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Author Topic: Cardioid Sub Array, Subwoofer Steering, HOW TO DO IT?  (Read 72362 times)

HarryBrillJr.

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Re: Cardioid Sub Array, Subwoofer Steering
« Reply #70 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.
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Harry Brill Jr.
Tiger Audio, Inc.

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HarryBrillJr.

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Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
« Reply #71 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.
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Harry Brill Jr.
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Tom Danley

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Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
« Reply #72 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?




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Nick Hickman

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Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
« Reply #73 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
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Michael 'Bink' Knowles

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Rear delay array
« Reply #74 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
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Dan Richardson

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Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
« Reply #75 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?

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Adam Schaible

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Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
« Reply #76 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.

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Art Welter

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Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
« Reply #77 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
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Re: Cardioid Sub Array, Subwoofer Steering, OK I was wrong
« Reply #77 on: April 30, 2010, 02:09:15 pm »


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