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Author Topic: Amazing bass and Evans gig  (Read 76183 times)

SteveKirby

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Re: Amazing bass and Evans gig
« Reply #10 on: April 24, 2009, 03:22:45 pm »

Christian Tepfer wrote on Fri, 24 April 2009 13:24



Spacing in between the subs eases the beam as well...



+1, not as sophisticated as delays, but very effective.  The conventional wisdom (look up the origins of that phrase sometime) is to tight pack center clustered subs in order to achieve coupling and additional output.  In reality, at the wavelengths involved, they will still couple without being pressed together tighter than teenagers at the prom.

There have been postings with MAAP plots showing non-delayed subs spaced out across the front of a stage and showing more uniform coverage.

If you don't want to model it, start with the acoustic centers as far apart as you can get them and still get coupling at the top of your bandpass, and then pull the outer box(s) outwards to get the spread of coverage necessary for the room.
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Matthew Knischewsky

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Re: Amazing bass and Evans gig
« Reply #11 on: April 24, 2009, 03:26:47 pm »

As soon as you get a line of subs that approaches full wavelength (50hZ = 22') you will create a line array. In this case you're creating a line of subs that will cancel everywhere in horizontal that is not directly on axis with the subs. Anywhere but directly in front of the subs will be out of the coverage pattern of the subs.

Here a couple quick an' dirty things to try.

Space the sub cabinets so the drivers are 1/4 wavelength apart center to center. At 80 hz thats 3.5', but with the main array going down to 80, you could probably place them about 4'-4.5' apart. This will help widen the coverage pattern in front of the stage without loosing much output, as the subs are still coupled within 1/4 wavelength.

If you have enough DSP, this is what to try next. starting with the center 2 subs at 0ms, apply .5 ms delay to each sub on either side of the center pair. Now add .5 more delay to the next outside pair, (1ms) and so on. until you get to the outsides of the array. you might not even need .5ms per pair to cover the venue, but it's a start. If you don't have enough DSP channels you can physically place the subs in an arc to create delay.

Matt

(edit spelling)

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Art Welter

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Re: Amazing bass and Evans gig
« Reply #12 on: April 24, 2009, 03:27:19 pm »

Evan,

That is quite an arc going on, how many feet down stage of the subs is forward edge of the array?

Have you noticed how much acoustical overlap there is between sub and the 12”s?

I have been reading all the responses, but the lack of LF Ivan mentioned behind and above the front mix does not correlate in my mind with “too much of a good thing (directivity)”.

Art Welter
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Phillip_Graham

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Re: Amazing bass and Evans gig
« Reply #13 on: April 24, 2009, 05:33:12 pm »

Art Welter wrote on Fri, 24 April 2009 15:27

Evan,

That is quite an arc going on, how many feet down stage of the subs is forward edge of the array?

Have you noticed how much acoustical overlap there is between sub and the 12”s?

I have been reading all the responses, but the lack of LF Ivan mentioned behind and above the front mix does not correlate in my mind with “too much of a good thing (directivity)”.

Art Welter


Art,

The subwoofers are going to form a virtual dipole by coupling to the floor in the vertical plane.  Whenever LF boxes are placed against a solid boundary, its important to remember the boundary causes "virtual boxes" in the floor, creating basically a 2-high subwoofer array.

That is why in cardiod sub setups you reverse the box closest to the boundary, and not farthest away.  This insures the canceling boxes are closest to the center of the "virtual array", and that the vertical lobe behavior of the array is also the cardiod pattern you seek.

If the system was setup as shown, and then aligned in the vicinity of FOH, its not surprising that the relative bass amount other places in the arena was low.

Its also possible, but less likely that the slap back from the rear wall of the arena was cancelling some of the forward sub energy at important mix frequencies in the audience.

There is always the possibility of catching an unusual room mode in the acoustic space, but my guess is that this was more a function of the alignment sounding right at FOH, but causing insufficient bass in the rest of the venue due to the directivity of the bass array.

Physics is physics, and this remains the most likley explanation.

PS I don't know any of the system teching details for sure, I really don't want to seem like I am slagging on the CBA guy from my armchair.  Just consider it helpful musings.
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Too Tall (Curtis H. List)

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Re: Bass directivity musings
« Reply #14 on: April 24, 2009, 06:21:49 pm »

Phillip Graham wrote on Fri, 24 April 2009 14:13

It looks like a case of too much of a good thing (directivity).  Delay tapering the subs will help immensely, as Gabe said.

I personally really like the horizontal line array sub setup in old-style theaters or narrow venues, where the array essentially spans the venue width.  This makes for very even coverage.

If I had these 12 subs to work with, I would place 4 in the center, and the remaining 4 in a 3/1 cardiod at either end of the stage, angled out towards the audience.

Then set the delay time of the side sub arrays along the coverage seam of the center cluster where it intercepts the audience in the stands.

This PA looks like it could have used some outfill arrays, too, depending on how far the audience extended to the sides.

Another option would be a flown central subwoofer line array...

I should clarify that I like the cardiod solution more than the arced and/or progressive delay approaches because those can cause a large lobe of LF to show up right in the center of the stage.

If you are in a situation where you need defined coverage in a narrow area (such as multiple stages outdoors for a festival) the spaced horizontal array, these horizontal arrays work well to narrow the LF coverage in the horizontal.


Hi Phil,

Didn't you use to advocate adding a 12dB Butterworth low pass on the the left and right third of a bass sub horizontal line array.
Beside only using the center one third of the cabinets to cover the high bass where the line array would cause extremely narrow dispersion the Butterworth filter added the time delay you were looking for the outer boxes.

Another example this happened to Al Limberg at an outdoor gig.
He laid down four LAB subs accross the front of the stage which was so low that he could not stack them two high.

He was amazed at how narrow the dispersion was using only four boxes at 42" each (14' wide).
Much much narrower then what Evan was looking at.
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Too Tall
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DAVID J. SYRKO

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Re: Amazing bass and Evans gig
« Reply #15 on: April 24, 2009, 07:05:11 pm »

A number of years ago on the lab sub forum when the labsub was in it's infancy, I posed the question to Mark Seton about setting up a large number of labsubs mainly center clustered.  He said group them in 4's. Then cross the center cluster over at 100 HZ. Depending on how many subs you have, you cross the next group at 90 HZ, then the next group at 80 HZ. This lessens the power alley effect of the subs. I asked this question originally on the lab sub forum, then was directed to the Servodrive forum.  However, I think all of that is defunct now. I tried a while back to search for something, and didn't get anywhere.
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Art Welter

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Re: Amazing bass and Evans gig
« Reply #16 on: April 24, 2009, 07:09:57 pm »

Phil,

I am aware the boundary causes "virtual boxes" in the floor, creating basically a 2-high subwoofer array.

In this case that would only be 90 inches or so, not enough height to impart much vertical directivity below 80 HZ.

I’m not sure what you mean by “virtual dipole”, could you explain that?

Art Welter
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Phillip_Graham

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Re: Bass directivity musings
« Reply #17 on: April 24, 2009, 07:12:03 pm »

Too Tall (Curtis H. List) wrote on Fri, 24 April 2009 18:21


Hi Phil,

Didn't you use to advocate adding a 12dB Butterworth low pass on the the left and right third of a bass sub horizontal line array.
Beside only using the center one third of the cabinets to cover the high bass where the line array would cause extremely narrow dispersion the Butterworth filter added the time delay you were looking for the outer boxes.


Hey Curtis,

That sounds like something I might have speculated on, and it seems like it should work, but I don't think that original idea can be attributed to me.

I first started playing with cardiod/endfire/horizontal line arrays for low frequencies a decade ago, so its conceivable I said something on the SAC list back in the day?
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Phillip_Graham

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Re: Amazing bass and Evans gig
« Reply #18 on: April 24, 2009, 07:17:49 pm »

Art Welter wrote on Fri, 24 April 2009 19:09

Phil,

I am aware the boundary causes "virtual boxes" in the floor, creating basically a 2-high subwoofer array.

In this case that would only be 90 inches or so, not enough height to impart much vertical directivity below 80 HZ.

I’m not sure what you mean by “virtual dipole”, could you explain that?

Art Welter


The second set of "virtual boxes" forms two spaced sources playing in phase and at essentially the same level, IOW a dipole.

The vertical lobing above the sub axial level would be representative of this dipole.

See Dave Gunness' excellent exposition here:
http://fulcrum-acoustic.com/wordpress/wp-content/uploads/200 8/07/comments-on-half-space.pdf
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Jens Brewer

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Re: Amazing bass and Evans gig
« Reply #19 on: April 25, 2009, 12:29:04 am »

Phillip Graham wrote on Fri, 24 April 2009 17:33

That is why in cardioid sub setups you reverse the box closest to the boundary, and not farthest away.  This insures the canceling boxes are closest to the center of the "virtual array", and that the vertical lobe behavior of the array is also the cardioid pattern you seek.


Phil, in this example, you're talking about a 2 box vertically stacked cardioid arrangement, right?  One sub facing 'forward' and the other faced opposite.  I just want to be clear on that since the first thing I think of when I think of cardioid subs is two boxes on the same plane spaced apart by x' with delay added and polarity reversed on the cabinet closest to the audience.  Or have I pictured it wrong?
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