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Author Topic: Does Anybody Know Who These Guys Are?  (Read 8823 times)

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Re: Does Anybody Know Who These Guys Are?
« Reply #10 on: October 12, 2005, 11:33:39 pm »

The sources just need to be separated by no more than one wavelength of the highest frequency to be reproduced. As best as I can remember. The separation on those Grubsrof boxes looks a bit wide to me. It wouldn't behave like a line radiator unless you had lots of boxes and got far away from them. Looks like B&C and Beyma drivers are used.
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Hasse Queisser

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Re: Does Anybody Know Who These Guys Are?
« Reply #11 on: October 16, 2005, 02:14:51 pm »

I always thought it was 1/4 of a wavelength at the highest frequency.
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Geri O'Neil

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Re: Does Anybody Know Who These Guys Are?-Another spec stretcher---
« Reply #12 on: October 17, 2005, 10:00:25 am »

Ivan Beaver wrote on Wed, 12 October 2005 14:49

Whatever happened to the truth!


To quote..."You can't handle the truth!!".. Twisted Evil

Sorry, couldn't resist. Seems plausible though, eh?

Geri O
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Mark Hartzell

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Re: Does Anybody Know Who These Guys Are?
« Reply #13 on: October 17, 2005, 06:57:14 pm »

I think it's 1/4 as well.
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RYAN LOUDMUSIC JENKINS

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Re: Does Anybody Know Who These Guys Are?
« Reply #14 on: October 17, 2005, 10:07:22 pm »

At 18Khz the wave length would be approx .75"  1/4 wavelength = .19"  Those pics don't look like they would support 1/4 wave length.
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Tracy Sherwood

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Re: Does Anybody Know Who These Guys Are?
« Reply #15 on: October 25, 2005, 06:32:31 am »

Yes wavelength spacing on vert. arrays is a conundrum. Above about 10K the physical size of a compression driver limits any 1/2 wave spacing. Not many 1" comp drivers are smaller than 1". Kind of a problem. Slap an "emulator" on that comp. driver, i.e a stack of diffraction slots, a grid of sectoral veins or a phase plug and its all fixed. Yeah.
Other than a true ribbon source like SLS is doing all "line arrays" are hybrids that transition from line source to an array of point sources at higher freq. EV, Vertec, Vdosc, Adamson, Isis, maybe Geo gets some kind of reprieve but...tested them all. And yes that is my little dual horn in that box. works well for small rigs with 10" cones.
-Tracy Sherwood, DDS LLC.
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Re: Does Anybody Know Who These Guys Are?
« Reply #16 on: October 25, 2005, 11:15:34 am »

In my own speculation, what I think happens is that the compression drivers really do look like point sources at those higher frequencies, and then further out away from the line, the radiation patterns (which should be very narrow in the vertical plane) appear to sum into a line.
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Doug Fowler

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Re: Does Anybody Know Who These Guys Are?
« Reply #17 on: October 25, 2005, 01:57:04 pm »

Rory Buszka wrote on Tue, 25 October 2005 10:15

In my own speculation, what I think happens is that the compression drivers really do look like point sources at those higher frequencies, and then further out away from the line, the radiation patterns (which should be very narrow in the vertical plane) appear to sum into a line.


???

So the higher the frequency, the closer the multiple compression drivers come to emulating a point source?

Please explain yourself.

This should be good....


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Tim Padrick

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Re: Does Anybody Know Who These Guys Are?
« Reply #18 on: October 27, 2005, 12:56:26 am »

I think he did - he just left out a word:  They appear as multiple point sources that, once you get sufficiently far away, sum and thus appear as a line source.

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Re: Does Anybody Know Who These Guys Are?
« Reply #19 on: November 01, 2005, 10:38:43 pm »

Yes, the compression drivers each look like separate point sources at frequencies whose wavelengths are less than the diameter of the opening. It might actually be 1/4 wavelength, I don't remember for sure. I corresponded with a more knowledgable friend on the subject of high frequency horn design and we kicked some figure around and I don't now remember what it is. I'll see if I haven't already deleted the email. According to this white paper (http://www.audiodiycentral.com/resource/pdf/nflawp.pdf) dealing with near-field performance aspects of line arrays, the line array applies Fresnel optical techniques to sound reproduction. Many of these optical techniques (among them diffraction slots) can also be applied (with suitable adaptation of theory to the slower speed of sound waves) to the high frequency spectrum where drivers function as velocity sources instead of pressure sources. Professional line arrays need to be able to operate in both the near and far fields, but in the far field, the drivers appear to sum more coherently than in the near field. The ideal spacing between line array high frequency elements with spherical radiation is 1/2 wavelength or less of the highest frequency to be reproduced, or else the traveling spherical sound wave vertically between adjacent high frequency drivers will cancel out the radiation of the other adjacent driver because by that point, the other driver will be moving inward, creating a rarefaction that is (in the case of a perfect sine wave) of equal magnitude to the compression created by the high frequency driver that originated the wave. The highest frequency to be reproduced is almost never higher than 20,000 Hz, and some professional speakers go as low as 16,000 Hz before the threshold for when pattern control becomes a nonissue.

A lot of commercial line arrays I have seen actually use some means of generating a near-cylindrical wavefront (see Electro-Voice's Hydra plane wave generator) by dividing the spherical wavefront longitudinally into parts and then applying small amounts of delay so that these parts are all in phase at the entrance to the horn waveguide. I think that since the dimensions of these waveguides are still small compared to the wavelengths being passed, they can avoid comb filtering effects from large diameter compression drivers loaded together on one horn in a line array use. I find EV's particular implementation most interesting.

I don't know what you thought I was insinuating, but line arrays only appear as a single point source as the distance from the array approaches infinity, and generating sound loud enough to travel an infinite distance in air without attenuation would be impractical. It shouldn't have any relationship to frequency, just distance, though.
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Re: Does Anybody Know Who These Guys Are?
« Reply #19 on: November 01, 2005, 10:38:43 pm »


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