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Author Topic: Crossover Help  (Read 1783 times)

John Woodfield

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Re: Crossover Help
« Reply #10 on: December 27, 2012, 12:03:22 am »

This is a pic of the computer screen that hooked up via firewire to the Sl24.

This one is a little closer to the "factory recommended setting"

I'm not worried about that, I'm trying to figure out how you have adjustable Q on your Studiolive when I can't find it on mine.
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Tom Young

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Re: Crossover Help
« Reply #11 on: December 27, 2012, 07:29:45 am »

I'm not worried about that, I'm trying to figure out how you have adjustable Q on your Studiolive when I can't find it on mine.

Perhaps you do not understand the term "Q", which is (sort of) the same as "bandwidth". DSP manufacturers employ either Q or bandwidth, or allow you to select one of these,  in parametric equalizers and (in some cases) high- or low- pass filters and to characterize their shape (width).

Your digital mixer probably displays the filters in fractional octaves and you may be able to change this to display in (or using) Q.

RTFM   ;)

Q employs a mathematically-derived number to describe the sharpness of a resonant circuit (aka: filter) whereas bandwidth is provided as a fractional octave (1/3, 3/4, 1/1, 2/1, etc. ocatve) or with a decimal (0.35, 5.00, 8.00, 1.00, 2.50, etc. octave).  With Q, the smaller the number the wider/broader the filter.

In my experience, the Q of a filter is nonintuitive. But this may be because for several decades (before DSP) the equalizers (and analyzers) we used displayed filters as fractional octaves and I have no reference for Q values burned into my brain. But a 1/3-octave filter, or notch, is inherently easier to visualize than the same thing described as having a Q of 4.32. Right ?

You can find numerous articles on Q, as well as cross-reference charts of Q versus fractional-octave, on the internet. Here are two:

http://www.rane.com/note170.html

http://www.astralsound.com/parametric_eq.htm
« Last Edit: December 27, 2012, 08:17:32 am by Tom Young »
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Tom Young
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Ivan Beaver

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Re: Crossover Help
« Reply #12 on: December 27, 2012, 08:03:23 am »

Ivan,

I mistakenly figured there was a simple formula of where to set the bottoms since the frequency of the tops has already been determined.

When you say "measurements" are you referring to the specs of the boxes or measurements taken in-room?

Volume is not the concern here. The frequency and slopes is what I need to determine.

If you can point me in the right direction, even a starting point that isn't perfect, I'll work with it.
Measurements in the room would be best-as the physical distance between boxes can also greatly affect how the crossovers and delay times are set.

As Jay said-the phase response is one of the main concerns.  You can't get the amplitude right-unless the phase is also right.

Manufacturers curves would be a small start-but generally there is not enough information there to align the different devices-especially when they are from different manufacturers.

Also remember that there is getting it "correct" and close enough.  Most people are happy with "close enough".  Especially since you cannot get it correct for the whole audience at the same time.  You have to choose a seat-(which is most important-the operators seat-the Pastors seat-an average set and so forth) and use that as your basis-and the rest of the room will be "off", but that is part of the compromise of providing audio for more than one person.
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John Woodfield

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Re: Crossover Help
« Reply #13 on: December 27, 2012, 09:02:54 am »

Perhaps you do not understand the term "Q", which is (sort of) the same as "bandwidth". DSP manufacturers employ either Q or bandwidth, or allow you to select one of these,  in parametric equalizers and (in some cases) high- or low- pass filters and to characterize their shape (width).

Your digital mixer probably displays the filters in fractional octaves and you may be able to change this to display in (or using) Q.

RTFM   ;)

Q employs a mathematically-derived number to describe the sharpness of a resonant circuit (aka: filter) whereas bandwidth is provided as a fractional octave (1/3, 3/4, 1/1, 2/1, etc. ocatve) or with a decimal (0.35, 5.00, 8.00, 1.00, 2.50, etc. octave).  With Q, the smaller the number the wider/broader the filter.

In my experience, the Q of a filter is nonintuitive. But this may be because for several decades (before DSP) the equalizers (and analyzers) we used displayed filters as fractional octaves and I have no reference for Q values burned into my brain. But a 1/3-octave filter, or notch, is inherently easier to visualize than the same thing described as having a Q of 4.32. Right ?

You can find numerous articles on Q, as well as cross-reference charts of Q versus fractional-octave, on the internet. Here are two:

http://www.rane.com/note170.html

http://www.astralsound.com/parametric_eq.htm

Tom,

I'm sorry, apparently I'm not being clear enough. We are both using Studiolive boards. I can't seem to find the ability to make my Q settings adjustable on the fat channel or in any options. I can either use a fixed Q or I believe the other option is a HiQ (I'm not in front of my board, they may call it something else) I have never seen the option to have a variable Q like you show on your screenshot.

I posted this same question over on the Presonus forums and I was pretty quickly asked if you are using a SL24. That is probably where the difference is. You're using a SL24 which has some better features compared to my SL16's. If that is indeed the case its another one of those annoying things where I assumed the SL16 and SL24 would both have the same feature set.
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John Woodfield

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Re: Crossover Help
« Reply #14 on: December 27, 2012, 09:08:06 am »

Measurements in the room would be best-as the physical distance between boxes can also greatly affect how the crossovers and delay times are set.

As Jay said-the phase response is one of the main concerns.  You can't get the amplitude right-unless the phase is also right.

Manufacturers curves would be a small start-but generally there is not enough information there to align the different devices-especially when they are from different manufacturers.

Also remember that there is getting it "correct" and close enough.  Most people are happy with "close enough".  Especially since you cannot get it correct for the whole audience at the same time.  You have to choose a seat-(which is most important-the operators seat-the Pastors seat-an average set and so forth) and use that as your basis-and the rest of the room will be "off", but that is part of the compromise of providing audio for more than one person.

I think close enough will suffice in this application. The subs are in line with the tops but the tops are center flown and the subs are at stage level on either side. Time delay aside, I need measurements to set the crossover point in the DSP?

Let me fire up REW today and see what I can report back.
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Tim Perry

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Re: Crossover Help
« Reply #15 on: December 27, 2012, 09:46:56 am »

I guess the fat channel on the 16 is less fat :)
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John Woodfield

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Re: Crossover Help
« Reply #16 on: December 27, 2012, 09:52:01 am »

I guess the fat channel on the 16 is less fat :)


 >:(
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Garry Wilson

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Re: Crossover Help
« Reply #17 on: December 27, 2012, 10:55:20 am »


 >:(

John,

       I bought the 16 first, later bought the 24. The adjustable Q was one of the first feature set differences I noticed. I guess more real estate helped, they also added more control to gating and compression.


Garry W.
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Garry W.

John Woodfield

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Re: Crossover Help
« Reply #18 on: December 27, 2012, 11:35:38 am »

John,

       I bought the 16 first, later bought the 24. The adjustable Q was one of the first feature set differences I noticed. I guess more real estate helped, they also added more control to gating and compression.


Garry W.

I need to buy other board for portable use. I guess it will be the SL24. Glad I figured this out now.

Have fun on your side of the bridge. At least you're closer to Chuck Levin's over there.
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Tom Young

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Re: Crossover Help
« Reply #19 on: December 27, 2012, 12:22:37 pm »

Tom,

I'm sorry, apparently I'm not being clear enough. We are both using Studiolive boards. I can't seem to find the ability to make my Q settings adjustable on the fat channel or in any options. I can either use a fixed Q or I believe the other option is a HiQ (I'm not in front of my board, they may call it something else) I have never seen the option to have a variable Q like you show on your screenshot.

I posted this same question over on the Presonus forums and I was pretty quickly asked if you are using a SL24. That is probably where the difference is. You're using a SL24 which has some better features compared to my SL16's. If that is indeed the case its another one of those annoying things where I assumed the SL16 and SL24 would both have the same feature set.

OK. I did misunderstand your situation and query. My Bad.

But I did not post anything about "my SL24". That was someone else.

BTW - once you have 4 bands of parametric EQ at hand on each input, it is very frustrating to then work with anything less, even "semi parametric" filters.

But you already know this  ;-)
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Tom Young
Electroacoustic Design Services
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