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Old 15th March 2005, 01:45 PM   #1
icebear is offline icebear  Norway
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Default Linkwitz dipole question

I am on my way to build a pair of linkwitz dipole sub's (http://www.linkwitzlab.com/woofer.htm). I am going to use them with 2 dipole mainspeakers. The sub's should stand rigth behind the dipole baffle(mounted to it), and play trough a hole in the baffle. Tha hole in the baffle must be the same size as the opening in the front of the sub. There is just a little problem with that. There will be like a little space between the baffle and the sub, and I'm concerned that it will be like resonantbox. So I was thinking of just cut that part of the sub, so the spacers will be in conctact with the baffle, and no space will be left.
But do I change the way the sub works? Should I change other things to compensate this?

Rgds

Bjorn
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Old 15th March 2005, 02:06 PM   #2
MBK is offline MBK  Singapore
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I don't completely understand your layout, but it sounds like a difference of +/- 1 or 2 cm. This will not change much. Room resonances will do a lot more harm
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Old 15th March 2005, 02:20 PM   #3
icebear is offline icebear  Norway
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I will cut of more than a couple of cm. It's more like 2,25 ".

Like this: (the red line is the mainbaffle)
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Old 15th March 2005, 02:31 PM   #4
MBK is offline MBK  Singapore
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I see. I wouldn't cut it then - I would either make the main baffle hole square, and the size of the entire subwoofer width (use cloth to cover that hole) , or, just pad the space in front of E and G with thick felt/wool/polyurethane foam/mattress... (those 2.5" will generate resonance in a fairly high frequency and this qill be enough to dampen it). Or even fill the space with wood, as an added mass and point of attachment to the main baffle.

What counts is the path length to the front here - not the exact shape of the space in front of the spacers.
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Old 15th March 2005, 02:51 PM   #5
icebear is offline icebear  Norway
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That's a good idea. Why didn't I think of that :-)

I'll do that.

Rgds

Bjorn
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Old 15th March 2005, 07:34 PM   #6
Nuuk is offline Nuuk  United Kingdom
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I put my TL subs behind my OB's but made the aperture larger than the drive units in the subs. A grille hides everything nicely.

Click the image to open in full size.
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Old 15th March 2005, 11:22 PM   #7
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Just build only the driver manifold into your main baffle. Then, if you still need more extension, add the sides and top to form the typical W baffle box but attached to your main baffle.
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Old 16th March 2005, 07:17 AM   #8
icebear is offline icebear  Norway
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Hi John

I did not quite understand that. Is it possible to make a drawing?

rgds
bjorn
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Old 16th March 2005, 12:47 PM   #9
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Bjorn,

Never mind. Keeping it detachable has advantages, so just cut at the red line shown in your pic which will have no effect on bass extension, since there is no change in the extra distance for the rear wave to travel. It won't be pure dipole anymore, but putting a W baffle in back of another baffle wouldn't be pure dipole anyway because the front and rear pathways are not identical. Don't worry, the effect will be minimal, resulting in a small amount of bass at the sides instead of none.

Keep in mind that you are calling it a dipole subwoofer, but it's more of a dipole woofer, and you'll need EQ and the right drivers for a flat response down into the low 30's or lower. Think of it as a helper woofer to add bass extension to your main OB driver(s). It's a great way to get more air moving capacity (more bass potential), using push/pull for distortion reduction, and eliminating mechanical vibrations of the woofers.

Here's a pic of one one my OB's where I put four 6" drivers in a small manifold on the backside of my baffle to augment the bass. This is what I was talking about in my previous post, just a small rectangular box (manifold) firing through the front of the baffle and open in the back.
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Old 17th March 2005, 04:54 PM   #10
sumacSK is offline sumacSK  Slovakia
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Hi Nuuk,

Those OB looks wonderfull! What sub (what driver) and tweeter are you using with that Ciare drivers? I'm consedering building speakers based on CH250. Are they capable of playing complex music?

Thanks a lot Martin
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