Clamshell and Tunnel help needed

[CJ18]

I have a question about calculating the port tuning for a clamshell and rear ported tunnel.

When figuring the tuning of the port and port length do I need to take into consideration the distance from the front of the port to the front of the box. In the pic below on the rear ported tunnel if it were say 36" from the front of the box to back where the port is do I need to consider this distance when figuring my tuning? Sam for the clamshell.

Thanks for any help yall can give me.

[OBI]

http://www.stevemeadedesigns.com/board/topic/87933-12x12-clamshell-need-some-help-here-guys/page__p__1204144__fromsearch__1entry1204144 lots of usefull info here, Boon's and BITLD gave the best advice.

[Colin - STAPUFT]

x2 on checking with boon. He helped me tremendously when I built my box.

The short answer is this: It will tune lower than you think. That is from my experience. These boxes don't really design or tune like a regular ported box. There isn't really a program you can use to say- "that's it- tunes to 35 hz".

I used Bass Box Pro and some online tuning calculators to get me close- to what I thought was 32 hz or so (can't remember exactly), but once it was in and done, tuning proved to be lower than what I built it for... goes way low.

The best thing I can tell you is to build it like a ported box and estimate that the "port" that you build and think of as the port is the actual port. Any extra in front of the port- don't count. If you want a 30 hz tune and you can only get to 35 due to size constraints or what have you- then don't worry. It will get there.

I was really worried when I built my wall that it would sound like crap and all of that time and $ would be lost- but nope. Just build it strong and all should be well. If it turns out to be too low of a tune, you can always add material to the box to effectively lower the tune. If tune is too high, fill in some of the port.