Kerf Question

[NSTALN 10+ year member]

How do you determine the radius of a kerfed port? Is it somehow proportional to the post itself?

Thanks!

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[Buck 5,000+ posts]

It can be whatever you want it to be. Easiest way is just to make the kerf radius the port radius (width), or close to it. The size of the kerf doesn't matter as much as just making sure you know your tuning. Like check out this kerf I designed, and this box was built and doing hair tricks in the mid 20's:

That kerf is MASSIVE.

A kerf is just a coupling device for the port to couple with the cabin. It helps the waveforms more smoothly transition from the port to the cabin airspace, where the kerf helps the port air more slowly expand as it enters the cabin air, instead of brutally exiting a tiny port and rapidly expanding in every direction. Having flares/kerfs on ports raises their efficiency, because what it does, simply, is help the wave in the smaller port airspace somewhat controllably expand into the larger airspace of the cabin.

If you don't want to do a kerf, you can always do a 45 flared port, which is something like this:

45's are much easier to do than kerfs, IMO. So, that's a different option that does the same thing, just in a different way.

The size of the kerf generally doesn't matter, but you can run into loading problems if the kerf is wayyy too big and in a weird spot inside of the vehicle.

 

[SlugButter]

I'm starting a custom 15 build next week that will have 3 kerfs, making the front panel, right side panel and inside port panels all one continuous kerf. Also, the left side rear will also be kerfed, making a slot port with no right angles in it. My first attempt at 3 kerf cuts on the same panel. Hopefully I can do it without wasting 100$ worth of wood. Lol

 

[Slo_Ride 5,000+ posts]

How do you determine the radius of a kerfed port? Is it somehow proportional to the post itself?

Thanks!

Question doesn't make any sense

 

[NSTALN 10+ year member]

A ported box with a kerfed opening…I’m just curious if the rounded opening is somehow proportional to the dimensions of the port.

I see in my original post my phone auto-corrected the word ‘port’ to ‘post’. I guess that does seem like an odd question.

 

[SlugButter]

A ported box with a kerfed opening…I’m just curious if the rounded opening is somehow proportional to the dimensions of the port.

I see in my original post my phone auto-corrected the word ‘port’ to ‘post’. I guess that does seem like an odd question.

Not really. You could probably get really technical and kerf it to a specific radius compared to port width, but I don’t think it would make and audible difference. A cool talking point maybe. I do tend to do more of a wide arc on larger ports, but remember, port length only counts in half the kerfed part of the port. So if your kerf starts curving 4 inches before it hits the outside, only 2 inches of it counts in your port length. I always add 2 inches to overall port length in my design if I am doing a kerfed port.

 

[NSTALN 10+ year member]

Thank you all for the responses!