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Ultimate Dipole Line Array [message #69339]

Sun, 04 September 2011 14:51

AudioFred
Messages: 377
Registered: May 2009
Location: Houston

Illuminati (1st Degree)

I've finally dedided a rich guy like me shouldn't let price get in the way of building the ultimate line array speaker, so I've ordered the parts and will start building when they arrive from Parts Express. I'll be using twelve of these woofers per side. I realize they are obscenely expensive, but isn't it all about the music? http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-012

For the tweeter I'll be using a single center-mounted Vifa DX-25. Its low Fs, high sensitivity, and price make it almost a no-brainer.
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-1020

These will be dipole arrays using a 6' by 16" mdf baffle.

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Re: Ultimate Dipole Line Array [message #69340 is a reply to message #69339]

Sun, 04 September 2011 18:41

Wayne Parham
Messages: 18783
Registered: January 2001

Illuminati (33rd Degree)

As a price-no-object speaker, I think those Sony's will really shine. Very Happy

I'll bet you'll have 'em done by next May, so I hope to see 'em in Dallas!

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Re: Ultimate Dipole Line Array [message #69343 is a reply to message #69340]

Mon, 05 September 2011 06:55

AudioFred
Messages: 377
Registered: May 2009
Location: Houston

Illuminati (1st Degree)

Wayne Parham wrote on Sun, 04 September 2011 18:41

As a price-no-object speaker, I think those Sony's will really shine. Very Happy

I'll bet you'll have 'em done by next May, so I hope to see 'em in Dallas!

I know they will "shine" because the paper thin steel baskets ring like a bell at 5Khz Very Happy

These are the drivers you find in a $40 Sony boombox. But as everybody knows, when you diy a line array using cheap, terrible sounding drivers, the sound becomes amazingly good - better even than Rick Craig's $10K Selah Audio line arrays. It's a well known psychacoustic effect known by psychiatrists as "the DIY syndrome".

I built a pair like this once before using cheap buyout drivers, and they sounded "compromised", but when used with a subwoofer and a 100uF electrolytic cap to high pass the midwoofers they were the world's greatest party speakers. They would play compressed rock music at awesome levels. I gave them to my nephew, who still thinks he has the world's best speakers.

http://fredt300b.smugmug.com/Hobbies/Speakers/132721_kcDVmw#189064178_fy3mT

I doubt these will accompany me to Dallas.

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Re: Ultimate Dipole Line Array [message #69673 is a reply to message #69339]

Sun, 02 October 2011 16:03

AudioFred
Messages: 377
Registered: May 2009
Location: Houston

Illuminati (1st Degree)

Making some progress on these. Tomorrow I'll wire them and begin to design a crossover. So far I've spent more on hardware and mdf than I did on the drivers.

http://fredt300b.smugmug.com/Hobbies/Speakers/132721_kcDVmw#1508729179_FLgMG2J

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Re: Ultimate Dipole Line Array [message #69694 is a reply to message #69339]

Tue, 04 October 2011 08:51

AudioFred
Messages: 377
Registered: May 2009
Location: Houston

Illuminati (1st Degree)

Got them all together, and I'm pleased with the sound considering they cost about $100 to build. I also did some measurements, which are critical in designing a crossover. When you're talking "line array" you can forget about using a crossover design program, because woofers behave very differently when they are arranged in an array versus a point source.

Here's the in-room frequency response of one woofer measured at one meter. It's the one directly below the tweeter. No other drivers are connected. Notice the peak between 5 and 6khz. Any crossover you designed for this woofer would have to attenuate that peak.

index.php?t=getfile&id=608&private=0

Attachment: SonyOne.bmp
(Size: 1.35MB, Downloaded 8188 times)

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Re: Ultimate Dipole Line Array [message #69695 is a reply to message #69339]

Tue, 04 October 2011 08:54

AudioFred
Messages: 377
Registered: May 2009
Location: Houston

Illuminati (1st Degree)

Now here's the in-room frequency response of the twelve woofer array measured at one meter. Notice what's happened to the frequency response versus the single woofer.

index.php?t=getfile&id=609&private=0

Attachment: SonyArray.bmp
(Size: 1.35MB, Downloaded 8113 times)

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Re: Ultimate Dipole Line Array [message #69696 is a reply to message #69339]

Tue, 04 October 2011 09:01

AudioFred
Messages: 377
Registered: May 2009
Location: Houston

Illuminati (1st Degree)

But you don't listen to a line array at one meter. The listening position distance should be at least the length of the array, and ideally more than that. So here's the same in-room response of the twelve woofer array measured at the sofa, which is ten feet from the speakers. You can still see the 5-6khz peak, but the overall response is much smoother at this distance.

It is now possible to see how you could include a tweeter that would integrate fairly well with this array, but it's obvious it will need a low fs for a crossover frequency no higher than 2khz, it will have to be fairly efficient to match the woofer arrays's sensitivity, and you will need to use a higher order crossover to get it to play fairly loudly down to the crossover frequency.

index.php?t=getfile&id=610&private=0

Attachment: SonyArray3meters.bmp
(Size: 1.35MB, Downloaded 8080 times)

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Re: Ultimate Dipole Line Array [message #69697 is a reply to message #69339]

Tue, 04 October 2011 09:09

AudioFred
Messages: 377
Registered: May 2009
Location: Houston

Illuminati (1st Degree)

The tweeter also needs to be inexpensive. Forget about ribbons or horn-loaded compression drivers. Any good one would be too expensive. Enter the Vifa XT25. Low resonant frequency, high sensitivity. It also has a reputation for being very robust, and important feature for a tweeter that must match twelve woofers without breaking a sweat. Here's the array with the XT25 and a third order crossover (electrolytic caps, of course, because it must be inexpensive). I also experimented with tweeter attenuation resistors and found I like a 1.5 ohm resistor ahead of the tweeter crossover, which is included. The tweeter caps are a 15uF and a 31uF. The inductor is a 0.15mH. The woofer array is wired directly with no filter.

index.php?t=getfile&id=611&private=0