Dipole Woofer Array in Multiple W Frame? - diyAudio
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Old 31st July 2004, 03:47 AM   #1
MartinQ is offline MartinQ  Canada
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Question Dipole Woofer Array in Multiple W Frame?

Please take a look at this and give me any feedback. I should have a chance to 'test' them soon.

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During Construction

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Standing Tall


... sorry, the pics don't seem to be coming up. A Yahoo thing?
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Old 31st July 2004, 10:37 AM   #2
Hans L is offline Hans L  Netherlands
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You can also attach pictures. So you don't have to depend on webspace. Weird url from Yahoo btw.
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File Type: gif big_grin.gif (4.9 KB, 199 views)
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Old 31st July 2004, 12:23 PM   #3
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email them to me at bhg41088@aol.com, ill put them on here.
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Old 31st July 2004, 01:27 PM   #4
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http://img.photobucket.com/albums/v3...8/standing.jpg
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Old 31st July 2004, 01:54 PM   #5
MartinQ is offline MartinQ  Canada
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Click the image to open in full size.

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... ahhh, much better. Thanks!
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Old 31st July 2004, 05:03 PM   #6
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How does it sound? I think you're going to get cavity resonances that you will need to damp.

I'd make the side with the drivers near the opening the front and just block off everything past the depth of the drivers (it's just a cavity to resonate and wasted space). The remaining long back cavities will need damping to reduce the cavity resonances. Lastly, horizontal mounting of the drivers will significantly reduce your potential output due to the effect of gravity on excursion, so your array needs to lay on its side for best results. This is especially true for small magnet (high Qts) drivers. At Fs they will bottom out much easier with horizontal mounting of the drivers.

You should take a look at the NaO system at http://www.geocities.com/kreskovs/NaO-Woofer1.html . I think your setup will act more like that open backed woofer than a true dipole.
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Old 31st July 2004, 06:27 PM   #7
DougL is offline DougL  United States
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Quote:
I'd make the side with the drivers near the opening the front and just block off everything past the depth of the drivers (it's just a cavity to resonate and wasted space).
I am not a dipole expert, but if I understood the Linkwitz site correctly. The front to back dimension is "d", the distance that will determine the F-equal frequency of the enclosure.

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Old 31st July 2004, 07:25 PM   #8
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Doug,
Yes and no. This isn't a flat baffle. With drivers firing from deep at the back of a cavity or from the front with a deep cavity behind, you will have resonance. Also your sound radiation pattern won't have the same dipole nulls at the side. It will be more like the NaO U baffle woofer at http://www.geocities.com/kreskovs/NaO-Woofer1.html .
It's not a bad thing, just different in how it will interact with the room, plus you'll get higher output. You should look at that site.

You do need the drivers at the front of the enclosure, not the back. Also, you don't want to damp the deep closed cavity behind the drivers as that would just dissipate your output. You just need to close that off to get rid of the resonance and that won't affect "d" at all. The distance from the front to the back wave will remain the same.

Turn it around and lay it on its side. Close off the cavity directly behind the drivers where they open to the front. Put some kind of speaker grill to hide the drivers. Damp the rear open cavities walls with 3.5" fiberglass insulation on all the walls. Then you should have a good sounding sub with prodigous output.
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Old 3rd August 2004, 07:04 PM   #9
MartinQ is offline MartinQ  Canada
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johninCR: thanks for the link, that's the sort of information I was looking for.

A little more info:
Did some quick sweeps on it over the weekend, and the output is pretty strong down to 40Hz and it drops off very steep at that point (almost nothing below 30Hz). I'll do some measuring, but I think that the wavelength at 40Hz will work out in our dimensions.

This project is designed as a sub-woofer, and it wasn't actually designed. This was a last-minute, the-night-before, emergency-project. No napkins were harmed in the making.

The long 'ports' are for two reasons. We want to have room to mount 16 more drivers, and we want to lengthen the front-rear path.

... more details as they become available!
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Old 3rd August 2004, 09:20 PM   #10
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40hz is a little high. I think the drivers you are using have too high of an Fs for turning into a sub. Also, those relatively small drivers don't move a lot of air, so the chambers can be much narrower and get more drivers in a more compact cabinet.
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