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[Canute J. Chiverton]

I was amazed at this Demo and Configuration. It is called the Cardiod. The Sound from the Subs are a complete wrap around. Front Soundwaves meet those from the back. The speakers have to be deployed away from a wall. So if you are set up in an open area/Large Stage or a Gym, you may want to try this. This can be done either with the ETX 15SP or ETX 18SP with a 2+ per side or in the Middle Cluster. I was blown away by the sound. They used 1 ETX 10P and 2 ETX 15SP to demonstrate the effect. Note, some of you doing Weddings may not like the idea of facing the back of a speaker to the Audience with the two Cables Showing. If you are doing a Gym where the young ones don't care, just try it.

[Jerome Malsack]

Just get a black 4 x 4 table cloth and cover the first sub on the floor with the cables facing forward, Then stack the second one on the top. 

[Jerome Malsack]

This was clipped from an article on building the cardiod subs. 

Building a directional array begins with identical subwoofers, because while any closely matched sources can combine, it takes identical sources out of phase to maximize cancellation. First, our two loudspeakers are separated in space, one behind the other. This arrangement is a good option when stage height is low, but there is sufficient depth. With one subwoofer placed behind the other, a good spacing distance between them is a quarter-wavelength, or about 3.5 feet from the front of one cabinet front to the next.
Thus, if the subwoofers are 30 inches deep, there will be a foot between the back of the first enclosure and the front of the second. The second cabinet, placed behind the main subwoofer, will be used to cancel sound behind the pair, while reinforcing the sound in front of them both. Next we invert the polarity of the second, “upstage” enclosure. The polarity reversal causes it to create pressure opposite the main subwoofer at all frequencies. Opposite pressure is required for sound cancellation behind the array. For the rest of the article, we’ll call this rear cabinet the “cancellation sub.”
Now that we have spaced sources, with the cancellation sub polarity-reversed, we must adjust its arrival time to that of the main subwoofer in front. We want the inverted sub to add with the main subwoofer out in the audience, in front. Since we know that a half-wavelength offset produces maximum cancellation, half-wavelength spacing coupled with a polarity inversion produces maximum addition. We therefore need to a add quarter-wavelength of delay to the cancellation sub’s quarter-wavelength of physical spacing to create the full half-wavelength of offset. Adding 3.1 milliseconds (ms) of delay to the inverted sub provides an extra quarter-wavelength offset, but you may find that 4 ms will provide a more desirable result.
In front of both subs the rear cancellation sub arrives a quarter-wavelength late and is electronically delayed by a quarter-wavelength totaling a half-wavelength difference in arrival. This would normally create cancellation, but because the rear sub has its polarity inverted, it sums constructively in front of the pair in the audience area.
Behind the two subs, the front, primary sub arrives a quarter-wavelength late due to the offset, but because the rear sub is electronically delayed by a quarter-wavelength, they arrive at the same time. The rear sub’s polarity reversal causes the two to cancel behind them.
Finally, we need to turn the level of the cancellation enclosure down by 3 dB. This is because the sound level behind the main subwoofer is slightly lower than it is out front. We want to closely match the level of the rear cancellation subwoofer to the level of the main subwoofer to produce the best cancellation.
Quickly summarizing our creation of a directional subwoofer array from two identical subwoofers, we perform the following four steps:
1) Place one sub a quarter-wavelength (3.5 ft) behind the main sub.
2) Reverse the polarity of this rear “cancellation” sub.
3) Delay the cancellation sub by a quarter wavelength (3 to 4 ms).
4) Turn down the cancellation sub by 3 dB.
Two subwoofers, a little DSP, and four simple steps produce directional bass response to the benefit of your audience, musicians, and management. The details of this basic low frequency array are simple enough for anyone to utilize at their gigs!

[Steve M Smith]

Is there an advantage or difference between reversing and delaying the rear sub and keeping the polarity the same but delaying the front sub?


Steve,

[Jerome Malsack]

The difference would only be the stack is shorter.  The cables are not in front.  Less gear in the pictured.  no delay.

This works very well for the party that wants to keep the sub thump away from the house that wants quiet.

With the pictured I would presume they only turned the back down the 3 db. 
With passive subs it would require another amp channel to allow the 3db down. 

[Ivan Beaver]

Is there an advantage or difference between reversing and delaying the rear sub and keeping the polarity the same but delaying the front sub?


Steve,

There is a big difference in both the sound quality and the amount of cancellation.

With the rear sub in reverse polarity there is more cancellation in the rear, and less punch.

With the front sub delayed there is less cancellation in the rear, but more punch/impact out front.

The configuration with the front delayed (called an endfire configuration) also has a little bit more forward SPL-but not a lot.

In BOTH cases-the output SPL out front is LESS than if the same number of subs were all facing forward.  Something many people do not realize.

[Dave Garoutte]

There is a big difference in both the sound quality and the amount of cancellation.

With the rear sub in reverse polarity there is more cancellation in the rear, and less punch.

With the front sub delayed there is less cancellation in the rear, but more punch/impact out front.

The configuration with the front delayed (called an endfire configuration) also has a little bit more forward SPL-but not a lot.

In BOTH cases-the output SPL out front is LESS than if the same number of subs were all facing forward.  Something many people do not realize.

[Dave Garoutte]

Oops, I just hit post without posting.

Is there actually any reason to face the cancellation sub backwards?
If you do exactly the same thing with it facing forward, then you shouldn't have to attenuate the cancellator by 3db.
The front sub would be delayed 1/4 wavelength and the cancellator would not be phase inverted.
I saw an article about this somewhere, showing three subs in a line with varying delay.
It doesn't seem like stacking them would give you any time offset, allowing the front reinforce / rear cancel effect.

[Steve M Smith]

Is there actually any reason to face the cancellation sub backwards?

I assume that if you have them stacked pointing in the same direction, then there is no horizontal spacing between them.  Any delay you add to one will have an equal effect all around so you will not get frequencies adding in one direction or subtracting in the other.

Stacking one backwards gives you a separation distance (roughly) equal to the depth of the cabinet.  The same thing can be achieved by placing one behind the other, both the same way round, or the rear one reversed to give a greater separation.


Steve.

[Ivan Beaver]

Oops, I just hit post without posting.

Is there actually any reason to face the cancellation sub backwards?
If you do exactly the same thing with it facing forward, then you shouldn't have to attenuate the cancellator by 3db.
The front sub would be delayed 1/4 wavelength and the cancellator would not be phase inverted.
I saw an article about this somewhere, showing three subs in a line with varying delay.
It doesn't seem like stacking them would give you any time offset, allowing the front reinforce / rear cancel effect.

Typically (but not always) at the freq on the sub range-most cabinets are omni directional.

So it is the physical distance between drivers or sources of sound that make the difference-no the actual direction.

If you are talking about and endfire array (NOT cardioid), then yes the front speaker would be delayed.  And if you use 3, then each one in front of the rear sub would be delayed back to the rear sub.

With a Cardioid array- you cannot do 3 deep-only 2.

I am not sure what you are calling the "cancellator".

One speaker alone does not do the job-it is the COMBINATION of BOTH that cause the effect.  They both cause cancellation AND addition-it just depends on physically where you are talking.

[ProSoundWeb Community]