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Author Topic: Cardoid Design for Sub setup.  (Read 9361 times)

Tim McCulloch

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Re: Cardoid Design for Sub setup.
« Reply #10 on: February 17, 2017, 01:50:58 PM »

Hi Kevin-

The "in a nutshell" explanations-

A)  you need clearance of 1/4 wavelength to the sides and ideally > 1/2 wavelength behind the array for a "reversed box, polarity flipped & delayed" array to function correctly.  The wavelength in question is of the frequency you want the greatest cancellation.

B)  if you have only 2 subwoofers per array, Ivan's comments are spot on.

C)  if you have 3 per side the most common deployment is to stand the subs up (longest face dimension vertical) and put the reversed sub in the middle.  If you have to lay them on the side, put the reversed sub on the bottom.  This will give the most even coverage.

D)  test and verify that your cancellation freq (delay time) is correct as obstructions (or horizontal length of the array) can change the physical path length and hence the cancellation frequency.
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Kevin_Tisdall

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Re: Cardoid Design for Sub setup.
« Reply #11 on: February 17, 2017, 02:27:04 PM »

Luke G. -

I'm going to have to read that a few times to have it sink in.  I get the general idea, but the perspective of which to delay is counter to everything I've read so far (I think :)).    I'm very slowly starting to firm up the concepts in my head.  When it's a bit warmer around here I hope to play with this outside .

Tim McC. -

Thanks for that also. Especially "A".   Again, I'll need to fiddle with this to make it sink in.  Fortunately the boxes are really small (EV ZXA-1Sub).   Smaller than the ones pictured at the top of this thread but very good for the tiny gigs I do and for me to learn a bit about the way larger systems work. 


--Kevin
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Ivan Beaver

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Re: Cardoid Design for Sub setup.
« Reply #12 on: February 17, 2017, 02:32:50 PM »

You may have had better luck delaying the forward facing sub for maximum rear rejection.


Actually you will be maximum rear rejection when in the "Cardioid" mode vs the End fire.

Cardioid delays the rear sub and has the rear sub inverted polarity.

End fire has both in polarity and the front one delayed.

Cardiod has the most rear rejection, and has less "punch/impact out front due to the higher freq of the bass region being cancelled.

Endfire has the best sonic character (like a single box), but does not have as much rear rejection or as wide a cancellation bandwidth as the cardioid setup.

Both need around 4' separation (for a starting point) from the sound source of one cabinet vs the other.
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John L Nobile

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Re: Cardoid Design for Sub setup.
« Reply #13 on: February 17, 2017, 02:45:13 PM »

Actually you will be maximum rear rejection when in the "Cardioid" mode vs the End fire.

Cardioid delays the rear sub and has the rear sub inverted polarity.

End fire has both in polarity and the front one delayed.

Cardiod has the most rear rejection, and has less "punch/impact out front due to the higher freq of the bass region being cancelled.

Endfire has the best sonic character (like a single box), but does not have as much rear rejection or as wide a cancellation bandwidth as the cardioid setup.

Both need around 4' separation (for a starting point) from the sound source of one cabinet vs the other.

That answered my question which I was about to post. I was going to ask what advantages one method had over the other.

I have 2 subs that I setup last week in an end fire array for the first time. I played with it a bit but haven't used it on a real gig yet. I don't have any acts in the room for another 5 weeks.

I did like the initial results. Much less bass on stage and in front of them. I was killing the front row with bass before. I was thinking of trying cardioid while I have some time. However the reduced bass on stage with endfire is enough but the selling feature is the reduced bass in front.

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Kevin_Tisdall

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Re: Cardoid Design for Sub setup.
« Reply #14 on: February 17, 2017, 03:44:21 PM »

"Both need around 4' separation (for a starting point) from the sound source of one cabinet vs the other."

Ivan -

This sounds like a conflict of what was discussed above.   Essentially you are saying that the setup in the original thread post above won't work?

This is why I am confused - there are all sort of theories on this.  But I know you know the physics.

I really never have the room for endfire array and usually need more cancellation.   My focus is on the gradient / reversed-phased-delayed cardioid setup.   In that case, the boxes need to begin by being 4ft apart??

--Kevin

 
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Ivan Beaver

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Re: Cardoid Design for Sub setup.
« Reply #15 on: February 17, 2017, 04:09:07 PM »

"Both need around 4' separation (for a starting point) from the sound source of one cabinet vs the other."

Ivan -

This sounds like a conflict of what was discussed above.   Essentially you are saying that the setup in the original thread post above won't work?

This is why I am confused - there are all sort of theories on this.  But I know you know the physics.

I really never have the room for endfire array and usually need more cancellation.   My focus is on the gradient / reversed-phased-delayed cardioid setup.   In that case, the boxes need to begin by being 4ft apart??

--Kevin
The "theory" is that the spacing is 1/4 wavelength and the delay match the spacing.

4' is 1/4 wavelength of 70Hz.  Kinda the "center" of bass-if you are looking at 40-100Hz being the sub region.

OF course if you want to move the cancellation lower-you need larger spacing and more delay.

As usual-it STARTS with defining what you are "looking for".

THEN designing the system towards that goal.

NOT, taking a setup and "hoping" it will work for a particular situation.

But understanding HOW it works, and what the variables are is VERY IMPORTANT in any sound system DESIGN.  Vs the LAR (Looks About Right) method that most people use.
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Kevin_Tisdall

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Re: Cardoid Design for Sub setup.
« Reply #16 on: February 17, 2017, 04:20:07 PM »

The "theory" is that the spacing is 1/4 wavelength and the delay match the spacing.

4' is 1/4 wavelength of 70Hz.  Kinda the "center" of bass-if you are looking at 40-100Hz being the sub region.

OF course if you want to move the cancellation lower-you need larger spacing and more delay.

As usual-it STARTS with defining what you are "looking for".

THEN designing the system towards that goal.

NOT, taking a setup and "hoping" it will work for a particular situation.

But understanding HOW it works, and what the variables are is VERY IMPORTANT in any sound system DESIGN.  Vs the LAR (Looks About Right) method that most people use.

Ivan -

So what you are saying is, the setup pictured at the top of this thread would not work to cancel low freq effectively?

I'm not looking to stack up a bunch of stuff, make several fancy settings and call it good.   I'm trying to find out if what I'm seeing here on PSW and being shown as a way to effectively manage low frequency behind subs is actually effective.

If the boxes need to be 4' (or whatever distance per desired cancellation) apart, then also reversed, out of phase and time-delayed, so be it.  But that isn't what is pictured and given as the solution in the first thread post.    In most cases I don't have the space so I can just forget about implementing that way unless an unusual situation arises.

Again, I appreciate the discussion and education.

--Kevin
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Ivan Beaver

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Re: Cardoid Design for Sub setup.
« Reply #17 on: February 17, 2017, 05:01:33 PM »

Ivan -

So what you are saying is, the setup pictured at the top of this thread would not work to cancel low freq effectively?

I'm not looking to stack up a bunch of stuff, make several fancy settings and call it good.   I'm trying to find out if what I'm seeing here on PSW and being shown as a way to effectively manage low frequency behind subs is actually effective.

If the boxes need to be 4' (or whatever distance per desired cancellation) apart, then also reversed, out of phase and time-delayed, so be it.  But that isn't what is pictured and given as the solution in the first thread post.    In most cases I don't have the space so I can just forget about implementing that way unless an unusual situation arises.

Again, I appreciate the discussion and education.

--Kevin
It is all a mater of compromise.

I "highly suspect" (but have not measured) the setup in the OP would not cancel down very low.

But then again-the speakers don't go real low-so there is no need to cancel something that is not there.

The setup in the OP will cancel some of the bass freq-and often that is enough to impress people.

So if material is played that doesn't go low, it could be impressive.

You have to trade one thing for another.  In this case you get a smaller footprint-at the expense of deep bass-which may be fine.

As with any most any audio question, it must be followed by "At what freq?"

THAT starts to change everything when you realize that we are dealing with a 1000:1 ratio.

I am not aware of another industry that has that large of a ratio.

For example the lighting guys deal with less than 2:1.

Most of the RF guys are a little over 2:1 for specific ranges.

You CANNOT apply what happens at the higher end of our spectrum to the lower freq and vice versa.

They are very different animals.
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Luke Geis

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Re: Cardoid Design for Sub setup.
« Reply #18 on: February 17, 2017, 11:24:08 PM »

Cardiod, end fire, depending upon application, is roughly the same, but with different setup approaches. One is not the other, but the other can sorta be both.
Examples:

1. An endfire array is one where the subs are placed in a row with one in front of the other. The speaker furthest back is the starting point and each sub thereof is delayed so that it is in time and phase with that sub. The forward energy is all in exact phase and will couple. The energy in the rear is out of phase and cancellation occurs. This takes space and lots of subs to achieve the goal. The spacing of the subs determines which frequency will have the most rejection. 4' is usually a good starting point.

2. A cardiod array has the speakers grouped together in stacks of three ( typically ) with the center speaker facing backwards and the polarity inverted. The typical approach to this method is to delay the rear facing speaker in order to tune for the desired maximum rejection. The downside is that the rearward facing speaker is out of phase with the forward facing ones and does not couple with them. The slight delay in sound from that sub also smears the audio a little, but due to the fact there is a 2X the forward facing energy that is in phase, the effect it has in front is not as drastic.

3. The cardiod cluster end fire array. Just like above ( #2 ) you place the subs in a group with one facing backwards. Instead of delaying the rear facing speaker, you delay the forward facing ones so that they line up in phase with the rearward facing subs ( remember this sub has reversed polarity ) forward energy. This allows full coupling in the forward direction, but less controlled rejection in the rear of the array. This is the method that is more or less a hybrid of 1 & 2. The spacing of the subs will again determine the point of maximum rejection in the rear.

You CAN create a cardiod sub array with only two subs, but for best results, option #3 is probably the way to go. With only 2 subs you should desire to make it so that forward energy is preserved as much as possible. If you tune for maximum rearward rejection with only 2 subs, you will have diminished performance in the forward direction because the sound you hear will be out of phase and at nearly equal amplitude ( ala comb filtering ). It will be a matter of compromise.

Using a cardioid array with only 2 subs has one other advantage. If you tune the rear facing subs to be 180* out to the front facing one, there will be maximum rejection at all frequencies in the rearward direction. This will hinder forward performance though as there will be comb filtering due to the out of phase signal in the forward direction. For example: If you delay the rear facing sub by 1' ( assuming the drivers have 1' between them ) it would be in exact time with nearly the same energy coming from the front facing sub, but would be out of phase by 180* ( because the rear sub has reversed polarity ). The energy out front would be off by 2' though for that rear facing sub. It would actually couple pretty well below about 100hz because it would be within 1/4 of a wave length, but above 100hz it would not be and more comb filtering would be noticed.
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Merlijn van Veen

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Cardoid Design for Sub setup.
« Reply #19 on: February 18, 2017, 01:47:56 AM »

2. A cardiod array has the speakers grouped together in stacks of three ( typically ) with the center speaker facing backwards and the polarity inverted. The typical approach to this method is to delay the rear facing speaker in order to tune for the desired maximum rejection. The downside is that the rearward facing speaker is out of phase with the forward facing ones and does not couple with them.

Coupling implies time offsets of 120 deg or less.

Both in-line and inverted stack gradient are coupling in the front but 1/3 cycles to 2/3 cycles out of time.

The ratio of front and back facing subwoofers should be adjusted to offset differences in the polar plot of a single speaker and whether near- or far-field cancellation is required. Clean stage or clean environment.



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Cardoid Design for Sub setup.
« Reply #19 on: February 18, 2017, 01:47:56 AM »


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