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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Subwoofer Forum => Topic started by: Canute J. Chiverton on January 24, 2017, 10:33:17 AM
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I have a question relating to the Cardoid Setup for Subs as seen in the Photo from an EV Roadshow here in Houston.
Does this design give added db because the subs are in a sense "coupled" or is the design strictly for cancellation from behind? Thanks
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This design offers a bit of both coupling going forward and cancelation in the real. Also referred to as a gradient array, or reverse end fired.
Some trade offs with this array design: it doesn't sound as good as end fired however offers broadband reduction in the rear.
Where, end fired sounds better but only offers max reduction at a target frequency (two deep).
If you have the opportunity, create the two and have a listen.
https://timobeckmangeluid.wordpress.com/2011/11/14/the-gradient-sub-array-or-reversed-end-fired-as-i-call-it-english-only/
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When you use directional subs (either endfire or cardioid), the output will be LESS than the same number of subs placed side by side or on top of each other.
So for 2 subs the output in a directional configuration will be greater than a single sub, and less than 2 subs in a normal configuration.
Some people are spreading the false hood that directional subs produce MORE output than the same number normally setup.
Their "theory" (which has no data or evidence) is that the cancelled sound is somehow wrapped around to the front and added to the front sound.
WHere do they get these ideas----------
Just because you "want" it to do that DOES NOT mean that it will :(
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Thank you Ivan Beaver
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Thank you Chris Tsanjoures
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Heres a couple of dave ratt videos explaining types and setups
https://www.youtube.com/watch?v=VwLH7zP6Lwo
https://www.youtube.com/watch?v=B-3pURYOwfw
https://www.youtube.com/watch?v=aSZK9Altvm8
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I have a question relating to the Cardoid Setup for Subs as seen in the Photo from an EV Roadshow here in Houston.
Does this design give added db because the subs are in a sense "coupled" or is the design strictly for cancellation from behind? Thanks
If I have three subs per side and want to use one backward/reversed phased/delayed for rear cancellation, is it best positioned side-by-side in the middle, in the middle stacked vertically, or on the bottom stacked vertically? Or does it matter at all?
I have tried the setup pictured live and found that there seems to be just a little more in front. But I didn't really find that much cancellation in the rear. I'm hoping to spend more time experimenting with these setups but as I don't have any measurement tools like Smaart (and don't really have the know-how to use them) it will be all by ear.
--Kevin
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If I have three subs per side and want to use one backward/reversed phased/delayed for rear cancellation, is it best positioned side-by-side in the middle, in the middle stacked vertically, or on the bottom stacked vertically? Or does it matter at all?
I have tried the setup pictured live and found that there seems to be just a little more in front. But I didn't really find that much cancellation in the rear. I'm hoping to spend more time experimenting with these setups but as I don't have any measurement tools like Smaart (and don't really have the know-how to use them) it will be all by ear.
--Kevin
It depends on where you want the cancellation notch to be.
If you want it straight to the rear-then vertically stack.
If you want it a little bit to one side or the other, you put them side by side.
YES, it does make a difference.
There should have been a good bit of reduction in the rear.
Did you have the proper delay-polarity set on the proper cabinets-along with the proper spacing?
It takes all three setup correctly-delay-polarity and spacing to get the idea to work.
Were there any boundaries nearby? That will start to throw things off a bit.
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It depends on where you want the cancellation notch to be.
If you want it straight to the rear-then vertically stack.
If you want it a little bit to one side or the other, you put them side by side.
YES, it does make a difference.
There should have been a good bit of reduction in the rear.
Did you have the proper delay-polarity set on the proper cabinets-along with the proper spacing?
It takes all three setup correctly-delay-polarity and spacing to get the idea to work.
Were there any boundaries nearby? That will start to throw things off a bit.
Thanks Ivan -
Yes, there were hard 'theater wings' nearby. I didn't expect much and I got that :). I'll play with it a bit more, but yes I had the subs (2 per side) positioned as in the first post picture, reversed bottom one, and out of phase and delayed about 3.5ft. Trying to cancel around 80hz.
Again, seemed to help a bit with stage rumble, seemed to be a tiny bit easier to get more kik and low bass guitar in the house. Last time at that venue I just used one sub per side. So I had a bit of comparison as it was also the same band and about the same audience headcount.
--Kevin
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You may have had better luck delaying the forward facing sub for maximum rear rejection.
3.5' is quite a bit considering the drivers are only about 1' apart. Keep in mind the rear facing sub is essentially trying to place energy in the forward direction. So it was at that point roughly 4.5' delayed in respect to the forward direction with 3.5' of delay.
If you delayed the front sub to line up with the sound that would " wrap around " from the rear facing sub, you would have 2' or more of time difference in the rear, but the sound on the front side would be coupled and in phase. If you were to delay the front so it was 180* from the rear, but in phase with it, you would have maximum rear rejection with the sound in the front only being off by part of a cycle. That is to say the sound from the rear facing sub would lead before the front one, but as the sound comes out of the front sub it would be in phase with the rear still. The rear would be 180* out at all frequencies and you should have maximum rejection.
When you delay the rear facing speaker it is usually done in arrays of three. This is because you can use it to tune out a specific range of frequencies in the rear and it's major effect of the front side is not as bad. You can also tune the front to be in time with the rear facing subs forward energy and it would couple in the forward plane, but have reduced or less controlled rear rejection.
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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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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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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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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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"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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"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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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 -
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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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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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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