North Creek Big Kat North D28 User Manual - page 22
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North Creek Loudspeaker Kits can be tuned over about an octave by adjusting the
length of straws inside the port tube. The following facilitates port tube removal:
1) Add a 2" section of straight tube to the flared port tube assembly. Reserve the rest
for later.
2) Cut the straws into 5" lengths. Insert the straws into the end of the tube with one
inch sticking out. The fit should be so tight that the straws begin to go out of round
(about 125 straws for a 3" port).
3) Wrap the straw bunch sticking out of the port tube with tape. This secures the
straws and makes it easy to adjust the length emerging from the port.
4) Add gasket tape to the rear of the port tube flange. Install the port tube into the
cabinet. The fit should be tight but the tube should still be removable with a little pulling.
5) Secure the port with screws.
One can adjust the length of straws emerging from the port to adjust the tuning
frequency by ear. We have found the optimum to be between 1" and 2½".
Once the "perfect" tuning is reached, the port can be fixed by dipping the entire
assembly in clear shellac or black paint.
For those that are curious about the origin of this procedure, to the best of my knowledge it was first
discussed in writing by Dr. Neville Theile himself. The earliest reference I know of was in an article by Dr.
Theile in an ASA journal from the mid '60's, on non-linear port behavior. Which article and year it was
precisely is now unknown to me. -GS