Crossover and EQ advice - 4x T60s and 4x OT12s

EQ guys are using on their cabs/systems. A good starting place if you don't have your own RTA.
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monekh
Posts: 90
Joined: Mon Mar 31, 2014 5:56 pm
Location: London, UK

Crossover and EQ advice - 4x T60s and 4x OT12s

#1 Post by monekh »

Looking for a bit of advice on setting crossovers and eqing the system. We have 4x T60s and 4x OT12s up and running which sound pretty good, but I’m sure with correct treatment could sound better.

As a rookie most of my attempts at understanding what the hell is going on are informed by adjusting a single parameter, auto-eqing and looking at the resultant changes in the auto eq. Certain aspects of the auto eq remain fairly constant regardless of changes to gain or crossovers. These I am assuming are corrections relating to either the driver responses or maybe the room we are testing in. Others definitely vary. The parameters I’ve been adjusting have been:

- Gain (of sub / mid / high bands)
- Crossover frequencies
- Crossover slopes

But I am not really sure in what order to approach them.

My initial approach was to set the crossover frequencies the same on both sides (i.e. sub LP and mid HP both 100Hz, mid LP and top HP both 2kHz), change the gain to match the volume at the crossover frequency, then select the best crossover slope (by inverting the polarity and trying to achieve maximum cancellation). The most cancellation seemed to be achieved with LR48 slopes at both 100Hz and 2kHz.

The issue with this approach was that with the bands level matched at the crossover frequency, the overall response was far from flat, and subsequent EQ had to do a lot of work - extreme boosts and cuts which would be much less drastic with different gain settings. However, changing the gains to a more sensible levels for the EQ would mean they were no longer matched at the crossover points, which would I assume distort the alignment of crossover slopes and render this method of setting the slopes pointless.

My next approach was to set the gains to points that minimised how much the EQ had to do, and resulted in EQ cuts rather than boosts (crossovers still set to LR48 slopes at 100Hz and 2kHz). With the OT12s naturally outpowering the T60s, the EQ only stopped boosting in the sub band (to try and catch up with the other bands) with the mid band reduced by -15dB. In turn, the best level for the high band I found to be -6dB. With these gain settings, the boosts to the EQ were solely in the mid band, at 155Hz, 1kHz and 1.7 kHZ. In the sub band the EQ was scooping out -8dB around 70Hz (but no longer boosting around 30), and in the high band scooping out -8dB around 4kHz.

The bumps in the mid band at 155 and 1.7kHz I think are compensating for cancellations happening at the crossover frequencies, which are being distorted by the mid band gain being so much lower - I have seen posts about how differences in band gain can result in much higher or lower acoustic crossover points than the actual set frequencies. I tried changing the slopes at these points, but this either had no effect or caused an even larger cancellation/boost. I also tried decreasing the sub LP frequency as far as 70 Hz, to compensate for the sub/mid gain differences and hopefully eliminate this boost. To my ears, the system sounded much better like this – less honky/boomy in the upper sub range, generally tighter, though possibly lacking a bit of kick. However, the crossover eq boost remained, though it moved lower (to around 118Hz). There was also an additional boost between the crossover frequencies, around 90Hz.

I am unsure of the maths involved in factoring in the -15dB difference between sub and mid to calculate how low to move the sub LP crossover frequency to achieve an acoustic crossover of 100Hz (with LR48 slopes). Will try and figure this out... unless someone has a quick explanation at the ready…

Anyway, anyone who read this far – I salute you!
Any tips greatly appreciated.

sine143
Posts: 3066
Joined: Sat Feb 06, 2010 3:27 pm
Location: Raleigh NC

Re: Crossover and EQ advice - 4x T60s and 4x OT12s

#2 Post by sine143 »

dont use 48 db/octave slopes.

I would lower the slope to 24 db/octave, and drop your lopass for the subs down to about 80-90 (the rising response of the t60s moves the acoustic crossover point above the actual frequency you set the lopass, and in most cases, you run the subs at a higher level than the mains, which will move the acoustic crossover up a bit as well)

the only eq I would suggest on subs is potentially a hishelf set to about 100hz, dropping between 1-5 db to taste.

It sounds like you are using the autoeq, remember that indoors, you are mostly just correcting the in room response at that particular mic position (moving the mic, or changing the room will change your autoeq results).
Built:
2x Tuba 30s delta12lf loaded (gone)
4x Otop12 d2512 loaded
8x t48s (18, 18, 24, 24, 30, 30) 3015lf loaded
2x AT (1 mcm, 1 gto 804)
2x SLA Pro (dayton pa6, 6 goldwood piezo loaded)
1x bastard XF208

2x OT212 (delta pro 450a loaded, eminence psd)

monekh
Posts: 90
Joined: Mon Mar 31, 2014 5:56 pm
Location: London, UK

Re: Crossover and EQ advice - 4x T60s and 4x OT12s

#3 Post by monekh »

thanks sine

I'm trying out 24 slopes / lower sub crossover and hishelving the sub instead of the cut the auto-eq suggests.
I hadn't considered the rising response, definitely makes sense to hi shelf. Would you advise a shallow or steep slope on that? I'm guessing it interacts with the crossover filter to a certain extent.

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allroundFX
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Location: Netherlands

Re: Crossover and EQ advice - 4x T60s and 4x OT12s

#4 Post by allroundFX »

Here is my measurement of the otop12 with piezo 10x array and Delta pro 12a. Taken indoors at 1.9m height, 75db, mic at one meter distance.
The images are with eq applied.

Measurement with EQ applied:
Image

EQ settings:
Image
Famous BFM quotes: "Zobels are for those who don't know how to design crossovers"

wbredin
Posts: 32
Joined: Thu Jun 17, 2010 9:36 pm

Re: Crossover and EQ advice - 4x T60s and 4x OT12s

#5 Post by wbredin »

Hey I know this is an old thread, but i'm looking for advise on how to EQ my 4 Otop12's with 3012HO's and a CD driver. Is there anyway you could upload your EQ settings pic again? it won't load for me...

Grant Bunter
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Re: Crossover and EQ advice - 4x T60s and 4x OT12s

#6 Post by Grant Bunter »

wbredin wrote: Sun Apr 30, 2023 12:53 pm Hey I know this is an old thread, but i'm looking for advise on how to EQ my 4 Otop12's with 3012HO's and a CD driver. Is there anyway you could upload your EQ settings pic again? it won't load for me...
That Users last activity was in 2017. Good luck getting a response...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" KL3010LF , 2 x 28" 3012LF.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

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