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Old 24th July 2011, 02:07 AM   #31
CLS is offline CLS  Taiwan
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Good point

As the topic of this thread is "Stupid Cheap .... Array", I just think of DML. Ah~ it's banned here.
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Old 24th July 2011, 02:30 AM   #32
18Hurts is offline 18Hurts  United States
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Quote:
Originally Posted by Radugazon View Post
Looks like not said yet, but if you use a single tweeter in the middle of an array of other drivers, you gonna have a problem as the level of a single source (the tweeter) decays twice faster than the level of a line source (the other drivers) according to the listening distance.

In clear, this means that the relative levels will be matched only at a specific distance : too close = too much treble, too far = not enough. Now, if you always listen from the same place it's less an issue as it could be in PA.
Hence the recommandation of an array of tweeters vs a single unit, could it be a compression, that will also extend dramatically the power handling of the whole system, one of the big advantages of an array...my 2 cents.
I was considering the single tweeter design then looked at how JBL does theirs (dome tweeter line) how Peavey does theirs (ribbon tweeters) and the funky narrow lens type horns I see from Meyer etc so I went for the dome tweeter line. If it didn't matter--you can bet Peavey would not of used ribbons!

Since I copied from the Velvet Hammer build, his results was the larger than life dynamic sound I was after. If the things overwhelm the floor and metal roof bounce as implied over point source; then I consider it worth building.

Read this report of building the bizarre creatures and think if that is what you want. My original plan was a more conventional 12" Beta LTA with phase plug and Fostex super tweeter but after building my conventional surround sound speakers/sub (well, mostly conventional) It was time to raise the pirate flag and go for line arrays and tapped horns. The extra bonus of huge power handling, much lower distortion and insane volume levels from 48 tweeters per line (106 dB at one watt) clinched it for me. Let the amp clip!

My Line Array Project Log

P.S. In defense of the UniBomber arrays, he is a musician and uses them as monitors. I'm just confused who needs an 8 foot tall monitor?
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Old 24th July 2011, 06:20 AM   #33
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Quote:
Looks like not said yet, but if you use a single tweeter in the middle of an array of other drivers, you gonna have a problem as the level of a single source (the tweeter) decays twice faster than the level of a line source (the other drivers) according to the listening distance.
Why is this?

Greg
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Old 24th July 2011, 11:46 AM   #34
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Quote:
Originally Posted by gmcalabria View Post

"as the level of a single source (the tweeter) decays twice faster than the level of a line source (the other drivers) according to the listening distance."

Why is this?

Greg
Point source, line source, plane source.

It in the nature of the source. As you move away from a point source its energy gets diluted because it spreads both wider and taller. Typically it drops 6dB every time you double your distance from it.

With a line source (an infinite line, say lots of flourescent light bulbs in a row) the energy may be spreading laterally (across the line) but not vertically, as you move away. It will drop 3dB for every doubling. Half as fast.

Moving away from a (infinite) plane source you would see no drop in level.

If you mix sources you can decide on a distance and correct (flatten) for that. The variation fore and aft shouldn't be too bad. Better yet, create a small array of tweeters (3 tweets and the right network can be lobe free) and you can get the characteristics of the sections reasonably close.

The goal is that each section has the same effective length in terms of radiated wavelength. i.e. the array dimension doubles for each lower Octave.

David S.
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Old 24th July 2011, 02:20 PM   #35
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Click. There it is. Now that makes sense. Now all of those graphs showing signal radiation from a point and line are coming back to me. That seems to explain why a 12" sub is a point source when a small electrostatic grid is a planar source.

I hate to say it, but power response just clicked to me like that recently. I love that feeling of instantaneous omniscience.

All these theories still apply directly to an open field or anechoic chamber (not including the floor/ceiling reflections that make an infinite line array). It seems like a single tweeter with wide dispersion and fairly level power response in a real semi-reflective room wouldn't have that problem (as much). Reflections are always a debated problem/benefit, but since I don't have the money for a proper theater room, it sounds like a point source for HF won't be as much of a problem.

Also, it seems like a narrow dispersion horn would minimize this problem at the expense of aggravating it; larger front-to-rear sweet spot, smaller lateral/vertical sweet spot. This is just like a flashlight set to narrow beam carrying its equal brightness farther than on wide. Then again, if these are corner arrays, and we clearly don't care about how they sound when standing at the front wall right between them, then a narrow dispersion lens will project into the area you'll be standing/sitting anyway. Then again, this is at the expense of the last paragraph: lower dispersion=lower room reflection=greater effect of the diminishing SPLs over distance...
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Old 24th July 2011, 02:48 PM   #36
18Hurts is offline 18Hurts  United States
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Here is an interesting site I read about arrays and their issues

Did I Hear Someone Say “Line Array?”

Then there is the monster array thread here on DIY

Constant Beam Width Transducers line arrays

I've read other sites and came to the conclusion that I need to make some sawdust. Since the baffle is held on with machine screws to a sub-frame and the woofer/tweeter mix is 12/48 or 4 to 1, it allows me to easily experiment with. Just something crazy in the garage (my wife don't want them in the house) I can tinker around with and learn a few things.

The cognac HT system is in the house, the cold ale party speakers are in the garage.

Live Sound: Everything You Wanted To Know About Line Array Technology, And Then Some - Pro Sound Web
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Old 24th July 2011, 06:31 PM   #37
opc is offline opc  Canada
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Hi Guys,

I just thought I would chime in here since I've built and have been living with a full range line array for the past year and a half.

I used 25 Vifa TC9FD18-08 3" drivers per channel, for a total of 50 drivers. The lines stand about 88" high, and the ceilings are about 125" high. The drivers are mounted frame to frame to get the closest possible C-C spacing which ends up being 3 5/16". The drivers are arranged in groups of 5 where each 5 driver group is wired in parallel and shares a common sealed section of the enclosure. Each group of five is then wired in series so you end up right back at the same impedance as a single driver. This arrangement is important because it does two things:

1. Prevents standing waves in an 88" high enclosure.
2. Prevents series drivers from sharing the same enclosure volume (this is critical)

I use a Behringer DEQ2496 before my DAC (entirely in the digital domain) to provide the necessary EQ for the lines. I'm sure you could tackle the EQ in the analog domain, but the DEQ is such a capable device that it's worth 10 times what it costs to buy, and the end result is better than you'd get with an analog filter. If you're building a line with full range drivers you absolutely will need active EQ of some sort.

I'm running the lines full range (without a sub) in a very large room, and I get genuinely flat response (-3dB) down to 20Hz. It's the absolute best bottom end you will ever hear from a loudspeaker. It has all the impact and depth of a really good subwoofer, with none of the horrible integration problems. It's literally seamless. My jaw dropped the first time I heard what they were capable of. They are also capable of playing at astonishingly loud levels, which translates into very good dynamics. If I were to relax the bottom end EQ so they rolled off at 40Hz, they would be more than capable in PA applications.

Of course, there's the elephant in the room which I'm sure half of you were repeating constantly in your heads as you read this: comb filtering.

Honestly, it's not that big of deal. As speaker dave mentioned a while back, if you're playing pink noise, and standing within a meter or so of the loudspeakers, you can definitely hear the lobing effect by moving your head up and down. It's also very easy to measure with a measurement mic. Once you're out around the 2 meter mark, it's barely noticeable, and any farther than that, you simply can't hear it anymore. Same applies with music, except you need to be about half the above distances to get the same effect. In other words, if you're playing music, and you're more than a meter from the array, it's not an issue.

The common argument is that point sources that radiate spherically into space will start to interfere with one another at frequencies with wavelengths that are equal to or shorter than the C-C spacing of the sources. This is indeed true, but since we're dealing with full range drivers, they're not perfect spherical radiators, especially at high frequencies. The narrowing dispersion at high frequencies helps to counteract this effect, and makes the drivers behave more like a line of ribbons at very high frequencies, which is exactly what you want. In practice, the arrays require very little EQ in the top end to counter this effect. For me, it's about a 6dB rise from 10kHz to 20kHz to make it sound and measure flat. My listening position is about 3.5 meters away from the front of the speakers.

Finally, I'd like to address the single biggest problem I have with the way people build these things:

DON'T USE CRUMMY DRIVERS!!!!!

This thread started off just like so many others:

"I found out that I can get a box of 50 terrible drivers for $25 and I think I'm going to build a line array out of them".

This is a HUGE mistake, and I can promise you that if you start with junk, you'll end up with junk (just more of it). All 50 of my drivers cost me $333 which is actually cheap compared to most loudspeaker projects. I picked them after carefully considering and auditioning 8 different 3" drivers. You really need to listen to the driver you plan on using as a full range driver with just one driver in a mocked up cabinet. If you don't like the way it sounds by itself, then using 50 of them isn't going to change that. I listened to each driver exactly the way it was, and then with EQ to make it flat. The Vifa drivers I chose were a little bright straight out of the box, but with some EQ they were by far the best sounding of the group.

The amount of work involved in actually building a pair is enormous, which is why you really need to put the effort and money into using a good driver to start with. Putting that much work into something only to ruin it by using 50 cent drivers is a genuine shame. Time and time again I see people putting hundreds of hours of their time into building a pair, and then skimping on the drivers to save a few hundred dollars. It's really sad, especially when there's so much potential!

I've attached a few pictures of the finished arrays, and hopefully someday I'll get around to properly documenting these in a proper project thread.

Cheers,
Owen
Attached Images
File Type: jpg Array Side.jpg (228.0 KB, 2084 views)
File Type: jpg Driver - Side.JPG (73.3 KB, 1992 views)
File Type: jpg Driver - Rear.JPG (105.1 KB, 1740 views)
File Type: jpg Finished - Painted base and white sock.JPG (268.8 KB, 1746 views)
File Type: png Frequency Response of a single raw driver.png (63.3 KB, 1708 views)
File Type: jpg Screenshot - Line Array.jpg (73.5 KB, 621 views)
File Type: jpg Unfinished.JPG (479.7 KB, 889 views)
File Type: jpg Unpainted base and no sock.JPG (214.5 KB, 906 views)
File Type: jpg Finished Line Array.JPG (209.5 KB, 787 views)

Last edited by opc; 24th July 2011 at 06:36 PM. Reason: typo
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Old 24th July 2011, 09:07 PM   #38
18Hurts is offline 18Hurts  United States
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Thank you for the report, Owen

After I read about arrays, I decided to run a 2-way crossed at around 4,200 Hz to limit beaming. The tweeter line should also limit excessive EQ requirements which is important when used with guitar amps etc.

Very interested in your comments of the 1 to 2 meter sound change. I noted that when I was 1.5 to 2 meters back, testing my 5" woofers "full range" sounded much improved. Can't wait until I can hear the tweeter line come to life as I'm still waiting for XO parts to arrive.

You stated you tested eight different brands of 3" woofers and FRs--any of them Dayton ND-91s or Tangbands? My only concern is up to 4KHz with efficiency and bass response critical factors. My minimum efficiency is 85dB 1w/1m since I'll be using it with lower power amplifiers (guitar, car amps etc) and need final efficiency at least 96dB at one watt/one meter. The dream 3.5" would run 89dB with decent Xmax and Fs of 65Hz but I'm not holding my breath.

Fully agree with you on the amount of TIME it takes to build such things. Since I didn't know if I was building scrambled hash in an echo box, I made allowances to make it easily to upgrade the woofer line. Pull the machine screws, removed the bezel and cut out the 5" woofer holes portion and glue in a new bezel cut for 3 to 3.5" speakers. (The tweeter lines stay!) The Dayton ND-91 looks to be purpose built for arrays, I just wish it had more sensitivity.

Thanks again for the report, it helps pass the time and make me feel better while waiting for parts. Temp is 110F (43C) so the speakers get extra time to cook in the garage.

Quote:
Originally Posted by opc View Post
Hi Guys,

I just thought I would chime in here since I've built and have been living with a full range line array for the past year and a half.

I'm running the lines full range (without a sub) in a very large room, and I get genuinely flat response (-3dB) down to 20Hz. It's the absolute best bottom end you will ever hear from a loudspeaker.

Of course, there's the elephant in the room which I'm sure half of you were repeating constantly in your heads as you read this: comb filtering.

Honestly, it's not that big of deal. As speaker dave mentioned a while back, if you're playing pink noise, and standing within a meter or so of the loudspeakers, you can definitely hear the lobing effect by moving your head up and down. It's also very easy to measure with a measurement mic. Once you're out around the 2 meter mark, it's barely noticeable, and any farther than that, you simply can't hear it anymore.

Finally, I'd like to address the single biggest problem I have with the way people build these things:

DON'T USE CRUMMY DRIVERS!!!!!

This is a HUGE mistake, and I can promise you that if you start with junk, you'll end up with junk (just more of it). All 50 of my drivers cost me $333 which is actually cheap compared to most loudspeaker projects. The Vifa drivers I chose were a little bright straight out of the box, but with some EQ they were by far the best sounding of the group.

The amount of work involved in actually building a pair is enormous, which is why you really need to put the effort and money into using a good driver to start with. Putting that much work into something only to ruin it by using 50 cent drivers is a genuine shame.

I've attached a few pictures of the finished arrays, and hopefully someday I'll get around to properly documenting these in a proper project thread.

Cheers,
Owen
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Old 24th July 2011, 09:09 PM   #39
Vix is offline Vix  Yugoslavia
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Hi Owen,

Don't want to get things off topic, but can't resist: What is the other "hidden by a plant" speaker next to line array?

Nice Line Array
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Old 24th July 2011, 09:22 PM   #40
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opc, very nice looking speakers. Do you have unequalized frequency response of an array, from far distance (1meter maybe) I'd be interested to see it.
Is there a reason (besides cost) why you didn't build them up to the ceiling height?
I agree with you about choosing good drivers, but sometimes sound quality is not the first priority.
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