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How To......Cardioid Sub Arrays
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jeddere View Drop Down
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    Posted: 10 May 2022 at 10:14am
Summation at the front will be roughly 1.5 dB below what you would have if you faced all 3 cabinets forward, with up to approx. 6 dB ripple in the response as some frequencies will be closer in phase than others when comparing the signal propagating forward from the rear facing and front facing cabinets.

The delay time that you set needs to be long enough so that you do not get cancellation out front at the lowest frequency your cabinet will play. This means making sure that the signal out front from the rear facing and forward facing cabinets has a phase difference of less than 120 degrees either side of 360 degrees. For example:
Cabinet low cut off: 30 Hz
Period (time taken for 1 wavelength of 30 Hz), T=1/f = 33 ms
120 degrees at 30 Hz = (120/360) x 33 = 11 ms
The rear signal is 180 degrees out of phase (polarity flipped) = (180/360) x 33 = 16.5 ms
When this combines with the signal from the front facing cabinets it needs to be at least 33-11 = 22 ms behind them. This will then sum with the signal from the front facing cabinets, but 1 phase wrap later.
There is already 16.5 ms of delay, or offset due to the polarity flip, so only another 22-16.5 = 5.5 ms is required.
The rear facing cabinet is delayed twice by the time its signal combines on the frontside, once by the delay setting in LMS and once by the physical path length. Therefore the minimum delay setting is 5.5/2 = 2.75 ms.

TLDR: If you end up with a delay setting for the rearward facing cabinets of less than about 3 ms then the bottom end of the bass frequencies are not going to sum as well as they could out front. Solution: move the rear facing cabinets backwards to increase the physical path length delay to about 3 ms.


Edited by jeddere - 10 May 2022 at 12:50pm
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dymondaudio View Drop Down
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Originally posted by jeddere jeddere wrote:

Originally posted by dymondaudio dymondaudio wrote:

So… flip the centre sub, reverse its polarity and delay it by the distance between the rear driver and the drivers in front. 

Is this it or have I missed something? (Seems too simple!)

That is essentially it however the required delay will not be exactly equal to the measured direct path difference. Ideally you would setup up a mic behind the speakers (where you want the cancellation to occur) and measure the forward facing speakers to get a phase response. Then measure the rearward speaker (polarity reversed) and adjust the delay until they are 180 degrees out of phase. Alternatively stand some distance behind and adjust the delay until it is quietest. I've not tried this but I'd start with the measured path difference and increase from there.

Summation on the front side is not going to be perfect but you are sacrificing sound quality out front to get the reduction behind.

EDIT: to avoid confusion my reply relates to a inverted type of cardoid bass array which it seems you are proposing. Other posts earlier in this topic relate to different types of cardoid bass array.

Thanks for this :)

To clarify regarding summation at the front, as long as I'm not going to loose output at the front then it's fine.  Main concern is rejection behind the system.
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Originally posted by dymondaudio dymondaudio wrote:

So… flip the centre sub, reverse its polarity and delay it by the distance between the rear driver and the drivers in front. 

Is this it or have I missed something? (Seems too simple!)

That is essentially it however the required delay will not be exactly equal to the measured direct path difference. Ideally you would setup up a mic behind the speakers (where you want the cancellation to occur) and measure the forward facing speakers to get a phase response. Then measure the rearward speaker (polarity reversed) and adjust the delay until they are 180 degrees out of phase. Alternatively stand some distance behind and adjust the delay until it is quietest. I've not tried this but I'd start with the measured path difference and increase from there.

Summation on the front side is not going to be perfect but you are sacrificing sound quality out front to get the reduction behind.

EDIT: to avoid confusion my reply relates to a inverted type of cardoid bass array which it seems you are proposing. Other posts earlier in this topic relate to different types of cardoid bass array.


Edited by jeddere - 09 May 2022 at 5:59pm
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Originally posted by VECTORDJ VECTORDJ wrote:

K.I.S.S........DSP and Digital Mixers have allowed for so much more adjustment then ever before.......Maybe too much...A Friend does Sound and uses EVERY button of his gear...Time delay the Drums to the mains, Gates, Compressor, EQ, Effects on every channel...Some rear facing subs...etc, etc, sounded like Dog Shit.....I went to one of His Shows and turned off most of that stuff...Used Gates on Drums, 2;1 Compressor on Vocals, and a very small amount of EQ and Reverb on Vocals....WOW! His system delivered cranking Sound....He was over Thinking Sound....Sometimes K.I.S.S. is the Best.....

I understand what KISS means and I completely agree with you regards to keeping the signal chain clean etc. but this is not what I'm suggesting here. 

I'm looking to set-up cardioid subs to mitigate/reduce a possible noise complaint issue, not because I think it's fashionable ;)
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Originally posted by dymondaudio dymondaudio wrote:

Originally posted by VECTORDJ VECTORDJ wrote:

K.I.S.S.

Could you expand on this, is what I'm saying correct?

I'm going for it being an acronym for keep it simple stupid. Or maybe he was listening to the hair metal band. Either way very helpful lol
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K.I.S.S........DSP and Digital Mixers have allowed for so much more adjustment then ever before.......Maybe too much...A Friend does Sound and uses EVERY button of his gear...Time delay the Drums to the mains, Gates, Compressor, EQ, Effects on every channel...Some rear facing subs...etc, etc, sounded like Dog Shit.....I went to one of His Shows and turned off most of that stuff...Used Gates on Drums, 2;1 Compressor on Vocals, and a very small amount of EQ and Reverb on Vocals....WOW! His system delivered cranking Sound....He was over Thinking Sound....Sometimes K.I.S.S. is the Best.....
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Originally posted by VECTORDJ VECTORDJ wrote:

K.I.S.S.

Could you expand on this, is what I'm saying correct?
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K.I.S.S.
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Originally posted by FOO FOO wrote:

The easy way... Nexo CD18, or if your budget is low'ish, Nexo CD12. 
CD18 is a mean piece of kit! But you need some hands to throw them around. Big Box with Big Sound!
CD12 on the other hand.. That is a fun little box which pack quite a good punch without being fridge sized LOL

Was this posted in the correct topic?
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The easy way... Nexo CD18, or if your budget is low'ish, Nexo CD12. 
CD18 is a mean piece of kit! But you need some hands to throw them around. Big Box with Big Sound!
CD12 on the other hand.. That is a fun little box which pack quite a good punch without being fridge sized LOL


Edited by FOO - 08 May 2022 at 5:33pm
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Sorry for dragging up an old thread but I think most of the contributors are still active members. 

I am starting to get into sub arrays and am looking to do a simple set up for a gig in a couple of weeks

My aim is to reduce bass behind the speakers as there are premises quite close by. 

The venue is a big tent. 

I will be using three 18” reflex subs each side of the stage (this is the only config available because of the venue set-up)

So… flip the centre sub, reverse its polarity and delay it by the distance between the rear driver and the drivers in front. 

Is this it or have I missed something? (Seems too simple!)

Cheers all


Edited by dymondaudio - 08 May 2022 at 12:55pm
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How does this works out with horn coupling & mouth area?

If I reverse 2 in a stack of 6 bandpasshorns (bph) will the reversed box uncouple?

If I do end fire distance have to be kept big enough not to "stuff" horn mouth (negative expansion).

I guess end fire could make rear horns see a bigger horn or a corner, front stack is delayed to couple.

I can't really figure out what happens to 2 reversed boxes and the horn coupling? Will it overexcurt fron cancelation or the opposite couple the delayed half wave from front? I'm a little worried about this, no drivers to waste.
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