alignment solo low and high

I do not like to use delay for this kind of an alignment so first i find the spot where both traces are about a 180dg apart which is at 752Hz in this case. This will be my frequency to insert a 2nd order All-pass filter (this will shift the phase with a 180dg).

The low drivers phase trace has a less steep angle so that’s the driver where i have to apply the ap2 filter.

017 Solo traces high low not aligned

By applying the 2nd order all-pass filter the processor trace changes the timing of frequencies on that driver (an x-tra cycle in the phase trace so more group delay).

018 Processor out put low thick line ap2@752Hz

And finally i got a setting on this loudspeaker i consider a good start for using it on a production. It’s tuned to “flat”. This will probably change when it’s put in to action specially around the 2ish to 5ish kHz range bacause of a few fellow’s named fletcher and munson. Has to do with our ears perception of sound at different levels.

The high driver needs some work still but it’s work in progress.

019 A good start

Equipment used here:

SMAART 7.4 – 5 SMAART i/o’s – ALLdsp processing – Vision Acoustics 12”coax cab – Lot’s of coffee (otherwise i’ll not tune anything) – patience.

Regards Timo

5 responses to “EQ’ing a system

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  1. Really interesting and well explained information, Thanks a lot.

    Arnau Pro Audio
  2. Hey Timo, great one! all pass filter trick is very interesting. What about your processor outputs, do you only split the signal with Y-cable?
    Thanks

    gdesbois@gmail.com
  3. Thank you, that’s a good option indeed.

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