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Title: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Justin Sumrall on January 15, 2010, 01:12:32 am
Hey Guys and Gals,

    I have been reading up on the contreversal topic of Cardiod Sub Arrays and bass steering. I get the jist that the whole point is to capture the energy that is being wasted under the stage and elsewhere in the plane and shooting it twards the audience. What I don't get is the physics behind it. I know that Dave Rat has written about this several times but I need a down to the basics explanation of how it is done and the theory behind it. If anyone has a good explanation or has and artical that you could share I would appreciate it. Thanks!
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: HarryBrillJr. on January 15, 2010, 01:59:09 am
A simplistic way to look at it but a good way to get started.


http://www.tigeraudioinc.com/endfire2.jpg

Better rejection of more frequencies in the rear, and better overall control, less impact.


http://www.tigeraudioinc.com/endfire.jpg

Better impact, but less control.


Some prefer to pick a higher frequency to work with.  The choice is yours.


In real life you won't get exactly 6dB gain in front compared to 1 speaker.


If you want to deploy what d&b calls a CSA array, you can simply do this.....

http://www.rationalacoustics.com/forums/showpost.php?p=1726&postcount=2


Here's a shot of that in MAPP.....

http://www.tigeraudioinc.com/csa.jpg


The LINES coming from the speakers indicate the direction that speaker is facing.

Edit: link repairs
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Bennett Prescott on January 15, 2010, 03:14:44 am
What's controversial about it? If you understand phase, it is a simple concept. If you don't, great, I need to pay my bills.

The basic question is, are you willing to sacrifice a few dB of forward output for directionality? That can be very important. Having the pattern of your sub array match your mains array is uncommon. Some of us spend a lot of time on that sort of thing.
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Tim McCulloch on January 15, 2010, 03:29:02 am
For a different take on using delay and arraying:


http://www.jblpro.com/catalog/support/getfile.aspx?docid=234&doctype=3


Then taking the concept a bit further:


http://www.jblpro.com/catalog/support/getfile.aspx?docid=272&doctype=3


Harry's 'quick and dirty' shows you what to do.  The JBL docs give you a bit more of the 'how'.


If you own an advanced calculator and know what the buttons do, try Chapter 12 of "Sound System Engineering", 3rd, D. Davis & E. Patronis, Jr. Focal Press.  Hell, just buy the book.  And get a copy of Bob McCarthy's "Sound Systems: Design and Optimization" while you're investing in your education. 


The more I learn, the less I know.  I'm still figuring out how big a dunce I can be.  <img src="images/smiley_icons/icon_rolleyes.gif" border=0 alt="Rolling Eyes">


Have fun, good luck.


Tim Mc

Edit: link repairs
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Dave Sturzenbecher on January 15, 2010, 11:05:06 am
Bob McCarthy states on his blog that the second edition of his book goes into this topic a little more then the first.  I haven't seen this edition though.
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Bennett Prescott on January 15, 2010, 11:21:53 am
I feel I should add that conventional cardioid arrays, as mentioned by the OP, have the SPL tradeoff in favor of compactness and reliable pattern. End-fire arrays, as mentioned by everyone else, do not suffer from a loss of forward SPL but do suffer from unreliable pattern control and a much larger physical footprint.

Once you get into large subwoofer arrays, regardless of whether you build in any "extra" directionality or not, you had better have a pretty good handle on how phase operates. It's not just about how the array(s) interact with itself/themselves, but also how they interact with the mains at crossover.

If you're not careful, you can end up with three power alleys, an extremely narrow pattern from your ground-stacked subwoofers, and cancellation that happens at varying audience depths. Solving the traditional left/right stacked subwoofer power alley problem for large PA systems is non-trivial. Modeling is your friend!
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Charlie Hughes on January 15, 2010, 05:17:12 pm
Very nice illustration of what's going on Harry.  I would like to make a couple of comments to clarify things.

HarryBrillJr. wrote on Fri, 15 January 2010 01:59

http://www.tigeraudioinc.com/endfire2.jpg
Better rejection of more frequencies in the rear, and better overall control, less impact.
The image in the link above illustrates a cardioid set-up.  Not an end-fire array, per se.


HarryBrillJr. wrote on Fri, 15 January 2010 01:59

http://www.tigeraudioinc.com/endfire.jpg
Better impact, but less control.
The image in this link is of an end-fire array.

More sources (subs) can be added to the end-fire array, with each one delayed to the end source (sub).  The result of adding more sources with the appropriate delay is tighter pattern control.

Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: HarryBrillJr. on January 15, 2010, 06:51:53 pm
Charlie Hughes wrote on Fri, 15 January 2010 16:17

Very nice illustration of what's going on Harry.  I would like to make a couple of comments to clarify things.

HarryBrillJr. wrote on Fri, 15 January 2010 01:59

http://www.tigeraudioinc.com/endfire2.jpg
Better rejection of more frequencies in the rear, and better overall control, less impact.
The image in the link above illustrates a cardioid set-up.  Not an end-fire array, per se.



Thank you for the comments Charlie.  I expected someone to reply.
I fundamentally disagree with that naming scheme, although I go out of my way in class to mention that people "call" that deployment cardioid.  It's all about communication.  Cardioid is a POLAR PATTERN, end fire is the deployment (or array) used to achieve that polar pattern.  No need to argue, we can agree to disagree on that.  The 4 deep end fire is also cardioid and even approaches super cardioid although it varies by frequency.  I think all of these implementations should have names.  What they are named, I don't care, but cardioid (or any other polar pattern description should not be one of the names.  It's very confusing for the average sound guy like me.
At the show I'm currently working they deployed an "omni sub array."  That doesn't describe the way the cabinets are stacked, just the polar pattern, which is the result of that deployment.

I don't see anything controversial about it.
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Justin Sumrall on January 15, 2010, 10:30:43 pm
Bennett Prescott wrote on Fri, 15 January 2010 02:14

What's controversial about it?



Looks like that has been proven  Very Happy
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Jerome Casinger on January 16, 2010, 06:24:32 am
How is it that between endfire and endfire2 links everything is the same except you flip the polarity on endfire2 but get the same result as the first link. If you have everything set up the same as shown in the two links but then flip the polarity in one of them would that cause cancelation unless you turned and pointed one sub backwards?
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Greg Longtin on January 16, 2010, 09:13:48 am
Jerome,

Sorry, I don't think anyone implied the two methods are the same.

EndFire2 - Alternative Method - Cardioid

 1. 'perfect' on axis *rear* cancellation, front has a comb effect

 2. From the rear, acoustic alignment of two *out* of phase sources

 3. At VLF, 360 deg response is cancellation


EndFire - End Fire

 1. 'perfect' on axis *front* summation, rear has a comb effect

 2. From the front, acoustic alignment of two *in* of phase sources

 3. At VLF, 360 deg response is summation

Greg
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: HarryBrillJr. on January 16, 2010, 01:05:26 pm
They are not the same.  In addition to having the rear polarity inverted, the rear is also delayed.
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Jerome Casinger on January 16, 2010, 10:22:10 pm
Greg Longtin wrote on Sat, 16 January 2010 08:13

Jerome,

Sorry, I don't think anyone implied the two methods are the same.

EndFire2 - Alternative Method - Cardioid

 1. 'perfect' on axis *rear* cancellation, front has a comb effect

 2. From the rear, acoustic alignment of two *out* of phase sources

 3. At VLF, 360 deg response is cancellation


EndFire - End Fire

 1. 'perfect' on axis *front* summation, rear has a comb effect

 2. From the front, acoustic alignment of two *in* of phase sources

 3. At VLF, 360 deg response is summation

Greg



Got it, thanks for the clarificiation!
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Justin Sumrall on January 16, 2010, 10:40:11 pm
Thanks guys. If Dave Rat is out there, id love to hear your take on it!
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Tim McCulloch on January 16, 2010, 11:59:23 pm
Justin Sumrall wrote on Sat, 16 January 2010 21:40

Thanks guys. If Dave Rat is out there, id love to hear your take on it!


DR's take on what?  He's very into LF arrays of various types and has (and is) writing about them extensively on his blog.  He has strong opinions about some of the methods, both positive and negative.

You might want to read his blog on ratsound.com as he's discussed both of the methods Harry illustrated.

Have fun, good luck.

Tim Mc
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Bob McCarthy on February 01, 2010, 01:47:12 pm
I posted to my blog two of the figures from the 2nd ed of my book that show how the phase response steers the end-fire array. The pic shows how the spacing and delay sync in forward direction and scramble in the rearward direction.index.php/fa/27786/0/

Here is one of the pics here. (limit is 1 pic)
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Art Welter on February 01, 2010, 07:12:34 pm
Bob,

Wow, a life size sub diagram  Laughing !

What are the dB differences between each color contour?

How well do real world measurements compare to the prediction?

index.php/fa/27808/0/
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Bob McCarthy on February 01, 2010, 07:28:46 pm
Art,

I agree the pic did come out really big here. Is this Texas?

The colors on the MAPP plot are 3 dB per shade.

The real world measurements of such things confirm what we see here - BUT it is much harder to see so clearly due to the presence of reflections etc, which is something we never get away from in subwoofer world

6o6
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Rog Mogale on February 02, 2010, 12:42:02 am
Hi,

I’ve done some basic playing around with cardioid setups and other bass arrays. Here’s some links to a few papers that might help.

http://www.voidaudio.com/pdf/bass%20guide.pdf

http://www.voidaudio.com/pdf/lffaq.pdf

http://www.voidaudio.com/pdf/trucksim.pdf

http://www.voidaudio.com/support.asp




Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Adam Schaible on March 27, 2010, 11:10:53 pm
Sorry to dig this up... but curious about what you folks think.

With 8 subs, is this about as good as it gets?

63hz shown, no boundaries (outdoor show)

index.php/fa/29024/0/
Title: Re: Cardioid Sub Array, Subwoofer Steering, WHY TO DO IT?
Post by: Mac Kerr on March 28, 2010, 12:13:27 pm
Adam Schaible wrote on Sat, 27 March 2010 23:10

Sorry to dig this up... but curious about what you folks think.

With 8 subs, is this about as good as it gets?


That would depend on what you were trying to accomplish. It seems like a complicated array that makes a big lobe in the center. If that is what you are going for it may be great.

Some explanation about what is going on in the arrays, and what the purpose is might make the question clearer.

Mac
Title: Re: Cardioid Sub Array, Subwoofer Steering, WHY TO DO IT?
Post by: Adam Schaible on March 28, 2010, 12:24:44 pm
I'm trying to get the most coverage out of 8 subs.  I spent a few hours working different patterns and didn't find anything that came close to as much forward coverage with 8 subs, and this had the advantage of rearward rejection.  
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Timo Beckman on March 28, 2010, 12:26:51 pm
I have build that set up 1 time only this one works very well if the stage is on the long side of the venue . If you have 8 subs i would go for a "normal" sub line and not for the some what V shape you have now .

(You might take a look at some predictions i map did

https://sites.google.com/site/timobeckmangeluid/een-evenement-en-nu (sorry the text is in dutch)


If you have enough amps and processor power you might go for a arc . Just make a straight sub line . The 2 middle ones stay at 0 ms delay (not taking the delay needed to allign them with the main lft/rght in account) Then delay the next sub with maybe 1 or 2 ms and go on 'till you get to the last one .

The other possibility is to displace the subs into a arc (so not doing it with delay but really bending the line of subs into a oval form . Damn this is hard to explain in english . Looks a little like this
 

http://cid-5933da57cf499561.skydrive.live.com/play.aspx/.res/5933da57cf499561!533/5933DA57CF499561!540?ct=photos

Edit: link repairs
Title: Re: Cardioid Sub Array, Subwoofer Steering, WHY TO DO IT?
Post by: Ivan Beaver on March 28, 2010, 04:12:44 pm
Adam Schaible wrote on Sun, 28 March 2010 12:24

I'm trying to get the most coverage out of 8 subs.  I spent a few hours working different patterns and didn't find anything that came close to as much forward coverage with 8 subs, and this had the advantage of rearward rejection.  

What exactly are you trying to do?  Use 8 subs or get a particular coverage pattern.

Remember that when you use an endfire array approach you will not get the same SPL out front as if you just used the same number of subs facing forward.

To get the same SPL, you will need more subs in an endfire or "cardoid" array.

It is all a tradeoff.  Which one is more important is up to you.
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Bob McCarthy on April 15, 2010, 10:47:12 pm
Harry's pic is great.

Here is a pic I did recently that shows how the phase response drives the end fire array into the cardioid shape - interesting terminology point by Harry also - I agree that cardioid is an effect/result, not a configuration. Many ways to skin that cat.
This plot (and a second to follow that pairs with it) are excerpted from a more extensive blog post on the end fire.

Enjoy
Title: Re: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?
Post by: Bob McCarthy on April 15, 2010, 10:48:24 pm
second pic as promised
Title: Re: Cardioid Sub Array, Subwoofer Steering, WHY TO DO IT?
Post by: Greg Longtin on April 16, 2010, 08:35:26 am
Ivan,

Ivan Beaver wrote on Sun, 28 March 2010 15:12

Remember that when you use an endfire array approach you will not get the same SPL out front as if you just used the same number of subs facing forward.

To get the same SPL, you will need more subs in an endfire or "cardoid" array.



To clarify, I assume you are saying that SPL will drop if all cabinets are not in phase?

IOW, if all cabinets are in phase and delayed according to their spacing, front output should be very similar to a 'regular' stack...

Greg
Title: Re: Cardioid Sub Array, Subwoofer Steering, WHY TO DO IT?
Post by: Ivan Beaver on April 16, 2010, 07:22:44 pm
Greg Longtin wrote on Fri, 16 April 2010 08:35

Ivan,

Ivan Beaver wrote on Sun, 28 March 2010 15:12

Remember that when you use an endfire array approach you will not get the same SPL out front as if you just used the same number of subs facing forward.

To get the same SPL, you will need more subs in an endfire or "cardoid" array.



To clarify, I assume you are saying that SPL will drop if all cabinets are not in phase?

IOW, if all cabinets are in phase and delayed according to their spacing, front output should be very similar to a 'regular' stack...

Greg

One might "think" that.  But when I did my outdoor measurements in a fairly large parking lot (no models or predictions-but actual measurements using real loudspeakers in a real space-WOW what a concept Rolling Eyes  Laughing ) using a 135' (if I remember correctly-not sure of the exact size-it was 2 years ago) dia circle, with every setup (I used from 2 to 4 cabinets and different models), I first took a measuremet (polar response in 10
Title: Re: Cardioid Sub Array, Subwoofer Steering, WHY TO DO IT?
Post by: HarryBrillJr. on April 16, 2010, 11:50:34 pm
Ivan Beaver wrote on Fri, 16 April 2010 18:22

Greg Longtin wrote on Fri, 16 April 2010 08:35

Ivan,

Ivan Beaver wrote on Sun, 28 March 2010 15:12

Remember that when you use an endfire array approach you will not get the same SPL out front as if you just used the same number of subs facing forward.

To get the same SPL, you will need more subs in an endfire or "cardoid" array.



To clarify, I assume you are saying that SPL will drop if all cabinets are not in phase?

IOW, if all cabinets are in phase and delayed according to their spacing, front output should be very similar to a 'regular' stack...

Greg

One might "think" that.  But when I did my outdoor measurements in a fairly large parking lot (no models or predictions-but actual measurements using real loudspeakers in a real space-WOW what a concept Rolling Eyes  Laughing ) using a 135' (if I remember correctly-not sure of the exact size-it was 2 years ago) dia circle, with every setup (I used from 2 to 4 cabinets and different models), I first took a measuremet (polar response in 10
Title: Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
Post by: Ivan Beaver on April 17, 2010, 09:29:52 am
HarryBrillJr. wrote on Fri, 16 April 2010 23:50


I generally use the CENTER of the array as the ZERO distance point to make these comparisons but I don't think the difference would account for 3dB on axis.  Something else was going on.  My experience on axis has been different than yours.

And there in where the "problem" starts in any measurement situation.

This was a fairly large empty parking lot and I choose the particular size kinda as a "This should be large enough" type thing-ya know real scientific Laughing .  While the on axis 0 position was about 67' the closest boundary (which was a slopping hill with trees on it) was about 250' from the 0 point (that was on axis 0).  The side closest boundaries were probably 1500' or more away (and they were trees) and the rear closest boundary (again trees) was probably 500' away.  So I don't "think" any boundary reflection was an issue. There was a building (about 250
Title: Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
Post by: John Roberts {JR} 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
Title: Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
Post by: HarryBrillJr. 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.
Title: Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
Post by: Ivan Beaver 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.


Title: Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
Post by: Art Welter 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.
Title: Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
Post by: Bob McCarthy 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.



Title: Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
Post by: Bennett Prescott 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.
Title: Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
Post by: HarryBrillJr. 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.
Title: Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
Post by: carlos del valle 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"?
Title: Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
Post by: HarryBrillJr. 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.
Title: Re: Cardioid Sub Array, Subwoofer Steering, Why I stand behind my work.
Post by: Ivan Beaver 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.
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Ivan Beaver on April 19, 2010, 08:22:52 am
OK I was wrong.  I was relying on my memory and stating up to 3dB difference.

It was actually a LARGER difference (at some freq).

Below is a screen capture of the array of 4 TH minis (top white trace) and some (not all) of the various endfire and "cardioid" arrangements that I did, below that.

As you can tell, there is quite a bit of difference.

These were all taken at the 0 point on axis-again about 67 feet away.  So that should be far enough away to negate most of the array depths.
index.php/fa/29583/0/
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Tom Danley on April 19, 2010, 11:12:16 am
Hi Guys

There is some confusion about Ivan’s measurements and what is happening with these arrays.

When two or more sound sources like  subwoofers, of equal amplitude and phase are placed less than about a quarter wavelength apart, they feel the radiation pressure of the adjacent units and by mutual coupling are more efficient than a single unit would be.
In a perfect world, 4 identical subwoofers close together, would have 6 dB greater power handling AND 6 dB high sensitivity than one.
This effect is retained up to about 20-25% combined efficiency which is a practical limit for direct radiators.

Directivity?
The array above produces the same polar pattern as a single unit. The coherent addition in all directionsindex.php/fa/29586/0/ results in a round (spherical) radiation or pattern.
A horn can raise efficiency and produce directivity but many do not realize that it is entirely different parts of the horn which are working doing each job even at a single frequency.
For example, for a typical HF horn, all of the impedance transformation takes place at the small end or even within the driver itself above 10Khz, while the other end is what governs pattern.  In other words, here the directivity generally is a result of the larger acoustical dimensions while acoustic coupling at small acoustic dimensions..

If one were to take two of the lf sources above and place them about 1 / 2  wl apart, then one finds the spacing is large enough to cause figure 8 radiation pattern broad side to the array.  In antenna theory these arrays are called “broadside arrays”, often made of many sources AND often tapered in amplitude and or phase towards each edge.
It was that tapering that made me try that in the Shaded amplitude horns fwiw.

If one has experienced the “power alley” effect, this is the experience being in that forward lobe, that same lobe also extends up and to the rear with nulls in line to the array.
Anyway, if you picture the ½ wavelength spacing it is easy to see why there is a figure 8 shape, on axis in line, you have two sources, a half wavelength apart so on axis, they will cancel out. Anywhere the path length difference is less than 120 degrees, the sources begin to constructively add (at 120 degrees, two sources add but have no increase).
Now, while a slice of this pattern looks like a figure 8, it is like a doughnut in 3d, where the in line nulls are the holes.
This produces a significantly different radiation pattern than the point source BUT one would note the spacing is too large to have the mutual coupling observed in the close coupled array.

Endfire arrays are another antenna configuration which is applied in audio.
Here one can picture the same array as the broadside except now one source is driven opposite the other. This rotates the strongest axis 90 degrees AND changes the shape of the beam    A very directional antenna can be made from a long row of sources each with the appropriate phasing and can often be made to project 90 degrees away by re-phasing

These types of arrays use local interference or they “self cancel” in some directions while adding in others, the sources are too far apart to add coherently like the close spacing does.

So what if you don’t want a rear lobe that is as strong as a front lobe?
Enter the time delay array or cardioid.

Take the two sources, place them physically a quarter wl apart (at or just past the limit for mutual coupling) and then add a phase difference via time delay which then kills the mutual coupling but produces a desired shape radiation lobe shape.

What Ivan had observed with his field measurements is correct, the greatest acoustic power would be produced by a close coupled array of the four units which add coherently, it doesn’t matter that these are Tapped Horns, it is the same for direct radiators.  
That would be especially clear if one were to integrate the power over 360 degrees, having less to the rear is accomplished by canceling some of it out with another source.
Thus the total radiated power is less than the sum of the radiated powers of source A and source B if they were adding coherently..

The issue would be how important is the radiation pattern VS how important is it to use the minimum cost / complexity..  With subwoofers this is can be a real problem as the total power needed can be large and this requires a lot of boxes and that means a physically large array which has physical directivity.

Conversely, for a given acoustic power, the desirable radiation patterns produced by local interference of sources comes at the expense of requiring more drivers, amplifiers , pounds of gear and processing.


Lastly, before running too far with this, we have to keep in mind how sound works to be realistic.  You cannot deal with sound in one plane except under a few circumstances, what looks like a row of sources conceptually in one plane, has to be a stack of them when you model height and width and wish symmetry.

Also, computer modeling is invaluable……but only to the degree it predicts what you actually measure in real life.
There is an increasing tendency in our industry to depend on modeling without any measurement backup.  Even some speaker EASE models are not actual measurements but models of the drivers in an array.
As a speaker designer, that is really a scary idea, I know of no software or collection of software I would trust enough to hang up the microphone.

This is the wrong way to look at things I think, a proper measurement trumps any computer model and what good is a computer model if it doesn’t predict the reality you construct from it?
It has never been easier to take good measurements, let those steer your way.
Anyway, some thoughts and Ivan’s parking lot test.
Best,
Tom Danley
















Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Bob McCarthy on April 19, 2010, 02:02:25 pm
Most of what is stated in Mr. Danley extensive is understandable to me and fall in line with my experience.........but a couple of parts aren't and don't.

His advice to favor empirical measured data over predictions is wise. I have never found any prediction worth looking at that cannot be measured and found to be in close agreement. Suffice to say, I am a big fan of measurement.

1) the statement "The array above produces the same polar pattern as a single unit. "

I have never observed an array of speakers that produced the same pattern as a single unit. I don't see how such a thing is possible with even two displaced sources - much less four.  

2) the statements about 1/4 wavelength apart providing mutual coupling etc.....

In my measurements I have never seen "mutual coupling" show up on my analyzer screen as a special circumstance (i.e one where the combined behavior could not be deduced by the behavior of the individuals. What I mean by this is that I have never seen a break in continuity of behavior. If two sources are 120 degrees apart they "couple" just like two sources 120 degress apart, i.e. 0dB + 0 dB = 0 dB, which is to say it couples like a marriage between people who never see each other (half the folks in our field).  If they are 90 deg apart (the 1/4 wave distance), you get 3dB addition, i.e. better coupling.  91 degrees couples a little less than 3dB, 89 degrees a little more. Two sources, 90 degrees, or 89, or 60, or 30 degrees apart do not (in my experience of measurement) leave the pattern unchanged from a single source. The couple better (6dB) in the location where they are 0 deg apart - and they couple not so good (5.99999 down to 3 dB) in the direction where the displacement is maximum.

Maybe I am missing something, as I am not a theoretician. I don't do particle velocity, intensity, or wave theory. I can work a wrench but I am no quantum mechanic. I do amplitude and phase.

Here is what I do:
1) Measure speaker A (solo) - chart amplitude and phase
2) Measure speaker B (solo) - chart amplitude and phase
3) Compute expectations of A+B based on the solo data
4) Measure A+B and compare to expectations

To date I have never observed behavior that gave unexpected results (except when I screwed up something in my data acquisition).
To date the polar of A+B has never just been a louder version of A.

No disrespect is intended - I hope that is understood. I love that you guys took the time and expense to do these measurements. The results and conclusions just don't add up for me yet.  I would love to attend your next parking lot session.  I love to see the data going in.
Thanks

6o6  

Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Tom Danley on April 19, 2010, 03:24:58 pm
Hi Bob


"the statement "The array above produces the same polar pattern as a single unit. "

I have never observed an array of speakers that produced the same pattern as a single unit. I don't see how such a thing is possible with even two displaced sources - much less four."


Ah, your observation is correct, when I added the photo, it appeared in the beginning of the post instead of the end where the tag is.

I can see this would be confusing, as what I was saying referred to the closely grouped array in text above not the in line array shown photograph which appeared above.


"In my measurements I have never seen "mutual coupling" show up on my analyzer screen as a special circumstance  snip>

Maybe I am missing something, as I am not a theoretician. I don't do particle velocity, intensity, or wave theory. I can work a wrench but I am no quantum mechanic. I do amplitude and phase.


I'm a wrench guy too.

You described vector addition just fine that is how it is.


It is the radiation resistance curve which drive one to use a horn to increase the efficiency of a driver, when you examine such a curve for either a radiator or horn, one sees that on the sloped portion, the efficiency goes up with radiator size.

The object of the horn then is to connect the driver which sits FAR down on the resistance curve, to be coupled to a point (ideally) where the radiation resistance is constant with frequency, without the mass a giant radiator that large would have.


When you take a small subwoofer, you are also very far down that curve, hence low efficiency but if you take two identical units and place them in close acoustic proximity, then, one finds the electroacoustic efficiency goes up by 3dB and combined with the 3dB you get from having twice the power handling, you get the 6 dB increase.

The closest thing to a free lunch in acoustics there is.

With direct radiators, there is a practical limit to the increase in efficiency somewhere around 20-25% where the wasted space between drivers and losses begin to limit.

Ref;

http://books.google.com/books?id=b_wxNccLhXoC&pg=PA78&lpg=PA78&dq=woofer+mutual+coupling&source=bl&ots=Kf8hiDxN9H&sig=RlyeqVubZnrUsvu_m3q6OWR6hcM&hl=en&ei=manMS5X_M4T2MMaeofsE&sa=X&oi=book_result&ct=result&resnum=4&ved=0CAwQ6AEwAzgK#v=onepage&q&f=false


Keep in mind, if your talking about acoustic power, it is only simple if you have an omni directional source like one too small to produce directivity, then one measurement point tells most of the story..    If you produce a polar pattern, acoustic power can only be assessed by a bunch of  spherical measurements, much more involved or measured in an appropriate reverberant room.


I would love to attend your next parking lot session. I love to see the data going in.


Well Mike, Ivan and Doug have talked about having some kind of fun / measurement seminar and maybe some sonic entertainment after dark for a while now.

They also have some great BBQ near the shop. 

So, it makes sense to mix Speakers BBQ, Measurements, listening to music.

Anyway, if that happens, you should come.

Best,

Tom Danley

Edit: link repair
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Greg Longtin on April 19, 2010, 06:21:47 pm
Tom,

Tom Danley wrote on Mon, 19 April 2010 14:24


if you take two identical units and place them in close acoustic proximity, then, one finds the electroacoustic efficiency goes up by 3dB and combined with the 3dB you get from having twice the power handling, you get the 6 dB increase.


Some might just attribute that to coherent wave summing.

IOW, coherent is 6 dB, incoherent is 3 dB...

Greg
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Nick Hickman on April 20, 2010, 07:16:02 am
Two thoughts in response to Bob and Tom:

First, the principle of superposition (wave addition) will correctly predict the results of combining sources; there's no need to consider radiation impedance ("mutual coupling") as a separate issue.  Thus, predictions for everything from subs to line-arrays can be successful with simple superposition of sources.

Second, energy is always conserved.  If multiple sources are radiating sound energy, then all of that energy goes somewhere.  However, things are not always as straight forward as they may first appear, and issues of radiation impedance much be considered in order to see the whole picture.

In the hope it might help others following, I've found this thought experiment helpful in attempting to understand this ...

Take a small sub radiating at a low frequency into free space.  It's omnidirectional.  Integrate the sound power over space to find the sum of its output.

Now take a second identical sub driven in the same way with an identical amplifier and place it at a large distance (relative to wavelength) from the first.  We've added +3dB (double power) to the system by virtue of the second amplifier.  If we measure sound pressure, we find that it has increased +6dB in some directions relative to the first case but is greatly diminished in other directions.  If we integrate the sound power over space, we'll find it's +3dB.  Energy is conserved.

Now invert the polarity of one of the subs.  We find the pattern of peaks and nulls in the response will change but, if we integrate sound power over space, it's still +3dB.

Now restore the original polarity and slide the two subs so that they're right next to each other, closely spaced with respect to the wavelength of the sound.  We find that all the nulls in the response pattern that we had when the subs were widely spaced have now gone and, if we measure sound pressure, we have +6dB everywhere relative to the original single sub.  This is predicted by superposition.  If we integrate sound power over space, it's +6dB so, at first sight, it looks as if we've added 3dB to the system and got 6dB out.  But there has been another change: the radiation resistance into which both subs are radiating has been doubled by their effect on each other.  The effect of one sub on the other is making the air "stiffer" and enabling them to operate more efficiently.  Because the acoustic impedance is such a tiny part of the electrical load being driven by the amplifier, the change from the amplifier's perspective is small.

Last, invert the polarity of one of the subs while they remain close together.  The sound almost completely disappears and the power integrated over space is way down on the original case.  Again, this is predicted by superposition.  It looks like the energy has "cancelled" but, in reality, the subs' effects on each other is to radically reduce the radiation resistance by making the air "floppy".  As a consequence, little acoustic power ever gets delivered, and energy is conserved.

In all these cases, superposition predicts the result without any additional consideration of "mutual coupling".  To understand how this comes about with respect to the conservation of energy, however, it's necessary to consider the effect of mutual coupling on radiation impedance.

Nick
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Tom Danley on April 20, 2010, 09:37:35 am
Hi Greg, Nick

I could have explained things a bit more clearly in places.

One has to be careful where one applies general rules of physics, for example a first blush look at “conservation of energy” might suggest that adding two energy sources always results in more.  Active sound cancellation is based on having two equal but opposite sources which add ideally to zero .    
As Bob mentioned, it is magnitude and phase that govern the result when signals combine so no need to restate the obvious.

So far as mutual coupling, it is a real effect as is the radiation resistance curve.
The problem is, as soon as one has produced directivity, then one has eliminated the chance to determine the acoustic power with a single measurement like one can with a point source.

So, a thought experiments if you choose not to measure the real things.

Picture your in a huge and very live room.  
You place woofer A in the room playing noise in the spectrum of interest.
Given the surface area of the room and it’s absorption as well as the reverberant field sound level, one can calculate the acoustic power radiated by that speaker.

Now, add a second subwoofer NOT very close to the first and the reverberant sound level goes up 3dB, a factor of two which represents the doubling of source power.  

Place that second unit very close to the first and driven with the same power, the sound level in the room goes up 6dB over a single unit, representing the 3 dB you get from twice the power capacity and 3 dB or doubling if it’s acoustic efficiency because of mutual coupling / moving up on the radiation resistance curve.
Horns can be 10X or more efficient than direct radiators because of having a way to deal with that radiation resistance curve but when direct radiators are acoustically small, they show signs they follow along.

It is that coupling which makes the four close coupled subs, the most powerful acoustically (total acoustic power) while some of that power can be sacrificed for a more advantageous polar pattern.
Best,
Tom Danley




Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Nick Hickman on April 20, 2010, 12:31:46 pm
Hi Tom,

Tom Danley wrote on Tue, 20 April 2010 14:37

One has to be careful where one applies general rules of physics, for example a first blush look at “conservation of energy” might suggest that adding two energy sources always results in more. Active sound cancellation is based on having two equal but opposite sources which add ideally to zero .

Sometimes "cancellation" means there is no energy in the system, and sometimes it means that we don't see any energy because it went somewhere else or is in another form.  The "other form" arises because a sound field has a particle velocity component as well as a pressure component (what we hear).  Both fields must exist (over time and space) but it's quite possible to have velocity at a point and no pressure (or vice versa).

Take my example of two widely-spaced subs with inverted polarity.  You can put a pressure-sensitive microphone (or human ear) in the centre between the two sources and hear nothing.  There's no sound pressure, but there's still a velocity field (which can be detected with a velocity-sensitive microphone); the energy hasn't really gone away.

On the other hand, take the example of the two closely-spaced subs with inverted polarity.  You can put a pressure-sensitive or a velocity-sensitive microphone anywhere and hear nothing.  There's no energy because no energy was ever radiated.

Sorry if this takes things too far off track.  It's also taking me further out of my depth!

Nick
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Bob McCarthy on April 20, 2010, 01:46:45 pm
I guess I am just a dyed-in-the-wool "superpositionist".  Two displaced speakers, two amplitude responses, two phase responses, one result (at a given location).

The Eargle reference Tom cited talks about "close together" and "tendency to act like a sinlge speaker".   I don't know what to do with this. What is close and how do I measure tendencies?

So much is made of 1/4 wavelength. But as I see it, it is just a milestone in our brains. The waveforms aren't checking for it.  If this "whatever effect" happens at 1/4 wavelength distance then what happens at 1/4 + 1/16th of a wavelength?  Or 1/4 less a 1/16th. If this event happens at 1/4 wave then what happens a 12th of an octave above or below? Something dramatic?  I have never seen a break in my data. I move the speakers an inch - the data moves an inch. I have never seen the fault line where some kind of transformation occurs.

Put two kids on a seesaw. The heavier kid sits on the ground and the lighter kid in the air - even if they are only different by a 1/4 pound.  The fulcrum of the seesaw is a transformational device. Give the skinny kid a dinner from KFC and we will see the fulcrum make a quantum shift.  I have not observed such a transformational device in the interaction of speakers.

Admittedly I don't use intensity probes so velocity and acoustic power are not in my vista.

I measure amplitude and phase with a single diaphragm mic. But I can (and do) put speakers right next to each other. In my expereience they never add 6 dB in all directions like people are saying here. The displacement pushes the phase responses apart by SOME amount in one plane - and along that line the addition is SOME amount less than 6 dB. Maybe a tiny amount... but the amount less than 6 tends to be consistent with the superposition principle.

I don't doubt the statements that my view is oversimplistic. But if somebody wants to give me a proceudure that I can use on my FFT analyzer to directly observe "tendencies to act like a single speaker" I will be happy to try them out.

Until then I will continue to do my best to avoid kryptonite

SuperpositionMan Laughing


Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Nick Hickman on April 20, 2010, 02:38:25 pm
Hi Bob,

As I wrote in the message you replied to, superposition predicts everything, so carry on being SuperpositionMan!

It's just that to fully understand the mechanisms at work behind the scenes, you must include changes to radiation impedance or you'll draw the incorrect conclusion that you're getting a free lunch in the form of more energy out than you put in.  (If not, why should moving boxes around change the amount of radiated energy?)  It's like attempting to compute a power change in an electrical circuit without accounting for a change in the circuit impedance.

Bob McCarthy wrote on Tue, 20 April 2010 18:46

So much is made of 1/4 wavelength. But as I see it, it is just a milestone in our brains.

Yes, absolutely.  Everything is gradual; no sharp boundaries.

Quote:

But I can (and do) put speakers right next to each other. In my expereience they never add 6 dB in all directions like people are saying here. The displacement pushes the phase responses apart by SOME amount in one plane - and along that line the addition is SOME amount less than 6 dB. Maybe a tiny amount... but the amount less than 6 tends to be consistent with the superposition principle.

Yes!  If the sources were truly co-located (which is impossible in the real world), you'd get +6dB, as predicted by superposition.

Nick
Title: Re: Cardioid Sub Array, Subwoofer Steering
Post by: Art Welter on April 20, 2010, 03:31:37 pm
index.php/fa/29633/0/
Bob,

All right, the 66th post here for 6o6 , and now he’s SuperpositionMan  Laughing

Whether called  superposition, wave addition, or mutual coupling,  you are of course correct in that length vs frequency is a continuum, though below 1/4 wave length the continuum does not change much, and above a quarter wave length the changes happen more rapidly.
Not that 1/4 + 1/16th of a wavelength would be a big change, just saying 1/2 wavelength to 1/4 is a bigger change than a 1/4 to 1/8th.

At 16 kHz, where a 1/4 wave length is about the size of the type on the page (+/- 3 dB depending on your eye condition), it is difficult to physically do anything about the differences, we can’t get loudspeakers to dance on the head of a pin.

Down in the <100 Hz range,  wave lengths are long enough that several speakers can be co-located in a near enough configuration to tend to act as a single speaker in the area of interest.  A single EV MTL-4 would be an old example of four 18” drivers with an exit less than 1/4 wavelength in width.

I have not used an FFT analyzer, but using a dB meter or Smaart, I have consistently measured a 6 dB increase doubling cones and power when the sources are within 1/4 wavelength.

That said, large sub arrays are generally well beyond 1/4 wavelength in width, so the “tendency to act as a single speaker” no longer applies.

Art Welter
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Tom Danley on April 20, 2010, 04:12:52 pm
Hi Bob, Nick

“So much is made of 1/4 wavelength. But as I see it, it is just a milestone in our brains.”

Well it like this I think, we have some definitions which have a strict meaning, for example, a square wave has harmonics which extend from DC to Microwaves. Or, in acoustics a point source is infinitely small or a line source is infinitely large in one dimension.

In real life on the other hand, there are practical definitions too, for example, on an oscilloscope, it takes a bandwidth about 10 X and 1/10 the fundamental to produce a square wave that looks good perfect to the eye.
A line source gradually stops changing acoustically when it is about 40 wavelengths long and  point sources can combine into a single point source of greater efficiency, if they are less than about ¼ wl apart

Trust me, I didn’t make radiation resistance up and neither did John Eargle or the numerous other acoustic references one can find. Mutual coupling, radiator wave number, radiation resistance curves  etc are real.


“But if somebody wants to give me a procedure that I can use on my FFT analyzer to directly observe "tendencies to act like a single speaker" I will be happy to try them out.”

Procedure?
Sure, I guess so, here are a couple.
Take a number of small identical subwoofers and scatter them around your parking lot.
These are small enough to be omni directional point sources in sub range.
Put your mic somewhere “out there” with a red cone so it won’t get squashed.

Do a narrow band energy vs time measurement with all the subs on.
Now gradually assemble them all in one location, measuring the narrow band ETC each time.
What you will see is they gradually look more like and then combine into one radiation in time.  Once you have all the radiations in less than ¼ wl spacing at the highest frequency in question, there is little further change moving them closer.

If you can do this in a large enough reverberant room with pink noise, you can also monitor the sound power by averaging the spl from a number of far locations, what you will see then is the reverberant sound level will climb from the initial level as the woofers begin to have mutual coupling.
This way you can see the effect of the mutual radiation as it raises the total acoustic power relative to the power of the individual sources up to the frequency where the drivers are too far apart..

If you to try and integrate that subwoofer system with a full range speaker above, you will also find your task becomes vastly easier once the individual subwoofers are all less than a quarter wavelength apart at xover.  
I guess those should do.

How this applies is in what Ivan measured, that the close coupled array of four woofers, produced more acoustic power than any of the “array” configurations, even the on axis SPL was less for the directive array, not just the total radiated power.
All that is good when you sell speakers and amplifiers though haha.

When you consider the essentially hemispherical pattern of the close-coupled sources and the power being more or less “area under the graph” it is clear that is so.
There are times when it is desirable to shape the dispersion pattern, the original issue was how best to construct arrays and how do they actually measure.
Best,
Tom Danley







Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Anthony Risi on April 20, 2010, 05:50:23 pm
Hello Tom,

I am a little confused about something here.  I have 4 of the TH-115s, and they are absolutely amazing.  I have always either stacked them on either side of the stage ( mainly because my tops need something to sit on) or have center clustered them.  I have always been amazed at the power increase by clustering them all together.  I understand by reading this post how that is happening, so here is my question.  If I got 4 more TH-115s would it be better to put 4 on each side of the stage, or center cluster a block of 8 of them.  I ask because would a block of 8 of them put the drivers further apart then a 1/4 WL at the highest frequency?  I am no expert on this and didn't know if I was understanding what was being said correctly.  

Thanks
Anthony
Title: Re: Cardioid Sub Array, Is it just me??
Post by: Ivan Beaver on April 20, 2010, 06:02:37 pm
Tom Danley wrote on Tue, 20 April 2010 16:12

How this applies is in what Ivan measured,




Is is just me or am I the only one who is actually interested in MEASURING something?

I mean it is not that hard-Heck for the point in this discussion you don't even need to do polars-just a simple on axis measurement-a decent distance away from the array-whatever type it is.  The argument is not about what is happening at 180
Title: Re: Cardioid Sub Array, Is it just me??
Post by: Adam Schaible on April 20, 2010, 06:33:17 pm
Valid point, but from my perspective it's nice to read a lot of the theory, comprehend, etc - so I think it's great.

Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Ivan Beaver on April 20, 2010, 06:40:38 pm
Anthony Risi wrote on Tue, 20 April 2010 17:50

Hello Tom,

I am a little confused about something here.  I have 4 of the TH-115s, and they are absolutely amazing.  I have always either stacked them on either side of the stage ( mainly because my tops need something to sit on) or have center clustered them.  I have always been amazed at the power increase by clustering them all together.  I understand by reading this post how that is happening, so here is my question.  If I got 4 more TH-115s would it be better to put 4 on each side of the stage, or center cluster a block of 8 of them.  I ask because would a block of 8 of them put the drivers further apart then a 1/4 WL at the highest frequency?  I am no expert on this and didn't know if I was understanding what was being said correctly.  

Thanks
Anthony

As usual-it depends.  There are two things at play here-center cluster vs side stacks.  There are advantages and disadvantages to each method and it depends on the particular situation and what works well in one does not work so well in another.

The best way to stack multiple TH115's is to lay 2 of them on their sides with the exits in the middle, and go as high as you can or have cabinets.  In the case of 8, you would go 4 high-but in a center cluster that would be to high for most stages.

If you just stand them up, then 8 would start to form a sideways "line array" and you would start to pull in the coverage on the sides.  This may or may not be a good thing-depending on what area you are trying to cover.

In most cases I would put 4 per side. 2 over 2.

You can help to reduce the power alley by turning down 1 side a little bit.

Everything regarding loudspeakers and how they are deplyed is a compromise.  It is all about finding the best compromise for a particular situation.
Title: Re: Cardioid Sub Array, Is it just me??
Post by: Bob McCarthy on April 20, 2010, 07:53:57 pm
Shazzam!!!! You mean there's analyzers out there! I always wanted to try one. Laughing

Ivan,

I have an opportunity next week during a seminar I am teaching to set up 4 subs in end-fire and monoblock config. It will be indoors in a small room - but since I am not a manufacturer, rental house or holding any research grants, it is the best I can do. My plan is to compare the forward direction SPL of these array configs to that of a single unit. Working title: "The Search for the Lost dB"

Will keep you posted but it will be some time before it leaves post-production.

6


Title: Re: Cardioid Sub Array, Is it just me??
Post by: Ivan Beaver on April 20, 2010, 08:05:32 pm
Adam Schaible wrote on Tue, 20 April 2010 18:33

Valid point, but from my perspective it's nice to read a lot of the theory, comprehend, etc - so I think it's great.



And the theory is great-but it is also a very good idea to see how the real world stands up to the theory and vice versa.
Title: Re: Cardioid Sub Array, Is it just me??
Post by: Ivan Beaver on April 20, 2010, 08:10:38 pm
Bob McCarthy wrote on Tue, 20 April 2010 19:53

Shazzam!!!! You mean there's analyzers out there! I always wanted to try one. Laughing




That is exactly my point.  I first brought up the point of the directional arrays not having the output of the same number of stacked boxes almost 2 years ago.

And to date NOBDOY (that I am aware of) has tried to repeat even the on axis measurements. Rolling Eyes

Surely there are people on here who have access to all the needed gear.

Lots of people have disagreed-but none have even taken a measurement to prove their point.  I am not sure what that is saying. Confused

And remember that my measurements were taken outdoor in a free field.  (OK-a parking lot).  I have not done any indoor measurements to compare the different types-so I have no idea what the results would be.  I would suspect the room will have lots to do with the final outcome.
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Bob McCarthy on April 20, 2010, 08:22:25 pm
Tom Danley wrote:

Quote:

Trust me, I didn’t make radiation resistance up and neither did John Eargle or the numerous other acoustic references one can find. Mutual coupling, radiator wave number, radiation resistance curves etc are real.



Understood that you did not make these terms up and no skepticism as to their having demonstrable effects. Hats off to you for working them into a sentence. Laughing

Understood also that as sources get closer together they more closely resemble a single source.  Here is where (I believe) the expression/wording etc. got fuzzy: Way up this thread it was stated that the 4 closely coupled boxes would have the same polar pattern a single speaker- I think it was in your first one of this thread.  This is what I disputed but wait.....

If you meant that it will have the polar of A single speaker. Fine.  
If you meant (and this is what I took it to mean) that the combined will have the same pattern as the 4 individual elements that comprise it - that is where I diverge - and everything I have posted on this thread is prediciated on THAT premise.

Combined to create a NEW and UNIQUE quasi-"single" speaker, yes I am with you, regardless of whether it is the result of resistance, radiators or air conditioners. Laughing  the lack of nulls that comes with 1/4 wl spacing makes it look similar to a single speaker.  

The combined "speaker" is narrower than the unit component by SOME amount (as previously stated). Kind of looks like we built some horn steering for the speaker, although it is a funny horn - leaks out the back!

So, yes I completely agree that we can fuse the speaker together, but the displacement, however small will reshape it into a new polar - albeit - a polar recognizable as a combined entity.

Cheers

6o6

ps: If there is "mutual coupling" then there must be "non-mutual coupling" eh? Laughing  
Title: Re: Cardioid Sub Array, Is it just me??
Post by: Bob McCarthy on April 20, 2010, 08:25:37 pm
Ivan,
Sorry I am two years late to the dance. i will give it my best shot next week. Yes the room will have an effect. Parking lot is mo' better. Class in a Mexican parking lot? Not mo' better.

6o6
Title: Re: Cardioid Sub Array, Is it just me??
Post by: Andy Peters on April 20, 2010, 08:53:48 pm
Ivan Beaver wrote on Tue, 20 April 2010 17:05

Adam Schaible wrote on Tue, 20 April 2010 18:33

Valid point, but from my perspective it's nice to read a lot of the theory, comprehend, etc - so I think it's great.



And the theory is great-but it is also a very good idea to see how the real world stands up to the theory and vice versa.


Wow, this thread is great and should be a sticky.

I agree with Adam here. The real-world measurements are great, but for the purposes of determining what configuration we'd like to use on tomorrow's show, it's nice to be able to predict how things should be arranged.

Why? Because, really, who has time to experiment on a gig?

Of course, having said that, accurate predictions of the subwoofer response in a room demands an accurate model of the room, and who has that?

-a
Title: Re: Cardioid Sub Array, Is it just me??
Post by: Bennett Prescott on April 20, 2010, 09:14:36 pm
Andy Peters wrote on Tue, 20 April 2010 20:53

Of course, having said that, accurate predictions of the subwoofer response in a room demands an accurate model of the room, and who has that?

There are rooms that I probably have a pretty accurate model of, up to 100Hz.
Title: Re: Cardioid Sub Array, Is it just me??
Post by: John Roberts {JR} on April 20, 2010, 10:21:12 pm
Ivan Beaver wrote on Tue, 20 April 2010 17:02



It ain't that hard.  I bet most people have at least 2 of the same type subs laying around and a measurement system.  OH you will also need a DSP, a couple of amps and some cables-so I guess that elimnates a lot of people Shocked

Yeah it takes a little bit of effort and you have to put some clothes on.  But hey-at least you have to take your computer outside with you Laughing -so it won't get lonely.

Or maybe I just see things differently.



I've only got one sub of any type, and no measurement system...  So I appreciate you sharing the fruits of your labor.

Thank you Ivan.

JR

PS: Do you perform indoor measurements au natural?
Title: Re: Cardioid Sub Array, Is it just me??
Post by: Ivan Beaver on April 21, 2010, 06:38:38 am
Bob McCarthy wrote on Tue, 20 April 2010 20:25

Parking lot is mo' better. Class in a Mexican parking lot? Not mo' better.

6o6

Why not?  I'm sure they will be glad to help you "move" the gear around Laughing

Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: HarryBrillJr. on April 21, 2010, 10:45:42 pm
Nick Hickman wrote on Tue, 20 April 2010 13:38

Hi Bob,

As I wrote in the message you replied to, superposition predicts everything, so carry on being SuperpositionMan!

It's just that to fully understand the mechanisms at work behind the scenes, you must include changes to radiation impedance or you'll draw the incorrect conclusion that you're getting a free lunch in the form of more energy out than you put in.  (If not, why should moving boxes around change the amount of radiated energy?)  It's like attempting to compute a power change in an electrical circuit without accounting for a change in the circuit impedance.

Bob McCarthy wrote on Tue, 20 April 2010 18:46

So much is made of 1/4 wavelength. But as I see it, it is just a milestone in our brains.

Yes, absolutely.  Everything is gradual; no sharp boundaries.

Quote:

But I can (and do) put speakers right next to each other. In my expereience they never add 6 dB in all directions like people are saying here. The displacement pushes the phase responses apart by SOME amount in one plane - and along that line the addition is SOME amount less than 6 dB. Maybe a tiny amount... but the amount less than 6 tends to be consistent with the superposition principle.

Yes!  If the sources were truly co-located (which is impossible in the real world), you'd get +6dB, as predicted by superposition.

Nick



I have yet to be convinced that ON Axis I should be looking for 3 or more dB less output from an End fire array than a 2x2 array of equal distance to the acoustic center of the array.  I do not care about total energy.  I only care that the maximum energy I can get out of that system is going in the direction I want it to go and not spraying all over the wall 15ft behind it.  I don't need to know all the details, but I think it's fun, so I seek that knowledge, when I'm off work!

Oops gate change!!!  Gotta go!

OK managed to get back on for just a minute.  When I am working, it is important to know how to get the most energy where it will do the most good, where the audience is, and keep energy that will tend to do harm, away from the audience.
Title: Re: Cardioid Sub Array, Subwoofer Steering
Post by: HarryBrillJr. on April 21, 2010, 11:13:20 pm
Art,

A. Bob wrote the book.  He can call himself anything he wants.

B. Whether or not I measure the subs next to each other (within 1/4 wave) or apart but equal distances from the mic or my ears, I still get almost 6dB.  1/4 wave distance can apply to the distance from the HUMAN that is listening and the subs can still be apart.

C. Smaart IS and FFT Analyzer
Title: Re: Cardioid Sub Array, Subwoofer Steering
Post by: Guenter J. Krauss on April 22, 2010, 02:28:38 am
Hi,

on page 9 of the following paper you can see measurements of a single sub and a 2*4 stack of the same cabinet.

http://www.dynacord.com/downloads/dsp244_info_bass_en.pdf

The measurement microphone was in 10m distance on axis of the single sub and the 2*4 stack, respectively.

The measurement results clearly support the superposition approach. The SPL difference was 18dB, as expected. No significant deviation due to "mutual coupling" visible.

The  slight ripple on the SPL curve of the single sub is due to
some noise during the measurements in a large parking lot and the comparably large measurement distance of 10m.  

GJK

Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Ivan Beaver on April 22, 2010, 07:52:14 am
HarryBrillJr. wrote on Wed, 21 April 2010 22:45

I have yet to be convinced that ON Axis I should be looking for 3 or more dB less output from an End fire array than a 2x2 array of equal distance to the acoustic center of the array.  I do not care about total energy.  I only care that the maximum energy I can get out of that system is going in the direction I want it to go and not spraying all over the wall 15ft behind it.  .


If you wat to REALLY see what is happening-go outside and MEASURE it yourself-and see for yourself.  That is the ONLY way you will be convinced one way or the other.  All the theory and argument by people who have never done it is not gonna do it.

For what it is worth, the measurements I gave were for a 4 box setup.  I did not do 2 boxes, so the results may be different.

I agree, that what you should be concerned with is the output out front-where the people are.

But you need to take the measurements from the FRONT of the array- to see what is really happening.

In a real world concert situation, you will not be able to move the bass array forward into the crowd-so the effective front is in the same place-so the LISTENING distance is from the front of the array-not the acoustic center.

Of course as you move far enough away the physical differences between the two will not matter.  BUT-if you don't measure at least a decent distance away (say a MINIMUM of 10M-that is whay I went about 20M away) then you are likely to get all sorts of data that is not entirely correct-or will translate into the real world experience for the majority of the audience.

And isn't that the whole purpose of measurement/alignment anyway? To translate what we measure into something that can also be perceived by our hearing?  Sure we can measure into all kinds of detail-but do our ears actually hear that?
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Nick Hickman on April 22, 2010, 08:40:23 am
Hi Harry,

HarryBrillJr. wrote on Thu, 22 April 2010 03:45

I have yet to be convinced that ON Axis I should be looking for 3 or more dB less output from an End fire array than a 2x2 array of equal distance to the acoustic center of the array.

Why would you expect that?  (I'm probably not paying sufficient attention to the thread!)  For a 2x2 array, I'd expect (in an ideal world) +12dB at low frequency relative to a single box.  For a four-deep end-fire array at any frequency, I'd expect +12dB on-axis.

Using the end-fire example posted by Bob (four boxes with 1m spacing and 2.9ms delay between boxes), simple superposition assuming omnidirectional sources gives this for far-field response:

http://100dB.com/misc/endfire.png

6dB per division.  Black=single box, green=2x2 array, others four-box end-fire: cyan=30Hz, yellow=40Hz, red=50Hz, magenta=60Hz, blue=70Hz.

Nick
Title: Re: Cardioid Sub Array, Subwoofer Steering
Post by: HarryBrillJr. on April 23, 2010, 11:39:05 pm
Guenter J. Krauss wrote on Thu, 22 April 2010 01:28

Hi,

on page 9 of the following paper you can see measurements of a single sub and a 2*4 stack of the same cabinet.

http://www.dynacord.com/downloads/dsp244_info_bass_en.pdf

The measurement microphone was in 10m distance on axis of the single sub and the 2*4 stack, respectively.

The measurement results clearly support the superposition approach. The SPL difference was 18dB, as expected. No significant deviation due to "mutual coupling" visible.

The  slight ripple on the SPL curve of the single sub is due to
some noise during the measurements in a large parking lot and the comparably large measurement distance of 10m.  

GJK





Without having read the article yet, I can only say you won't get an argument from me on that.  In fact I don't know what I could have said to make you think I disagreed and that you had to post that to me.  I'll read it as soon as I can.
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: HarryBrillJr. on April 23, 2010, 11:43:19 pm
Nick Hickman wrote on Thu, 22 April 2010 07:40

Hi Harry,

HarryBrillJr. wrote on Thu, 22 April 2010 03:45

I have yet to be convinced that ON Axis I should be looking for 3 or more dB less output from an End fire array than a 2x2 array of equal distance to the acoustic center of the array.

Why would you expect that?  (I'm probably not paying sufficient attention to the thread!)  For a 2x2 array, I'd expect (in an ideal world) +12dB at low frequency relative to a single box.  For a four-deep end-fire array at any frequency, I'd expect +12dB on-axis.

Using the end-fire example posted by Bob (four boxes with 1m spacing and 2.9ms delay between boxes), simple superposition assuming omnidirectional sources gives this for far-field response:

http://100dB.com/misc/endfire.png

6dB per division.  Black=single box, green=2x2 array, others four-box end-fire: cyan=30Hz, yellow=40Hz, red=50Hz, magenta=60Hz, blue=70Hz.

Nick



Agreed on both counts.  You and I are saying the same thing, and you are not paying close enough attention to the thread which exists as it does because Ivan measured a greater than 3dB loss of output when implementing an end fire compared to a 2x2 stack of the same cabinets.
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Tom Danley on April 24, 2010, 10:07:41 am
Hi Harry

Ivan and I are pretty big on measuring the real thing as it were, I have commented on the usefulness of computer modeling being related to it’s ability to predict what you measure from the real thing and a tendency to live virtually.
It is also not my job to correct several aspects of this thread which are curious or technically / acoustically misleading, in spite of my urge to spill some beans.

In the bad old days, I used to spend a lot of time in parking lots measuring subwoofers, for a long time, using an oscillator and B&K sound level meter.
By measuring at a number of distances,  I noticed what appeared to be a violation of the inverse square law.
So what was right, what the meter said or what theory said?

Both are right but it was a case of not recognizing what I was actually dealing with.  Theory (the inverse square law in this case) assumed a tiny source, what I measured as differences was the actual result of a real and “not tiny” source.  

You might have noticed, we measure ALL of our subwoofer larger cabinets at 10 meters instead of 1 meter, this way the error caused by a larger source is reduced relative to one meter.  

In Ivan’s array or any array one might make, one has to ask, “Am I concerned about acoustic infinity the land where the posted computer models live, or, am I interested in what happens at a finite distance like 40-90 feet where the people are likely to be?”

At what distance does the "source or array size" stop distorting the nearfield relative to the inverse square law, as observed in the far field?

A useful rule of thumb for head scratching time;
A proper measurement trumps the computer model every time, when they don’t match, usually, the model doesn’t describe what you’re measuring closely enough.
Best,
Tom Danley

Your going to be in Atlanta?




Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Nick Hickman on April 26, 2010, 09:28:41 pm
Hi Harry,

HarryBrillJr. wrote on Sat, 24 April 2010 04:43

You and I are saying the same thing, and you are not paying close enough attention to the thread which exists as it does because Ivan measured a greater than 3dB loss of output when implementing an end fire compared to a 2x2 stack of the same cabinets.

As a general point, it may be instructive to record the responses of the four boxes (in situ) individually.  To whatever extent their responses on-axis vary (other than by inverse-square loss, such as front boxes obstructing rear boxes), a simple model assuming point sources obviously won't hold.  Still, Ivan's results appear to show a consistent disparity down to LF which is intriguing.

Nick
Title: Rear delay array
Post by: Michael 'Bink' Knowles on April 29, 2010, 11:17:04 am
Charlie Hughes wrote on Fri, 15 January 2010 14:17

Very nice illustration of what's going on Harry.  I would like to make a couple of comments to clarify things.

HarryBrillJr. wrote on Fri, 15 January 2010 01:59

http://www.tigeraudioinc.com/endfire2.jpg
Better rejection of more frequencies in the rear, and better overall control, less impact.
The image in the link above illustrates a cardioid set-up.  Not an end-fire array, per se.


I would call this a rear delay array, same name as the d&b "CSA", or "cardioid subwoofer array", even though two cabs are shown, not multiples of three.

End-fire array has no rear delay.

-Bink
Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Dan Richardson on April 30, 2010, 12:56:34 pm
Tom Danley wrote on Sat, 24 April 2010 10:07

“Am I concerned about acoustic infinity the land where the posted computer models live, or, am I interested in what happens at a finite distance like 40-90 feet where the people are likely to be?”

Actually, I'm interested in what happens inside a club.

Got neighbor issues with a new all-ages all-volunteer DIY venue.
Subs are a pair of double 18s a side, and they sound wonderful.
They also sound wonderful in the neighbor's apartment, 50' from the backstage wall.

I'm wondering if the delayed array discussed here is likely to help,
or will the enclosure of the room negate the directionality?

Obviously, just trying it out would be best, but the PA is ground stacked.
Flying the tops would be distinctly non-trivial, and is out of the question for a test.
There are people here who actually know things, so I thought I'd ask.

Any opinions?

Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Adam Schaible on April 30, 2010, 01:12:12 pm
I'm not one of the guys that knows something but I have been researching sound isolation techniques and I think while the CSA will reduce levels behind, depending on the size of the club, the reflected energy off of the walls may not be much down from the direct radition.

I think you might be better off adding another wall, staggered or even double stud and then using some sound isolation clips to re-do the ceiling in that area.  You'll probably get 10+db out of that, if you need more you could use quiet rock and/or mass loaded vinyl.  Also build your accoustic walls with studs 24" on center rather than 16" as the additional flex is desired.

Probably a thread swerve, but just model CSA with walls about the size of the club in mapp online - only problem is that it's 2 dimensional so even if the levels are reduced behind the array in the horizontal plane, I'm not sure how much the effect is negated when the vertical plane is taken into consideration.

Title: Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
Post by: Art Welter on April 30, 2010, 02:09:15 pm
Dan Richardson wrote on Fri, 30 April 2010 10:56

Tom Danley wrote on Sat, 24 April 2010 10:07

“Am I concerned about acoustic infinity the land where the posted computer models live, or, am I interested in what happens at a finite distance like 40-90 feet where the people are likely to be?”

Actually, I'm interested in what happens inside a club.

Got neighbor issues with a new all-ages all-volunteer DIY venue.
Subs are a pair of double 18s a side, and they sound wonderful.
They also sound wonderful in the neighbor's apartment, 50' from the backstage wall.

I'm wondering if the delayed array discussed here is likely to help,
or will the enclosure of the room negate the directionality?

Obviously, just trying it out would be best, but the PA is ground stacked.
Flying the tops would be distinctly non-trivial, and is out of the question for a test.
There are people here who actually know things, so I thought I'd ask.

Any opinions?


If the LF in the neighbor's apartment is primarily through diaphragmatic transmission from the backstage wall, doors and windows, a cardioid pattern array could help. There are configurations that involve turning the top sub backwards, reversing its polarity, and adding delay to the bottom sub that would allow your stack to be the same footprint it is now.

However, if the LF is also exiting elsewhere (likely), from side walls, roof, windows,front door, etc. the rear reduction may not  be significant in the apartment.

Using an RTA, you may find the apartment has a narrow frequency band being excited, a deep notch at that frequency in your subs may cure the problem and have  minimal sonic effect in the club.

More minimal than being shut down due to noise complaints  Laughing .

Art Welter