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Author Topic: subs and deploying them 'in the round'  (Read 85520 times)

Phillip_Graham

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Re: subs and deploying them 'in the round'
« Reply #20 on: January 05, 2005, 09:32:23 am »

Eytan Gidron wrote on Wed, 05 January 2005 09:02



Thanks Phill for this explenation. I am not sure that I got it right. Can you get a bit more specific - can you give an example with actual numbers (such as which delay time to which spacing, which frequencies will it affect?)

Will this method work well with horn loaded subs (such as the Turbo subs)?


Place both subs facing forwards, one behind the other.  Space them 1/4 wavelength of the center frequency of the desired bandpass.  Invert the polarity of the rear box, and then delay it the equivalent quarter wavelength time (i.e. .9ms/ft.).

Otherwise, process all the boxes the same, so that they have the same basic phase response (x.o. phase + acoustic phase).

Hopefully that's clearer.
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Re: subs and deploying them 'in the round'
« Reply #21 on: January 05, 2005, 10:45:01 pm »

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Andy Leviss

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Re: subs and deploying them 'in the round'
« Reply #22 on: January 06, 2005, 01:03:30 am »

gtphill wrote on Mon, 03 January 2005 15:23


Mike also could have placed the two subs back to back (i.e. speakon to speakon) and then delayed the front boxes. DF file for pictures of a horizontal sub line array+cardiod model.


I'm not sure I'm entirely following this. Why would you then delay the front ones instead of the back? Isn't turning the back box 180 degrees the same as reversing its polarity, once you account for the different spacing between the drivers from having them located on the other side of the box (which is just a factor of the delay setting, right?)?

Also, here's a real world question for those of you who have much more experience and knowlege of these sort of things than I do. I'm touring an arena show (typical end stage setup, with the stage about 2/3 back in a standard hockey arena, with the remaining 1/3 or so as backstage). There's a small ramp and a circular thrust stage that ends up just slightly off-center (yup, even Elmo gets an ego ramp ;o)

Being as it's a family show with tracked music and equipment is limited, they've got me out with a pair of Meyer USW-1s. Yup, just two.

The original rig had the subs one per side under the front edge of the stage, directly below the main array on each side. Needless to say, the power alley issues were less than desireable. Between that and a couple venues in a row where we couldn't fit the subs under the deck, I ended up moving the two subs to the center line under the thrust stage, and delaying them to align them with the main arrays, angling them out slightly to help cover the sides that the boxes were now on the side of/behind instead of in front of).

This has helped improve things a lot, so that there's now much more consistent low end throughout the venue (and at notably lower levels than I needed before), but I'm always on the lookout for a better solution (aside from adding more subs, which, while the best solution, isn't going to happen). Any thoughts?

I should add that if it is a viable solution for this situation (which I'm not sure it is, especially with only two boxes), cardioid is, unfortunately, also not an easy option, since the USWs require a speaker processor directly before the amps (and tied in after the amps to provide safety limiting), and I (of course) only have one processor, the split coming after the processor. If it really would help, I could try to make a case to the folks back at the office for a second processor if they have one at the shop, but I don't know how successful that would be.
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Phillip_Graham

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Re: subs and deploying them 'in the round'
« Reply #23 on: January 06, 2005, 03:06:47 pm »

Andy Leviss wrote on Thu, 06 January 2005 01:03

gtphill wrote on Mon, 03 January 2005 15:23


Mike also could have placed the two subs back to back (i.e. speakon to speakon) and then delayed the front boxes. DF file for pictures of a horizontal sub line array+cardiod model.


I'm not sure I'm entirely following this. Why would you then delay the front ones instead of the back? Isn't turning the back box 180 degrees the same as reversing its polarity, once you account for the different spacing between the drivers from having them located on the other side of the box (which is just a factor of the delay setting, right?)?


Hey Andy,

[Edited after realizing I didn't need to second guess myself]

Actually, this a correct way of doing it.

Mike B's way:
You need to cancel the waves behind the front box.  So (for simplicities sake) if the front box is producing cos(x) then the rear box needs to produce -cos(x + D) where D is the time it takes for the sound from the front box to reach the rear.  The "-" comes from the polarity invert/box direction, and the D comes by delaying the rear box long enough from the sound from the front box to get there.

Alternative way:
Space the boxes 1/4 wavelength apart (90 degrees apart).  Now delay the front box another 1/4 wavelength (90 degrees).  The output from the the front box takes 1/4 wavelength to reach the rear box, and other 1/4 wavelength you added artificially, so cancellation ensues.  The undelayed sound from the rear box takes 1/4 wavelength to get to the front box, so it sums in phase out front.  Because sound diffracts around the rear box almost perfectly, it makes very little difference whether it is facing forwards or backwards, and you can't think of turning it around as a polarity inversion.

Note that the second method doesn't work as well as the first, because the individual box does provide some degree of forward directivity, and there is slightly less (3dB or so) less sound behind the box than in front.  This leads to a more hypercardiod-like pattern, which can be mitigated by turning down the rear sub about 3dB.  But, by turning down the rear sub 3dB you lose that energy in the main lobe:

index.php/fa/931/0/
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William Mortensen

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Re: subs and deploying them 'in the round'
« Reply #24 on: January 06, 2005, 08:46:59 pm »

When did they add that bandwidth menu to MAPP Online? (I haven't used it in a few months, so they could have added it recently and I just didn't notice.) Or do you guys have MAPP Online Professional?

Also, for what it's worth, I kind of doubt that Meyer's (and Nexo's, for that matter) cardioid subs use a technique that's this simple, since it works best at only one frequency, and I doubt that Meyer would reveal one of their great secrets to you guys like that anyway. Smile They seem to have figured out how to do this on a broadband basis.

WM
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Re: subs and deploying them 'in the round'
« Reply #25 on: January 06, 2005, 10:22:55 pm »

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William Mortensen

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Re: subs and deploying them 'in the round'
« Reply #26 on: January 06, 2005, 11:23:13 pm »

Harry, I'm confused. I think you took me completely the wrong way.

Harry wrote on Thu, 06 January 2005 19:22

I work for a Meyer house currently.


I did not know that.

Quote:

They don't seem to have any issues with teaching anyone and everyone.  What makes you think they are trying to hide anything?


I didn't say they were. I was just saying that I didn't think that this technique was all there is to Meyer's cardioid LF technology, because I doubt that a company would invest years of R&D into perfecting something that no one else has done and then tell the world about it. And there is definitely more to the PSW-6 and M3D(-Sub) than this. Here's the entirety of a Q&A on the website about it:

Quote:

How does the M3D-Sub steer without digital delay?

We use analog phase networks to control the cardioid behavior of the M3D and the M3D-Sub.


Which is not the same thing as the (still very interesting and useful) technique that they have told us about through you, Mike, and Phill.

Quote:

I have also used the CD18s and CD12s.  The CD12 uses EXACTLY this method, with perhaps a bit of frequency response shading to make up for the fact that the rear is facing back.
This is not only good for 1 frequency either.  The wavelengths are long.  It works very well about an octave in each direction, see for yourself.

That's good to know. I don't think anyone had mentioned what kind of bandwidth this technique is really effective over in this thread. I figured it was maybe an octave (total), and certainly less than two. But obviously I was wrong, so thank you for setting me straight on that.

Quote:

(The GEO T uses a similar method with a low pass filter that has a slope that works with the front speakers to add control as the frequency drops.)

Back to Meyer.  I don't know what the M3D and M3DSub are doing exactly,


Right. Because they didn't tell you. And I wouldn't expect them, or any other company, to do so. That's all I was trying to say, Harry!

Quote:

but according to Mauricio it is not advantages to have rear firing drivers, except for the package and repeatability of an all in one box.  The full benefits are only realized with all the boxes facing the same direction.  This method with only 2 sources is not he best.  A better method uses 4 sourced, spaced 1/4 wavelength of the highest frequency of interest, then delay 3 of them back to the one in the back.  This method yields about a 23dB difference front to back.


Okay. I believe I've read that the PSW-6, or the M3D, or something, can achieve even better directivity than that. Because it uses the aforementioned analog phase networks that Meyer most likely spent years developing. And that's what I was referring to when I said "great secrets"--I meant the kind of processing that they do, which again is apparently much more complicated than a simple delay.

Quote:

I find your attitude disturbing.  I would be happy to pass Mauricio's phone number to you, and you can also speak with Dr. Don Pearson, whome I sat next to in the class.


I'm sure they have much better things to do than talk to me. Honestly.

Quote:

Would that be proof enough for you that Meyer is interested in improving the quality of audio in the industry as a whole?

Again, I didn't say they weren't. In fact I'm very impressed with the educational efforts (that they're touting on the front page of their website right now).

All I meant was that, while they are certainly making a huge effort to, as you say, "improve the quality of audio in the industry as a whole", obviously they're not going to give away their intellectual property for free, i.e. tell the world how their proprietary technologies work. I just didn't want anyone reading to get the idea that that's all their cardioid technologies are. Fact is, I have no idea what they are, and I doubt I could understand how they work.

Okay? I'm sorry if my post was less than clear. I wasn't trying to say anything particularly important. Just an idle thought.

WM
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Phillip_Graham

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Re: subs and deploying them 'in the round'
« Reply #27 on: January 06, 2005, 11:33:12 pm »

Quote:


Okay? I'm sorry if my post was less than clear. I wasn't trying to say anything particularly important. Just an idle thought.

WM


Don't let Harry get to you.  He misread the smirk in your post, and his post shouldn't be read as seriously as it seems.  He's the first to admit he comes on too strong in print at times.

Back to the topic!
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Peter Morris

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Re: subs and deploying them 'in the round'
« Reply #28 on: January 07, 2005, 12:18:36 am »

Hi Phil,

This is all great stuff and it works …..

But, there are a few points to note:

It only works over a limited bandwidth, probably about an octave, so with the EAW subs operating 40 to 80hz and with the distances and delays based on a centre frequency of 60hz - no problems.

The impulse response is not perfect.  Imagine if the waveform was a single pulse - the top half of a 60hz sine wave.

The front box will be producing sound for the equivalent of 180 degrees of time (at 60hz) before anything from the rear box is received.  What is received (from the rear box) is inverted and delayed by 180 degrees equivalent of time.

So the original sound is the top half of a sine wave, but the received sound is a complete sine wave, the original plus a delayed and inverted original.

I guess you could call it distortion, it will still sound “nice” and could well be the best compromise in many situations.  At back however every thing cancels perfectly.

Peter
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Phillip_Graham

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Re: subs and deploying them 'in the round'
« Reply #29 on: January 07, 2005, 12:47:53 am »

Peter wrote on Fri, 07 January 2005 00:18


The impulse response is not perfect.  Imagine if the waveform was a single pulse - the top half of a 60hz sine wave.

The front box will be producing sound for the equivalent of 180 degrees of time (at 60hz) before anything from the rear box is received.  What is received (from the rear box) is inverted and delayed by 180 degrees equivalent of time.

So the original sound is the top half of a sine wave, but the received sound is a complete sine wave, the original plus a delayed and inverted original.

I guess you could call it distortion, it will still sound “nice” and could well be the best compromise in many situations.  At back however every thing cancels perfectly.

Peter



The impulse arguement is of little consequence at these frequencies, as the group delay incurred is of the order of magnitude of the crossover filters, the box tuning, etc.  Plus, as you are well aware, the notion of anything "impulsive" in such a bandwidth limited system is a little nebulous.

The fact you get good summation for most of the space in front of the array is indicative of the relatively good phasor sum across a broad range of azimuths.

I feel any phase penalties incurred by such a setup, in the frequency region where most system phase issues lies anyway, is a good compromise to make relative to the mess of room acoustics/stage bleed issues in the low frequencies.
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Re: subs and deploying them 'in the round'
« Reply #29 on: January 07, 2005, 12:47:53 am »


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