Using a 31 band Eq

EQ guys are using on their cabs/systems. A good starting place if you don't have your own RTA.
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hermanmonker
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Using a 31 band Eq

#1 Post by hermanmonker »

This might sound like a stupid question but using the spl charts as a reference curve for setting the 31 band eq ,where on the spl chart is considered 0 to coinside with the 0 on the eq unit.

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BrentEvans
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Re: Using a 31 band Eq

#2 Post by BrentEvans »

Draw a line horizontally on the graph such that the area between the curve and your line is roughly equal both above and below the line.
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Rich4349
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Re: Using a 31 band Eq

#3 Post by Rich4349 »

More noob questions:

I am running a pair of DR250s on one channel of a Crown XTi4000 and a pair of T-39s on the other, mono of course. Would it be possible / an accepted way to run the line signal through a single channel EQ BEFORE getting to the XTi? This way the lower end of the EQ could control the Titans, the rest controlling the DRs. I was about to pull the trigger on a Rane or DBX 31 band EQ, but then the thought came to me (uh-oh) that most bands of both channels will go unused / unneeded for the uninvolved freq portion. Will a single channel EQ work for controlling highs and lows?

thanks
Rich
2 DR250s, 2 27" Lab15 T-60s, 2 30" Neo Titan 39s, 1 Autotuba...and looking for more!

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Bill Fitzmaurice
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Re: Using a 31 band Eq

#4 Post by Bill Fitzmaurice »

Rich4349 wrote: Would it be possible / an accepted way to run the line signal through a single channel EQ BEFORE getting to the XTi? This way the lower end of the EQ could control the Titans, the rest controlling the DRs.
That's the usual method.

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Re: Using a 31 band Eq

#5 Post by Rich4349 »

Would there be any benefit of HAVING a 2 channel EQ (for some kind of expansion down the line that I don't know of now) ?
2 DR250s, 2 27" Lab15 T-60s, 2 30" Neo Titan 39s, 1 Autotuba...and looking for more!

Gregory East
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Re: Using a 31 band Eq

#6 Post by Gregory East »

You should have eq already. Tweak your xti for flat overall and use the eq for correcting rooms. Two channels of eq can cover mono foh and a monitor mix if you're doing bands.
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Rich4349
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Rack placement

#7 Post by Rich4349 »

Yes, I'm aware of the XTi's great capabilities. I find its PC interface (System Architect) to be a kind of laborious to change, from song to song, compensating for recording differences. But doing what you say, using setting the XTi, like the course focus on a microscope, then using the EQ like fine focus, sounds much better. I, personally, much prefer a good old analog slider to a mouse and keypad. Adding 2-3 Hz here and there is incredibly flexible, but equally tedious.

While we're at it: is there any method to the madness of placement of rack gear in the rack? Amps up top, so the heat doesn't build up / stays insulated in by EQs or other components?

And has anyone heard of the brand HQ? Decent brand? I'm looking at an HQ-231 ?
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Bruce Weldy
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Re: Rack placement

#8 Post by Bruce Weldy »

Rich4349 wrote:Yes, I'm aware of the XTi's great capabilities. I find its PC interface (System Architect) to be a kind of laborious to change, from song to song, compensating for recording differences. But doing what you say, using setting the XTi, like the course focus on a microscope, then using the EQ like fine focus, sounds much better. I, personally, much prefer a good old analog slider to a mouse and keypad. Adding 2-3 Hz here and there is incredibly flexible, but equally tedious.

While we're at it: is there any method to the madness of placement of rack gear in the rack? Amps up top, so the heat doesn't build up / stays insulated in by EQs or other components?

And has anyone heard of the brand HQ? Decent brand? I'm looking at an HQ-231 ?
Amps on bottom, lighter stuff on top - don't want 'em top heavy. The amps are fine in the bottom.

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"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Re: Using a 31 band Eq

#9 Post by Rich4349 »

Ok, so I picked up a dual 31 band EQ (Ashly GQX 3102) to use with my
XTi 4000,
a pair of T-60s (OR pair of 30" wide T-39's)
a pair of DR250s

1) I'm working on figuring out limiting, to keep it under 50v to the Tubas. Does it stay at 50v for 2 Tubas in parallel? It couldn't jump to 100, or most amps wouldn't be able to supply that, right?

2) I've read all about maxing out the amp gain knobs, then dropping down until you hit your voltage (IIRC). BUT, that damn Ashly eq has SO MUCH gain potential, between the individual frequency sliders, the 6 / 15 db boost buttons, and the 6 db gain slider, I don't know HOW to keep the voltage under control. There is also volume on my pc, on the player interface on my pc, as well as all of the multiple places to boost in System Architect. If I boosted all of those up, the Xti gain knob would be 1 click off of 0, and would probably still clip!

I guess I probably need one of those spectrum analyzers, such as:

http://www.parts-express.com/pe/showdet ... er=245-262 or

http://www.parts-express.com/pe/showdet ... er=390-792

Man, I'm getting tired of 'needing' yet another $300-1100 piece of equipment. I just read (Nordo's opinion):

"When EQing, reduce the peaks but try not to boosts the dips - you will use up all your amps headroom. Just work on the peaks. "

but then Gregory East said:

"The correct way to Eq is to average the cutting and boosting. If your amp is out of headroom turn down your mixer or the eq output, whichever is appropriate. By only cutting you lose the headroom in your eq unit."

Help, I'm in the weeds with this! (no, not ON the weed!)

Rich
2 DR250s, 2 27" Lab15 T-60s, 2 30" Neo Titan 39s, 1 Autotuba...and looking for more!

Bruce Weldy
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Re: Using a 31 band Eq

#10 Post by Bruce Weldy »

All you need to set the limiter is a $10 voltmeter (or $5 if you find one on sale).

Since the EQ will be in front of the amp, it doesn't matter what you do with it - the amp will limit what comes out the backside (outputs).

Run the amps knobs all the way up, set the EQ gain at unity (usually 12 o'clock). Use a 60hz tone to run your mixer up to unity (or light into the first light past green), then using your voltmeter on the outputs of the amp (no speaker attached), set the limiter until it is at your threshold. Once there, push the master fader on the mixer all the way into the red. The voltmeter should have the same reading as before if the limiter is working properly.

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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BrentEvans
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Re: Using a 31 band Eq

#11 Post by BrentEvans »

What you're talking about is called gain structure. To set this, I like to think about working backwards from the speakers one step at a time. You want as much of your gain as possible to come from your amps. This is why we set limiters with the amps wide open. Work backwards from there, setting everything at unity gain... try not to use any boosts or cuts if you can. The last step would be your mic pre trims, which are usually the noisiest part of the system. If you keep your trims low, and pass unity gain all the way to the amps, you will have the lowest system noise you can have. Then, if you have to scale down, you can always turn the amps down (or turn down anywhere along the signal chain), and not have to worry about clipping anything.
99% of the time, things that aren't already being done aren't being done because they don't work. The other 1% is split evenly between fools and geniuses.

Rich4349
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Re: Using a 31 band Eq

#12 Post by Rich4349 »

At this moment I have a Lab 15 T60 hooked up to Ch1 (the preset lower end) of my XTi4000. The Lab is 6 ohms, the cabinet adds 2 more. (I realize this is not a static number; varying with frequency.) At 8 ohms, the XTi makes 650 watts (ok, 72 volts) (theoretical) max power. The Lab is rated for 600 constant, 1200 max.

(I don't understand why, unless the gain knob were cranked up near its limit, ANY clipping should happen. Is this due to the varying power spikes amps make, and why you never bridge an amp, unless it's drastically underpowered?)

I'm reading The Yamaha Sound Reinforcement Handbook, and it's sort of helping. The XTi CAN make 72 v, but I want, say, 50.
72/50=1.4.
Log 1.4 X 20 = 2.922

SO...does that mean since the Lab 15's power rating is so close to the max the XTi makes (at that resistance) that I only need to use the 3 dB limiter setting?
2 DR250s, 2 27" Lab15 T-60s, 2 30" Neo Titan 39s, 1 Autotuba...and looking for more!

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BrentEvans
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Re: Using a 31 band Eq

#13 Post by BrentEvans »

The knobs on the front of the amps are input trims, nothing more. Even if they're on the first detent, you can drive the amp with such a hot signal that it will clip the input stage, output stage, or both.

To set your limiters, supply tone to the amps sufficient to clip the output stage, then reduce the limiter incrementally until you reach the desired voltage on the outputs (provided in the plans, not calculated from anything else), meausured with an AC voltmeter connected to the terminals, and no speakers attached. By doing this with the gain knobs all the way up, you guarantee that the gain structure is most favorable.
99% of the time, things that aren't already being done aren't being done because they don't work. The other 1% is split evenly between fools and geniuses.

Rich4349
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Re: Using a 31 band Eq

#14 Post by Rich4349 »

I ran pink noise through the T-60, at -12, -6, and -3 db. There was a gradual increase of meter lights, but it never clipped. I didn't run it without any limiter on it, as I have for neighbors the only 25-35 year old single guys who DON'T appreciate or tolerate loud sounds. I then ran these same settings, without a driver, and checked the voltage across the terminals. The max at ALL of these limiter settings was right around 18v. Yes, the gains on player, pc, everything was wide open. So where is this alleged 72 volts that I'm afraid of lurking?

(And white noise, at 18v in a T-60, sounds like standing at the bottom of Niagara Falls!)
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Grant Bunter
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Re: Using a 31 band Eq

#15 Post by Grant Bunter »

Rich,
You have to make the limiter engage!
Transient spikes may be 10 x greater than your multimeter reading, ie you get a reading of 18V but there may be a (albeit very brief) transient of 180V. That's what you are trying to stop with the limiter...
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