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Old 22nd August 2004, 02:49 PM   #1
hifidan is offline hifidan  Canada
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This my latest mod. When I saw on the Polk audio web site that they were using some king of air wave guide, it got me thinking. So I designed some kind of wave guide and this is the result. The air movement is dead quiet and the bass is a lot tighter, I think that the phasing between the port and the speakers is also better. The air is actually coming out on the same plane as the one from the speakers. The end result is that it is working great.
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Old 22nd August 2004, 02:51 PM   #2
hifidan is offline hifidan  Canada
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Second photo.
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Old 22nd August 2004, 04:35 PM   #3
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What your attachment to the port exit does is add additional acoustic impedance to the air flow. which takes the box resonant frequency down. The effect is roughly the same as what would happen if you added a flared exit to the duct to increase its length and exit cross-section. It would work even better with a flared entrance to the duct (inside the box).
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Old 22nd August 2004, 07:43 PM   #4
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Actually, I used a 4 inch ABS pipe for the port (which is 33 inches lenght , i had to put a 90 degree elbow inside to achieve this lenght) and at the time was not able to do a flared port.
Actually, It was pretty easy to build this one, I used the MDF cut out from the actual driver and by hand, added some drywall paste until I achieved a smooth surface.
Thks for the details.
Dan
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Old 23rd August 2004, 11:02 AM   #5
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Dan,

I wouldn't use the word "waveguide" here as it normally refers to modern horn design for constrant directivity.

As I see it, polk use this as a flare so that the air movement of a down firing vent is smoother, with less turbulence. Imagine air hitting a flat perpundicular surface! Better to create a smoother flow to eliminate chuffing. In your case I can't see much point, but if you like it, no reason not to keep it. Did you have turbulence problems?
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Old 23rd August 2004, 12:49 PM   #6
hifidan is offline hifidan  Canada
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Hi Paul, actually, at high volume You could hear chuffing in the port. With this it is dead quiet. When I take them off, the bass is more round, go figure?
Thks for your post.
Dan
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