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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => SR Forum Archives => LAB: The Classic Live Audio Board FUD Forum Archive => Topic started by: [x] on October 11, 2005, 10:53:39 am

Title: Does Anybody Know Who These Guys Are?
Post by: [x] on October 11, 2005, 10:53:39 am
I was browsing aimlessly one morning and saw this web site.

http://www.grubsrof.com/index.html

The cabinetry of these guys certainly looks up to snuff, and some of their products really look for real. It looks like some unknown driver manufacturer and DDS fiberglass horns. I don't even know what places would sell these things or who their target market is.

What would it take for some small company like this G-Audio firm to gain credibility with touring professionals? Some FR and polar measurements would be a good start. But more importantly, how does a company get their products on a tech rider? Do they just need to pump customers full of "cool factor" like some companies have done with their line arrays?
Title: Re: Does Anybody Know Who These Guys Are?
Post by: Randy Pence on October 11, 2005, 11:15:27 am
sell a bunch of boxes so that enough engineers are familiar using the product.  I only look at joker riders, but when I am specing a system and my providers try selling me something i havent used, its  fairly easy to checkup on its reputation.
Title: Re: Does Anybody Know Who These Guys Are?
Post by: Hasse Queisser on October 11, 2005, 02:20:29 pm
Well, looking at their so called "line array", they either don't have a clue, or they just don't care. It's not a line array by any stretch, just a trap box turned sideways.
Title: Re: Does Anybody Know Who These Guys Are?
Post by: Luke Sheridan on October 11, 2005, 02:32:53 pm
How do you figure Hasse?
Title: Re: Does Anybody Know Who These Guys Are?
Post by: Hasse Queisser on October 11, 2005, 02:49:27 pm
Look at the HF horns. The centers of the drivers are a mile away from each other, and there is no waveguide in front of them to try to simulate a line source. Interference seems to be the order of the day.
Title: Re: Does Anybody Know Who These Guys Are?
Post by: Rex Ray on October 11, 2005, 03:07:38 pm
Hi,Guys. I'd agree with Hasse on this one....Definately NOT a line array,but no worse than any other trap box tossed up there.
I bought his book. He states (rather proudly), that his first
big boxes were knock-offs of an S-4. Ther were days when that would have gotten him a letter or two from Roy's lawyers.
Rex (OLD Clair guy) Ray
Title: Re: Does Anybody Know Who These Guys Are?
Post by: Adam@ASPaudio on October 12, 2005, 01:07:05 pm
I agree that these do not meet line source requirements. Also check out the vs736 sub- It is a Community VLF 218 Copy!
Title: Re: Does Anybody Know Who These Guys Are?-Another spec stretcher---
Post by: Ivan Beaver on October 12, 2005, 03:49:45 pm
Another company that can't figure out the math.  If you look at the FB936 sub.  It's rated sensitivity is 99dB 1w.  I might believe that-maybe.  It's rated peak power is 2800watts.  Lets assume that is also correct.  That makes for a 34.5dB difference referenced to 1 watt.  The last time I added 34.5 to 99 I got 133.5.  That is almost 6 dB from the stated max output of 139dB.  That also assumes no power compression.

I guess the current trend is to add whatever number you want to your actual specs (be it 6 or 12dB) and state it as fact.

Whatever happend to the truth!
Title: Re: Does Anybody Know Who These Guys Are?-Another spec stretcher---a couple more
Post by: Ivan Beaver on October 12, 2005, 07:27:44 pm
I wasted my time by looking at a couple more speakers on their site.  The front loaded 2x18" has a less sensitivity-I believe that.  However with the same power capability and less sensitivity-somehow the max output is claimed to be the same.  It must be that "new math"-or someone has been drinking the M%#$r Koolaid.

The full range boxes suffer from the same exarations, but they even stretch them further.
Title: Re: Does Anybody Know Who These Guys Are?
Post by: Peter Morris on October 12, 2005, 08:47:53 pm
FWIW the horn looks like this one --

http://www.ddshorns.com/catalog.php?page=DSLA1100

So I guess it no good Confused??

The box is also a bit like this one

http://www.linearraykits.com/GL10HPLespec.htm

Peter
Title: Re: Does Anybody Know Who These Guys Are?
Post by: [x] 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.
Title: Re: Does Anybody Know Who These Guys Are?
Post by: Hasse Queisser on October 16, 2005, 02:14:51 pm
I always thought it was 1/4 of a wavelength at the highest frequency.
Title: Re: Does Anybody Know Who These Guys Are?-Another spec stretcher---
Post by: Geri O'Neil 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
Title: Re: Does Anybody Know Who These Guys Are?
Post by: Mark Hartzell on October 17, 2005, 06:57:14 pm
I think it's 1/4 as well.
Title: Re: Does Anybody Know Who These Guys Are?
Post by: RYAN LOUDMUSIC JENKINS 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.
Title: Re: Does Anybody Know Who These Guys Are?
Post by: Tracy Sherwood 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.
Title: Re: Does Anybody Know Who These Guys Are?
Post by: [x] 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.
Title: Re: Does Anybody Know Who These Guys Are?
Post by: Doug Fowler 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....


Title: Re: Does Anybody Know Who These Guys Are?
Post by: Tim Padrick 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.
Title: Re: Does Anybody Know Who These Guys Are?
Post by: [x] 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.