Port entrance rounding, calculating it into the port length?

[tn2k]

I am designing a box for my swr-12d4. I'l be using a slotted port. I'll be rounding both ends of the port with a 3/4" router bit. My material will be 3/4" mdf. Im currently bouncing between torres and sketchup. Scratchin my head about this...

1. Does torres take into account the round of the entrance or do I have to add length to the port to accommodate the round?

2. How much of the 3/4" round on each end is considered part of the port and part of the entrance? I have read that the port starts at half way into the the round. Is this true?

I guess what I'm asking is if I my targeted port length was 10" long for my port/box tune, do I need to add to that 10" prior to rounding with my 3/4" bit? if so how much?

[rocking.that.eclipse]

Design the box for a square opening. The round-over won't affect tuning enough to even worry about.

[philrab]

Half the radius is considered port length for calculations. Mean, if the portion of your port (square or round) is 1/2" from the portion before the flare to the end, then 1/4" is considered port.

What I typically do on slot ports is use a 1/4" roundover inside and out, and add/subtract 1/4" from the port total.

Per rocking.that.eclipse's statement, small roundovers really don't affect port tuning much. If you're doing larger flares and picking nits, then yes it needs to be considered.

[Triticum Agricolam]

Like philrab said, half the radius is considered to be part of the port.

So if you want your port to be 10" long and are going to use a 3/4" roundover on both ends you should make it 10-3/4" long before using the roundover (+3/8" for each end).

[Joe X]

If not kerfing you don't need to factor in the length loss at all, in fact if you are using Torres, the calculator will introduce a much larger error in your tuning calculations.