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.
Attachments
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).
Iso Subs
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
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
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?
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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