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Author Topic: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?  (Read 67940 times)

John Roberts {JR}

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Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
« Reply #30 on: April 17, 2010, 10:02:09 am »

Ivan Beaver wrote on Sat, 17 April 2010 08:29

[

Of course indoors you are going to have boundaries-so that throws a whole new set of "problems" and issues into the measurement and every room/setup is going to be different-so I have not even thought about doing that.

And besides-how do you get rear measurements of a speaker array inside a typical room-at any kind of distance?  That rear wall kinda prevents that Laughing



I wonder if looking at the pattern results suggests an effective zero point?

It seems a rear boundary would be more common than not, if there isn't one (like outdoor concerts), there is probably merit in a scheme that cancels any back pattern while reinforcing the front.

Easy for me to say, I'm not a speaker guy who has to make these things not suck.

Keep up the good work.

JR
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HarryBrillJr.

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Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
« Reply #31 on: April 18, 2010, 03:35:57 pm »

Yes, Ivan I have measured these lots of times.  My comparisons are always 1 vs multiple and so I'm looking for the "increase" rather than directly comparing 4 to 4 if that makes sense.  Perhaps my data is flawed.

A question occurred to me though.  Were you using front loaded boxes?  I have never once done this with horns.  I always felt there was enough control as it is and I also rarely have access to them so I haven't had the chance.  I'm just wondering if that might have something to do with it.

Btw, I do not disagree the output is lower.  I'm just having a hard time with the 3dB number.  I'd love to get more of your data so I can properly wrap my head around it.
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Harry Brill Jr.
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Ivan Beaver

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Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
« Reply #32 on: April 18, 2010, 03:45:53 pm »

I have moved the data off of this computer-so don't have access to it right now.  As I stated I don't remember the exact numbers (and it varied with different configurations), but will look them up next week.  I believe I posted the actual measurements awhile back in another directional sub thread.

I will dig them up and post a couple of examples this week.

I used 2 different subs, the Danley TH 115 and the TH Mini.  I did not have access to multiples of front loaded boxes.

My statement was based on the same number of boxes-pretty much the only to to do that sort of comparisom.


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Art Welter

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Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
« Reply #33 on: April 18, 2010, 04:25:17 pm »

HarryBrillJr. wrote on Sun, 18 April 2010 13:35

Yes, Ivan I have measured these lots of times.  My comparisons are always 1 vs multiple and so I'm looking for the "increase" rather than directly comparing 4 to 4 if that makes sense.  Perhaps my data is flawed.

A question occurred to me though.  Were you using front loaded boxes?  I have never once done this with horns.  I always felt there was enough control as it is and I also rarely have access to them so I haven't had the chance.  I'm just wondering if that might have something to do with it.

Btw, I do not disagree the output is lower.  I'm just having a hard time with the 3dB number.  I'd love to get more of your data so I can properly wrap my head around it.


Comparing 1 vs multiple  rather than directly comparing 4 to 4 would be a different scenario.

A single front loaded box affords hardly any directivity, while four close packed two foot wide boxes is a half wavelength of 70 Hz, so you will get directive forward gain in addition to the expected level increase associated with quadrupling cone area and power.

In an arrangement where the boxes are behind each other and delayed to achieve directivity, they don’t gain frontal area, it seems logical they would have less forward gain than a side by side or vertically stacked, non time processed array.

Ivan said, “up to around 3dB” difference, that certainly seems understandable, especially in the top octave of a sub array’s range.
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Bob McCarthy

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Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
« Reply #34 on: April 18, 2010, 11:26:04 pm »

My 2dB worth........

4 boxes equal in level and with synchronous arrival gives 12 dB addition over the single box. This can never be achieved exactly unless you array them in a concave arc, wherein you will have a single equidistant, in phase, on-axis focal point. In practice approximately 12 dB can happen with sufficient distance. Four sub boxes tightly packed can achieve this in a very short distance - especially at the lowest freqs because of the lack of directional control and the forgivingly long wavelengths are close enough in phase at the center.

A 4 element end-fire array can never achieve the full 12 dB in front of the stack because you have a 3m (or so) spread between the boxes. A meter forward of the 1st box you would be adding 4 boxes at 0, -6, -10, -12 dB because they would be 1,2,3 and 4m away respectively (a total of 6 dB addition over a single box). Comparitively measured at 1m the mono-block would appear hugely more powerful than the end-fire.

As we move further afield, the 3m spread remains fixed in the endfire but the level differential decreases proportionally with distance.   By 8m forward of the first box you would be 11m forward of the last - from first and last you differ by (approx) -1,-2,-3 dB respectively. These would not be adding up to +12 by any means. (closer to 10.5). As we get further we will eventualy appoach a statistically insignificant reduction, but it will be more that 20 meters out.

3 dB is alot to lose. I would have no way to account for it other than a combination of the proximity-related and/or imperfect settings on the delay, resulting in less than perfect addition in front.

No disrespect for Ivan's work here. I wasn't there. But I do not consider the end-fire to be a highly lossy configuration (and 3 dB would be high). There are other cardioid-polar-pattern-making configurations (how's my terminology Harry? ) Laughing  that don't add perfectly in phase in front - and these are very lossy - but I don't see it in the end-fire.



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Bennett Prescott

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Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
« Reply #35 on: April 18, 2010, 11:42:15 pm »

Bob McCarthy wrote on Sun, 18 April 2010 23:26

A 4 element end-fire array can never achieve the full 12 dB in front of the stack because you have a 3m (or so) spread between the boxes. A meter forward of the 1st box you would be adding 4 boxes at 0, -6, -10, -12 dB because they would be 1,2,3 and 4m away respectively (a total of 6 dB addition over a single box). Comparitively measured at 1m the mono-block would appear hugely more powerful than the end-fire.

As we move further afield, the 3m spread remains fixed in the endfire but the level differential decreases proportionally with distance.   By 8m forward of the first box you would be 11m forward of the last - from first and last you differ by (approx) -1,-2,-3 dB respectively. These would not be adding up to +12 by any means. (closer to 10.5). As we get further we will eventualy appoach a statistically insignificant reduction, but it will be more that 20 meters out.

That is very interesting, Bob. I had never considered the summing differential between boxes depending on your distance from the array, and that would obviously create a (slight) advantage in audience area SPL linearity over a "normal" sub array. I have played very little with end-fire because I've been able to get the results I needed with "traditional" cardioid, and the dB loss was insignificant next to the compactness of the array and the (relative) predictability of the pattern. This makes me want to try end fire very much to see what I can gain in the first few yards of audience area, maybe I can lean on my front fills a little less.
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HarryBrillJr.

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Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
« Reply #36 on: April 19, 2010, 03:14:11 am »

Art Welter wrote on Sun, 18 April 2010 15:25

HarryBrillJr. wrote on Sun, 18 April 2010 13:35

Yes, Ivan I have measured these lots of times.  My comparisons are always 1 vs multiple and so I'm looking for the "increase" rather than directly comparing 4 to 4 if that makes sense.  Perhaps my data is flawed.

A question occurred to me though.  Were you using front loaded boxes?  I have never once done this with horns.  I always felt there was enough control as it is and I also rarely have access to them so I haven't had the chance.  I'm just wondering if that might have something to do with it.

Btw, I do not disagree the output is lower.  I'm just having a hard time with the 3dB number.  I'd love to get more of your data so I can properly wrap my head around it.


Comparing 1 vs multiple  rather than directly comparing 4 to 4 would be a different scenario.

A single front loaded box affords hardly any directivity, while four close packed two foot wide boxes is a half wavelength of 70 Hz, so you will get directive forward gain in addition to the expected level increase associated with quadrupling cone area and power.

In an arrangement where the boxes are behind each other and delayed to achieve directivity, they don’t gain frontal area, it seems logical they would have less forward gain than a side by side or vertically stacked, non time processed array.

Ivan said, “up to around 3dB” difference, that certainly seems understandable, especially in the top octave of a sub array’s range.


That sounds logical to me.  I was thinking in terms of coupling.  I think your idea works well particularly with very large subs.  I am not usually working with large subs so this would further reduce the difference.  With smaller subs, even a 2x2 stack is still going to be smaller than the wavelengths the subs are reproducing.  Good points Art.
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Harry Brill Jr.
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carlos del valle

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Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
« Reply #37 on: April 19, 2010, 03:24:26 am »

Bob McCarthy wrote on Mon, 19 April 2010 04:26

My  There are other cardioid-polar-pattern-making configurations (how's my terminology Harry? ) Laughing  that don't add perfectly in phase in front - and these are very lossy - but I don't see it in the end-fire.





And what about the "simple cardioid" method? the one ilustrated in the very first picture on this thread, spacing 1/4 the wavelength and delaying the rear 1/4 period and invert polarity method.
I've never been able to measure and analyse it but I use it extensively on a tour right now and it seems to work fine. would you consider it to be "lossy"?

HarryBrillJr.

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Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
« Reply #38 on: April 19, 2010, 03:30:05 am »

Bob McCarthy wrote on Sun, 18 April 2010 22:26

 There are other cardioid-polar-pattern-making configurations (how's my terminology Harry? ) Laughing  that don't add perfectly in phase in front - and these are very lossy - but I don't see it in the end-fire.




Where is the "LIKE" button?  LOL


On that note, it's amazing how in just a few years of networking websites, how long in the tooth this forum format is becoming, but I digress.

My gut tells me horn loaded subs are not going to be as forgiving to any error in placement, processor settings, etc.  Still I know Ivan is meticulous.  This makes me wonder if there is a gain  in output just by placing these horn mouths together.  Then Art brought up a similar point above which fits.  I'd love to understand what's going on though.  As I said before my comparisons are simply based on the idea that we should gain 6db by doubling, then 6 more by doubling again, for a total of 12dB over a single cabinet.  This doesn't take into account the increase in the frontal area of a 2x2 stack.  The significance of which I think depends on how large it really is relative to the frequencies involved.  ??  So armed with this information "2x2 should be 12dB more than 1x1" I then measure a single cabinet and an end fire and see almost as much gain as the assumed ideal for the 2x2 and take it for granted that I am not losing anything on axis, but maybe "it depends" applies here.  The very next chance I get, I will use a baseline of a 2x2 stack to compare.  These opportunities are far and few between since most of my shows require no more than 2 subs these days.
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Harry Brill Jr.
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Ivan Beaver

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Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
« Reply #39 on: April 19, 2010, 07:34:51 am »

HarryBrillJr. wrote on Mon, 19 April 2010 03:30

[
My gut tells me horn loaded subs are not going to be as forgiving to any error in placement, processor settings, etc.  .

I was not using normal horn loaded subs, but rather the Tapped horn.  It reacts differently than regular subs whose mouth area is to small.

The Tapped horn is designed to have a smooth response down to its low knee.  Putting multiples up just gets louder.

I would have liked to have some regular subs for the "session", but didn't.  So I could not get any data of those.  Maybe somebody who has a couple of subs could try it and get some measurements.
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Ivan Beaver
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