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Old 19th July 2012, 03:41 PM   #1
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Default Line array project

I'm scratching a m&k clone idea for the bose L-1 clone. I think my crossover needs will be much easier to reproduce. I'm looking at
264-1062 Vifa TC9FD-18-08 3-1/2" Full Range Paper Cone Woofer
and the
Peerless 830986 3" Full Range Woofer



I notice the bose angles every other driver opposite the other. If I go with the peerless I was thinking just cut it at 80hz and let the sub handle the rest. Any thoughts and how many drivers should be used? Bose say's the use 24 but I was thinking 10-12 would be good for my purpose.


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Old 19th July 2012, 05:28 PM   #2
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I was looking at trying this one out.
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Old 19th July 2012, 05:38 PM   #3
DrDyna is offline DrDyna  United States
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Quote:
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I was looking at trying this one out.
That looks like a disaster of edge diffraction to me, holy crap.
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Old 19th July 2012, 07:32 PM   #4
18Hurts is offline 18Hurts  United States
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That looks like a disaster of edge diffraction to me, holy crap.
Bose uses a special anti-edge diffraction cone and anti-diffraction coating since they spend so much money on their "research".

Before you build an array, I have a few pages of fun things to read before buying speakers and cutting wood. First up, the different types of them and how/how they don't work.

Live Sound International | Tech Talk: Understanding Line Array Systems

If you are going to build them for home use in a room, they act a bit differently up close than they do at distance. Here are the fun parts of listening to them up close.

http://diy-audio.narod.ru/litr/nflawp.pdf

Here are the results adason achieved when playing around with close out drivers.

keele line array, bad start...

A good comparison between one speaker and a dozen of them--notice how the frequency response shifts.

sony buyout - Page 14

Others have reported the Vifa 3.5 inch full range when stacked around 25 tall sound very good when used with parametric EQ with a DSP. I've completed building a 3-way line array with 12 five inch woofers, 20 three inch full ranges for mids and 48 tweeters...a major pain in the butt. If I had to do it again (under threats of death) I'd go for the Vifa 3.5 inch and EQ to taste.
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Old 19th July 2012, 09:19 PM   #5
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I'm unclear on why the freq response changed.

I think it did not, perhaps what was happening is that due to the higher freq energy beaming, and the LF energy combining, that effect was seen.

The ears might disagree with the measurements, not sure.

One could tell for pretty certain with a very close to the cone (6"?) measurement of a single and the array. Probably would try at the top and dead center of the array, just to see...

at least that is a theory...

_-_-bear
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Old 19th July 2012, 09:37 PM   #6
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...actually if accurate measurements from the same distance are/were made at the same input level (that might be tricky) per driver, then one would see if the response at HF was constant and the LF rises due to addition...

_-_-bear

or maybe the way to go is to normalize at say 1Khz for level at the measurement mic, then compare, etc.
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Last edited by bear; 19th July 2012 at 09:41 PM.
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Old 19th July 2012, 09:45 PM   #7
18Hurts is offline 18Hurts  United States
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Quote:
Originally Posted by bear View Post
I'm unclear on why the freq response changed.

I think it did not, perhaps what was happening is that due to the higher freq energy beaming, and the LF energy combining, that effect was seen.

The ears might disagree with the measurements, not sure.


_-_-bear
I call it the "tilt" effect

Once the center-to-center distance starts to intrude into the frequency response, the drivers start to destructively go out of phase with each other. The line then starts to drop 3dB per octave after that point--I learned that the hard way with my 2-way line array with 5" woofers.

Since the design is for garage use, I didn't want to go DSP just yet so went with a 3-way design to strongly boost the output of the midrange. TV speakers tend to have increasing output as the frequency increases, I used those and they came out smooth in the end. Rising response countered by falling response equals out for the most part.

The destructive phasing issue will show itself in treble response--I just bump up the 10K up a touch on the receiver--done. They work well in a garage or party speakers--have not tested them in the house since the WAF is calculated in negative numbers.
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Old 19th July 2012, 09:53 PM   #8
DrDyna is offline DrDyna  United States
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Bose uses a special anti-edge diffraction cone and anti-diffraction coating
lmfao.
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Old 20th July 2012, 03:05 AM   #9
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Thanks for all the good reading. I am still curious to know if the angle of each individual driver changes comb filtering, phasing and diffraction issues. I was going to use a behringer ultra curve pro for my dsp. Any more thoughts would be much appreciated.

Last edited by logans; 20th July 2012 at 03:19 AM.
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Old 20th July 2012, 11:30 AM   #10
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Quote:
Originally Posted by bear View Post
...actually if accurate measurements from the same distance are/were made at the same input level (that might be tricky) per driver, then one would see if the response at HF was constant and the LF rises due to addition...

_-_-bear

or maybe the way to go is to normalize at say 1Khz for level at the measurement mic, then compare, etc.
A nearfield measurement of the array will look pretty much as it would for a nearfield measurement of one woofer. The difference is that with a line you can get farther away and still be "nearfield".

The LF gain at a distance is from the in-phase sum of all the elements. You still get gain at high frequencies but it is a random phase summing so it is 3dB for twice the elements rather than the 6dB you see at lower frequencies.

David S.
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